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Lectures and Essays

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Title: Lectures and Essays

Author: Thomas Henry Huxley


        
Release date: September 1, 2004 [eBook #6414]
                Most recently updated: January 14, 2013

Language: English

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*** START OF THE PROJECT GUTENBERG EBOOK LECTURES AND ESSAYS ***




Produced by Sue Asscher





LECTURES AND ESSAYS

By T.H. Huxley


The People's Library


Cassell And Company, Ltd.


London, Paris, New York, Toronto & Melbourne.


MCMVIII.




EDITOR'S NOTE.

Of the great thinkers of the nineteenth century, Thomas Henry Huxley,
son of an Ealing schoolmaster, was undoubtedly the most noteworthy. His
researches in biology, his contributions to scientific controversy, his
pungent criticisms of conventional beliefs and thoughts have probably
had greater influence than the work of any other English scientist. And
yet he was a "self-made" intellectualist. In spite of the fact that
his father was a schoolmaster he passed through no regular course of
education. "I had," he said, "two years of a pandemonium of a school
(between eight and ten) and after that neither help nor sympathy in any
intellectual direction till I reached manhood." When he was twelve a
craving for reading found satisfaction in Hutton's "Geology," and when
fifteen in Hamilton's "Logic."

At seventeen Huxley entered as a student at Charing Cross Hospital, and
three years later he was M.B. and the possessor of the gold medal for
anatomy and physiology. An appointment as surgeon in the navy proved to
be the entry to Huxley's great scientific career, for he was gazetted to
the "Rattlesnake", commissioned for surveying work in Torres Straits. He
was attracted by the teeming surface life of tropical seas and his study
of it was the commencement of that revolution in scientific knowledge
ultimately brought about by his researches.

Thomas Henry Huxley was born at Ealing on May 4, 1825, and died at
Eastbourne June 29, 1895.



CONTENTS.


ON OUR KNOWLEDGE OF THE CAUSES OF THE PHENOMENA OF ORGANIC NATURE:

 THE PRESENT CONDITION OF ORGANIC NATURE.

 THE PAST CONDITION OF ORGANIC NATURE.

 THE METHOD BY WHICH THE CAUSES OF THE PRESENT AND PAST CONDITIONS OF
 ORGANIC NATURE ARE TO BE DISCOVERED.--THE ORIGINATION OF LIVING BEINGS.

 THE PERPETUATION OF LIVING BEINGS, HEREDITARY TRANSMISSION AND
 VARIATION.

 THE CONDITIONS OF EXISTENCE AS AFFECTING THE PERPETUATION OF LIVING
 BEINGS.

 A CRITICAL EXAMINATION OF THE POSITION OF MR. DARWIN'S WORK, "ON THE
 ORIGIN OF SPECIES," IN RELATION TO THE COMPLETE THEORY OF THE CAUSES OF
 THE PHENOMENA OF ORGANIC NATURE.


ESSAYS ON DARWIN'S "ORIGIN OF SPECIES":

 THE DARWINIAN HYPOTHESIS.

 TIME AND LIFE.

 THE ORIGIN OF SPECIES.

 CRITICISMS ON "THE ORIGIN OF SPECIES".


EVIDENCE AS TO MAN'S PLACE IN NATURE:

 ON THE NATURAL HISTORY OF THE MAN-LIKE APES.

 ON THE RELATIONS OF MAN TO THE LOWER ANIMALS.

 ON SOME FOSSIL REMAINS OF MAN.


ON THE ADVISABLENESS OF IMPROVING NATURAL KNOWLEDGE.


ON THE STUDY OF ZOOLOGY.


GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE.


CORAL AND CORAL REEFS.


YEAST.


THE CIRCULATION OF THE BLOOD.


*****




NOTICE TO THE FIRST EDITION.

The Publisher of these interesting Lectures, having made an arrangement
for their publication with Mr. J.A. Mays, the Reporter, begs to append
the following note from Professor Huxley:--

"Mr. J. Aldous Mays, who is taking shorthand notes of my 'Lectures to
Working Men,' has asked me to allow him, on his own account, to print
those Notes for the use of my audience. I willingly accede to this
request, on the understanding that a notice is prefixed to the effect
that I have no leisure to revise the Lectures, or to make alterations in
them, beyond the correction of any important error in a matter of fact."


*****




ON OUR KNOWLEDGE OF THE CAUSES OF THE PHENOMENA OF ORGANIC NATURE:




THE PRESENT CONDITION OF ORGANIC NATURE.

When it was my duty to consider what subject I would select for the
six lectures* ([Footnote] *To Working Men, at the Museum of Practical
Geology, 1863.) which I shall now have the pleasure of delivering to
you, it occurred to me that I could not do better than endeavour to put
before you in a true light, or in what I might perhaps with more modesty
call, that which I conceive myself to be the true light, the position
of a book which has been more praised and more abused, perhaps, than any
book which has appeared for some years;--I mean Mr. Darwin's work on the
"Origin of Species". That work, I doubt not, many of you have read; for
I know the inquiring spirit which is rife among you. At any rate, all
of you will have heard of it,--some by one kind of report and some by
another kind of report; the attention of all and the curiosity of all
have been probably more or less excited on the subject of that work. All
I can do, and all I shall attempt to do, is to put before you that kind
of judgment which has been formed by a man, who, of course, is liable
to judge erroneously; but, at any rate, of one whose business and
profession it is to form judgments upon questions of this nature.

And here, as it will always happen when dealing with an extensive
subject, the greater part of my course--if, indeed, so small a number of
lectures can be properly called a course--must be devoted to preliminary
matters, or rather to a statement of those facts and of those principles
which the work itself dwells upon, and brings more or less directly
before us. I have no right to suppose that all or any of you
are naturalists; and even if you were, the misconceptions and
misunderstandings prevalent even among naturalists on these matters
would make it desirable that I should take the course I now propose to
take,--that I should start from the beginning,--that I should endeavour
to point out what is the existing state of the organic world,--that I
should point out its past condition,--that I should state what is the
precise nature of the undertaking which Mr. Darwin has taken in hand;
that I should endeavour to show you what are the only methods by which
that undertaking can be brought to an issue, and to point out to you how
far the author of the work in question has satisfied those conditions,
how far he has not satisfied them, how far they are satisfiable by man,
and how far they are not satisfiable by man.

To-night, in taking up the first part of this question, I shall
endeavour to put before you a sort of broad notion of our knowledge of
the condition of the living world. There are many ways of doing this. I
might deal with it pictorially and graphically. Following the example of
Humboldt in his "Aspects of Nature", I might endeavour to point out the
infinite variety of organic life in every mode of its existence, with
reference to the variations of climate and the like; and such an attempt
would be fraught with interest to us all; but considering the subject
before us, such a course would not be that best calculated to assist us.
In an argument of this kind we must go further and dig deeper into the
matter; we must endeavour to look into the foundations of living Nature,
if I may so say, and discover the principles involved in some of her
most secret operations. I propose, therefore, in the first place, to
take some ordinary animal with which you are all familiar, and, by
easily comprehensible and obvious examples drawn from it, to show what
are the kind of problems which living beings in general lay before us;
and I shall then show you that the same problems are laid open to us by
all kinds of living beings. But first, let me say in what sense I have
used the words "organic nature." In speaking of the causes which lead
to our present knowledge of organic nature, I have used it almost as an
equivalent of the word "living," and for this reason,--that in almost
all living beings you can distinguish several distinct portions set
apart to do particular things and work in a particular way. These are
termed "organs," and the whole together is called "organic." And as it
is universally characteristic of them, this term "organic" has been very
conveniently employed to denote the whole of living nature,--the whole
of the plant world, and the whole of the animal world.

Few animals can be more familiar to you than that whose skeleton is
shown on our diagram. You need not bother yourselves with this "Equus
caballus" written under it; that is only the Latin name of it, and does
not make it any better. It simply means the common Horse. Suppose we
wish to understand all about the Horse. Our first object must be to
study the structure of the animal. The whole of his body is inclosed
within a hide, a skin covered with hair; and if that hide or skin be
taken off, we find a great mass of flesh, or what is technically called
muscle, being the substance which by its power of contraction enables
the animal to move. These muscles move the hard parts one upon the
other, and so give that strength and power of motion which renders the
Horse so useful to us in the performance of those services in which we
employ him.

And then, on separating and removing the whole of this skin and flesh,
you have a great series of bones, hard structures, bound together with
ligaments, and forming the skeleton which is represented here.

(FIGURE 1. Section through a horse.

FIGURE 2. Section through a cell.)

In that skeleton there are a number of parts to be recognized. The long
series of bones, beginning from the skull and ending in the tail, is
called the spine, and those in front are the ribs; and then there are
two pairs of limbs, one before and one behind; and there are what we
all know as the fore-legs and the hind-legs. If we pursue our researches
into the interior of this animal, we find within the framework of
the skeleton a great cavity, or rather, I should say, two great
cavities,--one cavity beginning in the skull and running through the
neck-bones, along the spine, and ending in the tail, containing the
brain and the spinal marrow, which are extremely important organs. The
second great cavity, commencing with the mouth, contains the gullet,
the stomach, the long intestine, and all the rest of those internal
apparatus which are essential for digestion; and then in the same great
cavity, there are lodged the heart and all the great vessels going from
it; and, besides that, the organs of respiration--the lungs: and then
the kidneys, and the organs of reproduction, and so on. Let us now
endeavour to reduce this notion of a horse that we now have, to
some such kind of simple expression as can be at once, and without
difficulty, retained in the mind, apart from all minor details. If
I make a transverse section, that is, if I were to saw a dead horse
across, I should find that, if I left out the details, and supposing I
took my section through the anterior region, and through the fore-limbs,
I should have here this kind of section of the body (Figure 1). Here
would be the upper part of the animal--that great mass of bones that we
spoke of as the spine (a, Figure 1). Here I should have the alimentary
canal (b, Figure 1). Here I should have the heart (c, Figure 1); and
then you see, there would be a kind of double tube, the whole being
inclosed within the hide; the spinal marrow would be placed in the upper
tube (a, Figure 1), and in the lower tube (d d, Figure 1), there would
be the alimentary canal (b), and the heart (c); and here I shall have
the legs proceeding from each side. For simplicity's sake, I represent
them merely as stumps (e e, Figure 1). Now that is a horse--as
mathematicians would say--reduced to its most simple expression. Carry
that in your minds, if you please, as a simplified idea of the structure
of the Horse. The considerations which I have now put before you belong
to what we technically call the 'Anatomy' of the Horse. Now, suppose
we go to work upon these several parts,--flesh and hair, and skin and
bone,--and lay open these various organs with our scalpels, and examine
them by means of our magnifying-glasses, and see what we can make of
them. We shall find that the flesh is made up of bundles of strong
fibres. The brain and nerves, too, we shall find, are made up of fibres,
and these queer-looking things that are called ganglionic corpuscles.
If we take a slice of the bone and examine it, we shall find that it is
very like this diagram of a section of the bone of an ostrich,
though differing, of course, in some details; and if we take any part
whatsoever of the tissue, and examine it, we shall find it all has a
minute structure, visible only under the microscope. All these
parts constitute microscopic anatomy or 'Histology.' These parts are
constantly being changed; every part is constantly growing, decaying,
and being replaced during the life of the animal. The tissue is
constantly replaced by new material; and if you go back to the young
state of the tissue in the case of muscle, or in the case of skin, or
any of the organs I have mentioned, you will find that they all come
under the same condition. Every one of these microscopic filaments
and fibres (I now speak merely of the general character of the whole
process)--every one of these parts--could be traced down to some
modification of a tissue which can be readily divided into little
particles of fleshy matter, of that substance which is composed of the
chemical elements, carbon, hydrogen, oxygen, and nitrogen, having such
a shape as this (Figure 2). These particles, into which all primitive
tissues break up, are called cells. If I were to make a section of a
piece of the skin of my hand, I should find that it was made up of these
cells. If I examine the fibres which form the various organs of all
living animals, I should find that all of them, at one time or other,
had been formed out of a substance consisting of similar elements; so
that you see, just as we reduced the whole body in the gross to that
sort of simple expression given in Figure 1, so we may reduce the
whole of the microscopic structural elements to a form of even greater
simplicity; just as the plan of the whole body may be so represented
in a sense (Figure 1), so the primary structure of every tissue may be
represented by a mass of cells (Figure 2).

Having thus, in this sort of general way, sketched to you what I may
call, perhaps, the architecture of the body of the Horse (what we term
technically its Morphology), I must now turn to another aspect. A horse
is not a mere dead structure: it is an active, living, working machine.
Hitherto we have, as it were, been looking at a steam-engine with the
fires out, and nothing in the boiler; but the body of the living animal
is a beautifully-formed active machine, and every part has its different
work to do in the working of that machine, which is what we call
its life. The Horse, if you see him after his day's work is done, is
cropping the grass in the fields, as it may be, or munching the oats in
his stable. What is he doing? His jaws are working as a mill--and a very
complex mill too--grinding the corn, or crushing the grass to a pulp. As
soon as that operation has taken place, the food is passed down to
the stomach, and there it is mixed with the chemical fluid called the
gastric juice, a substance which has the peculiar property of making
soluble and dissolving out the nutritious matter in the grass, and
leaving behind those parts which are not nutritious; so that you have,
first, the mill, then a sort of chemical digester; and then the food,
thus partially dissolved, is carried back by the muscular contractions
of the intestines into the hinder parts of the body, while the soluble
portions are taken up into the blood. The blood is contained in a vast
system of pipes, spreading through the whole body, connected with a
force pump,--the heart,--which, by its position and by the contractions
of its valves, keeps the blood constantly circulating in one direction,
never allowing it to rest; and then, by means of this circulation of
the blood, laden as it is with the products of digestion, the skin, the
flesh, the hair, and every other part of the body, draws from it that
which it wants, and every one of these organs derives those materials
which are necessary to enable it to do its work.

The action of each of these organs, the performance of each of these
various duties, involve in their operation a continual absorption of
the matters necessary for their support, from the blood, and a constant
formation of waste products, which are returned to the blood, and
conveyed by it to the lungs and the kidneys, which are organs that have
allotted to them the office of extracting, separating, and getting rid
of these waste products; and thus the general nourishment, labour, and
repair of the whole machine is kept up with order and regularity. But
not only is it a machine which feeds and appropriates to its own
support the nourishment necessary to its existence--it is an engine for
locomotive purposes. The Horse desires to go from one place to another;
and to enable it to do this, it has those strong contractile bundles of
muscles attached to the bones of its limbs, which are put in motion by
means of a sort of telegraphic apparatus formed by the brain and the
great spinal cord running through the spine or backbone; and to this
spinal cord are attached a number of fibres termed nerves, which proceed
to all parts of the structure. By means of these the eyes, nose,
tongue, and skin--all the organs of perception--transmit impressions
or sensations to the brain, which acts as a sort of great central
telegraph-office, receiving impressions and sending messages to all
parts of the body, and putting in motion the muscles necessary to
accomplish any movement that may be desired. So that you have here an
extremely complex and beautifully-proportioned machine, with all its
parts working harmoniously together towards one common object--the
preservation of the life of the animal.

Now, note this: the Horse makes up its waste by feeding, and its food
is grass or oats, or perhaps other vegetable products; therefore, in the
long run, the source of all this complex machinery lies in the vegetable
kingdom. But where does the grass, or the oat, or any other plant,
obtain this nourishing food-producing material? At first it is a little
seed, which soon begins to draw into itself from the earth and the
surrounding air matters which in themselves contain no vital properties
whatever; it absorbs into its own substance water, an inorganic body;
it draws into its substance carbonic acid, an inorganic matter; and
ammonia, another inorganic matter, found in the air; and then, by some
wonderful chemical process, the details of which chemists do not yet
understand, though they are near foreshadowing them, it combines
them into one substance, which is known to us as 'Protein,' a complex
compound of carbon, hydrogen, oxygen, and nitrogen, which alone
possesses the property of manifesting vitality and of permanently
supporting animal life. So that, you see, the waste products of the
animal economy, the effete materials which are continually being thrown
off by all living beings, in the form of organic matters, are constantly
replaced by supplies of the necessary repairing and rebuilding materials
drawn from the plants, which in their turn manufacture them, so to
speak, by a mysterious combination of those same inorganic materials.

Let us trace out the history of the Horse in another direction. After
a certain time, as the result of sickness or disease, the effect of
accident, or the consequence of old age, sooner or later, the animal
dies. The multitudinous operations of this beautiful mechanism flag in
their performance, the Horse loses its vigour, and after passing
through the curious series of changes comprised in its formation and
preservation, it finally decays, and ends its life by going back into
that inorganic world from which all but an inappreciable fraction of its
substance was derived. Its bones become mere carbonate and phosphate of
lime; the matter of its flesh, and of its other parts, becomes, in the
long run, converted into carbonic acid, into water, and into ammonia.
You will now, perhaps, understand the curious relation of the animal
with the plant, of the organic with the inorganic world, which is shown
in this diagram (Figure 3).

(FIGURE 3. Diagram showing material relationship of the Vegetable,
Animal and Inorganic Worlds.)

The plant gathers these inorganic materials together and makes them up
into its own substance. The animal eats the plant and appropriates the
nutritious portions to its own sustenance, rejects and gets rid of the
useless matters; and, finally, the animal itself dies, and its whole
body is decomposed and returned into the inorganic world. There is thus
a constant circulation from one to the other, a continual formation of
organic life from inorganic matters, and as constant a return of the
matter of living bodies to the inorganic world; so that the materials
of which our bodies are composed are largely, in all probability, the
substances which constituted the matter of long extinct creations, but
which have in the interval constituted a part of the inorganic world.

Thus we come to the conclusion, strange at first sight, that the MATTER
constituting the living world is identical with that which forms the
inorganic world. And not less true is it that, remarkable as are the
powers or, in other words, as are the FORCES which are exerted by living
beings, yet all these forces are either identical with those which exist
in the inorganic world, or they are convertible into them; I mean in
just the same sense as the researches of physical philosophers have
shown that heat is convertible into electricity, that electricity is
convertible into magnetism, magnetism into mechanical force or chemical
force, and any one of them with the other, each being measurable in
terms of the other,--even so, I say, that great law is applicable to
the living world. Consider why is the skeleton of this horse capable of
supporting the masses of flesh and the various organs forming the living
body, unless it is because of the action of the same forces of cohesion
which combines together the particles of matter composing this piece of
chalk? What is there in the muscular contractile power of the animal
but the force which is expressible, and which is in a certain sense
convertible, into the force of gravity which it overcomes? Or, if you go
to more hidden processes, in what does the process of digestion differ
from those processes which are carried on in the laboratory of the
chemist? Even if we take the most recondite and most complex operations
of animal life--those of the nervous system, these of late years
have been shown to be--I do not say identical in any sense with the
electrical processes--but this has been shown, that they are in some
way or other associated with them; that is to say, that every amount
of nervous action is accompanied by a certain amount of electrical
disturbance in the particles of the nerves in which that nervous action
is carried on. In this way the nervous action is related to electricity
in the same way that heat is related to electricity; and the same sort
of argument which demonstrates the two latter to be related to one
another shows that the nervous forces are correlated to electricity; for
the experiments of M. Dubois Reymond and others have shown that whenever
a nerve is in a state of excitement, sending a message to the muscles
or conveying an impression to the brain, there is a disturbance of the
electrical condition of that nerve which does not exist at other times;
and there are a number of other facts and phenomena of that sort; so
that we come to the broad conclusion that not only as to living matter
itself, but as to the forces that matter exerts, there is a close
relationship between the organic and the inorganic world--the difference
between them arising from the diverse combination and disposition of
identical forces, and not from any primary diversity, so far as we can
see.

