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The Descent of Man, and Selection in Relation to Sex

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Title: The Descent of Man, and Selection in Relation to Sex

Author: Charles Darwin


        
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Language: English

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THE DESCENT OF MAN AND SELECTION IN RELATION TO SEX

By Charles Darwin


CONTENTS

 PREFACE TO THE SECOND EDITION.
 DETAILED TABLE OF CONTENTS
 THE DESCENT OF MAN; AND SELECTION IN RELATION TO SEX.
 INTRODUCTION.

 PART I. THE DESCENT OR ORIGIN OF MAN.
 CHAPTER I. THE EVIDENCE OF THE DESCENT OF MAN FROM SOME LOWER FORM.
 CHAPTER II. — ON THE MANNER OF DEVELOPMENT OF MAN FROM SOME LOWER FORM.
 CHAPTER III. — COMPARISON OF THE MENTAL POWERS OF MAN AND THE LOWER ANIMALS.
 CHAPTER IV. — COMPARISON OF THE MENTAL POWERS OF MAN AND THE LOWER ANIMALS, continued.
 CHAPTER V. — ON THE DEVELOPMENT OF THE INTELLECTUAL AND MORAL FACULTIES DURING PRIMEVAL AND CIVILISED TIMES.
 CHAPTER VI. — ON THE AFFINITIES AND GENEALOGY OF MAN.
 CHAPTER VII. — ON THE RACES OF MAN.

 PART II. SEXUAL SELECTION.
 CHAPTER VIII. — PRINCIPLES OF SEXUAL SELECTION.
 CHAPTER IX. — SECONDARY SEXUAL CHARACTERS IN THE LOWER CLASSES OF THE ANIMAL KINGDOM.
 CHAPTER X. — SECONDARY SEXUAL CHARACTERS OF INSECTS.
 CHAPTER XI. — INSECTS, continued. ORDER LEPIDOPTERA. (BUTTERFLIES AND MOTHS.)
 CHAPTER XII. — SECONDARY SEXUAL CHARACTERS OF FISHES, AMPHIBIANS, AND REPTILES.
 CHAPTER XIII. — SECONDARY SEXUAL CHARACTERS OF BIRDS.
 CHAPTER XIV. — BIRDS—continued.
 CHAPTER XV. — BIRDS—continued.
 CHAPTER XVI. — BIRDS—concluded.
 CHAPTER XVII. — SECONDARY SEXUAL CHARACTERS OF MAMMALS.
 CHAPTER XVIII. — SECONDARY SEXUAL CHARACTERS OF MAMMALS, continued.

 PART III. — SEXUAL SELECTION IN RELATION TO MAN, AND CONCLUSION.
 CHAPTER XIX. — SECONDARY SEXUAL CHARACTERS OF MAN.
 CHAPTER XX. — SECONDARY SEXUAL CHARACTERS OF MAN, continued.
 CHAPTER XXI. — GENERAL A SUMMARY AND CONCLUSION.




PREFACE TO THE SECOND EDITION.


During the successive reprints of the first edition of this work,
published in 1871, I was able to introduce several important
corrections; and now that more time has elapsed, I have endeavoured to
profit by the fiery ordeal through which the book has passed, and have
taken advantage of all the criticisms which seem to me sound. I am also
greatly indebted to a large number of correspondents for the
communication of a surprising number of new facts and remarks. These
have been so numerous, that I have been able to use only the more
important ones; and of these, as well as of the more important
corrections, I will append a list. Some new illustrations have been
introduced, and four of the old drawings have been replaced by better
ones, done from life by Mr. T.W. Wood. I must especially call attention
to some observations which I owe to the kindness of Prof. Huxley (given
as a supplement at the end of Part I.), on the nature of the
differences between the brains of man and the higher apes. I have been
particularly glad to give these observations, because during the last
few years several memoirs on the subject have appeared on the
Continent, and their importance has been, in some cases, greatly
exaggerated by popular writers.

I may take this opportunity of remarking that my critics frequently
assume that I attribute all changes of corporeal structure and mental
power exclusively to the natural selection of such variations as are
often called spontaneous; whereas, even in the first edition of the
‘Origin of Species,’ I distinctly stated that great weight must be
attributed to the inherited effects of use and disuse, with respect
both to the body and mind. I also attributed some amount of
modification to the direct and prolonged action of changed conditions
of life. Some allowance, too, must be made for occasional reversions of
structure; nor must we forget what I have called “correlated” growth,
meaning, thereby, that various parts of the organisation are in some
unknown manner so connected, that when one part varies, so do others;
and if variations in the one are accumulated by selection, other parts
will be modified. Again, it has been said by several critics, that when
I found that many details of structure in man could not be explained
through natural selection, I invented sexual selection; I gave,
however, a tolerably clear sketch of this principle in the first
edition of the ‘Origin of Species,’ and I there stated that it was
applicable to man. This subject of sexual selection has been treated at
full length in the present work, simply because an opportunity was here
first afforded me. I have been struck with the likeness of many of the
half-favourable criticisms on sexual selection, with those which
appeared at first on natural selection; such as, that it would explain
some few details, but certainly was not applicable to the extent to
which I have employed it. My conviction of the power of sexual
selection remains unshaken; but it is probable, or almost certain, that
several of my conclusions will hereafter be found erroneous; this can
hardly fail to be the case in the first treatment of a subject. When
naturalists have become familiar with the idea of sexual selection, it
will, as I believe, be much more largely accepted; and it has already
been fully and favourably received by several capable judges.

DOWN, BECKENHAM, KENT, September, 1874.

First Edition February 24, 1871. Second Edition September, 1874.




DETAILED TABLE OF CONTENTS

INTRODUCTION.

PART I. THE DESCENT OR ORIGIN OF MAN.

CHAPTER I.
THE EVIDENCE OF THE DESCENT OF MAN FROM SOME LOWER FORM.
Nature of the evidence bearing on the origin of man—Homologous
structures in man and the lower animals—Miscellaneous points of
correspondence—Development—Rudimentary structures, muscles,
sense-organs, hair, bones, reproductive organs, etc.—The bearing of
these three great classes of facts on the origin of man.

CHAPTER II.
ON THE MANNER OF DEVELOPMENT OF MAN FROM SOME LOWER FORM.
Variability of body and mind in man—Inheritance—Causes of
variability—Laws of variation the same in man as in the lower
animals—Direct action of the conditions of life—Effects of the
increased use and disuse of parts—Arrested
development—Reversion—Correlated variation—Rate of increase—Checks to
increase—Natural selection—Man the most dominant animal in the
world—Importance of his corporeal structure—The causes which have led
to his becoming erect—Consequent changes of structure—Decrease in size
of the canine teeth—Increased size and altered shape of the
skull—Nakedness —Absence of a tail—Defenceless condition of man.

CHAPTER III.
COMPARISON OF THE MENTAL POWERS OF MAN AND THE LOWER ANIMALS.
The difference in mental power between the highest ape and the lowest
savage, immense—Certain instincts in common—The
emotions—Curiosity—Imitation—Attention—Memory—
Imagination—Reason—Progressive improvement —Tools and weapons used by
animals—Abstraction, Self-consciousness—Language—Sense of beauty—Belief
in God, spiritual agencies, superstitions.

CHAPTER IV.
COMPARISON OF THE MENTAL POWERS OF MAN AND THE LOWER ANIMALS,
continued.
The moral sense—Fundamental proposition—The qualities of social
animals—Origin of sociability—Struggle between opposed instincts—Man a
social animal—The more enduring social instincts conquer other less
persistent instincts—The social virtues alone regarded by savages—The
self-regarding virtues acquired at a later stage of development—The
importance of the judgment of the members of the same community on
conduct—Transmission of moral tendencies—Summary.

CHAPTER V.
ON THE DEVELOPMENT OF THE INTELLECTUAL AND MORAL FACULTIES DURING
PRIMEVAL AND CIVILISED TIMES.
Advancement of the intellectual powers through natural
selection—Importance of imitation—Social and moral faculties—Their
development within the limits of the same tribe—Natural selection as
affecting civilised nations—Evidence that civilised nations were once
barbarous.

CHAPTER VI.
ON THE AFFINITIES AND GENEALOGY OF MAN.
Position of man in the animal series—The natural system
genealogical—Adaptive characters of slight value—Various small points
of resemblance between man and the Quadrumana—Rank of man in the
natural system—Birthplace and antiquity of man—Absence of fossil
connecting-links—Lower stages in the genealogy of man, as inferred
firstly from his affinities and secondly from his structure—Early
androgynous condition of the Vertebrata —Conclusion.

CHAPTER VII.
ON THE RACES OF MAN.
The nature and value of specific characters—Application to the races of
man—Arguments in favour of, and opposed to, ranking the so-called races
of man as distinct species—Sub-species—Monogenists and
polygenists—Convergence of character—Numerous points of resemblance in
body and mind between the most distinct races of man—The state of man
when he first spread over the earth—Each race not descended from a
single pair—The extinction of races—The formation of races—The effects
of crossing—Slight influence of the direct action of the conditions of
life—Slight or no influence of natural selection—Sexual selection.

PART II. SEXUAL SELECTION.

CHAPTER VIII.
PRINCIPLES OF SEXUAL SELECTION.
Secondary sexual characters—Sexual selection—Manner of action—Excess of
males—Polygamy—The male alone generally modified through sexual
selection—Eagerness of the male—Variability of the male—Choice exerted
by the female—Sexual compared with natural selection—Inheritance at
corresponding periods of life, at corresponding seasons of the year,
and as limited by sex—Relations between the several forms of
inheritance—Causes why one sex and the young are not modified through
sexual selection—Supplement on the proportional numbers of the two
sexes throughout the animal kingdom—The proportion of the sexes in
relation to natural selection.

CHAPTER IX.
SECONDARY SEXUAL CHARACTERS IN THE LOWER CLASSES OF THE ANIMAL KINGDOM.
These characters are absent in the lowest classes—Brilliant
colours—Mollusca—Annelids—Crustacea, secondary sexual characters
strongly developed; dimorphism; colour; characters not acquired before
maturity—Spiders, sexual colours of; stridulation by the
males—Myriapoda.

CHAPTER X.
SECONDARY SEXUAL CHARACTERS OF INSECTS.
Diversified structures possessed by the males for seizing the
females—Differences between the sexes, of which the meaning is not
understood—Difference in size between the
sexes—Thysanura—Diptera—Hemiptera—Homoptera, musical powers possessed
by the males alone—Orthoptera, musical instruments of the males, much
diversified in structure; pugnacity; colours—Neuroptera, sexual
differences in colour—Hymenoptera, pugnacity and odours—Coleoptera,
colours; furnished with great horns, apparently as an ornament;
battles; stridulating organs generally common to both sexes.

CHAPTER XI.
INSECTS, continued. ORDER LEPIDOPTERA. (BUTTERFLIES AND MOTHS.)
Courtship of Butterflies—Battles—Ticking noise—Colours common to both
sexes, or more brilliant in the males—Examples—Not due to the direct
action of the conditions of life—Colours adapted for protection—Colours
of moths—Display—Perceptive powers of the
Lepidoptera—Variability—Causes of the difference in colour between the
males and females—Mimicry, female butterflies more brilliantly coloured
than the males—Bright colours of caterpillars—Summary and concluding
remarks on the secondary sexual character of insects—Birds and insects
compared.

CHAPTER XII.
SECONDARY SEXUAL CHARACTERS OF FISHES, AMPHIBIANS, AND REPTILES.
Fishes: Courtship and battles of the males—Larger size of the
females—Males, bright colours and ornamental appendages; other strange
characters—Colours and appendages acquired by the males during the
breeding-season alone—Fishes with both sexes brilliantly
coloured—Protective colours—The less conspicuous colours of the female
cannot be accounted for on the principle of protection—Male fishes
building nests, and taking charge of the ova and young. AMPHIBIANS:
Differences in structure and colour between the sexes—Vocal organs.
REPTILES: Chelonians—Crocodiles—Snakes, colours in some cases
protective—Lizards, battles of—Ornamental appendages—Strange
differences in structure between the sexes—Colours—Sexual differences
almost as great as with birds.

CHAPTER XIII.
SECONDARY SEXUAL CHARACTERS OF BIRDS.
Sexual differences—Law of battle—Special weapons—Vocal
organs—Instrumental music—Love-antics and dances—Decorations, permanent
and seasonal—Double and single annual moults—Display of ornaments by
the males.

CHAPTER XIV.
BIRDS—continued.
Choice exerted by the female—Length of courtship—Unpaired birds—Mental
qualities and taste for the beautiful—Preference or antipathy shewn by
the female for particular males—Variability of birds—Variations
sometimes abrupt—Laws of variation—Formation of ocelli—Gradations of
character—Case of Peacock, Argus pheasant, and Urosticte.

CHAPTER XV.
BIRDS—continued.
Discussion as to why the males alone of some species, and both sexes of
others are brightly coloured—On sexually-limited inheritance, as
applied to various structures and to brightly-coloured
plumage—Nidification in relation to colour—Loss of nuptial plumage
during the winter.

CHAPTER XVI.
BIRDS—concluded.
The immature plumage in relation to the character of the plumage in
both sexes when adult—Six classes of cases—Sexual differences between
the males of closely-allied or representative species—The female
assuming the characters of the male—Plumage of the young in relation to
the summer and winter plumage of the adults—On the increase of beauty
in the birds of the world—Protective colouring—Conspicuously coloured
birds—Novelty appreciated—Summary of the four chapters on birds.

CHAPTER XVII.
SECONDARY SEXUAL CHARACTERS OF MAMMALS.
The law of battle—Special weapons, confined to the males—Cause of
absence of weapons in the female—Weapons common to both sexes, yet
primarily acquired by the male—Other uses of such weapons—Their high
importance—Greater size of the male—Means of defence—On the preference
shewn by either sex in the pairing of quadrupeds.

CHAPTER XVIII.
SECONDARY SEXUAL CHARACTERS OF MAMMALS, continued.
Voice—Remarkable sexual peculiarities in seals—Odour—Development of the
hair—Colour of the hair and skin—Anomalous case of the female being
more ornamented than the male—Colour and ornaments due to sexual
selection—Colour acquired for the sake of protection—Colour, though
common to both sexes, often due to sexual selection—On the
disappearance of spots and stripes in adult quadrupeds—On the colours
and ornaments of the Quadrumana—Summary.

PART III. SEXUAL SELECTION IN RELATION TO MAN, AND CONCLUSION.

CHAPTER XIX.
SECONDARY SEXUAL CHARACTERS OF MAN.
Differences between man and woman—Causes of such differences, and of
certain characters common to both sexes—Law of battle—Differences in
mental powers, and voice—On the influence of beauty in determining the
marriages of mankind—Attention paid by savages to ornaments—Their ideas
of beauty in women—The tendency to exaggerate each natural peculiarity.

CHAPTER XX.
SECONDARY SEXUAL CHARACTERS OF MAN, continued.
On the effects of the continued selection of women according to a
different standard of beauty in each race—On the causes which interfere
with sexual selection in civilised and savage nations—Conditions
favourable to sexual selection during primeval times—On the manner of
action of sexual selection with mankind—On the women in savage tribes
having some power to choose their husbands—Absence of hair on the body,
and development of the beard—Colour of the skin—Summary.