I said just now that the Horse eventually died and became converted
into the same inorganic substances from whence all but an inappreciable
fraction of its substance demonstrably originated, so that the actual
wanderings of matter are as remarkable as the transmigrations of the
soul fabled by Indian tradition. But before death has occurred, in the
one sex or the other, and in fact in both, certain products or parts of
the organism have been set free, certain parts of the organisms of
the two sexes have come into contact with one another, and from that
conjunction, from that union which then takes place, there results the
formation of a new being. At stated times the mare, from a particular
part of the interior of her body, called the ovary, gets rid of a minute
particle of matter comparable in all essential respects with that which
we called a cell a little while since, which cell contains a kind of
nucleus in its centre, surrounded by a clear space and by a viscid
mass of protein substance (Figure 2); and though it is different in
appearance from the eggs which we are mostly acquainted with, it is
really an egg. After a time this minute particle of matter, which may
only be a small fraction of a grain in weight, undergoes a series of
changes,--wonderful, complex changes. Finally, upon its surface there
is fashioned a little elevation, which afterwards becomes divided and
marked by a groove. The lateral boundaries of the groove extend upwards
and downwards, and at length give rise to a double tube. In the upper
smaller tube the spinal marrow and brain are fashioned; in the lower,
the alimentary canal and heart; and at length two pairs of buds shoot
out at the sides of the body, which are the rudiments of the limbs. In
fact a true drawing of a section of the embryo in this state would in
all essential respects resemble that diagram of a horse reduced to its
simplest expression, which I first placed before you (Figure 1).

Slowly and gradually these changes take place. The whole of the body,
at first, can be broken up into "cells," which become in one place
metamorphosed into muscle,--in another place into gristle and bone,--in
another place into fibrous tissue,--and in another into hair; every part
becoming gradually and slowly fashioned, as if there were an artificer
at work in each of these complex structures that we have mentioned. This
embryo, as it is called, then passes into other conditions. I should
tell you that there is a time when the embryos of neither dog, nor
horse, nor porpoise, nor monkey, nor man, can be distinguished by any
essential feature one from the other; there is a time when they each and
all of them resemble this one of the Dog. But as development advances,
all the parts acquire their speciality, till at length you have the
embryo converted into the form of the parent from which it started. So
that you see, this living animal, this horse, begins its existence as
a minute particle of nitrogenous matter, which, being supplied with
nutriment (derived, as I have shown, from the inorganic world), grows up
according to the special type and construction of its parents, works
and undergoes a constant waste, and that waste is made good by nutriment
derived from the inorganic world; the waste given off in this way being
directly added to the inorganic world; and eventually the animal itself
dies, and, by the process of decomposition, its whole body is returned
to those conditions of inorganic matter in which its substance
originated.

This, then, is that which is true of every living form, from the lowest
plant to the highest animal--to man himself. You might define the life
of every one in exactly the same terms as those which I have now used;
the difference between the highest and the lowest being simply in the
complexity of the developmental changes, the variety of the structural
forms, the diversity of the physiological functions which are exerted by
each.

If I were to take an oak tree as a specimen of the plant world, I should
find that it originated in an acorn, which, too, commenced in a cell;
the acorn is placed in the ground, and it very speedily begins to absorb
the inorganic matters I have named, adds enormously to its bulk, and
we can see it, year after year, extending itself upward and downward,
attracting and appropriating to itself inorganic materials, which it
vivifies, and eventually, as it ripens, gives off its own proper acorns,
which again run the same course. But I need not multiply examples,--from
the highest to the lowest the essential features of life are the same,
as I have described in each of these cases.

So much, then, for these particular features of the organic world, which
you can understand and comprehend, so long as you confine yourself to
one sort of living being, and study that only.

But, as you know, horses are not the only living creatures in the world;
and again, horses, like all other animals, have certain limits--are
confined to a certain area on the surface of the earth on which we
live,--and, as that is the simpler matter, I may take that first. In its
wild state, and before the discovery of America, when the natural state
of things was interfered with by the Spaniards, the Horse was only to
be found in parts of the earth which are known to geographers as the Old
World; that is to say, you might meet with horses in Europe, Asia, or
Africa; but there were none in Australia, and there were none whatsoever
in the whole continent of America, from Labrador down to Cape Horn. This
is an empirical fact, and it is what is called, stated in the way I have
given it you, the 'Geographical Distribution' of the Horse.

Why horses should be found in Europe, Asia, and Africa, and not in
America, is not obvious; the explanation that the conditions of life in
America are unfavourable to their existence, and that, therefore, they
had not been created there, evidently does not apply; for when the
invading Spaniards, or our own yeomen farmers, conveyed horses to these
countries for their own use, they were found to thrive well and multiply
very rapidly; and many are even now running wild in those countries, and
in a perfectly natural condition. Now, suppose we were to do for every
animal what we have here done for the Horse,--that is, to mark off and
distinguish the particular district or region to which each belonged;
and supposing we tabulated all these results, that would be called the
Geographical Distribution of animals, while a corresponding study of
plants would yield as a result the Geographical Distribution of plants.

I pass on from that now, as I merely wished to explain to you what I
meant by the use of the term 'Geographical Distribution.' As I said,
there is another aspect, and a much more important one, and that is,
the relations of the various animals to one another. The Horse is a
very well-defined matter-of-fact sort of animal, and we are all pretty
familiar with its structure. I dare say it may have struck you, that
it resembles very much no other member of the animal kingdom, except
perhaps the Zebra or the Ass. But let me ask you to look along these
diagrams. Here is the skeleton of the Horse, and here the skeleton of
the Dog. You will notice that we have in the Horse a skull, a backbone
and ribs, shoulder-blades and haunch-bones. In the fore-limb, one upper
arm-bone, two fore arm-bones, wrist-bones (wrongly called knee), and
middle hand-bones, ending in the three bones of a finger, the last of
which is sheathed in the horny hoof of the fore-foot: in the hind-limb,
one thigh-bone, two leg-bones, anklebones, and middle foot-bones, ending
in the three bones of a toe, the last of which is encased in the hoof of
the hind-foot. Now turn to the Dog's skeleton. We find identically the
same bones, but more of them, there being more toes in each foot, and
hence more toe-bones.

Well, that is a very curious thing! The fact is that the Dog and the
Horse--when one gets a look at them without the outward impediments of
the skin--are found to be made in very much the same sort of fashion.
And if I were to make a transverse section of the Dog, I should find the
same organs that I have already shown you as forming parts of the Horse.
Well, here is another skeleton--that of a kind of Lemur--you see he has
just the same bones; and if I were to make a transverse section of it,
it would be just the same again. In your mind's eye turn him round,
so as to put his backbone in a position inclined obliquely upwards
and forwards, just as in the next three diagrams, which represent the
skeletons of an Orang, a Chimpanzee, a Gorilla, and you find you have no
trouble in identifying the bones throughout; and lastly turn to the end
of the series, the diagram representing a man's skeleton, and still you
find no great structural feature essentially altered. There are the
same bones in the same relations. From the Horse we pass on and on, with
gradual steps, until we arrive at last at the highest known forms. On
the other hand, take the other line of diagrams, and pass from the Horse
downwards in the scale to this fish; and still, though the modifications
are vastly greater, the essential framework of the organization remains
unchanged. Here, for instance, is a Porpoise: here is its strong
backbone, with the cavity running through it, which contains the spinal
cord; here are the ribs, here the shoulder blade; here is the little
short upper-arm bone, here are the two forearm bones, the wrist-bone,
and the finger-bones.

Strange, is it not, that the Porpoise should have in this queer-looking
affair--its flapper (as it is called), the same fundamental elements as
the fore-leg of the Horse or the Dog, or the Ape or Man; and here you
will notice a very curious thing,--the hinder limbs are absent. Now,
let us make another jump. Let us go to the Codfish: here you see is the
forearm, in this large pectoral fin--carrying your mind's eye onward
from the flapper of the Porpoise. And here you have the hinder limbs
restored in the shape of these ventral fins. If I were to make a
transverse section of this, I should find just the same organs that
we have before noticed. So that, you see, there comes out this strange
conclusion as the result of our investigations, that the Horse, when
examined and compared with other animals, is found by no means to
stand alone in nature; but that there are an enormous number of other
creatures which have backbones, ribs, and legs, and other parts arranged
in the same general manner, and in all their formation exhibiting the
same broad peculiarities.

I am sure that you cannot have followed me even in this extremely
elementary exposition of the structural relations of animals, without
seeing what I have been driving at all through, which is, to show you
that, step by step, naturalists have come to the idea of a unity of
plan, or conformity of construction, among animals which appeared at
first sight to be extremely dissimilar.

And here you have evidence of such a unity of plan among all the animals
which have backbones, and which we technically call "Vertebrata". But
there are multitudes of other animals, such as crabs, lobsters, spiders,
and so on, which we term "Annulosa". In these I could not point out to
you the parts that correspond with those of the Horse,--the backbone,
for instance,--as they are constructed upon a very different principle,
which is also common to all of them; that is to say, the Lobster, the
Spider, and the Centipede, have a common plan running through their
whole arrangement, in just the same way that the Horse, the Dog, and the
Porpoise assimilate to each other.

Yet other creatures--whelks, cuttlefishes, oysters, snails, and all
their tribe ("Mollusca")--resemble one another in the same way, but
differ from both "Vertebrata" and "Annulosa"; and the like is true of
the animals called "Coelenterata" (Polypes) and "Protozoa" (animalcules
and sponges).

Now, by pursuing this sort of comparison, naturalists have arrived at
the conviction that there are,--some think five, and some seven,--but
certainly not more than the latter number--and perhaps it is simpler to
assume five--distinct plans or constructions in the whole of the animal
world; and that the hundreds of thousands of species of creatures on
the surface of the earth, are all reducible to those five, or, at most,
seven, plans of organization.

But can we go no further than that? When one has got so far, one is
tempted to go on a step and inquire whether we cannot go back yet
further and bring down the whole to modifications of one primordial
unit. The anatomist cannot do this; but if he call to his aid the study
of development, he can do it. For we shall find that, distinct as those
plans are, whether it be a porpoise or man, or lobster, or any of those
other kinds I have mentioned, every one begins its existence with one
and the same primitive form,--that of the egg, consisting, as we have
seen, of a nitrogenous substance, having a small particle or nucleus
in the centre of it. Furthermore, the earlier changes of each are
substantially the same. And it is in this that lies that true "unity
of organization" of the animal kingdom which has been guessed at and
fancied for many years; but which it has been left to the present
time to be demonstrated by the careful study of development. But is it
possible to go another step further still, and to show that in the
same way the whole of the organic world is reducible to one primitive
condition of form? Is there among the plants the same primitive form of
organization, and is that identical with that of the animal kingdom?
The reply to that question, too, is not uncertain or doubtful. It is now
proved that every plant begins its existence under the same form; that
is to say, in that of a cell--a particle of nitrogenous matter having
substantially the same conditions. So that if you trace back the oak
to its first germ, or a man, or a horse, or lobster, or oyster, or any
other animal you choose to name, you shall find each and all of these
commencing their existence in forms essentially similar to each other:
and, furthermore, that the first processes of growth, and many of the
subsequent modifications, are essentially the same in principle in
almost all.

In conclusion, let me, in a few words, recapitulate the positions which
I have laid down. And you must understand that I have not been talking
mere theory; I have been speaking of matters which are as plainly
demonstrable as the commonest propositions of Euclid--of facts that must
form the basis of all speculations and beliefs in Biological science.
We have gradually traced down all organic forms, or, in other words, we
have analyzed the present condition of animated nature, until we found
that each species took its origin in a form similar to that under which
all the others commence their existence. We have found the whole of the
vast array of living forms, with which we are surrounded, constantly
growing, increasing, decaying and disappearing; the animal constantly
attracting, modifying, and applying to its sustenance the matter of the
vegetable kingdom, which derived its support from the absorption and
conversion of inorganic matter. And so constant and universal is this
absorption, waste, and reproduction, that it may be said with perfect
certainty that there is left in no one of our bodies at the present
moment a millionth part of the matter of which they were originally
formed! We have seen, again, that not only is the living matter derived
from the inorganic world, but that the forces of that matter are all of
them correlative with and convertible into those of inorganic nature.

This, for our present purposes, is the best view of the present
condition of organic nature which I can lay before you: it gives you
the great outlines of a vast picture, which you must fill up by your own
study.

In the next lecture I shall endeavour in the same way to go back into
the past, and to sketch in the same broad manner the history of life in
epochs preceding our own.

End of The Present Condition of Organic Nature.




THE PAST CONDITION OF ORGANIC NATURE.

In the lecture which I delivered last Monday evening, I endeavoured to
sketch in a very brief manner, but as well as the time at my disposal
would permit, the present condition of organic nature, meaning by
that large title simply an indication of the great, broad, and general
principles which are to be discovered by those who look attentively at
the phenomena of organic nature as at present displayed. The general
result of our investigations might be summed up thus: we found that the
multiplicity of the forms of animal life, great as that may be, may be
reduced to a comparatively few primitive plans or types of construction;
that a further study of the development of those different forms
revealed to us that they were again reducible, until we at last brought
the infinite diversity of animal, and even vegetable life, down to the
primordial form of a single cell.

We found that our analysis of the organic world, whether animals or
plants, showed, in the long run, that they might both be reduced into,
and were, in fact, composed of, the same constituents. And we saw
that the plant obtained the materials constituting its substance by
a peculiar combination of matters belonging entirely to the inorganic
world; that, then, the animal was constantly appropriating the
nitrogenous matters of the plant to its own nourishment, and returning
them back to the inorganic world, in what we spoke of as its waste; and
that finally, when the animal ceased to exist, the constituents of its
body were dissolved and transmitted to that inorganic world whence they
had been at first abstracted. Thus we saw in both the blade of grass and
the horse but the same elements differently combined and arranged. We
discovered a continual circulation going on,--the plant drawing in the
elements of inorganic nature and combining them into food for the animal
creation; the animal borrowing from the plant the matter for its own
support, giving off during its life products which returned immediately
to the inorganic world; and that, eventually, the constituent materials
of the whole structure of both animals and plants were thus returned to
their original source: there was a constant passage from one state of
existence to another, and a returning back again.

Lastly, when we endeavoured to form some notion of the nature of the
forces exercised by living beings, we discovered that they--if
not capable of being subjected to the same minute analysis as the
constituents of those beings themselves--that they were correlative
with--that they were the equivalents of the forces of inorganic
nature--that they were, in the sense in which the term is now used,
convertible with them. That was our general result.

And now, leaving the Present, I must endeavour in the same manner to put
before you the facts that are to be discovered in the Past history of
the living world, in the past conditions of organic nature. We have,
to-night, to deal with the facts of that history--a history involving
periods of time before which our mere human records sink into utter
insignificance--a history the variety and physical magnitude of whose
events cannot even be foreshadowed by the history of human life and
human phenomena--a history of the most varied and complex character.

We must deal with the history, then, in the first place, as we should
deal with all other histories. The historical student knows that his
first business should be to inquire into the validity of his evidence,
and the nature of the record in which the evidence is contained, that
he may be able to form a proper estimate of the correctness of the
conclusions which have been drawn from that evidence. So, here, we must
pass, in the first place, to the consideration of a matter which may
seem foreign to the question under discussion. We must dwell upon the
nature of the records, and the credibility of the evidence they contain;
we must look to the completeness or incompleteness of those records
themselves, before we turn to that which they contain and reveal. The
question of the credibility of the history, happily for us, will not
require much consideration, for, in this history, unlike those of human
origin, there can be no cavilling, no differences as to the reality and
truth of the facts of which it is made up; the facts state themselves,
and are laid out clearly before us.

But, although one of the greatest difficulties of the historical student
is cleared out of our path, there are other difficulties--difficulties
in rightly interpreting the facts as they are presented to us--which
may be compared with the greatest difficulties of any other kinds of
historical study.

What is this record of the past history of the globe, and what are the
questions which are involved in an inquiry into its completeness or
incompleteness? That record is composed of mud; and the question which
we have to investigate this evening resolves itself into a question
of the formation of mud. You may think, perhaps, that this is a
vast step--of almost from the sublime to the ridiculous--from the
contemplation of the history of the past ages of the world's existence
to the consideration of the history of the formation of mud! But,
in nature, there is nothing mean and unworthy of attention; there
is nothing ridiculous or contemptible in any of her works; and this
inquiry, you will soon see, I hope, takes us to the very root and
foundations of our subject.

How, then, is mud formed? Always, with some trifling exception, which
I need not consider now--always, as the result of the action of water,
wearing down and disintegrating the surface of the earth and rocks with
which it comes in contact--pounding and grinding it down, and carrying
the particles away to places where they cease to be disturbed by this
mechanical action, and where they can subside and rest. For the ocean,
urged by winds, washes, as we know, a long extent of coast, and every
wave, loaded as it is with particles of sand and gravel as it breaks
upon the shore, does something towards the disintegrating process. And
thus, slowly but surely, the hardest rocks are gradually ground down to
a powdery substance; and the mud thus formed, coarser or finer, as the
case may be, is carried by the rush of the tides, or currents, till it
reaches the comparatively deeper parts of the ocean, in which it can
sink to the bottom, that is, to parts where there is a depth of about
fourteen or fifteen fathoms, a depth at which the water is, usually,
nearly motionless, and in which, of course, the finer particles of this
detritus, or mud as we call it, sinks to the bottom.

Or, again, if you take a river, rushing down from its mountain sources,
brawling over the stones and rocks that intersect its path, loosening,
removing, and carrying with it in its downward course the pebbles and
lighter matters from its banks, it crushes and pounds down the rocks and
earths in precisely the same way as the wearing action of the sea waves.
The matters forming the deposit are torn from the mountain-side and
whirled impetuously into the valley, more slowly over the plain, thence
into the estuary, and from the estuary they are swept into the sea. The
coarser and heavier fragments are obviously deposited first, that is,
as soon as the current begins to lose its force by becoming amalgamated
with the stiller depths of the ocean, but the finer and lighter
particles are carried further on, and eventually deposited in a deeper
and stiller portion of the ocean.

It clearly follows from this that mud gives us a chronology; for it is
evident that supposing this, which I now sketch, to be the sea bottom,
and supposing this to be a coast-line; from the washing action of the
sea upon the rock, wearing and grinding it down into a sediment of mud,
the mud will be carried down, and at length, deposited in the deeper
parts of this sea bottom, where it will form a layer; and then, while
that first layer is hardening, other mud which is coming from the same
source will, of course, be carried to the same place; and, as it is
quite impossible for it to get beneath the layer already there, it
deposits itself above it, and forms another layer, and in that way you
gradually have layers of mud constantly forming and hardening one above
the other, and conveying a record of time.