CHAPTER XXI.
GENERAL A SUMMARY AND CONCLUSION.
Main conclusion that man is descended from some lower form—Manner of
development—Genealogy of man—Intellectual and moral faculties—Sexual
selection—Concluding remarks.




THE DESCENT OF MAN; AND SELECTION IN RELATION TO SEX.




INTRODUCTION.


The nature of the following work will be best understood by a brief
account of how it came to be written. During many years I collected
notes on the origin or descent of man, without any intention of
publishing on the subject, but rather with the determination not to
publish, as I thought that I should thus only add to the prejudices
against my views. It seemed to me sufficient to indicate, in the first
edition of my ‘Origin of Species,’ that by this work “light would be
thrown on the origin of man and his history;” and this implies that man
must be included with other organic beings in any general conclusion
respecting his manner of appearance on this earth. Now the case wears a
wholly different aspect. When a naturalist like Carl Vogt ventures to
say in his address as President of the National Institution of Geneva
(1869), “personne, en Europe au moins, n’ose plus soutenir la creation
indépendante et de toutes pièces, des espèces,” it is manifest that at
least a large number of naturalists must admit that species are the
modified descendants of other species; and this especially holds good
with the younger and rising naturalists. The greater number accept the
agency of natural selection; though some urge, whether with justice the
future must decide, that I have greatly overrated its importance. Of
the older and honoured chiefs in natural science, many unfortunately
are still opposed to evolution in every form.

In consequence of the views now adopted by most naturalists, and which
will ultimately, as in every other case, be followed by others who are
not scientific, I have been led to put together my notes, so as to see
how far the general conclusions arrived at in my former works were
applicable to man. This seemed all the more desirable, as I had never
deliberately applied these views to a species taken singly. When we
confine our attention to any one form, we are deprived of the weighty
arguments derived from the nature of the affinities which connect
together whole groups of organisms—their geographical distribution in
past and present times, and their geological succession. The
homological structure, embryological development, and rudimentary
organs of a species remain to be considered, whether it be man or any
other animal, to which our attention may be directed; but these great
classes of facts afford, as it appears to me, ample and conclusive
evidence in favour of the principle of gradual evolution. The strong
support derived from the other arguments should, however, always be
kept before the mind.

The sole object of this work is to consider, firstly, whether man, like
every other species, is descended from some pre-existing form;
secondly, the manner of his development; and thirdly, the value of the
differences between the so-called races of man. As I shall confine
myself to these points, it will not be necessary to describe in detail
the differences between the several races—an enormous subject which has
been fully described in many valuable works. The high antiquity of man
has recently been demonstrated by the labours of a host of eminent men,
beginning with M. Boucher de Perthes; and this is the indispensable
basis for understanding his origin. I shall, therefore, take this
conclusion for granted, and may refer my readers to the admirable
treatises of Sir Charles Lyell, Sir John Lubbock, and others. Nor shall
I have occasion to do more than to allude to the amount of difference
between man and the anthropomorphous apes; for Prof. Huxley, in the
opinion of most competent judges, has conclusively shewn that in every
visible character man differs less from the higher apes, than these do
from the lower members of the same order of Primates.

This work contains hardly any original facts in regard to man; but as
the conclusions at which I arrived, after drawing up a rough draft,
appeared to me interesting, I thought that they might interest others.
It has often and confidently been asserted, that man’s origin can never
be known: but ignorance more frequently begets confidence than does
knowledge: it is those who know little, and not those who know much,
who so positively assert that this or that problem will never be solved
by science. The conclusion that man is the co-descendant with other
species of some ancient, lower, and extinct form, is not in any degree
new. Lamarck long ago came to this conclusion, which has lately been
maintained by several eminent naturalists and philosophers; for
instance, by Wallace, Huxley, Lyell, Vogt, Lubbock, Buchner, Rolle,
etc. (1. As the works of the first-named authors are so well known, I
need not give the titles; but as those of the latter are less well
known in England, I will give them:—‘Sechs Vorlesungen über die
Darwin’sche Theorie:’ zweite Auflage, 1868, von Dr L. Buchner;
translated into French under the title ‘Conférences sur la Théorie
Darwinienne,’ 1869. ‘Der Mensch im Lichte der Darwin’sche Lehre,’ 1865,
von Dr. F. Rolle. I will not attempt to give references to all the
authors who have taken the same side of the question. Thus G.
Canestrini has published (‘Annuario della Soc. d. Nat.,’ Modena, 1867,
page 81) a very curious paper on rudimentary characters, as bearing on
the origin of man. Another work has (1869) been published by Dr.
Francesco Barrago, bearing in Italian the title of “Man, made in the
image of God, was also made in the image of the ape.”), and especially
by Haeckel. This last naturalist, besides his great work, ‘Generelle
Morphologie’ (1866), has recently (1868, with a second edition in
1870), published his ‘Natürliche Schöpfungsgeschichte,’ in which he
fully discusses the genealogy of man. If this work had appeared before
my essay had been written, I should probably never have completed it.
Almost all the conclusions at which I have arrived I find confirmed by
this naturalist, whose knowledge on many points is much fuller than
mine. Wherever I have added any fact or view from Prof. Haeckel’s
writings, I give his authority in the text; other statements I leave as
they originally stood in my manuscript, occasionally giving in the
foot-notes references to his works, as a confirmation of the more
doubtful or interesting points.

During many years it has seemed to me highly probable that sexual
selection has played an important part in differentiating the races of
man; but in my ‘Origin of Species’ (first edition, page 199) I
contented myself by merely alluding to this belief. When I came to
apply this view to man, I found it indispensable to treat the whole
subject in full detail. (2. Prof. Haeckel was the only author who, at
the time when this work first appeared, had discussed the subject of
sexual selection, and had seen its full importance, since the
publication of the ‘Origin’; and this he did in a very able manner in
his various works.) Consequently the second part of the present work,
treating of sexual selection, has extended to an inordinate length,
compared with the first part; but this could not be avoided.

I had intended adding to the present volumes an essay on the expression
of the various emotions by man and the lower animals. My attention was
called to this subject many years ago by Sir Charles Bell’s admirable
work. This illustrious anatomist maintains that man is endowed with
certain muscles solely for the sake of expressing his emotions. As this
view is obviously opposed to the belief that man is descended from some
other and lower form, it was necessary for me to consider it. I
likewise wished to ascertain how far the emotions are expressed in the
same manner by the different races of man. But owing to the length of
the present work, I have thought it better to reserve my essay for
separate publication.




PART I.
THE DESCENT OR ORIGIN OF MAN.




CHAPTER I.
THE EVIDENCE OF THE DESCENT OF MAN FROM SOME LOWER FORM.


Nature of the evidence bearing on the origin of man—Homologous
structures in man and the lower animals—Miscellaneous points of
correspondence—Development—Rudimentary structures, muscles, sense-
organs, hair, bones, reproductive organs, etc.—The bearing of these
three great classes of facts on the origin of man.

He who wishes to decide whether man is the modified descendant of some
pre-existing form, would probably first enquire whether man varies,
however slightly, in bodily structure and in mental faculties; and if
so, whether the variations are transmitted to his offspring in
accordance with the laws which prevail with the lower animals. Again,
are the variations the result, as far as our ignorance permits us to
judge, of the same general causes, and are they governed by the same
general laws, as in the case of other organisms; for instance, by
correlation, the inherited effects of use and disuse, etc.? Is man
subject to similar malconformations, the result of arrested
development, of reduplication of parts, etc., and does he display in
any of his anomalies reversion to some former and ancient type of
structure? It might also naturally be enquired whether man, like so
many other animals, has given rise to varieties and sub-races,
differing but slightly from each other, or to races differing so much
that they must be classed as doubtful species? How are such races
distributed over the world; and how, when crossed, do they react on
each other in the first and succeeding generations? And so with many
other points.

The enquirer would next come to the important point, whether man tends
to increase at so rapid a rate, as to lead to occasional severe
struggles for existence; and consequently to beneficial variations,
whether in body or mind, being preserved, and injurious ones
eliminated. Do the races or species of men, whichever term may be
applied, encroach on and replace one another, so that some finally
become extinct? We shall see that all these questions, as indeed is
obvious in respect to most of them, must be answered in the
affirmative, in the same manner as with the lower animals. But the
several considerations just referred to may be conveniently deferred
for a time: and we will first see how far the bodily structure of man
shews traces, more or less plain, of his descent from some lower form.
In succeeding chapters the mental powers of man, in comparison with
those of the lower animals, will be considered.

THE BODILY STRUCTURE OF MAN.

It is notorious that man is constructed on the same general type or
model as other mammals. All the bones in his skeleton can be compared
with corresponding bones in a monkey, bat, or seal. So it is with his
muscles, nerves, blood-vessels and internal viscera. The brain, the
most important of all the organs, follows the same law, as shewn by
Huxley and other anatomists. Bischoff (1. ‘Grosshirnwindungen des
Menschen,’ 1868, s. 96. The conclusions of this author, as well as
those of Gratiolet and Aeby, concerning the brain, will be discussed by
Prof. Huxley in the Appendix alluded to in the Preface to this
edition.), who is a hostile witness, admits that every chief fissure
and fold in the brain of man has its analogy in that of the orang; but
he adds that at no period of development do their brains perfectly
agree; nor could perfect agreement be expected, for otherwise their
mental powers would have been the same. Vulpian (2. ‘Lec. sur la Phys.’
1866, page 890, as quoted by M. Dally, ‘L’Ordre des Primates et le
Transformisme,’ 1868, page 29.), remarks: “Les différences réelles qui
existent entre l’encephale de l’homme et celui des singes supérieurs,
sont bien minimes. Il ne faut pas se faire d’illusions a cet égard.
L’homme est bien plus près des singes anthropomorphes par les
caractères anatomiques de son cerveau que ceux-ci ne le sont non
seulement des autres mammifères, mais même de certains quadrumanes, des
guenons et des macaques.” But it would be superfluous here to give
further details on the correspondence between man and the higher
mammals in the structure of the brain and all other parts of the body.

It may, however, be worth while to specify a few points, not directly
or obviously connected with structure, by which this correspondence or
relationship is well shewn.

Man is liable to receive from the lower animals, and to communicate to
them, certain diseases, as hydrophobia, variola, the glanders,
syphilis, cholera, herpes, etc. (3. Dr. W. Lauder Lindsay has treated
this subject at some length in the ‘Journal of Mental Science,’ July
1871; and in the ‘Edinburgh Veterinary Review,’ July 1858.); and this
fact proves the close similarity (4. A Reviewer has criticised
(‘British Quarterly Review,’ Oct. 1st, 1871, page 472) what I have here
said with much severity and contempt; but as I do not use the term
identity, I cannot see that I am greatly in error. There appears to me
a strong analogy between the same infection or contagion producing the
same result, or one closely similar, in two distinct animals, and the
testing of two distinct fluids by the same chemical reagent.) of their
tissues and blood, both in minute structure and composition, far more
plainly than does their comparison under the best microscope, or by the
aid of the best chemical analysis. Monkeys are liable to many of the
same non-contagious diseases as we are; thus Rengger (5.
‘Naturgeschichte der Säugethiere von Paraguay,’ 1830, s. 50.), who
carefully observed for a long time the Cebus Azarae in its native land,
found it liable to catarrh, with the usual symptoms, and which, when
often recurrent, led to consumption. These monkeys suffered also from
apoplexy, inflammation of the bowels, and cataract in the eye. The
younger ones when shedding their milk-teeth often died from fever.
Medicines produced the same effect on them as on us. Many kinds of
monkeys have a strong taste for tea, coffee, and spiritous liquors:
they will also, as I have myself seen, smoke tobacco with pleasure. (6.
The same tastes are common to some animals much lower in the scale. Mr.
A. Nichols informs me that he kept in Queensland, in Australia, three
individuals of the Phaseolarctus cinereus; and that, without having
been taught in any way, they acquired a strong taste for rum, and for
smoking tobacco.) Brehm asserts that the natives of north-eastern
Africa catch the wild baboons by exposing vessels with strong beer, by
which they are made drunk. He has seen some of these animals, which he
kept in confinement, in this state; and he gives a laughable account of
their behaviour and strange grimaces. On the following morning they
were very cross and dismal; they held their aching heads with both
hands, and wore a most pitiable expression: when beer or wine was
offered them, they turned away with disgust, but relished the juice of
lemons. (7. Brehm, ‘Thierleben,’ B. i. 1864, s. 75, 86. On the Ateles,
s. 105. For other analogous statements, see s. 25, 107.) An American
monkey, an Ateles, after getting drunk on brandy, would never touch it
again, and thus was wiser than many men. These trifling facts prove how
similar the nerves of taste must be in monkeys and man, and how
similarly their whole nervous system is affected.

Man is infested with internal parasites, sometimes causing fatal
effects; and is plagued by external parasites, all of which belong to
the same genera or families as those infesting other mammals, and in
the case of scabies to the same species. (8. Dr. W. Lauder Lindsay,
‘Edinburgh Vet. Review,’ July 1858, page 13.) Man is subject, like
other mammals, birds, and even insects (9. With respect to insects see
Dr. Laycock, “On a General Law of Vital Periodicity,” ‘British
Association,’ 1842. Dr. Macculloch, ‘Silliman’s North American Journal
of Science,’ vol. XVII. page 305, has seen a dog suffering from tertian
ague. Hereafter I shall return to this subject.), to that mysterious
law, which causes certain normal processes, such as gestation, as well
as the maturation and duration of various diseases, to follow lunar
periods. His wounds are repaired by the same process of healing; and
the stumps left after the amputation of his limbs, especially during an
early embryonic period, occasionally possess some power of
regeneration, as in the lowest animals. (10. I have given the evidence
on this head in my ‘Variation of Animals and Plants under
Domestication,’ vol. ii. page 15, and more could be added.)

The whole process of that most important function, the reproduction of
the species, is strikingly the same in all mammals, from the first act
of courtship by the male (11. Mares e diversis generibus Quadrumanorum
sine dubio dignoscunt feminas humanas a maribus. Primum, credo,
odoratu, postea aspectu. Mr. Youatt, qui diu in Hortis Zoologicis
(Bestiariis) medicus animalium erat, vir in rebus observandis cautus et
sagax, hoc mihi certissime probavit, et curatores ejusdem loci et alii
e ministris confirmaverunt. Sir Andrew Smith et Brehm notabant idem in
Cynocephalo. Illustrissimus Cuvier etiam narrat multa de hac re, qua ut
opinor, nihil turpius potest indicari inter omnia hominibus et
Quadrumanis communia. Narrat enim Cynocephalum quendam in furorem
incidere aspectu feminarum aliquarem, sed nequaquam accendi tanto
furore ab omnibus. Semper eligebat juniores, et dignoscebat in turba,
et advocabat voce gestuque.), to the birth and nurturing of the young.
Monkeys are born in almost as helpless a condition as our own infants;
and in certain genera the young differ fully as much in appearance from
the adults, as do our children from their full-grown parents. (12. This
remark is made with respect to Cynocephalus and the anthropomorphous
apes by Geoffroy Saint-Hilaire and F. Cuvier, ‘Histoire Nat. des
Mammifères,’ tom. i. 1824.) It has been urged by some writers, as an
important distinction, that with man the young arrive at maturity at a
much later age than with any other animal: but if we look to the races
of mankind which inhabit tropical countries the difference is not
great, for the orang is believed not to be adult till the age of from
ten to fifteen years. (13. Huxley, ‘Man’s Place in Nature,’ 1863, p.
34.) Man differs from woman in size, bodily strength, hairiness, etc.,
as well as in mind, in the same manner as do the two sexes of many
mammals. So that the correspondence in general structure, in the minute
structure of the tissues, in chemical composition and in constitution,
between man and the higher animals, especially the anthropomorphous
apes, is extremely close.