It is a necessary result of the operation of the law of gravitation that
the uppermost layer shall be the youngest and the lowest the oldest, and
that the different beds shall be older at any particular point or spot
in exactly the ratio of their depth from the surface. So that if they
were upheaved afterwards, and you had a series of these different layers
of mud, converted into sandstone, or limestone, as the case might be,
you might be sure that the bottom layer was deposited first, and that
the upper layers were formed afterwards. Here, you see, is the first
step in the history--these layers of mud give us an idea of time.

The whole surface of the earth,--I speak broadly, and leave out minor
qualifications,--is made up of such layers of mud, so hard, the majority
of them, that we call them rock whether limestone or sandstone, or other
varieties of rock. And, seeing that every part of the crust of the earth
is made up in this way, you might think that the determination of the
chronology, the fixing of the time which it has taken to form this crust
is a comparatively simple matter. Take a broad average, ascertain how
fast the mud is deposited upon the bottom of the sea, or in the estuary
of rivers; take it to be an inch, or two, or three inches a year, or
whatever you may roughly estimate it at; then take the total thickness
of the whole series of stratified rocks, which geologists estimate at
twelve or thirteen miles, or about seventy thousand feet, make a sum
in short division, divide the total thickness by that of the quantity
deposited in one year, and the result will, of course, give you the
number of years which the crust has taken to form.

Truly, that looks a very simple process! It would be so except for
certain difficulties, the very first of which is that of finding how
rapidly sediments are deposited; but the main difficulty--a difficulty
which renders any certain calculations of such a matter out of the
question--is this, the sea-bottom on which the deposit takes place is
continually shifting.

Instead of the surface of the earth being that stable, fixed thing that
it is popularly believed to be, being, in common parlance, the very
emblem of fixity itself, it is incessantly moving, and is, in fact,
as unstable as the surface of the sea, except that its undulations are
infinitely slower and enormously higher and deeper.

Now, what is the effect of this oscillation? Take the case to which
I have previously referred. The finer or coarser sediments that are
carried down by the current of the river, will only be carried out a
certain distance, and eventually, as we have already seen, on reaching
the stiller part of the ocean, will be deposited at the bottom.

(FIGURE 4. Section through deposits on sea-bottom and shore.)

Let C y (Figure 4) be the sea-bottom, y D the shore, x y the sea-level,
then the coarser deposit will subside over the region B, the finer over
A, while beyond A there will be no deposit at all; and, consequently, no
record will be kept, simply because no deposit is going on. Now, suppose
that the whole land, C, D, which we have regarded as stationary, goes
down, as it does so, both A and B go further out from the shore, which
will be at yl; x1, y1, being the new sea-level. The consequence will be
that the layer of mud (A), being now, for the most part, further than
the force of the current is strong enough to convey even the finest
'debris', will, of course, receive no more deposits, and having attained
a certain thickness will now grow no thicker.

We should be misled in taking the thickness of that layer, whenever it
may be exposed to our view, as a record of time in the manner in which
we are now regarding this subject, as it would give us only an imperfect
and partial record: it would seem to represent too short a period of
time.

Suppose, on the other hand, that the land (C D) had gone on rising
slowly and gradually--say an inch or two inches in the course of a
century,--what would be the practical effect of that movement? Why, that
the sediment A and B which has been already deposited, would eventually
be brought nearer to the shore-level, and again subjected to the wear
and tear of the sea; and directly the sea begins to act upon it, it
would of course soon cut up and carry it away, to a greater or less
extent, to be re-deposited further out.

Well, as there is, in all probability, not one single spot on the whole
surface of the earth, which has not been up and down in this way a great
many times, it follows that the thickness of the deposits formed at any
particular spot cannot be taken (even supposing we had at first obtained
correct data as to the rate at which they took place) as affording
reliable information as to the period of time occupied in its deposit.
So that you see it is absolutely necessary from these facts, seeing that
our record entirely consists of accumulations of mud, superimposed one
on the other; seeing in the next place that any particular spots on
which accumulations have occurred, have been constantly moving up and
down, and sometimes out of the reach of a deposit, and at other times
its own deposit broken up and carried away, it follows that our record
must be in the highest degree imperfect, and we have hardly a trace
left of thick deposits, or any definite knowledge of the area that they
occupied, in a great many cases. And mark this! That supposing even
that the whole surface of the earth had been accessible to the
geologist,--that man had had access to every part of the earth, and had
made sections of the whole, and put them all together,--even then his
record must of necessity be imperfect.

But to how much has man really access? If you will look at this Map you
will see that it represents the proportion of the sea to the earth: this
coloured part indicates all the dry land, and this other portion is the
water. You will notice at once that the water covers three-fifths of the
whole surface of the globe, and has covered it in the same manner ever
since man has kept any record of his own observations, to say nothing of
the minute period during which he has cultivated geological inquiry.
So that three-fifths of the surface of the earth is shut out from us
because it is under the sea. Let us look at the other two-fifths,
and see what are the countries in which anything that may be termed
searching geological inquiry has been carried out: a good deal of
France, Germany, and Great Britain and Ireland, bits of Spain, of
Italy, and of Russia, have been examined, but of the whole great mass of
Africa, except parts of the southern extremity, we know next to nothing;
little bits of India, but of the greater part of the Asiatic continent
nothing; bits of the Northern American States and of Canada, but of
the greater part of the continent of North America, and in still larger
proportion, of South America, nothing!

Under these circumstances, it follows that even with reference to that
kind of imperfect information which we can possess, it is only of about
the ten-thousandth part of the accessible parts of the earth that has
been examined properly. Therefore, it is with justice that the most
thoughtful of those who are concerned in these inquiries insist
continually upon the imperfection of the geological record; for, I
repeat, it is absolutely necessary, from the nature of things, that
that record should be of the most fragmentary and imperfect character.
Unfortunately this circumstance has been constantly forgotten. Men of
science, like young colts in a fresh pasture, are apt to be exhilarated
on being turned into a new field of inquiry, to go off at a hand-gallop,
in total disregard of hedges and ditches, losing sight of the real
limitation of their inquiries, and to forget the extreme imperfection of
what is really known. Geologists have imagined that they could tell us
what was going on at all parts of the earth's surface during a given
epoch; they have talked of this deposit being contemporaneous with
that deposit, until, from our little local histories of the changes at
limited spots of the earth's surface, they have constructed a universal
history of the globe as full of wonders and portents as any other story
of antiquity.

But what does this attempt to construct a universal history of the globe
imply? It implies that we shall not only have a precise knowledge of the
events which have occurred at any particular point, but that we shall
be able to say what events, at any one spot, took place at the same time
with those at other spots.

(FIGURE 5. Section through two beds of mud.)

Let us see how far that is in the nature of things practicable. Suppose
that here I make a section of the Lake of Killarney, and here the
section of another lake--that of Loch Lomond in Scotland for instance.
The rivers that flow into them are constantly carrying down deposits of
mud, and beds, or strata, are being as constantly formed, one above the
other, at the bottom of those lakes. Now, there is not a shadow of
doubt that in these two lakes the lower beds are all older than the
upper--there is no doubt about that; but what does 'this' tell us about
the age of any given bed in Loch Lomond, as compared with that of any
given bed in the Lake of Killarney? It is, indeed, obvious that if
any two sets of deposits are separated and discontinuous, there is
absolutely no means whatever given you by the nature of the deposit of
saying whether one is much younger or older than the other; but you may
say, as many have said and think, that the case is very much altered if
the beds which we are comparing are continuous. Suppose two beds of mud
hardened into rock,--A and B--are seen in section. (Figure 5.)

Well, you say, it is admitted that the lowermost bed is always the
older. Very well; B, therefore, is older than A. No doubt, 'as a whole',
it is so; or if any parts of the two beds which are in the same vertical
line are compared, it is so. But suppose you take what seems a very
natural step further, and say that the part 'a' of the bed A is younger
than the part 'b' of the bed B. Is this sound reasoning? If you find any
record of changes taking place at 'b', did they occur before any events
which took place while 'a' was being deposited? It looks all very plain
sailing, indeed, to say that they did; and yet there is no proof of
anything of the kind. As the former Director of this Institution, Sir
H. De la Beche, long ago showed, this reasoning may involve an entire
fallacy. It is extremely possible that 'a' may have been deposited ages
before 'b'. It is very easy to understand how that can be. To return
to Figure 4; when A and B were deposited, they were 'substantially'
contemporaneous; A being simply the finer deposit, and B the coarser
of the same detritus or waste of land. Now suppose that that sea-bottom
goes down (as shown in Figure 4), so that the first deposit is carried
no farther than 'a', forming the bed Al, and the coarse no farther
than 'b', forming the bed B1, the result will be the formation of two
continuous beds, one of fine sediment (A A1) over-lapping another of
coarse sediment (B Bl). Now suppose the whole sea-bottom is raised up,
and a section exposed about the point Al; no doubt, AT THIS SPOT, the
upper bed is younger than the lower. But we should obviously greatly err
if we concluded that the mass of the upper bed at A was younger than
the lower bed at B; for we have just seen that they are contemporaneous
deposits. Still more should we be in error if we supposed the upper bed
at A to be younger than the continuation of the lower bed at Bl; for
A was deposited long before B1. In fine, if, instead of comparing
immediately adjacent parts of two beds, one of which lies upon another,
we compare distant parts, it is quite possible that the upper may be any
number of years older than the under, and the under any number of years
younger than the upper.

Now you must not suppose that I put this before you for the purpose of
raising a paradoxical difficulty; the fact is, that the great mass of
deposits have taken place in sea-bottoms which are gradually sinking,
and have been formed under the very conditions I am here supposing.

Do not run away with the notion that this subverts the principle I
laid down at first. The error lies in extending a principle which is
perfectly applicable to deposits in the same vertical line to deposits
which are not in that relation to one another.

It is in consequence of circumstances of this kind, and of others that I
might mention to you, that our conclusions on and interpretations of
the record are really and strictly only valid so long as we confine
ourselves to one vertical section. I do not mean to tell you that there
are no qualifying circumstances, so that, even in very considerable
areas, we may safely speak of conformably superimposed beds being older
or younger than others at many different points. But we can never be
quite sure in coming to that conclusion, and especially we cannot
be sure if there is any break in their continuity, or any very great
distance between the points to be compared.

Well now, so much for the record itself,--so much for its
imperfections,--so much for the conditions to be observed in
interpreting it, and its chronological indications, the moment we pass
beyond the limits of a vertical linear section.

Now let us pass from the record to that which it contains,--from the
book itself to the writing and the figures on its pages. This writing
and these figures consist of remains of animals and plants which, in the
great majority of cases, have lived and died in the very spot in which
we now find them, or at least in the immediate vicinity. You must all of
you be aware--and I referred to the fact in my last lecture--that there
are vast numbers of creatures living at the bottom of the sea. These
creatures, like all others, sooner or later die, and their shells and
hard parts lie at the bottom; and then the fine mud which is being
constantly brought down by rivers and the action of the wear and tear of
the sea, covers them over and protects them from any further change
or alteration; and, of course, as in process of time the mud becomes
hardened and solidified, the shells of these animals are preserved
and firmly imbedded in the limestone or sandstone which is being thus
formed. You may see in the galleries of the Museum up stairs specimens
of limestones in which such fossil remains of existing animals are
imbedded. There are some specimens in which turtles' eggs have been
imbedded in calcareous sand, and before the sun had hatched the young
turtles, they became covered over with calcareous mud, and thus have
been preserved and fossilized.

Not only does this process of imbedding and fossilization occur with
marine and other aquatic animals and plants, but it affects those land
animals and plants which are drifted away to sea, or become buried in
bogs or morasses; and the animals which have been trodden down by their
fellows and crushed in the mud at the river's bank, as the herd have
come to drink. In any of these cases, the organisms may be crushed or be
mutilated, before or after putrefaction, in such a manner that perhaps
only a part will be left in the form in which it reaches us. It is,
indeed, a most remarkable fact, that it is quite an exceptional case
to find a skeleton of any one of all the thousands of wild land animals
that we know are constantly being killed, or dying in the course of
nature: they are preyed on and devoured by other animals or die in
places where their bodies are not afterwards protected by mud. There are
other animals existing in the sea, the shells of which form exceedingly
large deposits. You are probably aware that before the attempt was made
to lay the Atlantic telegraphic cable, the Government employed vessels
in making a series of very careful observations and soundings of the
bottom of the Atlantic; and although, as we must all regret, up to the
present time that project has not succeeded, we have the satisfaction
of knowing that it yielded some most remarkable results to science.
The Atlantic Ocean had to be sounded right across, to depths of several
miles in some places, and the nature of its bottom was carefully
ascertained. Well, now, a space of about 1,000 miles wide from east to
west, and I do not exactly know how many from north to south, but at
any rate 600 or 700 miles, was carefully examined, and it was found that
over the whole of that immense area an excessively fine chalky mud is
being deposited; and this deposit is entirely made up of animals whose
hard parts are deposited in this part of the ocean, and are doubtless
gradually acquiring solidity and becoming metamorphosed into a chalky
limestone. Thus, you see, it is quite possible in this way to preserve
unmistakable records of animal and vegetable life. Whenever the
sea-bottom, by some of those undulations of the earth's crust that I
have referred to, becomes upheaved, and sections or borings are made,
or pits are dug, then we become able to examine the contents and
constituents of these ancient sea-bottoms, and find out what manner of
animals lived at that period.

Now it is a very important consideration in its bearing on the
completeness of the record, to inquire how far the remains contained
in these fossiliferous limestones are able to convey anything like an
accurate or complete account of the animals which were in existence
at the time of its formation. Upon that point we can form a very clear
judgment, and one in which there is no possible room for any mistake.
There are of course a great number of animals--such as jelly-fishes,
and other animals--without any hard parts, of which we cannot reasonably
expect to find any traces whatever: there is nothing of them to
preserve. Within a very short time, you will have noticed, after they
are removed from the water, they dry up to a mere nothing; certainly
they are not of a nature to leave any very visible traces of their
existence on such bodies as chalk or mud. Then again, look at land
animals; it is, as I have said, a very uncommon thing to find a land
animal entire after death. Insects and other carnivorous animals very
speedily pull them to pieces, putrefaction takes place, and so, out of
the hundreds of thousands that are known to die every year, it is the
rarest thing in the world to see one imbedded in such a way that its
remains would be preserved for a lengthened period. Not only is this the
case, but even when animal remains have been safely imbedded, certain
natural agents may wholly destroy and remove them.

Almost all the hard parts of animals--the bones and so on--are composed
chiefly of phosphate of lime and carbonate of lime. Some years ago, I
had to make an inquiry into the nature of some very curious fossils
sent to me from the North of Scotland. Fossils are usually hard bony
structures that have become imbedded in the way I have described, and
have gradually acquired the nature and solidity of the body with which
they are associated; but in this case I had a series of 'holes' in some
pieces of rock, and nothing else. Those holes, however, had a certain
definite shape about them, and when I got a skilful workman to make
castings of the interior of these holes, I found that they were the
impressions of the joints of a backbone and of the armour of a great
reptile, twelve or more feet long. This great beast had died and got
buried in the sand; the sand had gradually hardened over the bones, but
remained porous. Water had trickled through it, and that water being
probably charged with a superfluity of carbonic acid, had dissolved all
the phosphate and carbonate of lime, and the bones themselves had thus
decayed and entirely disappeared; but as the sandstone happened to have
consolidated by that time, the precise shape of the bones was retained.
If that sandstone had remained soft a little longer, we should have
known nothing whatsoever of the existence of the reptile whose bones it
had encased.

How certain it is that a vast number of animals which have existed
at one period on this earth have entirely perished, and left no trace
whatever of their forms, may be proved to you by other considerations.
There are large tracts of sandstone in various parts of the world, in
which nobody has yet found anything but footsteps. Not a bone of any
description, but an enormous number of traces of footsteps. There is no
question about them. There is a whole valley in Connecticut covered with
these footsteps, and not a single fragment of the animals which made
them has yet been found. Let me mention another case while upon that
matter, which is even more surprising than those to which I have yet
referred. There is a limestone formation near Oxford, at a place called
Stonesfield, which has yielded the remains of certain very interesting
mammalian animals, and up to this time, if I recollect rightly, there
have been found seven specimens of its lower jaws, and not a bit of
anything else, neither limb-bones nor skull, or any part whatever; not
a fragment of the whole system! Of course, it would be preposterous
to imagine that the beasts had nothing else but a lower jaw!
The probability is, as Dr. Buckland showed, as the result of his
observations on dead dogs in the river Thames, that the lower jaw, not
being secured by very firm ligaments to the bones of the head, and being
a weighty affair, would easily be knocked off, or might drop away from
the body as it floated in water in a state of decomposition. The jaw
would thus be deposited immediately, while the rest of the body would
float and drift away altogether, ultimately reaching the sea, and
perhaps becoming destroyed. The jaw becomes covered up and preserved
in the river silt, and thus it comes that we have such a curious
circumstance as that of the lower jaws in the Stonesfield slates. So
that, you see, faulty as these layers of stone in the earth's crust
are, defective as they necessarily are as a record, the account of
contemporaneous vital phenomena presented by them is, by the necessity
of the case, infinitely more defective and fragmentary.

It was necessary that I should put all this very strongly before you,
because, otherwise, you might have been led to think differently of the
completeness of our knowledge by the next facts I shall state to you.

The researches of the last three-quarters of a century have, in truth,
revealed a wonderful richness of organic life in those rocks. Certainly
not fewer than thirty or forty thousand different species of fossils
have been discovered. You have no more ground for doubting that these
creatures really lived and died at or near the places in which we find
them than you have for like scepticism about a shell on the sea-shore.
The evidence is as good in the one case as in the other.

Our next business is to look at the general character of these fossil
remains, and it is a subject which it will be requisite to consider
carefully; and the first point for us is to examine how much the
extinct 'Flora' and 'Fauna' as a 'whole'--disregarding altogether
the 'succession' of their constituents, of which I shall speak
afterwards--differ from the 'Flora' and 'Fauna' of the present day;--how
far they differ in what we 'do' know about them, leaving altogether out
of consideration speculations based upon what we 'do not' know.

I strongly imagine that if it were not for the peculiar appearance that
fossilised animals have, any of you might readily walk through a museum
which contains fossil remains mixed up with those of the present forms
of life, and I doubt very much whether your uninstructed eyes would
lead you to see any vast or wonderful difference between the two. If
you looked closely, you would notice, in the first place, a great many
things very like animals with which you are acquainted now: you would
see differences of shape and proportion, but on the whole a close
similarity.

I explained what I meant by ORDERS the other day, when I described the
animal kingdom as being divided in sub-kingdoms, classes and orders. If
you divide the animal kingdom into orders, you will find that there are
about one hundred and twenty. The number may vary on one side or the
other, but this is a fair estimate. That is the sum total of the orders
of all the animals which we know now, and which have been known in past
times, and left remains behind.