EMBRYONIC DEVELOPMENT.

[Fig. 1. Shows a human embryo, from Ecker, and a dog embryo, from
Bischoff. Labelled in each are:

a. Fore-brain, cerebral hemispheres, etc. b. Mid-brain, corpora
quadrigemina. c. Hind-brain, cerebellum, medulla oblongata. d. Eye. e.
Ear. f. First visceral arch. g. Second visceral arch. H. Vertebral
columns and muscles in process of development. i. Anterior extremities.
K. Posterior extremities. L. Tail or os coccyx.]

Man is developed from an ovule, about the 125th of an inch in diameter,
which differs in no respect from the ovules of other animals. The
embryo itself at a very early period can hardly be distinguished from
that of other members of the vertebrate kingdom. At this period the
arteries run in arch-like branches, as if to carry the blood to
branchiae which are not present in the higher Vertebrata, though the
slits on the sides of the neck still remain (see f, g, fig. 1), marking
their former position. At a somewhat later period, when the extremities
are developed, “the feet of lizards and mammals,” as the illustrious
Von Baer remarks, “the wings and feet of birds, no less than the hands
and feet of man, all arise from the same fundamental form.” It is, says
Prof. Huxley (14. ‘Man’s Place in Nature,’ 1863, p. 67.), “quite in the
later stages of development that the young human being presents marked
differences from the young ape, while the latter departs as much from
the dog in its developments, as the man does. Startling as this last
assertion may appear to be, it is demonstrably true.”

As some of my readers may never have seen a drawing of an embryo, I
have given one of man and another of a dog, at about the same early
stage of development, carefully copied from two works of undoubted
accuracy. (15. The human embryo (upper fig.) is from Ecker, ‘Icones
Phys.,’ 1851-1859, tab. xxx. fig. 2. This embryo was ten lines in
length, so that the drawing is much magnified. The embryo of the dog is
from Bischoff, ‘Entwicklungsgeschichte des Hunde-Eies,’ 1845, tab. xi.
fig. 42B. This drawing is five times magnified, the embryo being
twenty-five days old. The internal viscera have been omitted, and the
uterine appendages in both drawings removed. I was directed to these
figures by Prof. Huxley, from whose work, ‘Man’s Place in Nature,’ the
idea of giving them was taken. Haeckel has also given analogous
drawings in his ‘Schopfungsgeschichte.’)

After the foregoing statements made by such high authorities, it would
be superfluous on my part to give a number of borrowed details, shewing
that the embryo of man closely resembles that of other mammals. It may,
however, be added, that the human embryo likewise resembles certain low
forms when adult in various points of structure. For instance, the
heart at first exists as a simple pulsating vessel; the excreta are
voided through a cloacal passage; and the os coccyx projects like a
true tail, “extending considerably beyond the rudimentary legs.” (16.
Prof. Wyman in ‘Proceedings of the American Academy of Sciences,’ vol.
iv. 1860, p. 17.) In the embryos of all air-breathing vertebrates,
certain glands, called the corpora Wolffiana, correspond with, and act
like the kidneys of mature fishes. (17. Owen, ‘Anatomy of Vertebrates,’
vol. i. p. 533.) Even at a later embryonic period, some striking
resemblances between man and the lower animals may be observed.
Bischoff says that “the convolutions of the brain in a human foetus at
the end of the seventh month reach about the same stage of development
as in a baboon when adult.” (18. ‘Die Grosshirnwindungen des Menschen,’
1868, s. 95.) The great toe, as Professor Owen remarks (19. ‘Anatomy of
Vertebrates,’ vol. ii. p. 553.), “which forms the fulcrum when standing
or walking, is perhaps the most characteristic peculiarity in the human
structure;” but in an embryo, about an inch in length, Prof. Wyman (20.
‘Proc. Soc. Nat. Hist.’ Boston, 1863, vol. ix. p. 185.) found “that the
great toe was shorter than the others; and, instead of being parallel
to them, projected at an angle from the side of the foot, thus
corresponding with the permanent condition of this part in the
quadrumana.” I will conclude with a quotation from Huxley (21. ‘Man’s
Place in Nature,’ p. 65.) who after asking, does man originate in a
different way from a dog, bird, frog or fish? says, “the reply is not
doubtful for a moment; without question, the mode of origin, and the
early stages of the development of man, are identical with those of the
animals immediately below him in the scale: without a doubt in these
respects, he is far nearer to apes than the apes are to the dog.”

RUDIMENTS.

This subject, though not intrinsically more important than the two
last, will for several reasons be treated here more fully. (22. I had
written a rough copy of this chapter before reading a valuable paper,
“Caratteri rudimentali in ordine all’ origine dell’ uomo” (‘Annuario
della Soc. d. Naturalisti,’ Modena, 1867, p. 81), by G. Canestrini, to
which paper I am considerably indebted. Haeckel has given admirable
discussions on this whole subject, under the title of Dysteleology, in
his ‘Generelle Morphologie’ and ‘Schöpfungsgeschichte.’) Not one of the
higher animals can be named which does not bear some part in a
rudimentary condition; and man forms no exception to the rule.
Rudimentary organs must be distinguished from those that are nascent;
though in some cases the distinction is not easy. The former are either
absolutely useless, such as the mammae of male quadrupeds, or the
incisor teeth of ruminants which never cut through the gums; or they
are of such slight service to their present possessors, that we can
hardly suppose that they were developed under the conditions which now
exist. Organs in this latter state are not strictly rudimentary, but
they are tending in this direction. Nascent organs, on the other hand,
though not fully developed, are of high service to their possessors,
and are capable of further development. Rudimentary organs are
eminently variable; and this is partly intelligible, as they are
useless, or nearly useless, and consequently are no longer subjected to
natural selection. They often become wholly suppressed. When this
occurs, they are nevertheless liable to occasional reappearance through
reversion—a circumstance well worthy of attention.

The chief agents in causing organs to become rudimentary seem to have
been disuse at that period of life when the organ is chiefly used (and
this is generally during maturity), and also inheritance at a
corresponding period of life. The term “disuse” does not relate merely
to the lessened action of muscles, but includes a diminished flow of
blood to a part or organ, from being subjected to fewer alternations of
pressure, or from becoming in any way less habitually active.
Rudiments, however, may occur in one sex of those parts which are
normally present in the other sex; and such rudiments, as we shall
hereafter see, have often originated in a way distinct from those here
referred to. In some cases, organs have been reduced by means of
natural selection, from having become injurious to the species under
changed habits of life. The process of reduction is probably often
aided through the two principles of compensation and economy of growth;
but the later stages of reduction, after disuse has done all that can
fairly be attributed to it, and when the saving to be effected by the
economy of growth would be very small (23. Some good criticisms on this
subject have been given by Messrs. Murie and Mivart, in ‘Transact.
Zoological Society,’ 1869, vol. vii. p. 92.), are difficult to
understand. The final and complete suppression of a part, already
useless and much reduced in size, in which case neither compensation
nor economy can come into play, is perhaps intelligible by the aid of
the hypothesis of pangenesis. But as the whole subject of rudimentary
organs has been discussed and illustrated in my former works (24.
‘Variation of Animals and Plants under Domestication,’ vol. ii pp. 317
and 397. See also ‘Origin of Species,’ 5th Edition p. 535.), I need
here say no more on this head.

Rudiments of various muscles have been observed in many parts of the
human body (25. For instance, M. Richard (‘Annales des Sciences Nat.,’
3rd series, Zoolog. 1852, tom. xviii. p. 13) describes and figures
rudiments of what he calls the “muscle pedieux de la main,” which he
says is sometimes “infiniment petit.” Another muscle, called “le tibial
posterieur,” is generally quite absent in the hand, but appears from
time to time in a more or less rudimentary condition.); and not a few
muscles, which are regularly present in some of the lower animals can
occasionally be detected in man in a greatly reduced condition. Every
one must have noticed the power which many animals, especially horses,
possess of moving or twitching their skin; and this is effected by the
panniculus carnosus. Remnants of this muscle in an efficient state are
found in various parts of our bodies; for instance, the muscle on the
forehead, by which the eyebrows are raised. The platysma myoides, which
is well developed on the neck, belongs to this system. Prof. Turner, of
Edinburgh, has occasionally detected, as he informs me, muscular
fasciculi in five different situations, namely in the axillae, near the
scapulae, etc., all of which must be referred to the system of the
panniculus. He has also shewn (26. Prof. W. Turner, ‘Proceedings of the
Royal Society of Edinburgh,’ 1866-67, p. 65.) that the musculus
sternalis or sternalis brutorum, which is not an extension of the
rectus abdominalis, but is closely allied to the panniculus, occurred
in the proportion of about three per cent. in upwards of 600 bodies: he
adds, that this muscle affords “an excellent illustration of the
statement that occasional and rudimentary structures are especially
liable to variation in arrangement.”

Some few persons have the power of contracting the superficial muscles
on their scalps; and these muscles are in a variable and partially
rudimentary condition. M. A. de Candolle has communicated to me a
curious instance of the long-continued persistence or inheritance of
this power, as well as of its unusual development. He knows a family,
in which one member, the present head of the family, could, when a
youth, pitch several heavy books from his head by the movement of the
scalp alone; and he won wagers by performing this feat. His father,
uncle, grandfather, and his three children possess the same power to
the same unusual degree. This family became divided eight generations
ago into two branches; so that the head of the above-mentioned branch
is cousin in the seventh degree to the head of the other branch. This
distant cousin resides in another part of France; and on being asked
whether he possessed the same faculty, immediately exhibited his power.
This case offers a good illustration how persistent may be the
transmission of an absolutely useless faculty, probably derived from
our remote semi-human progenitors; since many monkeys have, and
frequently use the power, of largely moving their scalps up and down.
(27. See my ‘Expression of the Emotions in Man and Animals,’ 1872, p.
144.)

The extrinsic muscles which serve to move the external ear, and the
intrinsic muscles which move the different parts, are in a rudimentary
condition in man, and they all belong to the system of the panniculus;
they are also variable in development, or at least in function. I have
seen one man who could draw the whole ear forwards; other men can draw
it upwards; another who could draw it backwards (28. Canestrini quotes
Hyrtl. (‘Annuario della Soc. dei Naturalisti,’ Modena, 1867, p. 97) to
the same effect.); and from what one of these persons told me, it is
probable that most of us, by often touching our ears, and thus
directing our attention towards them, could recover some power of
movement by repeated trials. The power of erecting and directing the
shell of the ears to the various points of the compass, is no doubt of
the highest service to many animals, as they thus perceive the
direction of danger; but I have never heard, on sufficient evidence, of
a man who possessed this power, the one which might be of use to him.
The whole external shell may be considered a rudiment, together with
the various folds and prominences (helix and anti-helix, tragus and
anti-tragus, etc.) which in the lower animals strengthen and support
the ear when erect, without adding much to its weight. Some authors,
however, suppose that the cartilage of the shell serves to transmit
vibrations to the acoustic nerve; but Mr. Toynbee (29. ‘The Diseases of
the Ear,’ by J. Toynbee, F.R.S., 1860, p. 12. A distinguished
physiologist, Prof. Preyer, informs me that he had lately been
experimenting on the function of the shell of the ear, and has come to
nearly the same conclusion as that given here.), after collecting all
the known evidence on this head, concludes that the external shell is
of no distinct use. The ears of the chimpanzee and orang are curiously
like those of man, and the proper muscles are likewise but very
slightly developed. (30. Prof. A. Macalister, ‘Annals and Magazine of
Natural History,’ vol. vii. 1871, p. 342.) I am also assured by the
keepers in the Zoological Gardens that these animals never move or
erect their ears; so that they are in an equally rudimentary condition
with those of man, as far as function is concerned. Why these animals,
as well as the progenitors of man, should have lost the power of
erecting their ears, we cannot say. It may be, though I am not
satisfied with this view, that owing to their arboreal habits and great
strength they were but little exposed to danger, and so during a
lengthened period moved their ears but little, and thus gradually lost
the power of moving them. This would be a parallel case with that of
those large and heavy birds, which, from inhabiting oceanic islands,
have not been exposed to the attacks of beasts of prey, and have
consequently lost the power of using their wings for flight. The
inability to move the ears in man and several apes is, however, partly
compensated by the freedom with which they can move the head in a
horizontal plane, so as to catch sounds from all directions. It has
been asserted that the ear of man alone possesses a lobule; but “a
rudiment of it is found in the gorilla” (31. Mr. St. George Mivart,
‘Elementary Anatomy,’ 1873, p. 396.); and, as I hear from Prof. Preyer,
it is not rarely absent in the negro.

[Fig. 2. Human Ear, modelled and drawn by Mr. Woolner. The projecting
point is labelled a.]