Now, how many of those are absolutely extinct? That is to say, how many
of these orders of animals have lived at a former period of the world's
history, but have at present no representatives? That is the sense in
which I meant to use the word "extinct." I mean that those animals did
live on this earth at one time, but have left no one of their kind
with us at the present moment. So that estimating the number of extinct
animals is a sort of way of comparing the past creation as a whole with
the present as a whole. Among the mammalia and birds there are none
extinct; but when we come to the reptiles there is a most wonderful
thing: out of the eight orders, or thereabouts, which you can make among
reptiles, one-half are extinct. These diagrams of the plesiosaurus,
the ichthyosaurus, the pterodactyle, give you a notion of some of these
extinct reptiles. And here is a cast of the pterodactyle and bones of
the ichthyosaurus and the plesiosaurus, just as fresh as if it had been
recently dug up in a churchyard. Thus, in the reptile class, there are
no less than half of the orders which are absolutely extinct. If we turn
to the 'Amphibia', there was one extinct order, the Labyrinthodonts,
typified by the large salamander-like beast shown in this diagram.

No order of fishes is known to be extinct. Every fish that we find in
the strata--to which I have been referring--can be identified and placed
in one of the orders which exist at the present day. There is not known
to be a single ordinal form of insect extinct. There are only two orders
extinct among the 'Crustacea'. There is not known to be an extinct order
of these creatures, the parasitic and other worms; but there are
two, not to say three, absolutely extinct orders of this class, the
'Echinodermata'; out of all the orders of the 'Coelenterata' and
'Protozoa' only one, the Rugose Corals.

So that, you see, out of somewhere about 120 orders of animals, taking
them altogether, you will not, at the outside estimate, find above ten
or a dozen extinct. Summing up all the orders of animals which have left
remains behind them, you will not find above ten or a dozen which cannot
be arranged with those of the present day; that is to say, that the
difference does not amount to much more than ten per cent.: and the
proportion of extinct orders of plants is still smaller. I think that
that is a very astounding, a most astonishing fact, seeing the enormous
epochs of time which have elapsed during the constitution of the surface
of the earth as it at present exists; it is, indeed, a most astounding
thing that the proportion of extinct ordinal types should be so
exceedingly small.

But now, there is another point of view in which we must look at this
past creation. Suppose that we were to sink a vertical pit through the
floor beneath us, and that I could succeed in making a section right
through in the direction of New Zealand, I should find in each of the
different beds through which I passed the remains of animals which I
should find in that stratum and not in the others. First, I should come
upon beds of gravel or drift containing the bones of large animals, such
as the elephant, rhinoceros, and cave tiger. Rather curious things to
fall across in Piccadilly! If I should dig lower still, I should come
upon a bed of what we call the London clay, and in this, as you will see
in our galleries upstairs, are found remains of strange cattle, remains
of turtles, palms, and large tropical fruits; with shell-fish such as
you see the like of now only in tropical regions. If I went below
that, I should come upon the chalk, and there I should find something
altogether different, the remains of ichthyosauri and pterodactyles, and
ammonites, and so forth.

I do not know what Mr. Godwin Austin would say comes next, but probably
rocks containing more ammonites, and more ichthyosauri and plesiosauri,
with a vast number of other things; and under that I should meet with
yet older rocks, containing numbers of strange shells and fishes; and in
thus passing from the surface to the lowest depths of the earth's crust,
the forms of animal life and vegetable life which I should meet with
in the successive beds would, looking at them broadly, be the more
different the further that I went down. Or, in other words, inasmuch
as we started with the clear principle, that in a series of
naturally-disposed mud beds the lowest are the oldest, we should come
to this result, that the further we go back in time the more difference
exists between the animal and vegetable life of an epoch and that which
now exists. That was the conclusion to which I wished to bring you at
the end of this Lecture.

End of The Past Condition of Organic Nature.




THE METHOD BY WHICH THE CAUSES OF THE PRESENT AND PAST CONDITIONS OF ORGANIC NATURE ARE TO BE DISCOVERED.--THE ORIGINATION OF LIVING BEINGS.

In the two preceding lectures I have endeavoured to indicate to you the
extent of the subject-matter of the inquiry upon which we are engaged;
and now, having thus acquired some conception of the Past and Present
phenomena of Organic Nature, I must now turn to that which constitutes
the great problem which we have set before ourselves;--I mean, the
question of what knowledge we have of the causes of these phenomena of
organic nature, and how such knowledge is obtainable.

Here, on the threshold of the inquiry, an objection meets us. There are
in the world a number of extremely worthy, well-meaning persons, whose
judgments and opinions are entitled to the utmost respect on account of
their sincerity, who are of opinion that Vital Phenomena, and especially
all questions relating to the origin of vital phenomena, are questions
quite apart from the ordinary run of inquiry, and are, by their very
nature, placed out of our reach. They say that all these phenomena
originated miraculously, or in some way totally different from the
ordinary course of nature, and that therefore they conceive it to be
futile, not to say presumptuous, to attempt to inquire into them.

To such sincere and earnest persons, I would only say, that a question
of this kind is not to be shelved upon theoretical or speculative
grounds. You may remember the story of the Sophist who demonstrated to
Diogenes in the most complete and satisfactory manner that he could not
walk; that, in fact, all motion was an impossibility; and that Diogenes
refuted him by simply getting up and walking round his tub. So, in the
same way, the man of science replies to objections of this kind, by
simply getting up and walking onward, and showing what science has done
and is doing--by pointing to that immense mass of facts which have been
ascertained and systematized under the forms of the great doctrines of
Morphology, of Development, of Distribution, and the like. He sees an
enormous mass of facts and laws relating to organic beings, which
stand on the same good sound foundation as every other natural law; and
therefore, with this mass of facts and laws before us, therefore,
seeing that, as far as organic matters have hitherto been accessible and
studied, they have shown themselves capable of yielding to scientific
investigation, we may accept this as proof that order and law reign
there as well as in the rest of nature; and the man of science says
nothing to objectors of this sort, but supposes that we can and shall
walk to a knowledge of the origin of organic nature, in the same way
that we have walked to a knowledge of the laws and principles of the
inorganic world.

But there are objectors who say the same from ignorance and ill-will. To
such I would reply that the objection comes ill from them, and that the
real presumption, I may almost say the real blasphemy, in this matter,
is in the attempt to limit that inquiry into the causes of phenomena
which is the source of all human blessings, and from which has sprung
all human prosperity and progress; for, after all, we can accomplish
comparatively little; the limited range of our own faculties bounds us
on every side,--the field of our powers of observation is small enough,
and he who endeavours to narrow the sphere of our inquiries is only
pursuing a course that is likely to produce the greatest harm to his
fellow-men.

But now, assuming, as we all do, I hope, that these phenomena are
properly accessible to inquiry, and setting out upon our search into the
causes of the phenomena of organic nature, or, at any rate, setting out
to discover how much we at present know upon these abstruse matters, the
question arises as to what is to be our course of proceeding, and what
method we must lay down for our guidance. I reply to that question,
that our method must be exactly the same as that which is pursued in any
other scientific inquiry, the method of scientific investigation being
the same for all orders of facts and phenomena whatsoever.

I must dwell a little on this point, for I wish you to leave this room
with a very clear conviction that scientific investigation is not, as
many people seem to suppose, some kind of modern black art. I say that
you might easily gather this impression from the manner in which
many persons speak of scientific inquiry, or talk about inductive and
deductive philosophy, or the principles of the "Baconian philosophy."
I do protest that, of the vast number of cants in this world, there are
none, to my mind, so contemptible as the pseudoscientific cant which is
talked about the "Baconian philosophy."

To hear people talk about the great Chancellor--and a very great man he
certainly was,--you would think that it was he who had invented science,
and that there was no such thing as sound reasoning before the time of
Queen Elizabeth. Of course you say, that cannot possibly be true; you
perceive, on a moment's reflection, that such an idea is absurdly wrong,
and yet, so firmly rooted is this sort of impression,--I cannot call it
an idea, or conception,--the thing is too absurd to be entertained,--but
so completely does it exist at the bottom of most men's minds, that this
has been a matter of observation with me for many years past. There
are many men who, though knowing absolutely nothing of the subject with
which they may be dealing, wish, nevertheless, to damage the author of
some view with which they think fit to disagree. What they do, then,
is not to go and learn something about the subject, which one would
naturally think the best way of fairly dealing with it; but they abuse
the originator of the view they question, in a general manner, and wind
up by saying that, "After all, you know, the principles and method
of this author are totally opposed to the canons of the Baconian
philosophy." Then everybody applauds, as a matter of course, and agrees
that it must be so. But if you were to stop them all in the middle of
their applause, you would probably find that neither the speaker nor his
applauders could tell you how or in what way it was so; neither the
one nor the other having the slightest idea of what they mean when they
speak of the "Baconian philosophy."

You will understand, I hope, that I have not the slightest desire to
join in the outcry against either the morals, the intellect, or the
great genius of Lord Chancellor Bacon. He was undoubtedly a very great
man, let people say what they will of him; but notwithstanding all that
he did for philosophy, it would be entirely wrong to suppose that the
methods of modern scientific inquiry originated with him, or with his
age; they originated with the first man, whoever he was; and indeed
existed long before him, for many of the essential processes of
reasoning are exerted by the higher order of brutes as completely and
effectively as by ourselves. We see in many of the brute creation the
exercise of one, at least, of the same powers of reasoning as that which
we ourselves employ.

The method of scientific investigation is nothing but the expression of
the necessary mode of working of the human mind. It is simply the mode
at which all phenomena are reasoned about, rendered precise and
exact. There is no more difference, but there is just the same kind of
difference, between the mental operations of a man of science and those
of an ordinary person, as there is between the operations and methods of
a baker or of a butcher weighing out his goods in common scales, and the
operations of a chemist in performing a difficult and complex analysis
by means of his balance and finely-graduated weights. It is not that
the action of the scales in the one case, and the balance in the other,
differ in the principles of their construction or manner of working; but
the beam of one is set on an infinitely finer axis than the other, and
of course turns by the addition of a much smaller weight.

You will understand this better, perhaps, if I give you some familiar
example. You have all heard it repeated, I dare say, that men of science
work by means of Induction and Deduction, and that by the help of these
operations, they, in a sort of sense, wring from Nature certain other
things, which are called Natural Laws, and Causes, and that out of
these, by some cunning skill of their own, they build up Hypotheses and
Theories. And it is imagined by many, that the operations of the common
mind can be by no means compared with these processes, and that they
have to be acquired by a sort of special apprenticeship to the craft.
To hear all these large words, you would think that the mind of a man of
science must be constituted differently from that of his fellow men; but
if you will not be frightened by terms, you will discover that you are
quite wrong, and that all these terrible apparatus are being used by
yourselves every day and every hour of your lives.

There is a well-known incident in one of Moliere's plays, where the
author makes the hero express unbounded delight on being told that he
had been talking prose during the whole of his life. In the same way, I
trust, that you will take comfort, and be delighted with yourselves, on
the discovery that you have been acting on the principles of inductive
and deductive philosophy during the same period. Probably there is not
one here who has not in the course of the day had occasion to set in
motion a complex train of reasoning, of the very same kind, though
differing of course in degree, as that which a scientific man goes
through in tracing the causes of natural phenomena.

A very trivial circumstance will serve to exemplify this. Suppose you
go into a fruiterer's shop, wanting an apple,--you take up one, and, on
biting it, you find it is sour; you look at it, and see that it is hard
and green. You take up another one, and that too is hard, green, and
sour. The shopman offers you a third; but, before biting it, you examine
it, and find that it is hard and green, and you immediately say that you
will not have it, as it must be sour, like those that you have already
tried.

Nothing can be more simple than that, you think; but if you will take
the trouble to analyze and trace out into its logical elements what
has been done by the mind, you will be greatly surprised. In the first
place, you have performed the operation of INDUCTION. You found that,
in two experiences, hardness and greenness in apples go together with
sourness. It was so in the first case, and it was confirmed by the
second. True, it is a very small basis, but still it is enough to make
an induction from; you generalize the facts, and you expect to find
sourness in apples where you get hardness and greenness. You found upon
that a general law, that all hard and green apples are sour; and that,
so far as it goes, is a perfect induction. Well, having got your natural
law in this way, when you are offered another apple which you find is
hard and green, you say, "All hard and green apples are sour; this
apple is hard and green, therefore this apple is sour." That train of
reasoning is what logicians call a syllogism, and has all its various
parts and terms,--its major premiss, its minor premiss, and its
conclusion. And, by the help of further reasoning, which, if drawn out,
would have to be exhibited in two or three other syllogisms, you arrive
at your final determination, "I will not have that apple." So that, you
see, you have, in the first place, established a law by Induction, and
upon that you have founded a Deduction, and reasoned out the special
conclusion of the particular case. Well now, suppose, having got your
law, that at some time afterwards, you are discussing the qualities
of apples with a friend: you will say to him, "It is a very curious
thing,--but I find that all hard and green apples are sour!" Your friend
says to you, "But how do you know that?" You at once reply, "Oh, because
I have tried it over and over again, and have always found them to be
so." Well, if we were talking science instead of common sense, we should
call that an Experimental Verification. And, if still opposed, you go
further, and say, "I have heard from the people in Somersetshire and
Devonshire, where a large number of apples are grown, that they have
observed the same thing. It is also found to be the case in Normandy,
and in North America. In short, I find it to be the universal experience
of mankind wherever attention has been directed to the subject."
Whereupon, your friend, unless he is a very unreasonable man, agrees
with you, and is convinced that you are quite right in the conclusion
you have drawn. He believes, although perhaps he does not know he
believes it, that the more extensive Verifications are,--that the more
frequently experiments have been made, and results of the same kind
arrived at,--that the more varied the conditions under which the same
results have been attained, the more certain is the ultimate conclusion,
and he disputes the question no further. He sees that the experiment has
been tried under all sorts of conditions, as to time, place, and people,
with the same result; and he says with you, therefore, that the law you
have laid down must be a good one, and he must believe it.

In science we do the same thing;--the philosopher exercises precisely
the same faculties, though in a much more delicate manner. In scientific
inquiry it becomes a matter of duty to expose a supposed law to every
possible kind of verification, and to take care, moreover, that this is
done intentionally, and not left to a mere accident, as in the case of
the apples. And in science, as in common life, our confidence in a law
is in exact proportion to the absence of variation in the result of our
experimental verifications. For instance, if you let go your grasp of
an article you may have in your hand, it will immediately fall to
the ground. That is a very common verification of one of the best
established laws of nature--that of gravitation. The method by which men
of science establish the existence of that law is exactly the same as
that by which we have established the trivial proposition about
the sourness of hard and green apples. But we believe it in such an
extensive, thorough, and unhesitating manner because the universal
experience of mankind verifies it, and we can verify it ourselves at any
time; and that is the strongest possible foundation on which any natural
law can rest.

So much by way of proof that the method of establishing laws in science
is exactly the same as that pursued in common life. Let us now turn
to another matter (though really it is but another phase of the same
question), and that is, the method by which, from the relations of
certain phenomena, we prove that some stand in the position of causes
towards the others.

I want to put the case clearly before you, and I will therefore show you
what I mean by another familiar example. I will suppose that one of you,
on coming down in the morning to the parlour of your house, finds that a
tea-pot and some spoons which had been left in the room on the previous
evening are gone,--the window is open, and you observe the mark of a
dirty hand on the window-frame, and perhaps, in addition to that, you
notice the impress of a hob-nailed shoe on the gravel outside. All these
phenomena have struck your attention instantly, and before two minutes
have passed you say, "Oh, somebody has broken open the window, entered
the room, and run off with the spoons and the tea-pot!" That speech is
out of your mouth in a moment. And you will probably add, "I know there
has; I am quite sure of it!" You mean to say exactly what you know; but
in reality what you have said has been the expression of what is, in all
essential particulars, an Hypothesis. You do not 'know' it at all; it is
nothing but an hypothesis rapidly framed in your own mind! And it is an
hypothesis founded on a long train of inductions and deductions.

What are those inductions and deductions, and how have you got at this
hypothesis? You have observed, in the first place, that the window
is open; but by a train of reasoning involving many Inductions and
Deductions, you have probably arrived long before at the General
Law--and a very good one it is--that windows do not open of themselves;
and you therefore conclude that something has opened the window. A
second general law that you have arrived at in the same way is, that
tea-pots and spoons do not go out of a window spontaneously, and you are
satisfied that, as they are not now where you left them, they have been
removed. In the third place, you look at the marks on the window-sill,
and the shoemarks outside, and you say that in all previous experience
the former kind of mark has never been produced by anything else but
the hand of a human being; and the same experience shows that no other
animal but man at present wears shoes with hob-nails on them such as
would produce the marks in the gravel. I do not know, even if we could
discover any of those "missing links" that are talked about, that they
would help us to any other conclusion! At any rate the law which states
our present experience is strong enough for my present purpose.--You
next reach the conclusion, that as these kinds of marks have not been
left by any other animals than men, or are liable to be formed in any
other way than by a man's hand and shoe, the marks in question have been
formed by a man in that way. You have, further, a general law, founded
on observation and experience, and that, too, is, I am sorry to say, a
very universal and unimpeachable one,--that some men are thieves;
and you assume at once from all these premisses--and that is what
constitutes your hypothesis--that the man who made the marks outside and
on the window-sill, opened the window, got into the room, and stole your
tea-pot and spoons. You have now arrived at a 'Vera Causa';--you have
assumed a Cause which it is plain is competent to produce all the
phenomena you have observed. You can explain all these phenomena only by
the hypothesis of a thief. But that is a hypothetical conclusion, of the
justice of which you have no absolute proof at all; it is only rendered
highly probable by a series of inductive and deductive reasonings.

I suppose your first action, assuming that you are a man of ordinary
common sense, and that you have established this hypothesis to your own
satisfaction, will very likely be to go off for the police, and set
them on the track of the burglar, with the view to the recovery of your
property. But just as you are starting with this object, some person
comes in, and on learning what you are about, says, "My good friend,
you are going on a great deal too fast. How do you know that the man who
really made the marks took the spoons? It might have been a monkey that
took them, and the man may have merely looked in afterwards." You would
probably reply, "Well, that is all very well, but you see it is contrary
to all experience of the way tea-pots and spoons are abstracted; so
that, at any rate, your hypothesis is less probable than mine." While
you are talking the thing over in this way, another friend arrives, one
of that good kind of people that I was talking of a little while ago.
And he might say, "Oh, my dear sir, you are certainly going on a great
deal too fast. You are most presumptuous. You admit that all these
occurrences took place when you were fast asleep, at a time when you
could not possibly have known anything about what was taking place. How
do you know that the laws of Nature are not suspended during the night?
It may be that there has been some kind of supernatural interference in
this case." In point of fact, he declares that your hypothesis is one
of which you cannot at all demonstrate the truth, and that you are by no
means sure that the laws of Nature are the same when you are asleep as
when you are awake.

Well, now, you cannot at the moment answer that kind of reasoning. You
feel that your worthy friend has you somewhat at a disadvantage. You
will feel perfectly convinced in your own mind, however, that you are
quite right, and you say to him, "My good friend, I can only be guided
by the natural probabilities of the case, and if you will be kind enough
to stand aside and permit me to pass, I will go and fetch the police."
Well, we will suppose that your journey is successful, and that by good
luck you meet with a policeman; that eventually the burglar is found
with your property on his person, and the marks correspond to his hand
and to his boots. Probably any jury would consider those facts a very
good experimental verification of your hypothesis, touching the cause
of the abnormal phenomena observed in your parlour, and would act
accordingly.