The celebrated sculptor, Mr. Woolner, informs me of one little
peculiarity in the external ear, which he has often observed both in
men and women, and of which he perceived the full significance. His
attention was first called to the subject whilst at work on his figure
of Puck, to which he had given pointed ears. He was thus led to examine
the ears of various monkeys, and subsequently more carefully those of
man. The peculiarity consists in a little blunt point, projecting from
the inwardly folded margin, or helix. When present, it is developed at
birth, and, according to Prof. Ludwig Meyer, more frequently in man
than in woman. Mr. Woolner made an exact model of one such case, and
sent me the accompanying drawing. (Fig. 2). These points not only
project inwards towards the centre of the ear, but often a little
outwards from its plane, so as to be visible when the head is viewed
from directly in front or behind. They are variable in size, and
somewhat in position, standing either a little higher or lower; and
they sometimes occur on one ear and not on the other. They are not
confined to mankind, for I observed a case in one of the spider-monkeys
(Ateles beelzebuth) in our Zoological Gardens; and Mr. E. Ray Lankester
informs me of another case in a chimpanzee in the gardens at Hamburg.
The helix obviously consists of the extreme margin of the ear folded
inwards; and this folding appears to be in some manner connected with
the whole external ear being permanently pressed backwards. In many
monkeys, which do not stand high in the order, as baboons and some
species of macacus (32. See also some remarks, and the drawings of the
ears of the Lemuroidea, in Messrs. Murie and Mivart’s excellent paper
in ‘Transactions of the Zoological Society,’ vol. vii. 1869, pp. 6 and
90.), the upper portion of the ear is slightly pointed, and the margin
is not at all folded inwards; but if the margin were to be thus folded,
a slight point would necessarily project inwards towards the centre,
and probably a little outwards from the plane of the ear; and this I
believe to be their origin in many cases. On the other hand, Prof. L.
Meyer, in an able paper recently published (33. ‘Über das Darwin’sche
Spitzohr,’ Archiv fur Path. Anat. und Phys., 1871, p. 485.), maintains
that the whole case is one of mere variability; and that the
projections are not real ones, but are due to the internal cartilage on
each side of the points not having been fully developed. I am quite
ready to admit that this is the correct explanation in many instances,
as in those figured by Prof. Meyer, in which there are several minute
points, or the whole margin is sinuous. I have myself seen, through the
kindness of Dr. L. Down, the ear of a microcephalous idiot, on which
there is a projection on the outside of the helix, and not on the
inward folded edge, so that this point can have no relation to a former
apex of the ear. Nevertheless in some cases, my original view, that the
points are vestiges of the tips of formerly erect and pointed ears,
still seems to me probable. I think so from the frequency of their
occurrence, and from the general correspondence in position with that
of the tip of a pointed ear. In one case, of which a photograph has
been sent me, the projection is so large, that supposing, in accordance
with Prof. Meyer’s view, the ear to be made perfect by the equal
development of the cartilage throughout the whole extent of the margin,
it would have covered fully one-third of the whole ear. Two cases have
been communicated to me, one in North America, and the other in
England, in which the upper margin is not at all folded inwards, but is
pointed, so that it closely resembles the pointed ear of an ordinary
quadruped in outline. In one of these cases, which was that of a young
child, the father compared the ear with the drawing which I have given
(34. ‘The Expression of the Emotions,’ p. 136.) of the ear of a monkey,
the Cynopithecus niger, and says that their outlines are closely
similar. If, in these two cases, the margin had been folded inwards in
the normal manner, an inward projection must have been formed. I may
add that in two other cases the outline still remains somewhat pointed,
although the margin of the upper part of the ear is normally folded
inwards—in one of them, however, very narrowly. [Fig.3. Foetus of an
Orang(?). Exact copy of a photograph, shewing the form of the ear at
this early age.] The following woodcut (No. 3) is an accurate copy of a
photograph of the foetus of an orang (kindly sent me by Dr. Nitsche),
in which it may be seen how different the pointed outline of the ear is
at this period from its adult condition, when it bears a close general
resemblance to that of man. It is evident that the folding over of the
tip of such an ear, unless it changed greatly during its further
development, would give rise to a point projecting inwards. On the
whole, it still seems to me probable that the points in question are in
some cases, both in man and apes, vestiges of a former condition.

The nictitating membrane, or third eyelid, with its accessory muscles
and other structures, is especially well developed in birds, and is of
much functional importance to them, as it can be rapidly drawn across
the whole eye-ball. It is found in some reptiles and amphibians, and in
certain fishes, as in sharks. It is fairly well developed in the two
lower divisions of the mammalian series, namely, in the monotremata and
marsupials, and in some few of the higher mammals, as in the walrus.
But in man, the quadrumana, and most other mammals, it exists, as is
admitted by all anatomists, as a mere rudiment, called the semilunar
fold. (35. Muller’s ‘Elements of Physiology,’ Eng. translat. 1842, vol.
ii. p. 1117. Owen, ‘Anatomy of Vertebrates,’ vol. iii. p. 260; ibid. on
the Walrus, ‘Proceedings of the Zoological Society,’ November 8, 1854.
See also R. Knox, ‘Great Artists and Anatomists,’ p. 106. This rudiment
apparently is somewhat larger in Negroes and Australians than in
Europeans, see Carl Vogt, ‘Lectures on Man,’ Eng. translat. p. 129.)

The sense of smell is of the highest importance to the greater number
of mammals—to some, as the ruminants, in warning them of danger; to
others, as the Carnivora, in finding their prey; to others, again, as
the wild boar, for both purposes combined. But the sense of smell is of
extremely slight service, if any, even to the dark coloured races of
men, in whom it is much more highly developed than in the white and
civilised races. (36. The account given by Humboldt of the power of
smell possessed by the natives of South America is well known, and has
been confirmed by others. M. Houzeau (‘Études sur les Facultés
Mentales,’ etc., tom. i. 1872, p. 91) asserts that he repeatedly made
experiments, and proved that Negroes and Indians could recognise
persons in the dark by their odour. Dr. W. Ogle has made some curious
observations on the connection between the power of smell and the
colouring matter of the mucous membrane of the olfactory region as well
as of the skin of the body. I have, therefore, spoken in the text of
the dark-coloured races having a finer sense of smell than the white
races. See his paper, ‘Medico-Chirurgical Transactions,’ London, vol.
liii. 1870, p. 276.) Nevertheless it does not warn them of danger, nor
guide them to their food; nor does it prevent the Esquimaux from
sleeping in the most fetid atmosphere, nor many savages from eating
half-putrid meat. In Europeans the power differs greatly in different
individuals, as I am assured by an eminent naturalist who possesses
this sense highly developed, and who has attended to the subject. Those
who believe in the principle of gradual evolution, will not readily
admit that the sense of smell in its present state was originally
acquired by man, as he now exists. He inherits the power in an
enfeebled and so far rudimentary condition, from some early progenitor,
to whom it was highly serviceable, and by whom it was continually used.
In those animals which have this sense highly developed, such as dogs
and horses, the recollection of persons and of places is strongly
associated with their odour; and we can thus perhaps understand how it
is, as Dr. Maudsley has truly remarked (37. ‘The Physiology and
Pathology of Mind,’ 2nd ed. 1868, p. 134.), that the sense of smell in
man “is singularly effective in recalling vividly the ideas and images
of forgotten scenes and places.”

Man differs conspicuously from all the other primates in being almost
naked. But a few short straggling hairs are found over the greater part
of the body in the man, and fine down on that of the woman. The
different races differ much in hairiness; and in the individuals of the
same race the hairs are highly variable, not only in abundance, but
likewise in position: thus in some Europeans the shoulders are quite
naked, whilst in others they bear thick tufts of hair. (38. Eschricht,
Über die Richtung der Haare am menschlichen Körper, Muller’s ‘Archiv
fur Anat. und Phys.’ 1837, s. 47. I shall often have to refer to this
very curious paper.) There can be little doubt that the hairs thus
scattered over the body are the rudiments of the uniform hairy coat of
the lower animals. This view is rendered all the more probable, as it
is known that fine, short, and pale-coloured hairs on the limbs and
other parts of the body, occasionally become developed into “thickset,
long, and rather coarse dark hairs,” when abnormally nourished near
old-standing inflamed surfaces. (39. Paget, ‘Lectures on Surgical
Pathology,’ 1853, vol. i. p. 71.)

I am informed by Sir James Paget that often several members of a family
have a few hairs in their eyebrows much longer than the others; so that
even this slight peculiarity seems to be inherited. These hairs, too,
seem to have their representatives; for in the chimpanzee, and in
certain species of Macacus, there are scattered hairs of considerable
length rising from the naked skin above the eyes, and corresponding to
our eyebrows; similar long hairs project from the hairy covering of the
superciliary ridges in some baboons.

The fine wool-like hair, or so-called lanugo, with which the human
foetus during the sixth month is thickly covered, offers a more curious
case. It is first developed, during the fifth month, on the eyebrows
and face, and especially round the mouth, where it is much longer than
that on the head. A moustache of this kind was observed by Eschricht
(40. Eschricht, ibid. s. 40, 47.) on a female foetus; but this is not
so surprising a circumstance as it may at first appear, for the two
sexes generally resemble each other in all external characters during
an early period of growth. The direction and arrangement of the hairs
on all parts of the foetal body are the same as in the adult, but are
subject to much variability. The whole surface, including even the
forehead and ears, is thus thickly clothed; but it is a significant
fact that the palms of the hands and the soles of the feet are quite
naked, like the inferior surfaces of all four extremities in most of
the lower animals. As this can hardly be an accidental coincidence, the
woolly covering of the foetus probably represents the first permanent
coat of hair in those mammals which are born hairy. Three or four cases
have been recorded of persons born with their whole bodies and faces
thickly covered with fine long hairs; and this strange condition is
strongly inherited, and is correlated with an abnormal condition of the
teeth. (41. See my ‘Variation of Animals and Plants under
Domestication,’ vol. ii. p. 327. Prof. Alex. Brandt has recently sent
me an additional case of a father and son, born in Russia, with these
peculiarities. I have received drawings of both from Paris.) Prof.
Alex. Brandt informs me that he has compared the hair from the face of
a man thus characterised, aged thirty-five, with the lanugo of a
foetus, and finds it quite similar in texture; therefore, as he
remarks, the case may be attributed to an arrest of development in the
hair, together with its continued growth. Many delicate children, as I
have been assured by a surgeon to a hospital for children, have their
backs covered by rather long silky hairs; and such cases probably come
under the same head.

It appears as if the posterior molar or wisdom-teeth were tending to
become rudimentary in the more civilised races of man. These teeth are
rather smaller than the other molars, as is likewise the case with the
corresponding teeth in the chimpanzee and orang; and they have only two
separate fangs. They do not cut through the gums till about the
seventeenth year, and I have been assured that they are much more
liable to decay, and are earlier lost than the other teeth; but this is
denied by some eminent dentists. They are also much more liable to
vary, both in structure and in the period of their development, than
the other teeth. (42. Dr. Webb, ‘Teeth in Man and the Anthropoid Apes,’
as quoted by Dr. C. Carter Blake in Anthropological Review, July 1867,
p. 299.) In the Melanian races, on the other hand, the wisdom-teeth are
usually furnished with three separate fangs, and are generally sound;
they also differ from the other molars in size, less than in the
Caucasian races. (43. Owen, ‘Anatomy of Vertebrates,’ vol. iii. pp.
320, 321, and 325.) Prof. Schaaffhausen accounts for this difference
between the races by “the posterior dental portion of the jaw being
always shortened” in those that are civilised (44. ‘On the Primitive
Form of the Skull,’ Eng. translat., in ‘Anthropological Review,’ Oct.
1868, p. 426), and this shortening may, I presume, be attributed to
civilised men habitually feeding on soft, cooked food, and thus using
their jaws less. I am informed by Mr. Brace that it is becoming quite a
common practice in the United States to remove some of the molar teeth
of children, as the jaw does not grow large enough for the perfect
development of the normal number. (45. Prof. Montegazza writes to me
from Florence, that he has lately been studying the last molar teeth in
the different races of man, and has come to the same conclusion as that
given in my text, viz., that in the higher or civilised races they are
on the road towards atrophy or elimination.)

With respect to the alimentary canal, I have met with an account of
only a single rudiment, namely the vermiform appendage of the caecum.
The caecum is a branch or diverticulum of the intestine, ending in a
cul-de-sac, and is extremely long in many of the lower
vegetable-feeding mammals. In the marsupial koala it is actually more
than thrice as long as the whole body. (46. Owen, ‘Anatomy of
Vertebrates,’ vol. iii. pp. 416, 434, 441.) It is sometimes produced
into a long gradually-tapering point, and is sometimes constricted in
parts. It appears as if, in consequence of changed diet or habits, the
caecum had become much shortened in various animals, the vermiform
appendage being left as a rudiment of the shortened part. That this
appendage is a rudiment, we may infer from its small size, and from the
evidence which Prof. Canestrini (47. ‘Annuario della Soc. d. Nat.’
Modena, 1867, p. 94.) has collected of its variability in man. It is
occasionally quite absent, or again is largely developed. The passage
is sometimes completely closed for half or two-thirds of its length,
with the terminal part consisting of a flattened solid expansion. In
the orang this appendage is long and convoluted: in man it arises from
the end of the short caecum, and is commonly from four to five inches
in length, being only about the third of an inch in diameter. Not only
is it useless, but it is sometimes the cause of death, of which fact I
have lately heard two instances: this is due to small hard bodies, such
as seeds, entering the passage, and causing inflammation. (48. M. C.
Martins (“De l’Unité Organique,” in ‘Revue des Deux Mondes,’ June 15,
1862, p. 16) and Haeckel (‘Generelle Morphologie,’ B. ii. s. 278), have
both remarked on the singular fact of this rudiment sometimes causing
death.)

In some of the lower Quadrumana, in the Lemuridae and Carnivora, as
well as in many marsupials, there is a passage near the lower end of
the humerus, called the supra-condyloid foramen, through which the
great nerve of the fore limb and often the great artery pass. Now in
the humerus of man, there is generally a trace of this passage, which
is sometimes fairly well developed, being formed by a depending
hook-like process of bone, completed by a band of ligament. Dr.
Struthers (49. With respect to inheritance, see Dr. Struthers in the
‘Lancet,’ Feb. 15, 1873, and another important paper, ibid. Jan. 24,
1863, p. 83. Dr. Knox, as I am informed, was the first anatomist who
drew attention to this peculiar structure in man; see his ‘Great
Artists and Anatomists,’ p. 63. See also an important memoir on this
process by Dr. Gruber, in the ‘Bulletin de l’Acad. Imp. de St.
Petersbourg,’ tom. xii. 1867, p. 448.), who has closely attended to the
subject, has now shewn that this peculiarity is sometimes inherited, as
it has occurred in a father, and in no less than four out of his seven
children. When present, the great nerve invariably passes through it;
and this clearly indicates that it is the homologue and rudiment of the
supra-condyloid foramen of the lower animals. Prof. Turner estimates,
as he informs me, that it occurs in about one per cent. of recent
skeletons. But if the occasional development of this structure in man
is, as seems probable, due to reversion, it is a return to a very
ancient state of things, because in the higher Quadrumana it is absent.

There is another foramen or perforation in the humerus, occasionally
present in man, which may be called the inter-condyloid. This occurs,
but not constantly, in various anthropoid and other apes (50. Mr. St.
George Mivart, ‘Transactions Phil. Soc.’ 1867, p. 310.), and likewise
in many of the lower animals. It is remarkable that this perforation
seems to have been present in man much more frequently during ancient
times than recently. Mr. Busk (51. “On the Caves of Gibraltar,”
‘Transactions of the International Congress of Prehistoric
Archaeology,’ Third Session, 1869, p. 159. Prof. Wyman has lately shewn
(Fourth Annual Report, Peabody Museum, 1871, p. 20), that this
perforation is present in thirty-one per cent. of some human remains
from ancient mounds in the Western United States, and in Florida. It
frequently occurs in the negro.) has collected the following evidence
on this head: Prof. Broca “noticed the perforation in four and a half
per cent. of the arm-bones collected in the ‘Cimetière du Sud,’ at
Paris; and in the Grotto of Orrony, the contents of which are referred
to the Bronze period, as many as eight humeri out of thirty-two were
perforated; but this extraordinary proportion, he thinks, might be due
to the cavern having been a sort of ‘family vault.’ Again, M. Dupont
found thirty per cent. of perforated bones in the caves of the Valley
of the Lesse, belonging to the Reindeer period; whilst M. Leguay, in a
sort of dolmen at Argenteuil, observed twenty-five per cent. to be
perforated; and M. Pruner-Bey found twenty-six per cent. in the same
condition in bones from Vaureal. Nor should it be left unnoticed that
M. Pruner-Bey states that this condition is common in Guanche
skeletons.” It is an interesting fact that ancient races, in this and
several other cases, more frequently present structures which resemble
those of the lower animals than do the modern. One chief cause seems to
be that the ancient races stand somewhat nearer in the long line of
descent to their remote animal-like progenitors.

In man, the os coccyx, together with certain other vertebrae hereafter
to be described, though functionless as a tail, plainly represent this
part in other vertebrate animals. At an early embryonic period it is
free, and projects beyond the lower extremities; as may be seen in the
drawing (Fig. 1.) of a human embryo. Even after birth it has been
known, in certain rare and anomalous cases (52. Quatrefages has lately
collected the evidence on this subject. ‘Revue des Cours
Scientifiques,’ 1867-1868, p. 625. In 1840 Fleischmann exhibited a
human foetus bearing a free tail, which, as is not always the case,
included vertebral bodies; and this tail was critically examined by the
many anatomists present at the meeting of naturalists at Erlangen (see
Marshall in Niederlandischen Archiv für Zoologie, December 1871).), to
form a small external rudiment of a tail. The os coccyx is short,
usually including only four vertebrae, all anchylosed together: and
these are in a rudimentary condition, for they consist, with the
exception of the basal one, of the centrum alone. (53. Owen, ‘On the
Nature of Limbs,’ 1849, p. 114.) They are furnished with some small
muscles; one of which, as I am informed by Prof. Turner, has been
expressly described by Theile as a rudimentary repetition of the
extensor of the tail, a muscle which is so largely developed in many
mammals.

The spinal cord in man extends only as far downwards as the last dorsal
or first lumbar vertebra; but a thread-like structure (the filum
terminale) runs down the axis of the sacral part of the spinal canal,
and even along the back of the coccygeal bones. The upper part of this
filament, as Prof. Turner informs me, is undoubtedly homologous with
the spinal cord; but the lower part apparently consists merely of the
pia mater, or vascular investing membrane. Even in this case the os
coccyx may be said to possess a vestige of so important a structure as
the spinal cord, though no longer enclosed within a bony canal. The
following fact, for which I am also indebted to Prof. Turner, shews how
closely the os coccyx corresponds with the true tail in the lower
animals: Luschka has recently discovered at the extremity of the
coccygeal bones a very peculiar convoluted body, which is continuous
with the middle sacral artery; and this discovery led Krause and Meyer
to examine the tail of a monkey (Macacus), and of a cat, in both of
which they found a similarly convoluted body, though not at the
extremity.

The reproductive system offers various rudimentary structures; but
these differ in one important respect from the foregoing cases. Here we
are not concerned with the vestige of a part which does not belong to
the species in an efficient state, but with a part efficient in the one
sex, and represented in the other by a mere rudiment. Nevertheless, the
occurrence of such rudiments is as difficult to explain, on the belief
of the separate creation of each species, as in the foregoing cases.
Hereafter I shall have to recur to these rudiments, and shall shew that
their presence generally depends merely on inheritance, that is, on
parts acquired by one sex having been partially transmitted to the
other. I will in this place only give some instances of such rudiments.
It is well known that in the males of all mammals, including man,
rudimentary mammae exist. These in several instances have become well
developed, and have yielded a copious supply of milk. Their essential
identity in the two sexes is likewise shewn by their occasional
sympathetic enlargement in both during an attack of the measles. The
vesicula prostatica, which has been observed in many male mammals, is
now universally acknowledged to be the homologue of the female uterus,
together with the connected passage. It is impossible to read
Leuckart’s able description of this organ, and his reasoning, without
admitting the justness of his conclusion. This is especially clear in
the case of those mammals in which the true female uterus bifurcates,
for in the males of these the vesicula likewise bifurcates. (54.
Leuckart, in Todd’s ‘Cyclopaedia of Anatomy’ 1849-52, vol. iv. p. 1415.
In man this organ is only from three to six lines in length, but, like
so many other rudimentary parts, it is variable in development as well
as in other characters.) Some other rudimentary structures belonging to
the reproductive system might have been here adduced. (55. See, on this
subject, Owen, ‘Anatomy of Vertebrates,’ vol. iii. pp. 675, 676, 706.)

The bearing of the three great classes of facts now given is
unmistakeable. But it would be superfluous fully to recapitulate the
line of argument given in detail in my ‘Origin of Species.’ The
homological construction of the whole frame in the members of the same
class is intelligible, if we admit their descent from a common
progenitor, together with their subsequent adaptation to diversified
conditions. On any other view, the similarity of pattern between the
hand of a man or monkey, the foot of a horse, the flipper of a seal,
the wing of a bat, etc., is utterly inexplicable. (56. Prof. Bianconi,
in a recently published work, illustrated by admirable engravings (‘La
Théorie Darwinienne et la création dite indépendante,’ 1874),
endeavours to shew that homological structures, in the above and other
cases, can be fully explained on mechanical principles, in accordance
with their uses. No one has shewn so well, how admirably such
structures are adapted for their final purpose; and this adaptation
can, as I believe, be explained through natural selection. In
considering the wing of a bat, he brings forward (p. 218) what appears
to me (to use Auguste Comte’s words) a mere metaphysical principle,
namely, the preservation “in its integrity of the mammalian nature of
the animal.” In only a few cases does he discuss rudiments, and then
only those parts which are partially rudimentary, such as the little
hoofs of the pig and ox, which do not touch the ground; these he shews
clearly to be of service to the animal. It is unfortunate that he did
not consider such cases as the minute teeth, which never cut through
the jaw in the ox, or the mammae of male quadrupeds, or the wings of
certain beetles, existing under the soldered wing-covers, or the
vestiges of the pistil and stamens in various flowers, and many other
such cases. Although I greatly admire Prof. Bianconi’s work, yet the
belief now held by most naturalists seems to me left unshaken, that
homological structures are inexplicable on the principle of mere
adaptation.) It is no scientific explanation to assert that they have
all been formed on the same ideal plan. With respect to development, we
can clearly understand, on the principle of variations supervening at a
rather late embryonic period, and being inherited at a corresponding
period, how it is that the embryos of wonderfully different forms
should still retain, more or less perfectly, the structure of their
common progenitor. No other explanation has ever been given of the
marvellous fact that the embryos of a man, dog, seal, bat, reptile,
etc., can at first hardly be distinguished from each other. In order to
understand the existence of rudimentary organs, we have only to suppose
that a former progenitor possessed the parts in question in a perfect
state, and that under changed habits of life they became greatly
reduced, either from simple disuse, or through the natural selection of
those individuals which were least encumbered with a superfluous part,
aided by the other means previously indicated.

Thus we can understand how it has come to pass that man and all other
vertebrate animals have been constructed on the same general model, why
they pass through the same early stages of development, and why they
retain certain rudiments in common. Consequently we ought frankly to
admit their community of descent: to take any other view, is to admit
that our own structure, and that of all the animals around us, is a
mere snare laid to entrap our judgment. This conclusion is greatly
strengthened, if we look to the members of the whole animal series, and
consider the evidence derived from their affinities or classification,
their geographical distribution and geological succession. It is only
our natural prejudice, and that arrogance which made our forefathers
declare that they were descended from demi-gods, which leads us to
demur to this conclusion. But the time will before long come, when it
will be thought wonderful that naturalists, who were well acquainted
with the comparative structure and development of man, and other
mammals, should have believed that each was the work of a separate act
of creation.




CHAPTER II.
ON THE MANNER OF DEVELOPMENT OF MAN FROM SOME LOWER FORM.


Variability of body and mind in man—Inheritance—Causes of
variability—Laws of variation the same in man as in the lower
animals—Direct action of the conditions of life—Effects of the
increased use and disuse of parts—Arrested
development—Reversion—Correlated variation—Rate of increase—Checks to
increase—Natural selection—Man the most dominant animal in the
world—Importance of his corporeal structure—The causes which have led
to his becoming erect—Consequent changes of structure—Decrease in size
of the canine teeth—Increased size and altered shape of the
skull—Nakedness —Absence of a tail—Defenceless condition of man.

It is manifest that man is now subject to much variability. No two
individuals of the same race are quite alike. We may compare millions
of faces, and each will be distinct. There is an equally great amount
of diversity in the proportions and dimensions of the various parts of
the body; the length of the legs being one of the most variable points.
(1. ‘Investigations in Military and Anthropological Statistics of
American Soldiers,’ by B.A. Gould, 1869, p. 256.) Although in some
quarters of the world an elongated skull, and in other quarters a short
skull prevails, yet there is great diversity of shape even within the
limits of the same race, as with the aborigines of America and South
Australia—the latter a race “probably as pure and homogeneous in blood,
customs, and language as any in existence”—and even with the
inhabitants of so confined an area as the Sandwich Islands. (2. With
respect to the “Cranial forms of the American aborigines,” see Dr.
Aitken Meigs in ‘Proc. Acad. Nat. Sci.’ Philadelphia, May 1868. On the
Australians, see Huxley, in Lyell’s ‘Antiquity of Man,’ 1863, p. 87. On
the Sandwich Islanders, Prof. J. Wyman, ‘Observations on Crania,’
Boston, 1868, p. 18.) An eminent dentist assures me that there is
nearly as much diversity in the teeth as in the features. The chief
arteries so frequently run in abnormal courses, that it has been found
useful for surgical purposes to calculate from 1040 corpses how often
each course prevails. (3. ‘Anatomy of the Arteries,’ by R. Quain.
Preface, vol. i. 1844.) The muscles are eminently variable: thus those
of the foot were found by Prof. Turner (4. ‘Transactions of the Royal
Society of Edinburgh,’ vol. xxiv. pp. 175, 189.) not to be strictly
alike in any two out of fifty bodies; and in some the deviations were
considerable. He adds, that the power of performing the appropriate
movements must have been modified in accordance with the several
deviations. Mr. J. Wood has recorded (5. ‘Proceedings Royal Society,’
1867, p. 544; also 1868, pp. 483, 524. There is a previous paper, 1866,
p. 229.) the occurrence of 295 muscular variations in thirty-six
subjects, and in another set of the same number no less than 558
variations, those occurring on both sides of the body being only
reckoned as one. In the last set, not one body out of the thirty-six
was “found totally wanting in departures from the standard descriptions
of the muscular system given in anatomical text books.” A single body
presented the extraordinary number of twenty-five distinct
abnormalities. The same muscle sometimes varies in many ways: thus
Prof. Macalister describes (6. ‘Proc. R. Irish Academy,’ vol. x. 1868,
p. 141.) no less than twenty distinct variations in the palmaris
accessorius.

The famous old anatomist, Wolff (7. ‘Act. Acad. St. Petersburg,’ 1778,
part ii. p. 217.), insists that the internal viscera are more variable
than the external parts: Nulla particula est quae non aliter et aliter
in aliis se habeat hominibus. He has even written a treatise on the
choice of typical examples of the viscera for representation. A
discussion on the beau-ideal of the liver, lungs, kidneys, etc., as of
the human face divine, sounds strange in our ears.

The variability or diversity of the mental faculties in men of the same
race, not to mention the greater differences between the men of
distinct races, is so notorious that not a word need here be said. So
it is with the lower animals. All who have had charge of menageries
admit this fact, and we see it plainly in our dogs and other domestic
animals. Brehm especially insists that each individual monkey of those
which he kept tame in Africa had its own peculiar disposition and
temper: he mentions one baboon remarkable for its high intelligence;
and the keepers in the Zoological Gardens pointed out to me a monkey,
belonging to the New World division, equally remarkable for
intelligence. Rengger, also, insists on the diversity in the various
mental characters of the monkeys of the same species which he kept in
Paraguay; and this diversity, as he adds, is partly innate, and partly
the result of the manner in which they have been treated or educated.
(8. Brehm, ‘Thierleben,’ B. i. ss. 58, 87. Rengger, ‘Säugethiere von
Paraguay,’ s. 57.)

I have elsewhere (9. ‘Variation of Animals and Plants under
Domestication,’ vol. ii. chap. xii.) so fully discussed the subject of
Inheritance, that I need here add hardly anything. A greater number of
facts have been collected with respect to the transmission of the most
trifling, as well as of the most important characters in man, than in
any of the lower animals; though the facts are copious enough with
respect to the latter. So in regard to mental qualities, their
transmission is manifest in our dogs, horses, and other domestic
animals. Besides special tastes and habits, general intelligence,
courage, bad and good temper, etc., are certainly transmitted. With man
we see similar facts in almost every family; and we now know, through
the admirable labours of Mr. Galton (10. ‘Hereditary Genius: an Inquiry
into its Laws and Consequences,’ 1869.), that genius which implies a
wonderfully complex combination of high faculties, tends to be
inherited; and, on the other hand, it is too certain that insanity and
deteriorated mental powers likewise run in families.

With respect to the causes of variability, we are in all cases very
ignorant; but we can see that in man as in the lower animals, they
stand in some relation to the conditions to which each species has been
exposed, during several generations. Domesticated animals vary more
than those in a state of nature; and this is apparently due to the
diversified and changing nature of the conditions to which they have
been subjected. In this respect the different races of man resemble
domesticated animals, and so do the individuals of the same race, when
inhabiting a very wide area, like that of America. We see the influence
of diversified conditions in the more civilised nations; for the
members belonging to different grades of rank, and following different
occupations, present a greater range of character than do the members
of barbarous nations. But the uniformity of savages has often been
exaggerated, and in some cases can hardly be said to exist. (11. Mr.
Bates remarks (‘The Naturalist on the Amazons,’ 1863, vol. ii p. 159),
with respect to the Indians of the same South American tribe, “no two
of them were at all similar in the shape of the head; one man had an
oval visage with fine features, and another was quite Mongolian in
breadth and prominence of cheek, spread of nostrils, and obliquity of
eyes.”) It is, nevertheless, an error to speak of man, even if we look
only to the conditions to which he has been exposed, as “far more
domesticated” (12. Blumenbach, ‘Treatises on Anthropology.’ Eng.
translat., 1865, p. 205.) than any other animal. Some savage races,
such as the Australians, are not exposed to more diversified conditions
than are many species which have a wide range. In another and much more
important respect, man differs widely from any strictly domesticated
animal; for his breeding has never long been controlled, either by
methodical or unconscious selection. No race or body of men has been so
completely subjugated by other men, as that certain individuals should
be preserved, and thus unconsciously selected, from somehow excelling
in utility to their masters. Nor have certain male and female
individuals been intentionally picked out and matched, except in the
well-known case of the Prussian grenadiers; and in this case man
obeyed, as might have been expected, the law of methodical selection;
for it is asserted that many tall men were reared in the villages
inhabited by the grenadiers and their tall wives. In Sparta, also, a
form of selection was followed, for it was enacted that all children
should be examined shortly after birth; the well-formed and vigorous
being preserved, the others left to perish. (13. Mitford’s ‘History of
Greece,’ vol. i. p. 282. It appears also from a passage in Xenophon’s
‘Memorabilia,’ B. ii. 4 (to which my attention has been called by the
Rev. J.N. Hoare), that it was a well recognised principle with the
Greeks, that men ought to select their wives with a view to the health
and vigour of their children. The Grecian poet, Theognis, who lived 550
B.C., clearly saw how important selection, if carefully applied, would
be for the improvement of mankind. He saw, likewise, that wealth often
checks the proper action of sexual selection. He thus writes:

    “With kine and horses, Kurnus! we proceed
    By reasonable rules, and choose a breed
    For profit and increase, at any price:
    Of a sound stock, without defect or vice.
    But, in the daily matches that we make,
    The price is everything:  for money’s sake,
    Men marry:  women are in marriage given
    The churl or ruffian, that in wealth has thriven,
    May match his offspring with the proudest race:
    Thus everything is mix’d, noble and base!
    If then in outward manner, form, and mind,
    You find us a degraded, motley kind,
    Wonder no more, my friend! the cause is plain,
    And to lament the consequence is vain.”