Now, in this supposititious case, I have taken phenomena of a very
common kind, in order that you might see what are the different steps in
an ordinary process of reasoning, if you will only take the trouble to
analyse it carefully. All the operations I have described, you will
see, are involved in the mind of any man of sense in leading him to
a conclusion as to the course he should take in order to make good a
robbery and punish the offender. I say that you are led, in that case,
to your conclusion by exactly the same train of reasoning as that which
a man of science pursues when he is endeavouring to discover the origin
and laws of the most occult phenomena. The process is, and always must
be, the same; and precisely the same mode of reasoning was employed by
Newton and Laplace in their endeavours to discover and define the causes
of the movements of the heavenly bodies, as you, with your own common
sense, would employ to detect a burglar. The only difference is, that
the nature of the inquiry being more abstruse, every step has to be most
carefully watched, so that there may not be a single crack or flaw in
your hypothesis. A flaw or crack in many of the hypotheses of daily life
may be of little or no moment as affecting the general correctness of
the conclusions at which we may arrive; but, in a scientific inquiry,
a fallacy, great or small, is always of importance, and is sure to be
constantly productive of mischievous, if not fatal results.

Do not allow yourselves to be misled by the common notion that an
hypothesis is untrustworthy simply because it is an hypothesis. It is
often urged, in respect to some scientific conclusion, that, after
all, it is only an hypothesis. But what more have we to guide us in
nine-tenths of the most important affairs of daily life than hypotheses,
and often very ill-based ones? So that in science, where the evidence of
an hypothesis is subjected to the most rigid examination, we may rightly
pursue the same course. You may have hypotheses and hypotheses. A man
may say, if he likes, that the moon is made of green cheese: that is an
hypothesis. But another man, who has devoted a great deal of time and
attention to the subject, and availed himself of the most powerful
telescopes and the results of the observations of others, declares that
in his opinion it is probably composed of materials very similar to
those of which our own earth is made up: and that is also only an
hypothesis. But I need not tell you that there is an enormous difference
in the value of the two hypotheses. That one which is based on sound
scientific knowledge is sure to have a corresponding value; and that
which is a mere hasty random guess is likely to have but little value.
Every great step in our progress in discovering causes has been made
in exactly the same way as that which I have detailed to you. A person
observing the occurrence of certain facts and phenomena asks, naturally
enough, what process, what kind of operation known to occur in nature
applied to the particular case, will unravel and explain the mystery?
Hence you have the scientific hypothesis; and its value will be
proportionate to the care and completeness with which its basis had been
tested and verified. It is in these matters as in the commonest affairs
of practical life: the guess of the fool will be folly, while the guess
of the wise man will contain wisdom. In all cases, you see that the
value of the result depends on the patience and faithfulness with
which the investigator applies to his hypothesis every possible kind of
verification.

I dare say I may have to return to this point by-and-by; but having
dealt thus far with our logical methods, I must now turn to something
which, perhaps, you may consider more interesting, or, at any rate,
more tangible. But in reality there are but few things that can be more
important for you to understand than the mental processes and the means
by which we obtain scientific conclusions and theories.* ([Footnote]
*Those who wish to study fully the doctrines of which I have endeavoured
to give some rough and ready illustrations, must read Mr. John Stuart
Mill's 'System of Logic'.) Having granted that the inquiry is a proper
one, and having determined on the nature of the methods we are to pursue
and which only can lead to success, I must now turn to the consideration
of our knowledge of the nature of the processes which have resulted in
the present condition of organic nature.

Here, let me say at once, lest some of you misunderstand me, that I have
extremely little to report. The question of how the present condition of
organic nature came about, resolves itself into two questions. The first
is: How has organic or living matter commenced its existence? And the
second is: How has it been perpetuated? On the second question I shall
have more to say hereafter. But on the first one, what I now have to say
will be for the most part of a negative character.

If you consider what kind of evidence we can have upon this matter, it
will resolve itself into two kinds. We may have historical evidence and
we may have experimental evidence. It is, for example, conceivable, that
inasmuch as the hardened mud which forms a considerable portion of the
thickness of the earth's crust contains faithful records of the past
forms of life, and inasmuch as these differ more and more as we go
further down,--it is possible and conceivable that we might come to
some particular bed or stratum which should contain the remains of those
creatures with which organic life began upon the earth. And if we did
so, and if such forms of organic life were preservable, we should have
what I would call historical evidence of the mode in which organic life
began upon this planet. Many persons will tell you, and indeed you will
find it stated in many works on geology, that this has been done, and
that we really possess such a record; there are some who imagine that
the earliest forms of life of which we have as yet discovered any
record, are in truth the forms in which animal life began upon the
globe. The grounds on which they base that supposition are these:--That
if you go through the enormous thickness of the earth's crust and get
down to the older rocks, the higher vertebrate animals--the quadrupeds,
birds, and fishes--cease to be found; beneath them you find only the
invertebrate animals; and in the deepest and lowest rocks those remains
become scantier and scantier, not in any very gradual progression,
however, until, at length, in what are supposed to be the oldest rocks,
the animal remains which are found are almost always confined to four
forms--'Oldhamia', whose precise nature is not known, whether plant or
animal; 'Lingula', a kind of mollusc; 'Trilobites', a crustacean animal,
having the same essential plan of construction, though differing in
many details from a lobster or crab; and Hymenocaris, which is also a
crustacean. So that you have all the 'Fauna' reduced, at this period,
to four forms: one a kind of animal or plant that we know nothing about,
and three undoubted animals--two crustaceans and one mollusc.

I think, considering the organization of these mollusca and crustacea,
and looking at their very complex nature, that it does indeed require a
very strong imagination to conceive that these were the first created of
all living things. And you must take into consideration the fact that
we have not the slightest proof that these which we call the oldest beds
are really so: I repeat, we have not the slightest proof of it. When you
find in some places that in an enormous thickness of rocks there are but
very scanty traces of life, or absolutely none at all; and that in other
parts of the world rocks of the very same formation are crowded with the
records of living forms, I think it is impossible to place any reliance
on the supposition, or to feel oneself justified in supposing that these
are the forms in which life first commenced. I have not time here
to enter upon the technical grounds upon which I am led to this
conclusion,--that could hardly be done properly in half a dozen lectures
on that part alone;--I must content myself with saying that I do not at
all believe that these are the oldest forms of life.

I turn to the experimental side to see what evidence we have there.
To enable us to say that we know anything about the experimental
origination of organization and life, the investigator ought to be able
to take inorganic matters, such as carbonic acid, ammonia, water, and
salines, in any sort of inorganic combination, and be able to build them
up into Protein matter, and that that Protein matter ought to begin to
live in an organic form. That, nobody has done as yet, and I suspect it
will be a long while before anybody does do it. But the thing is by no
means so impossible as it looks; for the researches of modern chemistry
have shown us--I won't say the road towards it, but, if I may so say,
they have shown the finger-post pointing to the road that may lead to
it.

It is not many years ago--and you must recollect that Organic Chemistry
is a young science, not above a couple of generations old,--you must not
expect too much of it; it is not many years ago since it was said to be
perfectly impossible to fabricate any organic compound; that is to say,
any non-mineral compound which is to be found in an organized being. It
remained so for a very long period; but it is now a considerable number
of years since a distinguished foreign chemist contrived to fabricate
Urea, a substance of a very complex character, which forms one of the
waste products of animal structures. And of late years a number of other
compounds, such as Butyric Acid, and others, have been added to the
list. I need not tell you that chemistry is an enormous distance from
the goal I indicate; all I wish to point out to you is, that it is by no
means safe to say that that goal may not be reached one day. It may be
that it is impossible for us to produce the conditions requisite to the
origination of life; but we must speak modestly about the matter, and
recollect that Science has put her foot upon the bottom round of the
ladder. Truly he would be a bold man who would venture to predict where
she will be fifty years hence.

There is another inquiry which bears indirectly upon this question,
and upon which I must say a few words. You are all of you aware of the
phenomena of what is called spontaneous generation. Our forefathers,
down to the seventeenth century, or thereabouts, all imagined, in
perfectly good faith, that certain vegetable and animal forms gave
birth, in the process of their decomposition, to insect life. Thus,
if you put a piece of meat in the sun, and allowed it to putrefy, they
conceived that the grubs which soon began to appear were the result
of the action of a power of spontaneous generation which the meat
contained. And they could give you receipts for making various animal
and vegetable preparations which would produce particular kinds of
animals. A very distinguished Italian naturalist, named Redi, took up
the question, at a time when everybody believed in it; among others our
own great Harvey, the discoverer of the circulation of the blood. You
will constantly find his name quoted, however, as an opponent of the
doctrine of spontaneous generation; but the fact is, and you will see it
if you will take the trouble to look into his works, Harvey believed
it as profoundly as any man of his time; but he happened to enunciate a
very curious proposition--that every living thing came from an 'egg'; he
did not mean to use the word in the sense in which we now employ it, he
only meant to say that every living thing originated in a little rounded
particle of organized substance; and it is from this circumstance,
probably, that the notion of Harvey having opposed the doctrine
originated. Then came Redi, and he proceeded to upset the doctrine in a
very simple manner. He merely covered the piece of meat with some very
fine gauze, and then he exposed it to the same conditions. The result
of this was that no grubs or insects were produced; he proved that the
grubs originated from the insects who came and deposited their eggs in
the meat, and that they were hatched by the heat of the sun. By
this kind of inquiry he thoroughly upset the doctrine of spontaneous
generation, for his time at least.

Then came the discovery and application of the microscope to scientific
inquiries, which showed to naturalists that besides the organisms which
they already knew as living beings and plants, there were an immense
number of minute things which could be obtained apparently almost at
will from decaying vegetable and animal forms. Thus, if you took some
ordinary black pepper or some hay, and steeped it in water, you would
find in the course of a few days that the water had become impregnated
with an immense number of animalcules swimming about in all directions.
From facts of this kind naturalists were led to revive the theory
of spontaneous generation. They were headed here by an English
naturalist,--Needham,--and afterwards in France by the learned Buffon.
They said that these things were absolutely begotten in the water of
the decaying substances out of which the infusion was made. It did not
matter whether you took animal or vegetable matter, you had only to
steep it in water and expose it, and you would soon have plenty of
animalcules. They made an hypothesis about this which was a very fair
one. They said, this matter of the animal world, or of the higher
plants, appears to be dead, but in reality it has a sort of dim life
about it, which, if it is placed under fair conditions, will cause it
to break up into the forms of these little animalcules, and they will go
through their lives in the same way as the animal or plant of which they
once formed a part.

The question now became very hotly debated. Spallanzani, an Italian
naturalist, took up opposite views to those of Needham and Buffon, and
by means of certain experiments he showed that it was quite possible to
stop the process by boiling the water, and closing the vessel in which
it was contained. "Oh!" said his opponents; "but what do you know you
may be doing when you heat the air over the water in this way? You may
be destroying some property of the air requisite for the spontaneous
generation of the animalcules."

However, Spallanzani's views were supposed to be upon the right side,
and those of the others fell into discredit; although the fact was
that Spallanzani had not made good his views. Well, then, the subject
continued to be revived from time to time, and experiments were made by
several persons; but these experiments were not altogether satisfactory.
It was found that if you put an infusion in which animalcules would
appear if it were exposed to the air into a vessel and boiled it, and
then sealed up the mouth of the vessel, so that no air, save such as
had been heated to 212 degrees, could reach its contents, that then no
animalcules would be found; but if you took the same vessel and exposed
the infusion to the air, then you would get animalcules. Furthermore, it
was found that if you connected the mouth of the vessel with a red-hot
tube in such a way that the air would have to pass through the tube
before reaching the infusion, that then you would get no animalcules.
Yet another thing was noticed: if you took two flasks containing the
same kind of infusion, and left one entirely exposed to the air, and
in the mouth of the other placed a ball of cotton wool, so that the air
would have to filter itself through it before reaching the infusion,
that then, although you might have plenty of animalcules in the first
flask, you would certainly obtain none from the second.

These experiments, you see, all tended towards one conclusion--that the
infusoria were developed from little minute spores or eggs which
were constantly floating in the atmosphere, which lose their power of
germination if subjected to heat. But one observer now made another
experiment which seemed to go entirely the other way, and puzzled
him altogether. He took some of this boiled infusion that I have been
speaking of, and by the use of a mercurial bath--a kind of trough used
in laboratories--he deftly inverted a vessel containing the infusion
into the mercury, so that the latter reached a little beyond the level
of the mouth of the 'inverted' vessel. You see that he thus had a
quantity of the infusion shut off from any possible communication with
the outer air by being inverted upon a bed of mercury.

He then prepared some pure oxygen and nitrogen gases, and passed them
by means of a tube going from the outside of the vessel, up through the
mercury into the infusion; so that he thus had it exposed to a perfectly
pure atmosphere of the same constituents as the external air. Of course,
he expected he would get no infusorial animalcules at all in that
infusion; but, to his great dismay and discomfiture, he found he almost
always did get them.

Furthermore, it has been found that experiments made in the manner
described above answer well with most infusions; but that if you fill
the vessel with boiled milk, and then stop the neck with cotton-wool,
you 'will' have infusoria. So that you see there were two experiments
that brought you to one kind of conclusion, and three to another; which
was a most unsatisfactory state of things to arrive at in a scientific
inquiry.

Some few years after this, the question began to be very hotly discussed
in France. There was M. Pouchet, a professor at Rouen, a very learned
man, but certainly not a very rigid experimentalist. He published a
number of experiments of his own, some of which were very ingenious, to
show that if you went to work in a proper way, there was a truth in
the doctrine of spontaneous generation. Well, it was one of the most
fortunate things in the world that M. Pouchet took up this question,
because it induced a distinguished French chemist, M. Pasteur, to take
up the question on the other side; and he has certainly worked it out
in the most perfect manner. I am glad to say, too, that he has published
his researches in time to enable me to give you an account of them. He
verified all the experiments which I have just mentioned to you--and
then finding those extraordinary anomalies, as in the case of the
mercury bath and the milk, he set himself to work to discover their
nature. In the case of milk he found it to be a question of temperature.
Milk in a fresh state is slightly alkaline; and it is a very curious
circumstance, but this very slight degree of alkalinity seems to have
the effect of preserving the organisms which fall into it from the
air from being destroyed at a temperature of 212 degrees, which is the
boiling point. But if you raise the temperature 10 degrees when you boil
it, the milk behaves like everything else; and if the air with which
it comes in contact, after being boiled at this temperature, is passed
through a red-hot tube, you will not get a trace of organisms.

He then turned his attention to the mercury bath, and found on
examination that the surface of the mercury was almost always covered
with a very fine dust. He found that even the mercury itself was
positively full of organic matters; that from being constantly exposed
to the air, it had collected an immense number of these infusorial
organisms from the air. Well, under these circumstances he felt that the
case was quite clear, and that the mercury was not what it had appeared
to M. Schwann to be,--a bar to the admission of these organisms; but
that, in reality, it acted as a reservoir from which the infusion was
immediately supplied with the large quantity that had so puzzled him.

But not content with explaining the experiments of others, M. Pasteur
went to work to satisfy himself completely. He said to himself: "If
my view is right, and if, in point of fact, all these appearances of
spontaneous generation are altogether due to the falling of minute germs
suspended in the atmosphere,--why, I ought not only to be able to show
the germs, but I ought to be able to catch and sow them, and produce
the resulting organisms." He, accordingly, constructed a very ingenious
apparatus to enable him to accomplish this trapping of this "germ dust"
in the air. He fixed in the window of his room a glass tube, in the
centre of which he had placed a ball of gun-cotton, which, as you all
know, is ordinary cotton-wool, which, from having been steeped in strong
acid, is converted into a substance of great explosive power. It is also
soluble in alcohol and ether. One end of the glass tube was, of course,
open to the external air; and at the other end of it he placed an
aspirator, a contrivance for causing a current of the external air to
pass through the tube. He kept this apparatus going for four-and-twenty
hours, and then removed the 'dusted' gun-cotton, and dissolved it in
alcohol and ether. He then allowed this to stand for a few hours, and
the result was, that a very fine dust was gradually deposited at
the bottom of it. That dust, on being transferred to the stage of a
microscope, was found to contain an enormous number of starch grains.
You know that the materials of our food and the greater portion of
plants are composed of starch, and we are constantly making use of it in
a variety of ways, so that there is always a quantity of it suspended
in the air. It is these starch grains which form many of those bright
specks that we see dancing in a ray of light sometimes. But besides
these, M. Pasteur found also an immense number of other organic
substances such as spores of fungi, which had been floating about in the
air and had got caged in this way.

He went farther, and said to himself, "If these really are the things
that give rise to the appearance of spontaneous generation, I ought to
be able to take a ball of this 'dusted' gun-cotton and put it into one
of my vessels, containing that boiled infusion which has been kept away
from the air, and in which no infusoria are at present developed, and
then, if I am right, the introduction of this gun-cotton will give rise
to organisms."

Accordingly, he took one of these vessels of infusion, which had been
kept eighteen months, without the least appearance of life, and by a
most ingenious contrivance, he managed to break it open and introduce
such a ball of gun-cotton, without allowing the infusion or the cotton
ball to come into contact with any air but that which had been subjected
to a red heat, and in twenty-four hours he had the satisfaction of
finding all the indications of what had been hitherto called spontaneous
generation. He had succeeded in catching the germs and developing
organisms in the way he had anticipated.

It now struck him that the truth of his conclusions might be
demonstrated without all the apparatus he had employed. To do this, he
took some decaying animal or vegetable substance, such as urine, which
is an extremely decomposable substance, or the juice of yeast, or
perhaps some other artificial preparation, and filled a vessel having a
long tubular neck with it. He then boiled the liquid and bent that
long neck into an S shape or zig-zag, leaving it open at the end. The
infusion then gave no trace of any appearance of spontaneous generation,
however long it might be left, as all the germs in the air were
deposited in the beginning of the bent neck. He then cut the tube close
to the vessel, and allowed the ordinary air to have free and direct
access; and the result of that was the appearance of organisms in it, as
soon as the infusion had been allowed to stand long enough to allow
of the growth of those it received from the air, which was about
forty-eight hours. The result of M. Pasteur's experiments proved,
therefore, in the most conclusive manner, that all the appearances of
spontaneous generation arose from nothing more than the deposition of
the germs of organisms which were constantly floating in the air.

To this conclusion, however, the objection was made, that if that were
the cause, then the air would contain such an enormous number of these
germs, that it would be a continual fog. But M. Pasteur replied that
they are not there in anything like the number we might suppose, and
that an exaggerated view has been held on that subject; he showed that
the chances of animal or vegetable life appearing in infusions, depend
entirely on the conditions under which they are exposed. If they are
exposed to the ordinary atmosphere around us, why, of course, you may
have organisms appearing early. But, on the other hand, if they are
exposed to air from a great height, or from some very quiet cellar, you
will often not find a single trace of life.

So that M. Pasteur arrived at last at the clear and definite result,
that all these appearances are like the case of the worms in the piece
of meat, which was refuted by Redi, simply germs carried by the air and
deposited in the liquids in which they afterwards appear. For my own
part, I conceive that, with the particulars of M. Pasteur's experiments
before us, we cannot fail to arrive at his conclusions; and that the
doctrine of spontaneous generation has received a final 'coup de grace'.