(The Works of J. Hookham Frere, vol. ii. 1872, p. 334.))

If we consider all the races of man as forming a single species, his
range is enormous; but some separate races, as the Americans and
Polynesians, have very wide ranges. It is a well-known law that
widely-ranging species are much more variable than species with
restricted ranges; and the variability of man may with more truth be
compared with that of widely-ranging species, than with that of
domesticated animals.

Not only does variability appear to be induced in man and the lower
animals by the same general causes, but in both the same parts of the
body are affected in a closely analogous manner. This has been proved
in such full detail by Godron and Quatrefages, that I need here only
refer to their works. (14. Godron, ‘De l’Espèce,’ 1859, tom. ii. livre
3. Quatrefages, ‘Unité de l’Espèce Humaine,’ 1861. Also Lectures on
Anthropology, given in the ‘Revue des Cours Scientifiques,’ 1866-1868.)
Monstrosities, which graduate into slight variations, are likewise so
similar in man and the lower animals, that the same classification and
the same terms can be used for both, as has been shewn by Isidore
Geoffroy St.-Hilaire. (15. ‘Hist. Gen. et Part. des Anomalies de
l’Organisation,’ in three volumes, tom. i. 1832.) In my work on the
variation of domestic animals, I have attempted to arrange in a rude
fashion the laws of variation under the following heads:—The direct and
definite action of changed conditions, as exhibited by all or nearly
all the individuals of the same species, varying in the same manner
under the same circumstances. The effects of the long-continued use or
disuse of parts. The cohesion of homologous parts. The variability of
multiple parts. Compensation of growth; but of this law I have found no
good instance in the case of man. The effects of the mechanical
pressure of one part on another; as of the pelvis on the cranium of the
infant in the womb. Arrests of development, leading to the diminution
or suppression of parts. The reappearance of long-lost characters
through reversion. And lastly, correlated variation. All these
so-called laws apply equally to man and the lower animals; and most of
them even to plants. It would be superfluous here to discuss all of
them (16. I have fully discussed these laws in my ‘Variation of Animals
and Plants under Domestication,’ vol. ii. chap. xxii. and xxiii. M.
J.P. Durand has lately (1868) published a valuable essay, ‘De
l’Influence des Milieux,’ etc. He lays much stress, in the case of
plants, on the nature of the soil.); but several are so important, that
they must be treated at considerable length.

THE DIRECT AND DEFINITE ACTION OF CHANGED CONDITIONS.

This is a most perplexing subject. It cannot be denied that changed
conditions produce some, and occasionally a considerable effect, on
organisms of all kinds; and it seems at first probable that if
sufficient time were allowed this would be the invariable result. But I
have failed to obtain clear evidence in favour of this conclusion; and
valid reasons may be urged on the other side, at least as far as the
innumerable structures are concerned, which are adapted for special
ends. There can, however, be no doubt that changed conditions induce an
almost indefinite amount of fluctuating variability, by which the whole
organisation is rendered in some degree plastic.

In the United States, above 1,000,000 soldiers, who served in the late
war, were measured, and the States in which they were born and reared
were recorded. (17. ‘Investigations in Military and Anthrop.
Statistics,’ etc., 1869, by B.A. Gould, pp. 93, 107, 126, 131, 134.)
From this astonishing number of observations it is proved that local
influences of some kind act directly on stature; and we further learn
that “the State where the physical growth has in great measure taken
place, and the State of birth, which indicates the ancestry, seem to
exert a marked influence on the stature.” For instance, it is
established, “that residence in the Western States, during the years of
growth, tends to produce increase of stature.” On the other hand, it is
certain that with sailors, their life delays growth, as shewn “by the
great difference between the statures of soldiers and sailors at the
ages of seventeen and eighteen years.” Mr. B.A. Gould endeavoured to
ascertain the nature of the influences which thus act on stature; but
he arrived only at negative results, namely that they did not relate to
climate, the elevation of the land, soil, nor even “in any controlling
degree” to the abundance or the need of the comforts of life. This
latter conclusion is directly opposed to that arrived at by Villerme,
from the statistics of the height of the conscripts in different parts
of France. When we compare the differences in stature between the
Polynesian chiefs and the lower orders within the same islands, or
between the inhabitants of the fertile volcanic and low barren coral
islands of the same ocean (18. For the Polynesians, see Prichard’s
‘Physical History of Mankind,’ vol. v. 1847, pp. 145, 283. Also Godron,
‘De l’Espèce,’ tom. ii. p. 289. There is also a remarkable difference
in appearance between the closely-allied Hindoos inhabiting the Upper
Ganges and Bengal; see Elphinstone’s ‘History of India,’ vol. i. p.
324.) or again between the Fuegians on the eastern and western shores
of their country, where the means of subsistence are very different, it
is scarcely possible to avoid the conclusion that better food and
greater comfort do influence stature. But the preceding statements shew
how difficult it is to arrive at any precise result. Dr. Beddoe has
lately proved that, with the inhabitants of Britain, residence in towns
and certain occupations have a deteriorating influence on height; and
he infers that the result is to a certain extent inherited, as is
likewise the case in the United States. Dr. Beddoe further believes
that wherever a “race attains its maximum of physical development, it
rises highest in energy and moral vigour.” (19. ‘Memoirs,
Anthropological Society,’ vol. iii. 1867-69, pp. 561, 565, 567.)

Whether external conditions produce any other direct effect on man is
not known. It might have been expected that differences of climate
would have had a marked influence, inasmuch as the lungs and kidneys
are brought into activity under a low temperature, and the liver and
skin under a high one. (20. Dr. Brakenridge, ‘Theory of Diathesis,’
‘Medical Times,’ June 19 and July 17, 1869.) It was formerly thought
that the colour of the skin and the character of the hair were
determined by light or heat; and although it can hardly be denied that
some effect is thus produced, almost all observers now agree that the
effect has been very small, even after exposure during many ages. But
this subject will be more properly discussed when we treat of the
different races of mankind. With our domestic animals there are grounds
for believing that cold and damp directly affect the growth of the
hair; but I have not met with any evidence on this head in the case of
man.

EFFECTS OF THE INCREASED USE AND DISUSE OF A PARTS.

It is well known that use strengthens the muscles in the individual,
and complete disuse, or the destruction of the proper nerve, weakens
them. When the eye is destroyed, the optic nerve often becomes
atrophied. When an artery is tied, the lateral channels increase not
only in diameter, but in the thickness and strength of their coats.
When one kidney ceases to act from disease, the other increases in
size, and does double work. Bones increase not only in thickness, but
in length, from carrying a greater weight. (21. I have given
authorities for these several statements in my ‘Variation of Animals
and Plants under Domestication,’ vol. ii. pp. 297-300. Dr. Jaeger,
“Über das Langenwachsthum der Knochen,” ‘Jenäischen Zeitschrift,’ B. v.
Heft. i.) Different occupations, habitually followed, lead to changed
proportions in various parts of the body. Thus it was ascertained by
the United States Commission (22. ‘Investigations,’ etc., by B.A.
Gould, 1869, p. 288.) that the legs of the sailors employed in the late
war were longer by 0.217 of an inch than those of the soldiers, though
the sailors were on an average shorter men; whilst their arms were
shorter by 1.09 of an inch, and therefore, out of proportion, shorter
in relation to their lesser height. This shortness of the arms is
apparently due to their greater use, and is an unexpected result: but
sailors chiefly use their arms in pulling, and not in supporting
weights. With sailors, the girth of the neck and the depth of the
instep are greater, whilst the circumference of the chest, waist, and
hips is less, than in soldiers.

Whether the several foregoing modifications would become hereditary, if
the same habits of life were followed during many generations, is not
known, but it is probable. Rengger (23. ‘Säugethiere von Paraguay,’
1830, s. 4.) attributes the thin legs and thick arms of the Payaguas
Indians to successive generations having passed nearly their whole
lives in canoes, with their lower extremities motionless. Other writers
have come to a similar conclusion in analogous cases. According to
Cranz (24. ‘History of Greenland,’ Eng. translat., 1767, vol. i. p.
230.), who lived for a long time with the Esquimaux, “the natives
believe that ingenuity and dexterity in seal-catching (their highest
art and virtue) is hereditary; there is really something in it, for the
son of a celebrated seal-catcher will distinguish himself, though he
lost his father in childhood.” But in this case it is mental aptitude,
quite as much as bodily structure, which appears to be inherited. It is
asserted that the hands of English labourers are at birth larger than
those of the gentry. (25. ‘Intermarriage,’ by Alex. Walker, 1838, p.
377.) From the correlation which exists, at least in some cases (26.
‘The Variation of Animals under Domestication,’ vol. i. p. 173.),
between the development of the extremities and of the jaws, it is
possible that in those classes which do not labour much with their
hands and feet, the jaws would be reduced in size from this cause. That
they are generally smaller in refined and civilised men than in
hard-working men or savages, is certain. But with savages, as Mr.
Herbert Spencer (27. ‘Principles of Biology,’ vol. i. p. 455.) has
remarked, the greater use of the jaws in chewing coarse, uncooked food,
would act in a direct manner on the masticatory muscles, and on the
bones to which they are attached. In infants, long before birth, the
skin on the soles of the feet is thicker than on any other part of the
body; (28. Paget, ‘Lectures on Surgical Pathology,’ vol. ii, 1853, p.
209.) and it can hardly be doubted that this is due to the inherited
effects of pressure during a long series of generations.

It is familiar to every one that watchmakers and engravers are liable
to be short-sighted, whilst men living much out of doors, and
especially savages, are generally long-sighted. (29. It is a singular
and unexpected fact that sailors are inferior to landsmen in their mean
distance of distinct vision. Dr. B.A. Gould (‘Sanitary Memoirs of the
War of the Rebellion,’ 1869, p. 530), has proved this to be the case;
and he accounts for it by the ordinary range of vision in sailors being
“restricted to the length of the vessel and the height of the masts.”)
Short-sight and long-sight certainly tend to be inherited. (30. ‘The
Variation of Animals under Domestication,’ vol. i. p. 8.) The
inferiority of Europeans, in comparison with savages, in eyesight and
in the other senses, is no doubt the accumulated and transmitted effect
of lessened use during many generations; for Rengger (31. ‘Säugethiere
von Paraguay,’ s. 8, 10. I have had good opportunities for observing
the extraordinary power of eyesight in the Fuegians. See also Lawrence
(‘Lectures on Physiology,’ etc., 1822, p. 404) on this same subject. M.
Giraud-Teulon has recently collected (‘Revue des Cours Scientifiques,’
1870, p. 625) a large and valuable body of evidence proving that the
cause of short-sight, “C’est le travail assidu, de près.”) states that
he has repeatedly observed Europeans, who had been brought up and spent
their whole lives with the wild Indians, who nevertheless did not equal
them in the sharpness of their senses. The same naturalist observes
that the cavities in the skull for the reception of the several
sense-organs are larger in the American aborigines than in Europeans;
and this probably indicates a corresponding difference in the
dimensions of the organs themselves. Blumenbach has also remarked on
the large size of the nasal cavities in the skulls of the American
aborigines, and connects this fact with their remarkably acute power of
smell. The Mongolians of the plains of northern Asia, according to
Pallas, have wonderfully perfect senses; and Prichard believes that the
great breadth of their skulls across the zygomas follows from their
highly-developed sense organs. (32. Prichard, ‘Physical History of
Mankind,’ on the authority of Blumenbach, vol. i. 1851, p. 311; for the
statement by Pallas, vol. iv. 1844, p. 407.)

The Quechua Indians inhabit the lofty plateaux of Peru; and Alcide
d’Orbigny states (33. Quoted by Prichard, ‘Researches into the Physical
History of Mankind,’ vol. v. p. 463.) that, from continually breathing
a highly rarefied atmosphere, they have acquired chests and lungs of
extraordinary dimensions. The cells, also, of the lungs are larger and
more numerous than in Europeans. These observations have been doubted,
but Mr. D. Forbes carefully measured many Aymaras, an allied race,
living at the height of between 10,000 and 15,000 feet; and he informs
me (34. Mr. Forbes’ valuable paper is now published in the ‘Journal of
the Ethnological Society of London,’ new series, vol. ii. 1870, p.193.)
that they differ conspicuously from the men of all other races seen by
him in the circumference and length of their bodies. In his table of
measurements, the stature of each man is taken at 1000, and the other
measurements are reduced to this standard. It is here seen that the
extended arms of the Aymaras are shorter than those of Europeans, and
much shorter than those of Negroes. The legs are likewise shorter; and
they present this remarkable peculiarity, that in every Aymara
measured, the femur is actually shorter than the tibia. On an average,
the length of the femur to that of the tibia is as 211 to 252; whilst
in two Europeans, measured at the same time, the femora to the tibiae
were as 244 to 230; and in three Negroes as 258 to 241. The humerus is
likewise shorter relatively to the forearm. This shortening of that
part of the limb which is nearest to the body, appears to be, as
suggested to me by Mr. Forbes, a case of compensation in relation with
the greatly increased length of the trunk. The Aymaras present some
other singular points of structure, for instance, the very small
projection of the heel.

These men are so thoroughly acclimatised to their cold and lofty abode,
that when formerly carried down by the Spaniards to the low eastern
plains, and when now tempted down by high wages to the gold-washings,
they suffer a frightful rate of mortality. Nevertheless Mr. Forbes
found a few pure families which had survived during two generations:
and he observed that they still inherited their characteristic
peculiarities. But it was manifest, even without measurement, that
these peculiarities had all decreased; and on measurement, their bodies
were found not to be so much elongated as those of the men on the high
plateau; whilst their femora had become somewhat lengthened, as had
their tibiae, although in a less degree. The actual measurements may be
seen by consulting Mr. Forbes’s memoir. From these observations, there
can, I think, be no doubt that residence during many generations at a
great elevation tends, both directly and indirectly, to induce
inherited modifications in the proportions of the body. (35. Dr.
Wilckens (‘Landwirthschaft. Wochenblatt,’ No. 10, 1869) has lately
published an interesting essay shewing how domestic animals, which live
in mountainous regions, have their frames modified.)

Although man may not have been much modified during the latter stages
of his existence through the increased or decreased use of parts, the
facts now given shew that his liability in this respect has not been
lost; and we positively know that the same law holds good with the
lower animals. Consequently we may infer that when at a remote epoch
the progenitors of man were in a transitional state, and were changing
from quadrupeds into bipeds, natural selection would probably have been
greatly aided by the inherited effects of the increased or diminished
use of the different parts of the body.

ARRESTS OF DEVELOPMENT.