You, of course, understand that all this in no way interferes with the
POSSIBILITY of the fabrication of organic matters by the direct method
to which I have referred, remote as that possibility may be.

End of The Origination of Living Beings.




THE PERPETUATION OF LIVING BEINGS, HEREDITARY TRANSMISSION AND VARIATION.

The inquiry which we undertook, at our last meeting, into the state of
our knowledge of the causes of the phenomena of organic nature,--of the
past and of the present,--resolved itself into two subsidiary inquiries:
the first was, whether we know anything, either historically or
experimentally, of the mode of origin of living beings; the second
subsidiary inquiry was, whether, granting the origin, we know anything
about the perpetuation and modifications of the forms of organic beings.
The reply which I had to give to the first question was altogether
negative, and the chief result of my last lecture was, that, neither
historically nor experimentally, do we at present know anything
whatsoever about the origin of living forms. We saw that, historically,
we are not likely to know anything about it, although we may perhaps
learn something experimentally; but that at present we are an enormous
distance from the goal I indicated.

I now, then, take up the next question, What do we know of the
reproduction, the perpetuation, and the modifications of the forms
of living beings, supposing that we have put the question as to their
origination on one side, and have assumed that at present the causes of
their origination are beyond us, and that we know nothing about them?
Upon this question the state of our knowledge is extremely different; it
is exceedingly large, and, if not complete, our experience is certainly
most extensive. It would be impossible to lay it all before you, and the
most I can do, or need do to-night, is to take up the principal points
and put them before you with such prominence as may subserve the
purposes of our present argument.

The method of the perpetuation of organic beings is of two kinds,--the
asexual and the sexual. In the first the perpetuation takes place from
and by a particular act of an individual organism, which sometimes may
not be classed as belonging to any sex at all. In the second case, it is
in consequence of the mutual action and interaction of certain portions
of the organisms of usually two distinct individuals,--the male and the
female. The cases of asexual perpetuation are by no means so common as
the cases of sexual perpetuation; and they are by no means so common in
the animal as in the vegetable world. You are all probably familiar with
the fact, as a matter of experience, that you can propagate plants
by means of what are called "cuttings;" for example, that by taking a
cutting from a geranium plant, and rearing it properly, by supplying it
with light and warmth and nourishment from the earth, it grows up
and takes the form of its parent, having all the properties and
peculiarities of the original plant.

Sometimes this process, which the gardener performs artificially, takes
place naturally; that is to say, a little bulb, or portion of the plant,
detaches itself, drops off, and becomes capable of growing as a separate
thing. That is the case with many bulbous plants, which throw off in
this way secondary bulbs, which are lodged in the ground and become
developed into plants. This is an asexual process, and from it results
the repetition or reproduction of the form of the original being from
which the bulb proceeds.

Among animals the same thing takes place. Among the lower forms of
animal life, the infusorial animalculae we have already spoken of throw
off certain portions, or break themselves up in various directions,
sometimes transversely or sometimes longitudinally; or they may give off
buds, which detach themselves and develop into their proper forms. There
is the common fresh-water Polype, for instance, which multiplies itself
in this way. Just in the same way as the gardener is able to multiply
and reproduce the peculiarities and characters of particular plants
by means of cuttings, so can the physiological experimentalist--as was
shown by the Abbe Trembley many years ago--so can he do the same thing
with many of the lower forms of animal life. M. de Trembley showed that
you could take a polype and cut it into two, or four, or many pieces,
mutilating it in all directions, and the pieces would still grow up
and reproduce completely the original form of the animal. These are
all cases of asexual multiplication, and there are other instances,
and still more extraordinary ones, in which this process takes place
naturally, in a more hidden, a more recondite kind of way. You are all
of you familiar with those little green insects, the 'Aphis' or blight,
as it is called. These little animals, during a very considerable part
of their existence, multiply themselves by means of a kind of internal
budding, the buds being developed into essentially asexual animals,
which are neither male nor female; they become converted into young
'Aphides', which repeat the process, and their offspring after them,
and so on again; you may go on for nine or ten, or even twenty or more
successions; and there is no very good reason to say how soon it might
terminate, or how long it might not go on if the proper conditions of
warmth and nourishment were kept up.

Sexual reproduction is quite a distinct matter. Here, in all these
cases, what is required is the detachment of two portions of the
parental organisms, which portions we know as the egg and the
spermatozoon. In plants it is the ovule and the pollen-grain, as in
the flowering plants, or the ovule and the antherozooid, as in the
flowerless. Among all forms of animal life, the spermatozoa proceed from
the male sex, and the egg is the product of the female. Now, what is
remarkable about this mode of reproduction is this, that the egg by
itself, or the spermatozoa by themselves, are unable to assume the
parental form; but if they be brought into contact with one another, the
effect of the mixture of organic substances proceeding from two sources
appears to confer an altogether new vigour to the mixed product. This
process is brought about, as we all know, by the sexual intercourse of
the two sexes, and is called the act of impregnation. The result of this
act on the part of the male and female is, that the formation of a new
being is set up in the ovule or egg; this ovule or egg soon begins to
be divided and subdivided, and to be fashioned into various complex
organisms, and eventually to develop into the form of one of its
parents, as I explained in the first lecture. These are the processes by
which the perpetuation of organic beings is secured. Why there should be
the two modes--why this re-invigoration should be required on the part
of the female element we do not know; but it is most assuredly the
fact, and it is presumable, that, however long the process of asexual
multiplication could be continued, I say there is good reason to believe
that it would come to an end if a new commencement were not obtained by
a conjunction of the two sexual elements.

That character which is common to these two distinct processes is
this, that, whether we consider the reproduction, or perpetuation, or
modification of organic beings as they take place asexually, or as they
may take place sexually,--in either case, I say, the offspring has a
constant tendency to assume, speaking generally, the character of the
parent. As I said just now, if you take a slip of a plant, and tend it
with care, it will eventually grow up and develop into a plant like
that from which it had sprung; and this tendency is so strong that, as
gardeners know, this mode of multiplying by means of cuttings is the
only secure mode of propagating very many varieties of plants; the
peculiarity of the primitive stock seems to be better preserved if you
propagate it by means of a slip than if you resort to the sexual mode.

Again, in experiments upon the lower animals, such as the polype, to
which I have referred, it is most extraordinary that, although cut up
into various pieces, each particular piece will grow up into the form of
the primitive stock; the head, if separated, will reproduce the body
and the tail; and if you cut off the tail, you will find that that will
reproduce the body and all the rest of the members, without in any way
deviating from the plan of the organism from which these portions have
been detached. And so far does this go, that some experimentalists have
carefully examined the lower orders of animals,--among them the
Abbe Spallanzani, who made a number of experiments upon snails and
salamanders,--and have found that they might mutilate them to an
incredible extent; that you might cut off the jaw or the greater part
of the head, or the leg or the tail, and repeat the experiment several
times, perhaps, cutting off the same member again and again; and yet
each of those types would be reproduced according to the primitive type:
nature making no mistake, never putting on a fresh kind of leg, or head,
or tail, but always tending to repeat and to return to the primitive
type.

It is the same in sexual reproduction: it is a matter of perfectly
common experience, that the tendency on the part of the offspring always
is, speaking broadly, to reproduce the form of the parents. The
proverb has it that the thistle does not bring forth grapes; so, among
ourselves, there is always a likeness, more or less marked and distinct,
between children and their parents. That is a matter of familiar and
ordinary observation. We notice the same thing occurring in the cases
of the domestic animals--dogs, for instance, and their offspring. In
all these cases of propagation and perpetuation, there seems to be
a tendency in the offspring to take the characters of the parental
organisms. To that tendency a special name is given--it is called
'Atavism', it expresses this tendency to revert to the ancestral type,
and comes from the Latin word 'atavus', ancestor.

Well, this 'Atavism' which I shall speak of, is, as I said before, one
of the most marked and striking tendencies of organic beings; but, side
by side with this hereditary tendency there is an equally distinct and
remarkable tendency to variation. The tendency to reproduce the original
stock has, as it were, its limits, and side by side with it there is a
tendency to vary in certain directions, as if there were two opposing
powers working upon the organic being, one tending to take it in a
straight line, and the other tending to make it diverge from that
straight line, first to one side and then to the other.

So that you see these two tendencies need not precisely contradict one
another, as the ultimate result may not always be very remote from what
would have been the case if the line had been quite straight.

This tendency to variation is less marked in that mode of propagation
which takes place asexually; it is in that mode that the minor
characters of animal and vegetable structures are most completely
preserved. Still, it will happen sometimes, that the gardener, when he
has planted a cutting of some favourite plant, will find, contrary to
his expectation, that the slip grows up a little different from the
primitive stock--that it produces flowers of a different colour or make,
or some deviation in one way or another. This is what is called the
'sporting' of plants.

In animals the phenomena of asexual propagation are so obscure, that
at present we cannot be said to know much about them; but if we turn to
that mode of perpetuation which results from the sexual process, then
we find variation a perfectly constant occurrence, to a certain extent;
and, indeed, I think that a certain amount of variation from the
primitive stock is the necessary result of the method of sexual
propagation itself; for, inasmuch as the thing propagated proceeds from
two organisms of different sexes and different makes and temperaments,
and as the offspring is to be either of one sex or the other, it is
quite clear that it cannot be an exact diagonal of the two, or it would
be of no sex at all; it cannot be an exact intermediate form between
that of each of its parents--it must deviate to one side or the other.
You do not find that the male follows the precise type of the male
parent, nor does the female always inherit the precise characteristics
of the mother,--there is always a proportion of the female character in
the male offspring, and of the male character in the female offspring.
That must be quite plain to all of you who have looked at all
attentively on your own children or those of your neighbours; you will
have noticed how very often it may happen that the son shall exhibit the
maternal type of character, or the daughter possess the characteristics
of the father's family. There are all sorts of intermixtures and
intermediate conditions between the two, where complexion, or beauty,
or fifty other different peculiarities belonging to either side of the
house, are reproduced in other members of the same family. Indeed, it
is sometimes to be remarked in this kind of variation, that the variety
belongs, strictly speaking, to neither of the immediate parents; you
will see a child in a family who is not like either its father or its
mother; but some old person who knew its grandfather or grandmother, or,
it may be, an uncle, or, perhaps, even a more distant relative, will see
a great similarity between the child and one of these. In this way it
constantly happens that the characteristic of some previous member
of the family comes out and is reproduced and recognised in the most
unexpected manner.

But apart from that matter of general experience, there are some cases
which put that curious mixture in a very clear light. You are aware that
the offspring of the Ass and the Horse, or rather of the he-Ass and the
Mare, is what is called a Mule; and, on the other hand, the offspring
of the Stallion and the she-Ass is what is called a 'Hinny'. I never saw
one myself; but they have been very carefully studied. Now, the
curious thing is this, that although you have the same elements in
the experiment in each case, the offspring is entirely different in
character, according as the male influence comes from the Ass or the
Horse. Where the Ass is the male, as in the case of the Mule, you find
that the head is like that of the Ass, that the ears are long, the
tail is tufted at the end, the feet are small, and the voice is an
unmistakable bray; these are all points of similarity to the Ass; but,
on the other hand, the barrel of the body and the cut of the neck are
much more like those of the Mare. Then, if you look at the Hinny,--the
result of the union of the Stallion and the she-Ass, then you find it is
the Horse that has the predominance; that the head is more like that
of the Horse, the ears are shorter, the legs coarser, and the type is
altogether altered; while the voice, instead of being a bray, is the
ordinary neigh of the Horse. Here, you see, is a most curious thing: you
take exactly the same elements, Ass and Horse, but you combine the sexes
in a different manner, and the result is modified accordingly. You
have in this case, however, a result which is not general and
universal--there is usually an important preponderance, but not always
on the same side.

Here, then, is one intelligible, and, perhaps, necessary cause of
variation: the fact, that there are two sexes sharing in the production
of the offspring, and that the share taken by each is different and
variable, not only for each combination, but also for different members
of the same family.

Secondly, there is a variation, to a certain extent--though, in
all probability, the influence of this cause has been very much
exaggerated--but there is no doubt that variation is produced, to a
certain extent, by what are commonly known as external conditions,--such
as temperature, food, warmth, and moisture. In the long run, every
variation depends, in some sense, upon external conditions, seeing that
everything has a cause of its own. I use the term "external conditions"
now in the sense in which it is ordinarily employed: certain it is, that
external conditions have a definite effect. You may take a plant which
has single flowers, and by dealing with the soil, and nourishment, and
so on, you may by-and-by convert single flowers into double flowers,
and make thorns shoot out into branches. You may thicken or make various
modifications in the shape of the fruit. In animals, too, you may
produce analogous changes in this way, as in the case of that deep
bronze colour which persons rarely lose after having passed any length
of time in tropical countries. You may also alter the development of
the muscles very much, by dint of training; all the world knows that
exercise has a great effect in this way; we always expect to find the
arm of a blacksmith hard and wiry, and possessing a large development
of the brachial muscles. No doubt training, which is one of the forms
of external conditions, converts what are originally only instructions,
teachings, into habits, or, in other words, into organizations, to a
great extent; but this second cause of variation cannot be considered
to be by any means a large one. The third cause that I have to mention,
however, is a very extensive one. It is one that, for want of a better
name, has been called "spontaneous variation;" which means that when
we do not know anything about the cause of phenomena, we call it
spontaneous. In the orderly chain of causes and effects in this world,
there are very few things of which it can be said with truth that they
are spontaneous. Certainly not in these physical matters,--in
these there is nothing of the kind,--everything depends on previous
conditions. But when we cannot trace the cause of phenomena, we call
them spontaneous.

Of these variations, multitudinous as they are, but little is known with
perfect accuracy. I will mention to you some two or three cases, because
they are very remarkable in themselves, and also because I shall want to
use them afterwards. Reaumur, a famous French naturalist, a great
many years ago, in an essay which he wrote upon the art of hatching
chickens,--which was indeed a very curious essay,--had occasion to speak
of variations and monstrosities. One very remarkable case had come under
his notice of a variation in the form of a human member, in the person
of a Maltese, of the name of Gratio Kelleia, who was born with six
fingers upon each hand, and the like number of toes to each of his feet.
That was a case of spontaneous variation. Nobody knows why he was born
with that number of fingers and toes, and as we don't know, we call it a
case of "spontaneous" variation. There is another remarkable case also.
I select these, because they happen to have been observed and noted very
carefully at the time. It frequently happens that a variation occurs,
but the persons who notice it do not take any care in noting down the
particulars, until at length, when inquiries come to be made, the exact
circumstances are forgotten; and hence, multitudinous as may be such
"spontaneous" variations, it is exceedingly difficult to get at the
origin of them.

The second case is one of which you may find the whole details in the
"Philosophical Transactions" for the year 1813, in a paper communicated
by Colonel Humphrey to the President of the Royal Society,--"On a new
Variety in the Breed of Sheep," giving an account of a very remarkable
breed of sheep, which at one time was well known in the northern states
of America, and which went by the name of the Ancon or the Otter breed
of sheep. In the year 1791, there was a farmer of the name of Seth
Wright in Massachusetts, who had a flock of sheep, consisting of a ram
and, I think, of some twelve or thirteen ewes. Of this flock of ewes,
one at the breeding-time bore a lamb which was very singularly formed;
it had a very long body, very short legs, and those legs were bowed!
I will tell you by-and-by how this singular variation in the breed of
sheep came to be noted, and to have the prominence that it now has. For
the present, I mention only these two cases; but the extent of variation
in the breed of animals is perfectly obvious to any one who has studied
natural history with ordinary attention, or to any person who compares
animals with others of the same kind. It is strictly true that there are
never any two specimens which are exactly alike; however similar, they
will always differ in some certain particular.

Now let us go back to Atavism,--to the hereditary tendency I spoke
of. What will come of a variation when you breed from it, when Atavism
comes, if I may say so, to intersect variation? The two cases of which
I have mentioned the history, give a most excellent illustration of
what occurs. Gratio Kelleia, the Maltese, married when he was twenty-two
years of age, and, as I suppose there were no six-fingered ladies in
Malta, he married an ordinary five-fingered person. The result of that
marriage was four children; the first, who was christened Salvator, had
six fingers and six toes, like his father; the second was George, who
had five fingers and toes, but one of them was deformed, showing a
tendency to variation; the third was Andre; he had five fingers and five
toes, quite perfect; the fourth was a girl, Marie; she had five fingers
and five toes, but her thumbs were deformed, showing a tendency toward
the sixth.

These children grew up, and when they came to adult years, they all
married, and of course it happened that they all married five-fingered
and five-toed persons. Now let us see what were the results. Salvator
had four children; they were two boys, a girl, and another boy; the
first two boys and the girl were six-fingered and six-toed like their
grandfather; the fourth boy had only five fingers and five toes. George
had only four children; there were two girls with six fingers and six
toes; there was one girl with six fingers and five toes on the right
side, and five fingers and five toes on the left side, so that she was
half and half. The last, a boy, had five fingers and five toes. The
third, Andre, you will recollect, was perfectly well-formed, and he had
many children whose hands and feet were all regularly developed. Marie,
the last, who, of course, married a man who had only five fingers, had
four children; the first, a boy, was born with six toes, but the other
three were normal.

Now observe what very extraordinary phenomena are presented here.
You have an accidental variation arising from what you may call a
monstrosity; you have that monstrosity tendency or variation diluted in
the first instance by an admixture with a female of normal construction,
and you would naturally expect that, in the results of such an union,
the monstrosity, if repeated, would be in equal proportion with the
normal type; that is to say, that the children would be half and half,
some taking the peculiarity of the father, and the others being of
the purely normal type of the mother; but you see we have a great
preponderance of the abnormal type. Well, this comes to be mixed once
more with the pure, the normal type, and the abnormal is again produced
in large proportion, notwithstanding the second dilution. Now what would
have happened if these abnormal types had intermarried with each other;
that is to say, suppose the two boys of Salvator had taken it into their
heads to marry their first cousins, the two first girls of George, their
uncle? You will remember that these are all of the abnormal type of
their grandfather. The result would probably have been, that their
offspring would have been in every case a further development of that
abnormal type. You see it is only in the fourth, in the person of
Marie, that the tendency, when it appears but slightly in the second
generation, is washed out in the third, while the progeny of Andre, who
escaped in the first instance, escape altogether.

We have in this case a good example of nature's tendency to the
perpetuation of a variation. Here it is certainly a variation which
carried with it no use or benefit; and yet you see the tendency to
perpetuation may be so strong, that, notwithstanding a great admixture
of pure blood, the variety continues itself up to the third generation,
which is largely marked with it. In this case, as I have said, there
was no means of the second generation intermarrying with any but
five-fingered persons, and the question naturally suggests itself, What
would have been the result of such marriage? Reaumur narrates this case
only as far as the third generation. Certainly it would have been
an exceedingly curious thing if we could have traced this matter any
further; had the cousins intermarried, a six-fingered variety of the
human race might have been set up.

To show you that this supposition is by no means an unreasonable one,
let me now point out what took place in the case of Seth Wright's sheep,
where it happened to be a matter of moment to him to obtain a breed
or raise a flock of sheep like that accidental variety that I have
described--and I will tell you why. In that part of Massachusetts where
Seth Wright was living, the fields were separated by fences, and the
sheep, which were very active and robust, would roam abroad, and without
much difficulty jump over these fences into other people's farms. As
a matter of course, this exuberant activity on the part of the
sheep constantly gave rise to all sorts of quarrels, bickerings, and
contentions among the farmers of the neighbourhood; so it occurred to
Seth Wright, who was, like his successors, more or less 'cute, that if
he could get a stock of sheep like those with the bandy legs, they would
not be able to jump over the fences so readily, and he acted upon that
idea. He killed his old ram, and as soon as the young one arrived at
maturity, he bred altogether from it. The result was even more striking
than in the human experiment which I mentioned just now. Colonel
Humphreys testifies that it always happened that the offspring were
either pure Ancons or pure ordinary sheep; that in no case was there
any mixing of the Ancons with the others. In consequence of this, in
the course of a very few years, the farmer was able to get a very
considerable flock of this variety, and a large number of them were
spread throughout Massachusetts. Most unfortunately, however--I suppose
it was because they were so common--nobody took enough notice of them to
preserve their skeletons; and although Colonel Humphreys states that he
sent a skeleton to the President of the Royal Society at the same time
that he forwarded his paper, I am afraid that the variety has entirely
disappeared; for a short time after these sheep had become prevalent in
that district, the Merino sheep were introduced; and as their wool was
much more valuable, and as they were a quiet race of sheep, and showed
no tendency to trespass or jump over fences, the Otter breed of sheep,
the wool of which was inferior to that of the Merino, was gradually
allowed to die out.

You see that these facts illustrate perfectly well what may be done if
you take care to breed from stocks that are similar to each other. After
having got a variation, if, by crossing a variation with the original
stock, you multiply that variation, and then take care to keep that
variation distinct from the original stock, and make them breed
together,--then you may almost certainly produce a race whose tendency
to continue the variation is exceedingly strong.

This is what is called "selection"; and it is by exactly the same
process as that by which Seth Wright bred his Ancon sheep, that
our breeds of cattle, dogs, and fowls, are obtained. There are some
possibilities of exception, but still, speaking broadly, I may say that
this is the way in which all our varied races of domestic animals have
arisen; and you must understand that it is not one peculiarity or one
characteristic alone in which animals may vary. There is not a single
peculiarity or characteristic of any kind, bodily or mental, in which
offspring may not vary to a certain extent from the parent and other
animals.

Among ourselves this is well known. The simplest physical peculiarity is
mostly reproduced. I know a case of a man whose wife has the lobe of
one of her ears a little flattened. An ordinary observer might scarcely
notice it, and yet every one of her children has an approximation to the
same peculiarity to some extent. If you look at the other extreme, too,
the gravest diseases, such as gout, scrofula, and consumption, may be
handed down with just the same certainty and persistence as we noticed
in the perpetuation of the bandy legs of the Ancon sheep.

However, these facts are best illustrated in animals, and the extent
of the variation, as is well known, is very remarkable in dogs. For
example, there are some dogs very much smaller than others; indeed, the
variation is so enormous that probably the smallest dog would be about
the size of the head of the largest; there are very great variations in
the structural forms not only of the skeleton but also in the shape of
the skull, and in the proportions of the face and the disposition of the
teeth.

The Pointer, the Retriever, Bulldog, and the Terrier, differ very
greatly, and yet there is every reason to believe that every one
of these races has arisen from the same source,--that all the most
important races have arisen by this selective breeding from accidental
variation.

A still more striking case of what may be done by selective breeding,
and it is a better case, because there is no chance of that partial
infusion of error to which I alluded, has been studied very carefully by
Mr. Darwin,--the case of the domestic pigeons. I dare say there may
be some among you who may be pigeon 'fanciers', and I wish you to
understand that in approaching the subject, I would speak with all
humility and hesitation, as I regret to say that I am not a pigeon
fancier. I know it is a great art and mystery, and a thing upon which
a man must not speak lightly; but I shall endeavour, as far as
my understanding goes, to give you a summary of the published and
unpublished information which I have gained from Mr. Darwin.

Among the enormous variety,--I believe there are somewhere about a
hundred and fifty kinds of pigeons,--there are four kinds which may
be selected as representing the extremest divergences of one kind from
another. Their names are the Carrier, the Pouter, the Fantail, and
the Tumbler. In the large diagrams they are each represented in their
relative sizes to each other. This first one is the Carrier; you will
notice this large excrescence on its beak; it has a comparatively small
head; there is a bare space round the eyes; it has a long neck, a very
long beak, very strong legs, large feet, long wings, and so on. The
second one is the Pouter, a very large bird, with very long legs and
beak. It is called the Pouter because it is in the habit of causing its
gullet to swell up by inflating it with air. I should tell you that all
pigeons have a tendency to do this at times, but in the Pouter it is
carried to an enormous extent. The birds appear to be quite proud of
their power of swelling and puffing themselves out in this way; and I
think it is about as droll a sight as you can well see to look at a
cage full of these pigeons puffing and blowing themselves out in this
ridiculous manner.

The third kind I mentioned--the Fantail--is a small bird, with
exceedingly small legs and a very small beak. It is most curiously
distinguished by the size and extent of its tail, which, instead of
containing twelve feathers, may have many more,--say thirty, or even
more--I believe there are some with as many as forty-two. This bird has
a curious habit of spreading out the feathers of its tail in such a
way that they reach forward, and touch its head; and if this can be
accomplished, I believe it is looked upon as a point of great beauty.

But here is the last great variety,--the Tumbler; and of that great
variety, one of the principal kinds, and one most prized, is the
specimen represented here--the short-faced Tumbler. Its beak is reduced
to a mere nothing. Just compare the beak of this one and that of the
first one, the Carrier--I believe the orthodox comparison of the head
and beak of a thoroughly well-bred Tumbler is to stick an oat into a
cherry, and that will give you the proper relative proportions of the
head and beak. The feet and legs are exceedingly small, and the bird
appears to be quite a dwarf when placed side by side with this great
Carrier.

These are differences enough in regard to their external appearance; but
these differences are by no means the whole or even the most important
of the differences which obtain between these birds. There is hardly
a single point of their structure which has not become more or less
altered; and to give you an idea of how extensive these alterations
are, I have here some very good skeletons, for which I am indebted to my
friend, Mr. Tegetmeier, a great authority in these matters; by means
of which, if you examine them by-and-by, you will be able to see the
enormous difference in their bony structures.

I had the privilege, some time ago, of access to some important MSS. of
Mr. Darwin, who, I may tell you, has taken very great pains and
spent much valuable time and attention on the investigation of these
variations, and getting together all the facts that bear upon them.
I obtained from these MSS. the following summary of the differences
between the domestic breeds of pigeons; that is to say, a notification
of the various points in which their organization differs. In the first
place, the back of the skull may differ a good deal, and the development
of the bones of the face may vary a great deal; the back varies a good
deal; the shape of the lower jaw varies; the tongue varies very greatly,
not only in correlation to the length and size of the beak, but it seems
also to have a kind of independent variation of its own. Then the amount
of naked skin round the eyes, and at the base of the beak, may vary
enormously; so may the length of the eyelids, the shape of the nostrils,
and the length of the neck. I have already noticed the habit of blowing
out the gullet, so remarkable in the Pouter, and comparatively so in the
others. There are great differences, too, in the size of the female and
the male, the shape of the body, the number and width of the processes
of the ribs, the development of the ribs, and the size, shape, and
development of the breastbone. We may notice, too,--and I mention
the fact because it has been disputed by what is assumed to be high
authority,--the variation in the number of the sacral vertebrae. The
number of these varies from eleven to fourteen, and that without any
diminution in the number of the vertebrae of the back or of the tail.
Then the number and position of the tail-feathers may vary enormously,
and so may the number of the primary and secondary feathers of the
wings. Again, the length of the feet and of the beak,--although they
have no relation to each other, yet appear to go together,--that is, you
have a long beak wherever you have long feet. There are differences also
in the periods of the acquirement of the perfect plumage,--the size
and shape of the eggs,--the nature of flight, and the powers of
flight,--so-called "homing" birds having enormous flying powers;*
([Footnote] *The "Carrier," I learn from Mr. Tegetmeier, does not
'carry'; a high-bred bird of this breed being but a poor flier. The
birds which fly long distances, and come home,--"homing" birds,--and are
consequently used as carriers, are not "carriers" in the fancy sense.)
while, on the other hand, the little Tumbler is so called because of its
extraordinary faculty of turning head over heels in the air, instead of
pursuing a direct course. And, lastly, the dispositions and voices of
the birds may vary. Thus the case of the pigeons shows you that there
is hardly a single particular,--whether of instinct, or habit, or
bony structure, or of plumage,--of either the internal economy or the
external shape, in which some variation or change may not take place,
which, by selective breeding, may become perpetuated, and form the
foundation of, and give rise to, a new race.

If you carry in your mind's eye these four varieties of pigeons, you
will bear with you as good a notion as you can have, perhaps, of the
enormous extent to which a deviation from a primitive type may be
carried by means of this process of selective breeding.

End of The Perpetuation of Living Beings.




THE CONDITIONS OF EXISTENCE AS AFFECTING THE PERPETUATION OF LIVING BEINGS.

In the last Lecture I endeavoured to prove to you that, while, as a
general rule, organic beings tend to reproduce their kind, there is
in them, also, a constantly recurring tendency to vary--to vary to a
greater or to a less extent. Such a variety, I pointed out to you, might
arise from causes which we do not understand; we therefore called it
spontaneous; and it might come into existence as a definite and marked
thing, without any gradations between itself and the form which preceded
it. I further pointed out, that such a variety having once arisen,
might be perpetuated to some extent, and indeed to a very marked extent,
without any direct interference, or without any exercise of that process
which we called selection. And then I stated further, that by such
selection, when exercised artificially--if you took care to breed only
from those forms which presented the same peculiarities of any variety
which had arisen in this manner--the variation might be perpetuated, as
far as we can see, indefinitely.

The next question, and it is an important one for us, is this: Is there
any limit to the amount of variation from the primitive stock which can
be produced by this process of selective breeding? In considering this
question, it will be useful to class the characteristics, in respect of
which organic beings vary, under two heads: we may consider structural
characteristics, and we may consider physiological characteristics.

In the first place, as regards structural characteristics, I endeavoured
to show you, by the skeletons which I had upon the table, and by
reference to a great many well-ascertained facts, that the different
breeds of Pigeons, the Carriers, Pouters, and Tumblers, might vary in
any of their internal and important structural characters to a very
great degree; not only might there be changes in the proportions of the
skull, and the characters of the feet and beaks, and so on; but that
there might be an absolute difference in the number of the vertebrae of
the back, as in the sacral vertebrae of the Pouter; and so great is the
extent of the variation in these and similar characters that I pointed
out to you, by reference to the skeletons and the diagrams, that these
extreme varieties may absolutely differ more from one another in their
structural characters than do what naturalists call distinct SPECIES
of pigeons; that is to say, that they differ so much in structure that
there is a greater difference between the Pouter and the Tumbler than
there is between such wild and distinct forms as the Rock Pigeon or
the Ring Pigeon, or the Ring Pigeon and the Stock Dove; and indeed
the differences are of greater value than this, for the structural
differences between these domesticated pigeons are such as would be
admitted by a naturalist, supposing he knew nothing at all about their
origin, to entitle them to constitute even distinct genera.

As I have used this term SPECIES, and shall probably use it a good deal,
I had better perhaps devote a word or two to explaining what I mean by
it.

Animals and plants are divided into groups, which become gradually
smaller, beginning with a KINGDOM, which is divided into SUB-KINGDOMS;
then come the smaller divisions called PROVINCES; and so on from a
PROVINCE to a CLASS from a CLASS to an ORDER, from ORDERS to FAMILIES,
and from these to GENERA, until we come at length to the smallest
groups of animals which can be defined one from the other by constant
characters, which are not sexual; and these are what naturalists call
SPECIES in practice, whatever they may do in theory.

If, in a state of nature, you find any two groups of living beings,
which are separated one from the other by some constantly-recurring
characteristic, I don't care how slight and trivial, so long as it is
defined and constant, and does not depend on sexual peculiarities, then
all naturalists agree in calling them two species; that is what is meant
by the use of the word species--that is to say, it is, for the practical
naturalist, a mere question of structural differences.* ([Footnote] * I
lay stress here on the PRACTICAL signification of "Species." Whether
a physiological test between species exist or not, it is hardly ever
applicable by the practical naturalist.)

We have seen now--to repeat this point once more, and it is very
essential that we should rightly understand it--we have seen that
breeds, known to have been derived from a common stock by selection, may
be as different in their structure from the original stock as species
may be distinct from each other.

But is the like true of the physiological characteristics of animals?
Do the physiological differences of varieties amount in degree to those
observed between forms which naturalists call distinct species? This is
a most important point for us to consider.

As regards the great majority of physiological characteristics, there
is no doubt that they are capable of being developed, increased, and
modified by selection.

There is no doubt that breeds may be made as different as species in
many physiological characters. I have already pointed out to you very
briefly the different habits of the breeds of Pigeons, all of which
depend upon their physiological peculiarities,--as the peculiar habit of
tumbling, in the Tumbler--the peculiarities of flight, in the "homing"
birds,--the strange habit of spreading out the tail, and walking in a
peculiar fashion, in the Fantail,--and, lastly, the habit of blowing
out the gullet, so characteristic of the Pouter. These are all due
to physiological modifications, and in all these respects these birds
differ as much from each other as any two ordinary species do.

So with Dogs in their habits and instincts. It is a physiological
peculiarity which leads the Greyhound to chase its prey by sight,--that
enables the Beagle to track it by the scent,--that impels the Terrier to
its rat-hunting propensity,--and that leads the Retriever to its
habit of retrieving. These habits and instincts are all the results of
physiological differences and peculiarities, which have been developed
from a common stock, at least there is every reason to believe so.
But it is a most singular circumstance, that while you may run through
almost the whole series of physiological processes, without finding a
check to your argument, you come at last to a point where you do find
a check, and that is in the reproductive processes. For there is a most
singular circumstance in respect to natural species--at least about some
of them--and it would be sufficient for the purposes of this argument if
it were true of only one of them, but there is, in fact, a great number
of such cases--and that is, that, similar as they may appear to be
to mere races or breeds, they present a marked peculiarity in the
reproductive process. If you breed from the male and female of the same
race, you of course have offspring of the like kind, and if you make the
offspring breed together, you obtain the same result, and if you breed
from these again, you will still have the same kind of offspring; there
is no check. But if you take members of two distinct species, however
similar they may be to each other and make them breed together, you will
find a check, with some modifications and exceptions, however, which I
shall speak of presently. If you cross two such species with each other,
then,--although you may get offspring in the case of the first cross,
yet, if you attempt to breed from the products of that crossing, which
are what are called HYBRIDS--that is, if you couple a male and a female
hybrid--then the result is that in ninety-nine cases out of a hundred
you will get no offspring at all; there will be no result whatsoever.

The reason of this is quite obvious in some cases; the male hybrids,
although possessing all the external appearances and characteristics
of perfect animals, are physiologically imperfect and deficient in the
structural parts of the reproductive elements necessary to generation.
It is said to be invariably the case with the male mule, the cross
between the Ass and the Mare; and hence it is, that, although crossing
the Horse with the Ass is easy enough, and is constantly done, as far as
I am aware, if you take two mules, a male and a female, and endeavour to
breed from them, you get no offspring whatever; no generation will take
place. This is what is called the sterility of the hybrids between two
distinct species.

You see that this is a very extraordinary circumstance; one does not see
why it should be. The common teleological explanation is, that it is
to prevent the impurity of the blood resulting from the crossing of one
species with another, but you see it does not in reality do anything of
the kind. There is nothing in this fact that hybrids cannot breed with
each other, to establish such a theory; there is nothing to prevent the
Horse breeding with the Ass, or the Ass with the Horse. So that this
explanation breaks down, as a great many explanations of this kind do,
that are only founded on mere assumptions.

Thus you see that there is a great difference between "mongrels," which
are crosses between distinct races, and "hybrids," which are crosses
between distinct species. The mongrels are, so far as we know, fertile
with one another. But between species, in many cases, you cannot succeed
in obtaining even the first cross: at any rate it is quite certain that
the hybrids are often absolutely infertile one with another.

Here is a feature, then, great or small as it may be, which
distinguishes natural species of animals. Can we find any approximation
to this in the different races known to be produced by selective
breeding from a common stock? Up to the present time the answer to that
question is absolutely a negative one. As far as we know at present,
there is nothing approximating to this check. In crossing the breeds
between the Fantail and the Pouter, the Carrier and the Tumbler, or any
other variety or race you may name--so far as we know at present--there
is no difficulty in breeding together the mongrels. Take the Carrier and
the Fantail, for instance, and let them represent the Horse and the Ass
in the case of distinct species; then you have, as the result of their
breeding, the Carrier-Fantail mongrel,--we will say the male and female
mongrel,--and, as far as we know, these two when crossed would not be
less fertile than the original cross, or than Carrier with Carrier.
Here, you see, is a physiological contrast between the races produced
by selective modification and natural species. I shall inquire into the
value of this fact, and of some modifying circumstances by and by; for
the present I merely put it broadly before you.

But while considering this question of the limitations of species, a
word must be said about what is called RECURRENCE--the tendency of races
which have been developed by selective breeding from varieties to return
to their primitive type. This is supposed by many to put an absolute
limit to the extent of selective and all other variations. People say,
"It is all very well to talk about producing these different races,
but you know very well that if you turned all these birds wild, these
Pouters, and Carriers, and so on, they would all return to their
primitive stock." This is very commonly assumed to be a fact, and it is
an argument that is commonly brought forward as conclusive; but if you
will take the trouble to inquire into it rather closely, I think you
will find that it is not worth very much. The first question of course
is, Do they thus return to the primitive stock? And commonly as the
thing is assumed and accepted, it is extremely difficult to get anything
like good evidence of it. It is constantly said, for example, that if
domesticated Horses are turned wild, as they have been in some parts of
Asia Minor and South America, that they return at once to the primitive
stock from which they were bred. But the first answer that you make to
this assumption is, to ask who knows what the primitive stock was; and
the second answer is, that in that case the wild Horses of Asia Minor
ought to be exactly like the wild Horses of South America. If they are
both like the same thing, they ought manifestly to be like each other!
The best authorities, however, tell you that it is quite different. The
wild Horse of Asia is said to be of a dun colour, with a largish head,
and a great many other peculiarities; while the best authorities on
the wild Horses of South America tell you that there is no similarity
between their wild Horses and those of Asia Minor; the cut of their
heads is very different, and they are commonly chestnut or bay-coloured.
It is quite clear, therefore, that as by these facts there ought to
have been two primitive stocks, they go for nothing in support of the
assumption that races recur to one primitive stock, and so far as this
evidence is concerned, it falls to the ground.