There is a difference between arrested development and arrested growth,
for parts in the former state continue to grow whilst still retaining
their early condition. Various monstrosities come under this head; and
some, as a cleft palate, are known to be occasionally inherited. It
will suffice for our purpose to refer to the arrested brain-development
of microcephalous idiots, as described in Vogt’s memoir. (36. ‘Mémoire
sur les Microcephales,’ 1867, pp. 50, 125, 169, 171, 184-198.) Their
skulls are smaller, and the convolutions of the brain are less complex
than in normal men. The frontal sinus, or the projection over the
eye-brows, is largely developed, and the jaws are prognathous to an
“effrayant” degree; so that these idiots somewhat resemble the lower
types of mankind. Their intelligence, and most of their mental
faculties, are extremely feeble. They cannot acquire the power of
speech, and are wholly incapable of prolonged attention, but are much
given to imitation. They are strong and remarkably active, continually
gambolling and jumping about, and making grimaces. They often ascend
stairs on all-fours; and are curiously fond of climbing up furniture or
trees. We are thus reminded of the delight shewn by almost all boys in
climbing trees; and this again reminds us how lambs and kids,
originally alpine animals, delight to frisk on any hillock, however
small. Idiots also resemble the lower animals in some other respects;
thus several cases are recorded of their carefully smelling every
mouthful of food before eating it. One idiot is described as often
using his mouth in aid of his hands, whilst hunting for lice. They are
often filthy in their habits, and have no sense of decency; and several
cases have been published of their bodies being remarkably hairy. (37.
Prof. Laycock sums up the character of brute-like idiots by calling
them “theroid;” ‘Journal of Mental Science,’ July 1863. Dr. Scott (‘The
Deaf and Dumb,’ 2nd ed. 1870, p. 10) has often observed the imbecile
smelling their food. See, on this same subject, and on the hairiness of
idiots, Dr. Maudsley, ‘Body and Mind,’ 1870, pp. 46-51. Pinel has also
given a striking case of hairiness in an idiot.)

REVERSION.

Many of the cases to be here given, might have been introduced under
the last heading. When a structure is arrested in its development, but
still continues growing, until it closely resembles a corresponding
structure in some lower and adult member of the same group, it may in
one sense be considered as a case of reversion. The lower members in a
group give us some idea how the common progenitor was probably
constructed; and it is hardly credible that a complex part, arrested at
an early phase of embryonic development, should go on growing so as
ultimately to perform its proper function, unless it had acquired such
power during some earlier state of existence, when the present
exceptional or arrested structure was normal. The simple brain of a
microcephalous idiot, in as far as it resembles that of an ape, may in
this sense be said to offer a case of reversion. (38. In my ‘Variation
of Animals under Domestication’ (vol. ii. p. 57), I attributed the not
very rare cases of supernumerary mammae in women to reversion. I was
led to this as a probable conclusion, by the additional mammae being
generally placed symmetrically on the breast; and more especially from
one case, in which a single efficient mamma occurred in the inguinal
region of a woman, the daughter of another woman with supernumerary
mammae. But I now find (see, for instance, Prof. Preyer, ‘Der Kampf um
das Dasein,’ 1869, s. 45) that mammae erraticae, occur in other
situations, as on the back, in the armpit, and on the thigh; the mammae
in this latter instance having given so much milk that the child was
thus nourished. The probability that the additional mammae are due to
reversion is thus much weakened; nevertheless, it still seems to me
probable, because two pairs are often found symmetrically on the
breast; and of this I myself have received information in several
cases. It is well known that some Lemurs normally have two pairs of
mammae on the breast. Five cases have been recorded of the presence of
more than a pair of mammae (of course rudimentary) in the male sex of
mankind; see ‘Journal of Anat. and Physiology,’ 1872, p. 56, for a case
given by Dr. Handyside, in which two brothers exhibited this
peculiarity; see also a paper by Dr. Bartels, in ‘Reichert’s and du
Bois-Reymond’s Archiv.,’ 1872, p. 304. In one of the cases alluded to
by Dr. Bartels, a man bore five mammae, one being medial and placed
above the navel; Meckel von Hemsbach thinks that this latter case is
illustrated by a medial mamma occurring in certain Cheiroptera. On the
whole, we may well doubt if additional mammae would ever have been
developed in both sexes of mankind, had not his early progenitors been
provided with more than a single pair.

In the above work (vol. ii. p. 12), I also attributed, though with much
hesitation, the frequent cases of polydactylism in men and various
animals to reversion. I was partly led to this through Prof. Owen’s
statement, that some of the Ichthyopterygia possess more than five
digits, and therefore, as I supposed, had retained a primordial
condition; but Prof. Gegenbaur (‘Jenaischen Zeitschrift,’ B. v. Heft 3,
s. 341), disputes Owen’s conclusion. On the other hand, according to
the opinion lately advanced by Dr. Gunther, on the paddle of Ceratodus,
which is provided with articulated bony rays on both sides of a central
chain of bones, there seems no great difficulty in admitting that six
or more digits on one side, or on both sides, might reappear through
reversion. I am informed by Dr. Zouteveen that there is a case on
record of a man having twenty-four fingers and twenty-four toes! I was
chiefly led to the conclusion that the presence of supernumerary digits
might be due to reversion from the fact that such digits, not only are
strongly inherited, but, as I then believed, had the power of regrowth
after amputation, like the normal digits of the lower vertebrata. But I
have explained in the second edition of my Variation under
Domestication why I now place little reliance on the recorded cases of
such regrowth. Nevertheless it deserves notice, inasmuch as arrested
development and reversion are intimately related processes; that
various structures in an embryonic or arrested condition, such as a
cleft palate, bifid uterus, etc., are frequently accompanied by
polydactylism. This has been strongly insisted on by Meckel and Isidore
Geoffroy St.-Hilaire. But at present it is the safest course to give up
altogether the idea that there is any relation between the development
of supernumerary digits and reversion to some lowly organised
progenitor of man.) There are other cases which come more strictly
under our present head of reversion. Certain structures, regularly
occurring in the lower members of the group to which man belongs,
occasionally make their appearance in him, though not found in the
normal human embryo; or, if normally present in the human embryo, they
become abnormally developed, although in a manner which is normal in
the lower members of the group. These remarks will be rendered clearer
by the following illustrations.

In various mammals the uterus graduates from a double organ with two
distinct orifices and two passages, as in the marsupials, into a single
organ, which is in no way double except from having a slight internal
fold, as in the higher apes and man. The rodents exhibit a perfect
series of gradations between these two extreme states. In all mammals
the uterus is developed from two simple primitive tubes, the inferior
portions of which form the cornua; and it is in the words of Dr. Farre,
“by the coalescence of the two cornua at their lower extremities that
the body of the uterus is formed in man; while in those animals in
which no middle portion or body exists, the cornua remain ununited. As
the development of the uterus proceeds, the two cornua become gradually
shorter, until at length they are lost, or, as it were, absorbed into
the body of the uterus.” The angles of the uterus are still produced
into cornua, even in animals as high up in the scale as the lower apes
and lemurs.

Now in women, anomalous cases are not very infrequent, in which the
mature uterus is furnished with cornua, or is partially divided into
two organs; and such cases, according to Owen, repeat “the grade of
concentrative development,” attained by certain rodents. Here perhaps
we have an instance of a simple arrest of embryonic development, with
subsequent growth and perfect functional development; for either side
of the partially double uterus is capable of performing the proper
office of gestation. In other and rarer cases, two distinct uterine
cavities are formed, each having its proper orifice and passage. (39.
See Dr. A. Farre’s well-known article in the ‘Cyclopaedia of Anatomy
and Physiology,’ vol. v. 1859, p. 642. Owen, ‘Anatomy of Vertebrates,’
vol. iii. 1868, p. 687. Professor Turner, in ‘Edinburgh Medical
Journal,’ February, 1865.) No such stage is passed through during the
ordinary development of the embryo; and it is difficult to believe,
though perhaps not impossible, that the two simple, minute, primitive
tubes should know how (if such an expression may be used) to grow into
two distinct uteri, each with a well-constructed orifice and passage,
and each furnished with numerous muscles, nerves, glands and vessels,
if they had not formerly passed through a similar course of
development, as in the case of existing marsupials. No one will pretend
that so perfect a structure as the abnormal double uterus in woman
could be the result of mere chance. But the principle of reversion, by
which a long-lost structure is called back into existence, might serve
as the guide for its full development, even after the lapse of an
enormous interval of time.

Professor Canestrini, after discussing the foregoing and various
analogous cases, arrives at the same conclusion as that just given. He
adduces another instance, in the case of the malar bone (40. ‘Annuario
della Soc. dei Naturalisti,’ Modena, 1867, p. 83. Prof. Canestrini
gives extracts on this subject from various authorities. Laurillard
remarks, that as he has found a complete similarity in the form,
proportions, and connection of the two malar bones in several human
subjects and in certain apes, he cannot consider this disposition of
the parts as simply accidental. Another paper on this same anomaly has
been published by Dr. Saviotti in the ‘Gazzetta delle Cliniche,’ Turin,
1871, where he says that traces of the division may be detected in
about two per cent. of adult skulls; he also remarks that it more
frequently occurs in prognathous skulls, not of the Aryan race, than in
others. See also G. Delorenzi on the same subject; ‘Tre nuovi casi
d’anomalia dell’ osso malare,’ Torino, 1872. Also, E. Morselli, ‘Sopra
una rara anomalia dell’ osso malare,’ Modena, 1872. Still more recently
Gruber has written a pamphlet on the division of this bone. I give
these references because a reviewer, without any grounds or scruples,
has thrown doubts on my statements.), which, in some of the Quadrumana
and other mammals, normally consists of two portions. This is its
condition in the human foetus when two months old; and through arrested
development, it sometimes remains thus in man when adult, more
especially in the lower prognathous races. Hence Canestrini concludes
that some ancient progenitor of man must have had this bone normally
divided into two portions, which afterwards became fused together. In
man the frontal bone consists of a single piece, but in the embryo, and
in children, and in almost all the lower mammals, it consists of two
pieces separated by a distinct suture. This suture occasionally
persists more or less distinctly in man after maturity; and more
frequently in ancient than in recent crania, especially, as Canestrini
has observed, in those exhumed from the Drift, and belonging to the
brachycephalic type. Here again he comes to the same conclusion as in
the analogous case of the malar bones. In this, and other instances
presently to be given, the cause of ancient races approaching the lower
animals in certain characters more frequently than do the modern races,
appears to be, that the latter stand at a somewhat greater distance in
the long line of descent from their early semi-human progenitors.

Various other anomalies in man, more or less analogous to the
foregoing, have been advanced by different authors, as cases of
reversion; but these seem not a little doubtful, for we have to descend
extremely low in the mammalian series, before we find such structures
normally present. (41. A whole series of cases is given by Isidore
Geoffroy St.-Hilaire, ‘Hist. des Anomalies,’ tom, iii, p. 437. A
reviewer (‘Journal of Anatomy and Physiology,’ 1871, p. 366) blames me
much for not having discussed the numerous cases, which have been
recorded, of various parts arrested in their development. He says that,
according to my theory, “every transient condition of an organ, during
its development, is not only a means to an end, but once was an end in
itself.” This does not seem to me necessarily to hold good. Why should
not variations occur during an early period of development, having no
relation to reversion; yet such variations might be preserved and
accumulated, if in any way serviceable, for instance, in shortening and
simplifying the course of development? And again, why should not
injurious abnormalities, such as atrophied or hypertrophied parts,
which have no relation to a former state of existence, occur at an
early period, as well as during maturity?)

In man, the canine teeth are perfectly efficient instruments for
mastication. But their true canine character, as Owen (42. ‘Anatomy of
Vertebrates,’ vol. iii. 1868, p. 323.) remarks, “is indicated by the
conical form of the crown, which terminates in an obtuse point, is
convex outward and flat or sub-concave within, at the base of which
surface there is a feeble prominence. The conical form is best
expressed in the Melanian races, especially the Australian. The canine
is more deeply implanted, and by a stronger fang than the incisors.”
Nevertheless, this tooth no longer serves man as a special weapon for
tearing his enemies or prey; it may, therefore, as far as its proper
function is concerned, be considered as rudimentary. In every large
collection of human skulls some may be found, as Haeckel (43.
‘Generelle Morphologie,’ 1866, B. ii. s. clv.) observes, with the
canine teeth projecting considerably beyond the others in the same
manner as in the anthropomorphous apes, but in a less degree. In these
cases, open spaces between the teeth in the one jaw are left for the
reception of the canines of the opposite jaw. An inter-space of this
kind in a Kaffir skull, figured by Wagner, is surprisingly wide. (44.
Carl Vogt’s ‘Lectures on Man,’ Eng. translat., 1864, p. 151.)
Considering how few are the ancient skulls which have been examined,
compared to recent skulls, it is an interesting fact that in at least
three cases the canines project largely; and in the Naulette jaw they
are spoken of as enormous. (45. C. Carter Blake, on a jaw from La
Naulette, ‘Anthropological Review,’ 1867, p. 295. Schaaffhausen, ibid.
1868, p. 426.)

Of the anthropomorphous apes the males alone have their canines fully
developed; but in the female gorilla, and in a less degree in the
female orang, these teeth project considerably beyond the others;
therefore the fact, of which I have been assured, that women sometimes
have considerably projecting canines, is no serious objection to the
belief that their occasional great development in man is a case of
reversion to an ape-like progenitor. He who rejects with scorn the
belief that the shape of his own canines, and their occasional great
development in other men, are due to our early forefathers having been
provided with these formidable weapons, will probably reveal, by
sneering, the line of his descent. For though he no longer intends, nor
has the power, to use these teeth as weapons, he will unconsciously
retract his “snarling muscles” (thus named by Sir C. Bell) (46. The
Anatomy of Expression, 1844, pp. 110, 131.), so as to expose them ready
for action, like a dog prepared to fight.

Many muscles are occasionally developed in man, which are proper to the
Quadrumana or other mammals. Professor Vlacovich (47. Quoted by Prof.
Canestrini in the ‘Annuario della Soc. dei Naturalisti,’ 1867, p. 90.)
examined forty male subjects, and found a muscle, called by him the
ischio-pubic, in nineteen of them; in three others there was a ligament
which represented this muscle; and in the remaining eighteen no trace
of it. In only two out of thirty female subjects was this muscle
developed on both sides, but in three others the rudimentary ligament
was present. This muscle, therefore, appears to be much more common in
the male than in the female sex; and on the belief in the descent of
man from some lower form, the fact is intelligible; for it has been
detected in several of the lower animals, and in all of these it serves
exclusively to aid the male in the act of reproduction.