Suppose for a moment that it were so, and that domesticated races, when
turned wild, did return to some common condition, I cannot see that this
would prove much more than that similar conditions are likely to produce
similar results; and that when you take back domesticated animals into
what we call natural conditions, you do exactly the same thing as if you
carefully undid all the work you had gone through, for the purpose of
bringing the animal from its wild to its domesticated state. I do not
see anything very wonderful in the fact, if it took all that trouble to
get it from a wild state, that it should go back into its original state
as soon as you removed the conditions which produced the variation to
the domesticated form. There is an important fact, however, forcibly
brought forward by Mr. Darwin, which has been noticed in connection with
the breeding of domesticated pigeons; and it is, that however different
these breeds of pigeons may be from each other, and we have already
noticed the great differences in these breeds, that if, among any of
those variations, you chance to have a blue pigeon turn up, it will be
sure to have the black bars across the wings, which are characteristic
of the original wild stock, the Rock Pigeon.

Now, this is certainly a very remarkable circumstance; but I do not see
myself how it tells very strongly either one way or the other. I think,
in fact, that this argument in favour of recurrence to the primitive
type might prove a great deal too much for those who so constantly
bring it forward. For example, Mr. Darwin has very forcibly urged,
that nothing is commoner than if you examine a dun horse--and I had an
opportunity of verifying this illustration lately, while in the islands
of the West Highlands, where there are a great many dun horses--to find
that horse exhibit a long black stripe down his back, very often stripes
on his shoulder, and very often stripes on his legs. I, myself, saw
a pony of this description a short time ago, in a baker's cart, near
Rothesay, in Bute: it had the long stripe down the back, and stripes on
the shoulders and legs, just like those of the Ass, the Quagga, and the
Zebra. Now, if we interpret the theory of recurrence as applied to
this case, might it not be said that here was a case of a variation
exhibiting the characters and conditions of an animal occupying
something like an intermediate position between the Horse, the Ass, the
Quagga, and the Zebra, and from which these had been developed? In the
same way with regard even to Man. Every anatomist will tell you that
there is nothing commoner, in dissecting the human body, than to meet
with what are called muscular variations--that is, if you dissect
two bodies very carefully, you will probably find that the modes of
attachment and insertion of the muscles are not exactly the same in
both, there being great peculiarities in the mode in which the muscles
are arranged; and it is very singular, that in some dissections of the
human body you will come upon arrangements of the muscles very similar
indeed to the same parts in the Apes. Is the conclusion in that case to
be, that this is like the black bars in the case of the Pigeon, and that
it indicates a recurrence to the primitive type from which the animals
have been probably developed? Truly, I think that the opponents of
modification and variation had better leave the argument of recurrence
alone, or it may prove altogether too strong for them.

To sum up--the evidence as far as we have gone is against the argument
as to any limit to divergences, so far as structure is concerned; and
in favour of a physiological limitation. By selective breeding we can
produce structural divergences as great as those of species, but we
cannot produce equal physiological divergences. For the present I leave
the question there.

Now, the next problem that lies before us--and it is an extremely
important one--is this: Does this selective breeding occur in nature?
Because, if there is no proof of it, all that I have been telling you
goes for nothing in accounting for the origin of species. Are natural
causes competent to play the part of selection in perpetuating
varieties? Here we labour under very great difficulties. In the last
lecture I had occasion to point out to you the extreme difficulty of
obtaining evidence even of the first origin of those varieties which we
know to have occurred in domesticated animals. I told you, that almost
always the origin of these varieties is overlooked, so that I could only
produce two of three cases, as that of Gratio Kelleia and of the Ancon
sheep. People forget, or do not take notice of them until they come to
have a prominence; and if that is true of artificial cases, under our
own eyes, and in animals in our own care, how much more difficult it
must be to have at first hand good evidence of the origin of varieties
in nature! Indeed, I do not know that it is possible by direct evidence
to prove the origin of a variety in nature, or to prove selective
breeding; but I will tell you what we can prove--and this comes to the
same thing--that varieties exist in nature within the limits of species,
and, what is more, that when a variety has come into existence in
nature, there are natural causes and conditions, which are amply
competent to play the part of a selective breeder; and although that
is not quite the evidence that one would like to have--though it is
not direct testimony--yet it is exceeding good and exceedingly powerful
evidence in its way.

As to the first point, of varieties existing among natural species, I
might appeal to the universal experience of every naturalist, and of any
person who has ever turned any attention at all to the characteristics
of plants and animals in a state of nature; but I may as well take a few
definite cases, and I will begin with Man himself.

I am one of those who believe that, at present, there is no evidence
whatever for saying, that mankind sprang originally from any more than a
single pair; I must say, that I cannot see any good ground whatever, or
even any tenable sort of evidence, for believing that there is more than
one species of Man. Nevertheless, as you know, just as there are numbers
of varieties in animals, so there are remarkable varieties of men. I
speak not merely of those broad and distinct variations which you see at
a glance. Everybody, of course, knows the difference between a Negro and
a white man, and can tell a Chinaman from an Englishman. They each
have peculiar characteristics of colour and physiognomy; but you must
recollect that the characters of these races go very far deeper--they
extend to the bony structure, and to the characters of that most
important of all organs to us--the brain; so that, among men belonging
to different races, or even within the same race, one man shall have a
brain a third, or half, or even seventy per cent. bigger than another;
and if you take the whole range of human brains, you will find a
variation in some cases of a hundred per cent. Apart from these
variations in the size of the brain, the characters of the skull vary.
Thus if I draw the figures of a Mongul and of a Negro head on the
blackboard, in the case of the last the breadth would be about
seven-tenths, and in the other it would be nine-tenths of the total
length. So that you see there is abundant evidence of variation among
men in their natural condition. And if you turn to other animals there
is just the same thing. The fox, for example, which has a very large
geographical distribution all over Europe, and parts of Asia, and on the
American Continent, varies greatly. There are mostly large foxes in the
North, and smaller ones in the South. In Germany alone, the foresters
reckon some eight different sorts.

Of the tiger, no one supposes that there is more than one species; they
extend from the hottest parts of Bengal, into the dry, cold, bitter
steppes of Siberia, into a latitude of 50 degrees,--so that they may
even prey upon the reindeer. These tigers have exceedingly different
characteristics, but still they all keep their general features, so that
there is no doubt as to their being tigers. The Siberian tiger has a
thick fur, a small mane, and a longitudinal stripe down the back, while
the tigers of Java and Sumatra differ in many important respects from
the tigers of Northern Asia. So lions vary; so birds vary; and so, if
you go further back and lower down in creation, you find that fishes
vary. In different streams, in the same country even, you will find the
trout to be quite different to each other and easily recognisable by
those who fish in the particular streams. There is the same differences
in leeches; leech collectors can easily point out to you the differences
and the peculiarities which you yourself would probably pass by; so with
fresh-water mussels; so, in fact, with every animal you can mention.

In plants there is the same kind of variation. Take such a case even as
the common bramble. The botanists are all at war about it; some of
them wanting to make out that there are many species of it, and others
maintaining that they are but many varieties of one species; and they
cannot settle to this day which is a species and which is a variety!

So that there can be no doubt whatsoever that any plant and any
animal may vary in nature; that varieties may arise in the way I have
described,--as spontaneous varieties,--and that those varieties may be
perpetuated in the same way that I have shown you spontaneous varieties
are perpetuated; I say, therefore, that there can be no doubt as to the
origin and perpetuation of varieties in nature.

But the question now is:--Does selection take place in nature? is there
anything like the operation of man in exercising selective breeding,
taking place in nature? You will observe that, at present, I say nothing
about species; I wish to confine myself to the consideration of the
production of those natural races which everybody admits to exist. The
question is, whether in nature there are causes competent to produce
races, just in the same way as man is able to produce by selection, such
races of animals as we have already noticed.

When a variety has arisen, the CONDITIONS OF EXISTENCE are such as to
exercise an influence which is exactly comparable to that of artificial
selection. By Conditions of Existence I mean two things,--there are
conditions which are furnished by the physical, the inorganic world,
and there are conditions of existence which are furnished by the organic
world. There is, in the first place, CLIMATE; under that head I include
only temperature and the varied amount of moisture of particular places.
In the next place there is what is technically called STATION, which
means--given the climate, the particular kind of place in which an
animal or a plant lives or grows; for example, the station of a fish
is in the water, of a fresh-water fish in fresh water; the station of a
marine fish is in the sea, and a marine animal may have a station higher
or deeper. So again with land animals: the differences in their stations
are those of different soils and neighbourhoods; some being best adapted
to a calcareous, and others to an arenaceous soil. The third condition
of existence is FOOD, by which I mean food in the broadest sense, the
supply of the materials necessary to the existence of an organic being;
in the case of a plant the inorganic matters, such as carbonic acid,
water, ammonia, and the earthy salts or salines; in the case of the
animal the inorganic and organic matters, which we have seen they
require; then these are all, at least the two first, what we may
call the inorganic or physical conditions of existence. Food takes a
mid-place, and then come the organic conditions; by which I mean the
conditions which depend upon the state of the rest of the organic
creation, upon the number and kind of living beings, with which an
animal is surrounded. You may class these under two heads: there are
organic beings, which operate as 'opponents', and there are organic
beings which operate as 'helpers' to any given organic creature. The
opponents may be of two kinds: there are the 'indirect opponents', which
are what we may call 'rivals'; and there are the 'direct opponents',
those which strive to destroy the creature; and these we call 'enemies'.
By rivals I mean, of course, in the case of plants, those which require
for their support the same kind of soil and station, and, among animals,
those which require the same kind of station, or food, or climate; those
are the indirect opponents; the direct opponents are, of course, those
which prey upon an animal or vegetable. The 'helpers' may also be
regarded as direct and indirect: in the case of a carnivorous animal,
for example, a particular herbaceous plant may in multiplying be an
indirect helper, by enabling the herbivora on which the carnivore preys
to get more food, and thus to nourish the carnivore more abundantly;
the direct helper may be best illustrated by reference to some parasitic
creature, such as the tape-worm. The tape-worm exists in the human
intestines, so that the fewer there are of men the fewer there will be
of tape-worms, other things being alike. It is a humiliating reflection,
perhaps, that we may be classed as direct helpers to the tape-worm, but
the fact is so: we can all see that if there were no men there would be
no tape-worms.

It is extremely difficult to estimate, in a proper way, the importance
and the working of the Conditions of Existence. I do not think there
were any of us who had the remotest notion of properly estimating them
until the publication of Mr. Darwin's work, which has placed them before
us with remarkable clearness; and I must endeavour, as far as I can in
my own fashion, to give you some notion of how they work. We shall find
it easiest to take a simple case, and one as free as possible from every
kind of complication.

I will suppose, therefore, that all the habitable part of this
globe--the dry land, amounting to about 51,000,000 square miles,--I will
suppose that the whole of that dry land has the same climate, and that
it is composed of the same kind of rock or soil, so that there will be
the same station everywhere; we thus get rid of the peculiar influence
of different climates and stations. I will then imagine that there shall
be but one organic being in the world, and that shall be a plant. In
this we start fair. Its food is to be carbonic acid, water and ammonia,
and the saline matters in the soil, which are, by the supposition,
everywhere alike. We take one single plant, with no opponents, no
helpers, and no rivals; it is to be a "fair field, and no favour". Now,
I will ask you to imagine further that it shall be a plant which shall
produce every year fifty seeds, which is a very moderate number for a
plant to produce; and that, by the action of the winds and currents,
these seeds shall be equally and gradually distributed over the whole
surface of the land. I want you now to trace out what will occur, and
you will observe that I am not talking fallaciously any more than a
mathematician does when he expounds his problem. If you show that the
conditions of your problem are such as may actually occur in nature and
do not transgress any of the known laws of nature in working out your
proposition, then you are as safe in the conclusion you arrive at as
is the mathematician in arriving at the solution of his problem. In
science, the only way of getting rid of the complications with which a
subject of this kind is environed, is to work in this deductive method.
What will be the result, then? I will suppose that every plant requires
one square foot of ground to live upon; and the result will be that,
in the course of nine years, the plant will have occupied every single
available spot in the whole globe! I have chalked upon the blackboard
the figures by which I arrive at the result:--


                  Plants.                               Plants
                    1 x 50 in 1st year =                    50
                   50 x 50 "  2nd "    =                 2,500
                2,500 x 50 "  3rd "    =               125,000
              125,000 x 50 "  4th "    =             6,250,000
            6,250,000 x 50 "  5th "    =           312,500,000
          312,500,000 x 50 "  6th "    =        15,625,000,000
       15,625,000,000 x 50 "  7th "    =       781,250,000,000
      781,250,000,000 x 50 "  8th "    =    39,062,500,000,000
   39,062,500,000,000 x 50 "  9th "    = 1,953,125,000,000,000


51,000,000 sq. miles--the dry surface of the earth x 27,878,400--the
number of sq. ft. in 1 sq. mile = sq. ft. 1,421,798,400,000,000 being
531,326,600,000,000 square feet less than would be required at the end
of the ninth year.

You will see from this that, at the end of the first year the single
plant will have produced fifty more of its kind; by the end of the
second year these will have increased to 2,500; and so on, in succeeding
years, you get beyond even trillions; and I am not at all sure that I
could tell you what the proper arithmetical denomination of the total
number really is; but, at any rate, you will understand the meaning of
all those noughts. Then you see that, at the bottom, I have taken the
51,000,000 of square miles, constituting the surface of the dry land;
and as the number of square feet are placed under and subtracted from
the number of seeds that would be produced in the ninth year, you can
see at once that there would be an immense number more of plants than
there would be square feet of ground for their accommodation. This is
certainly quite enough to prove my point; that between the eighth and
ninth year after being planted the single plant would have stocked the
whole available surface of the earth.

This is a thing which is hardly conceivable--it seems hardly
imaginable--yet it is so. It is indeed simply the law of Malthus
exemplified. Mr. Malthus was a clergyman, who worked out this
subject most minutely and truthfully some years ago; he showed quite
clearly,--and although he was much abused for his conclusions at the
time, they have never yet been disproved and never will be--he showed
that in consequence of the increase in the number of organic beings in
a geometrical ratio, while the means of existence cannot be made to
increase in the same ratio, that there must come a time when the number
of organic beings will be in excess of the power of production of
nutriment, and that thus some check must arise to the further increase
of those organic beings. At the end of the ninth year we have seen that
each plant would not be able to get its full square foot of ground, and
at the end of another year it would have to share that space with fifty
others the produce of the seeds which it would give off.

What, then, takes place? Every plant grows up, flourishes, occupies its
square foot of ground, and gives off its fifty seeds; but notice this,
that out of this number only one can come to anything; there is thus,
as it were, forty-nine chances to one against its growing up; it depends
upon the most fortuitous circumstances whether any one of these fifty
seeds shall grow up and flourish, or whether it shall die and perish.
This is what Mr. Darwin has drawn attention to, and called the "STRUGGLE
FOR EXISTENCE"; and I have taken this simple case of a plant because
some people imagine that the phrase seems to imply a sort of fight.

I have taken this plant and shown you that this is the result of the
ratio of the increase, the necessary result of the arrival of a time
coming for every species when exactly as many members must be destroyed
as are born; that is the inevitable ultimate result of the rate of
production. Now, what is the result of all this? I have said that there
are forty-nine struggling against every one; and it amounts to this,
that the smallest possible start given to any one seed may give it an
advantage which will enable it to get ahead of all the others; anything
that will enable any one of these seeds to germinate six hours before
any of the others will, other things being alike, enable it to choke
them out altogether. I have shown you that there is no particular in
which plants will not vary from each other; it is quite possible
that one of our imaginary plants may vary in such a character as the
thickness of the integument of its seeds; it might happen that one of
the plants might produce seeds having a thinner integument, and that
would enable the seeds of that plant to germinate a little quicker
than those of any of the others, and those seeds would most inevitably
extinguish the forty-nine times as many that were struggling with them.

I have put it in this way, but you see the practical result of the
process is the same as if some person had nurtured the one and destroyed
the other seeds. It does not matter how the variation is produced, so
long as it is once allowed to occur. The variation in the plant once
fairly started tends to become hereditary and reproduce itself; the
seeds would spread themselves in the same way and take part in the
struggle with the forty-nine hundred, or forty-nine thousand, with which
they might be exposed. Thus, by degrees, this variety, with some slight
organic change or modification, must spread itself over the whole
surface of the habitable globe, and extirpate or replace the other
kinds. That is what is meant by NATURAL SELECTION; that is the kind of
argument by which it is perfectly demonstrable that the conditions of
existence may play exactly the same part for natural varieties as man
does for domesticated varieties. No one doubts at all that particular
circumstances may be more favourable for one plant and less so for
another, and the moment you admit that, you admit the selective power of
nature. Now, although I have been putting a hypothetical case, you must
not suppose that I have been reasoning hypothetically. There are plenty
of direct experiments which bear out what we may call the theory of
natural selection; there is extremely good authority for the statement
that if you take the seed of mixed varieties of wheat and sow it,
collecting the seed next year and sowing it again, at length you will
find that out of all your varieties only two or three have lived, or
perhaps even only one. There were one or two varieties which were best
fitted to get on, and they have killed out the other kinds in just
the same way and with just the same certainty as if you had taken the
trouble to remove them. As I have already said, the operation of nature
is exactly the same as the artificial operation of man.

But if this be true of that simple case, which I put before you, where
there is nothing but the rivalry of one member of a species with others,
what must be the operation of selective conditions, when you recollect
as a matter of fact, that for every species of animal or plant there
are fifty or a hundred species which might all, more or less, be
comprehended in the same climate, food, and station;--that every plant
has multitudinous animals which prey upon it, and which are its direct
opponents; and that these have other animals preying upon them,--that
every plant has its indirect helpers in the birds that scatter abroad
its seed, and the animals that manure it with their dung;--I say, when
these things are considered, it seems impossible that any variation
which may arise in a species in nature should not tend in some way or
other either to be a little better or worse than the previous stock;
if it is a little better it will have an advantage over and tend to
extirpate the latter in this crush and struggle; and if it is a little
worse it will itself be extirpated.

I know nothing that more appropriately expresses this, than the phrase,
"the struggle for existence"; because it brings before your minds, in a
vivid sort of way, some of the simplest possible circumstances connected
with it. When a struggle is intense there must be some who are sure to
be trodden down, crushed, and overpowered by others; and there will be
some who just manage to get through only by the help of the slightest
accident. I recollect reading an account of the famous retreat of
the French troops, under Napoleon, from Moscow. Worn out, tired, and
dejected, they at length came to a great river over which there was
but one bridge for the passage of the vast army. Disorganised and
demoralised as that army was, the struggle must certainly have been a
terrible one--every one heeding only himself, and crushing through the
ranks and treading down his fellows. The writer of the narrative, who
was himself one of those who were fortunate enough to succeed in getting
over, and not among the thousands who were left behind or forced into
the river, ascribed his escape to the fact that he saw striding onward
through the mass a great strong fellow,--one of the French Cuirassiers,
who had on a large blue cloak--and he had enough presence of mind to
catch and retain a hold of this strong man's cloak. He says, "I caught
hold of his cloak, and although he swore at me and cut at and struck me
by turns, and at last, when he found he could not shake me off, fell to
entreating me to leave go or I should prevent him from escaping, besides
not assisting myself, I still kept tight hold of him, and would not quit
my grasp until he had at last dragged me through." Here you see was
a case of selective saving--if we may so term it--depending for its
success on the strength of the cloth of the Cui

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