Mr. J. Wood, in his valuable series of papers (48. These papers deserve
careful study by any one who desires to learn how frequently our
muscles vary, and in varying come to resemble those of the Quadrumana.
The following references relate to the few points touched on in my
text: ‘Proc. Royal Soc.’ vol. xiv. 1865, pp. 379-384; vol. xv. 1866,
pp. 241, 242; vol. xv. 1867, p. 544; vol. xvi. 1868, p. 524. I may here
add that Dr. Murie and Mr. St. George Mivart have shewn in their Memoir
on the Lemuroidea (‘Transactions, Zoological Society,’ vol. vii. 1869,
p. 96), how extraordinarily variable some of the muscles are in these
animals, the lowest members of the Primates. Gradations, also, in the
muscles leading to structures found in animals still lower in the
scale, are numerous in the Lemuroidea.), has minutely described a vast
number of muscular variations in man, which resemble normal structures
in the lower animals. The muscles which closely resemble those
regularly present in our nearest allies, the Quadrumana, are too
numerous to be here even specified. In a single male subject, having a
strong bodily frame, and well-formed skull, no less than seven muscular
variations were observed, all of which plainly represented muscles
proper to various kinds of apes. This man, for instance, had on both
sides of his neck a true and powerful “levator claviculae,” such as is
found in all kinds of apes, and which is said to occur in about one out
of sixty human subjects. (49. See also Prof. Macalister in
‘Proceedings, Royal Irish Academy,’ vol. x. 1868, p. 124.) Again, this
man had “a special abductor of the metatarsal bone of the fifth digit,
such as Professor Huxley and Mr. Flower have shewn to exist uniformly
in the higher and lower apes.” I will give only two additional cases;
the acromio-basilar muscle is found in all mammals below man, and seems
to be correlated with a quadrupedal gait, (50. Mr. Champneys in
‘Journal of Anatomy and Physiology,’ Nov. 1871, p. 178.) and it occurs
in about one out of sixty human subjects. In the lower extremities Mr.
Bradley (51. Ibid. May 1872, p. 421.) found an abductor ossis metatarsi
quinti in both feet of man; this muscle had not up to that time been
recorded in mankind, but is always present in the anthropomorphous
apes. The muscles of the hands and arms—parts which are so eminently
characteristic of man—are extremely liable to vary, so as to resemble
the corresponding muscles in the lower animals. (52. Prof. Macalister
(ibid. p. 121) has tabulated his observations, and finds that muscular
abnormalities are most frequent in the fore-arms, secondly, in the
face, thirdly, in the foot, etc.) Such resemblances are either perfect
or imperfect; yet in the latter case they are manifestly of a
transitional nature. Certain variations are more common in man, and
others in woman, without our being able to assign any reason. Mr. Wood,
after describing numerous variations, makes the following pregnant
remark. “Notable departures from the ordinary type of the muscular
structures run in grooves or directions, which must be taken to
indicate some unknown factor, of much importance to a comprehensive
knowledge of general and scientific anatomy.” (53. The Rev. Dr.
Haughton, after giving (‘Proc. R. Irish Academy,’ June 27, 1864, p.
715) a remarkable case of variation in the human flexor pollicis
longus, adds, “This remarkable example shews that man may sometimes
possess the arrangement of tendons of thumb and fingers characteristic
of the macaque; but whether such a case should be regarded as a macaque
passing upwards into a man, or a man passing downwards into a macaque,
or as a congenital freak of nature, I cannot undertake to say.” It is
satisfactory to hear so capable an anatomist, and so embittered an
opponent of evolutionism, admitting even the possibility of either of
his first propositions. Prof. Macalister has also described
(‘Proceedings Royal Irish Academy,’ vol. x. 1864, p. 138) variations in
the flexor pollicis longus, remarkable from their relations to the same
muscle in the Quadrumana.)

That this unknown factor is reversion to a former state of existence
may be admitted as in the highest degree probable. (54. Since the first
edition of this book appeared, Mr. Wood has published another memoir in
the Philosophical Transactions, 1870, p. 83, on the varieties of the
muscles of the human neck, shoulder, and chest. He here shews how
extremely variable these muscles are, and how often and how closely the
variations resemble the normal muscles of the lower animals. He sums up
by remarking, “It will be enough for my purpose if I have succeeded in
shewing the more important forms which, when occurring as varieties in
the human subject, tend to exhibit in a sufficiently marked manner what
may be considered as proofs and examples of the Darwinian principle of
reversion, or law of inheritance, in this department of anatomical
science.”) It is quite incredible that a man should through mere
accident abnormally resemble certain apes in no less than seven of his
muscles, if there had been no genetic connection between them. On the
other hand, if man is descended from some ape-like creature, no valid
reason can be assigned why certain muscles should not suddenly reappear
after an interval of many thousand generations, in the same manner as
with horses, asses, and mules, dark-coloured stripes suddenly reappear
on the legs, and shoulders, after an interval of hundreds, or more
probably of thousands of generations.

These various cases of reversion are so closely related to those of
rudimentary organs given in the first chapter, that many of them might
have been indifferently introduced either there or here. Thus a human
uterus furnished with cornua may be said to represent, in a rudimentary
condition, the same organ in its normal state in certain mammals. Some
parts which are rudimentary in man, as the os coccyx in both sexes, and
the mammae in the male sex, are always present; whilst others, such as
the supracondyloid foramen, only occasionally appear, and therefore
might have been introduced under the head of reversion. These several
reversionary structures, as well as the strictly rudimentary ones,
reveal the descent of man from some lower form in an unmistakable
manner.

CORRELATED VARIATION.

In man, as in the lower animals, many structures are so intimately
related, that when one part varies so does another, without our being
able, in most cases, to assign any reason. We cannot say whether the
one part governs the other, or whether both are governed by some
earlier developed part. Various monstrosities, as I. Geoffroy
repeatedly insists, are thus intimately connected. Homologous
structures are particularly liable to change together, as we see on the
opposite sides of the body, and in the upper and lower extremities.
Meckel long ago remarked, that when the muscles of the arm depart from
their proper type, they almost always imitate those of the leg; and so,
conversely, with the muscles of the legs. The organs of sight and
hearing, the teeth and hair, the colour of the skin and of the hair,
colour and constitution, are more or less correlated. (55. The
authorities for these several statements are given in my ‘Variation of
Animals under Domestication,’ vol. ii. pp. 320-335.) Professor
Schaaffhausen first drew attention to the relation apparently existing
between a muscular frame and the strongly-pronounced supra-orbital
ridges, which are so characteristic of the lower races of man.

Besides the variations which can be grouped with more or less
probability under the foregoing heads, there is a large class of
variations which may be provisionally called spontaneous, for to our
ignorance they appear to arise without any exciting cause. It can,
however, be shewn that such variations, whether consisting of slight
individual differences, or of strongly-marked and abrupt deviations of
structure, depend much more on the constitution of the organism than on
the nature of the conditions to which it has been subjected. (56. This
whole subject has been discussed in chap. xxiii. vol. ii. of my
‘Variation of Animals and Plants under Domestication.’)

RATE OF INCREASE.

Civilised populations have been known under favourable conditions, as
in the United States, to double their numbers in twenty-five years;
and, according to a calculation, by Euler, this might occur in a little
over twelve years. (57. See the ever memorable ‘Essay on the Principle
of Population,’ by the Rev. T. Malthus, vol. i. 1826. pp. 6, 517.) At
the former rate, the present population of the United States (thirty
millions), would in 657 years cover the whole terraqueous globe so
thickly, that four men would have to stand on each square yard of
surface. The primary or fundamental check to the continued increase of
man is the difficulty of gaining subsistence, and of living in comfort.
We may infer that this is the case from what we see, for instance, in
the United States, where subsistence is easy, and there is plenty of
room. If such means were suddenly doubled in Great Britain, our number
would be quickly doubled. With civilised nations this primary check
acts chiefly by restraining marriages. The greater death-rate of
infants in the poorest classes is also very important; as well as the
greater mortality, from various diseases, of the inhabitants of crowded
and miserable houses, at all ages. The effects of severe epidemics and
wars are soon counterbalanced, and more than counterbalanced, in
nations placed under favourable conditions. Emigration also comes in
aid as a temporary check, but, with the extremely poor classes, not to
any great extent.

There is reason to suspect, as Malthus has remarked, that the
reproductive power is actually less in barbarous, than in civilised
races. We know nothing positively on this head, for with savages no
census has been taken; but from the concurrent testimony of
missionaries, and of others who have long resided with such people, it
appears that their families are usually small, and large ones rare.
This may be partly accounted for, as it is believed, by the women
suckling their infants during a long time; but it is highly probable
that savages, who often suffer much hardship, and who do not obtain so
much nutritious food as civilised men, would be actually less prolific.
I have shewn in a former work (58. ‘Variation of Animals and Plants
under Domestication,’ vol ii. pp. 111-113, 163.), that all our
domesticated quadrupeds and birds, and all our cultivated plants, are
more fertile than the corresponding species in a state of nature. It is
no valid objection to this conclusion that animals suddenly supplied
with an excess of food, or when grown very fat; and that most plants on
sudden removal from very poor to very rich soil, are rendered more or
less sterile. We might, therefore, expect that civilised men, who in
one sense are highly domesticated, would be more prolific than wild
men. It is also probable that the increased fertility of civilised
nations would become, as with our domestic animals, an inherited
character: it is at least known that with mankind a tendency to produce
twins runs in families. (59. Mr. Sedgwick, ‘British and Foreign
Medico-Chirurgical Review,’ July 1863, p. 170.)

Notwithstanding that savages appear to be less prolific than civilised
people, they would no doubt rapidly increase if their numbers were not
by some means rigidly kept down. The Santali, or hill-tribes of India,
have recently afforded a good illustration of this fact; for, as shewn
by Mr. Hunter (60. ‘The Annals of Rural Bengal,’ by W.W. Hunter, 1868,
p. 259.), they have increased at an extraordinary rate since
vaccination has been introduced, other pestilences mitigated, and war
sternly repressed. This increase, however, would not have been possible
had not these rude people spread into the adjoining districts, and
worked for hire. Savages almost always marry; yet there is some
prudential restraint, for they do not commonly marry at the earliest
possible age. The young men are often required to shew that they can
support a wife; and they generally have first to earn the price with
which to purchase her from her parents. With savages the difficulty of
obtaining subsistence occasionally limits their number in a much more
direct manner than with civilised people, for all tribes periodically
suffer from severe famines. At such times savages are forced to devour
much bad food, and their health can hardly fail to be injured. Many
accounts have been published of their protruding stomachs and emaciated
limbs after and during famines. They are then, also, compelled to
wander much, and, as I was assured in Australia, their infants perish
in large numbers. As famines are periodical, depending chiefly on
extreme seasons, all tribes must fluctuate in number. They cannot
steadily and regularly increase, as there is no artificial increase in
the supply of food. Savages, when hard pressed, encroach on each
other’s territories, and war is the result; but they are indeed almost
always at war with their neighbours. They are liable to many accidents
on land and water in their search for food; and in some countries they
suffer much from the larger beasts of prey. Even in India, districts
have been depopulated by the ravages of tigers.

Malthus has discussed these several checks, but he does not lay stress
enough on what is probably the most important of all, namely
infanticide, especially of female infants, and the habit of procuring
abortion. These practices now prevail in many quarters of the world;
and infanticide seems formerly to have prevailed, as Mr. M’Lennan (61.
‘Primitive Marriage,’ 1865.) has shewn, on a still more extensive
scale. These practices appear to have originated in savages recognising
the difficulty, or rather the impossibility of supporting all the
infants that are born. Licentiousness may also be added to the
foregoing checks; but this does not follow from failing means of
subsistence; though there is reason to believe that in some cases (as
in Japan) it has been intentionally encouraged as a means of keeping
down the population.

If we look back to an extremely remote epoch, before man had arrived at
the dignity of manhood, he would have been guided more by instinct and
less by reason than are the lowest savages at the present time. Our
early semi-human progenitors would not have practised infanticide or
polyandry; for the instincts of the lower animals are never so
perverted (62. A writer in the ‘Spectator’ (March 12, 1871, p. 320)
comments as follows on this passage:—“Mr. Darwin finds himself
compelled to reintroduce a new doctrine of the fall of man. He shews
that the instincts of the higher animals are far nobler than the habits
of savage races of men, and he finds himself, therefore, compelled to
re-introduce,—in a form of the substantial orthodoxy of which he
appears to be quite unconscious,—and to introduce as a scientific
hypothesis the doctrine that man’s gain of KNOWLEDGE was the cause of a
temporary but long-enduring moral deterioration as indicated by the
many foul customs, especially as to marriage, of savage tribes. What
does the Jewish tradition of the moral degeneration of man through his
snatching at a knowledge forbidden him by his highest instinct assert
beyond this?”) as to lead them regularly to destroy their own
offspring, or to be quite devoid of jealousy. There would have been no
prudential restraint from marriage, and the sexes would have freely
united at an early age. Hence the progenitors of man would have tended
to increase rapidly; but checks of some kind, either periodical or
constant, must have kept down their numbers, even more severely than
with existing savages. What the precise nature of these checks were, we
cannot say, any more than with most other animals. We know that horses
and cattle, which are not extremely prolific animals, when first turned
loose in South America, increased at an enormous rate. The elephant,
the slowest breeder of all known animals, would in a few thousand years
stock the whole world. The increase of every species of monkey must be
checked by some means; but not, as Brehm remarks, by the attacks of
beasts of prey. No one will assume that the actual power of
reproduction in the wild horses and cattle of America, was at first in
any sensible degree increased; or that, as each district became fully
stocked, this same power was diminished. No doubt, in this case, and in
all others, many checks concur, and different checks under different
circumstances; periodical dearths, depending on unfavourable seasons,
being probably the most important of all. So it will have been with the
early progenitors of man.

NATURAL SELECTION.

We have now seen that man is variable in body and mind; and that the
variations are induced, either directly or indirectly, by the same
general causes, and obey the same general laws, as with the lower
animals. Man has spread widely over the face of the earth, and must
have been exposed, during his incessant migrations (63. See some good
remarks to this effect by W. Stanley Jevons, “A Deduction from Darwin’s
Theory,” ‘Nature,’ 1869, p. 231.), to the most diversified conditions.
The inhabitants of Tierra del Fuego, the Cape of Good Hope, and
Tasmania in the one hemisphere, and of the arctic regions in the other,
must have passed through many climates, and changed their habits many
times, before they reached their present homes. (64. Latham, ‘Man and
his Migrations,’ 1851, p. 135.) The early progenitors of man must also
have tended, like all other animals, to have increased beyond their
means of subsistence; they must, therefore, occasionally have been
exposed to a struggle for existence, and consequently to the rigid law
of natural selection. Beneficial variations of all kinds will thus,
either occasionally or habitually, have been preserved and injurious
ones eliminated. I do not refer to strongly-marked deviations of
structure, which occur only at long intervals of time, but to mere
individual differences. We know, for instance, that the muscles of our
hands and feet, which determine our powers of movement, are liable,
like those of the lower animals, (65. Messrs. Murie and Mivart in their
‘Anatomy of the Lemuroidea’ (‘Transact. Zoolog. Soc.’ vol. vii. 1869,
pp. 96-98) say, “some muscles are so irregular in their distribution
that they cannot be well classed in any of the above groups.” These
muscles differ even on the opposite sides of the same individual.) to
incessant variability. If then the progenitors of man inhabiting any
district, especially one undergoing some change in its conditions, were
divided into two equal bodies, the one half which included all the
individuals best adapted by their powers of movement for gaining
subsistence, or for defending themselves, would on an average survive
in greater numbers, and procreate more offspring than the other and
less well endowed half.

Man in the rudest state in which he now exists is the most dominant
animal that has ever appeared on this earth. He has spread more widely
than any other highly organised form: and all others have yielded
before him. He manifestly owes this immense superiority to his
intellectual faculties, to his social habits, which lead him to aid and
defend his fellows, and to his corporeal structure. The supreme
importance of these characters has been proved by the final arbitrament
of the battle for life. Through his powers of intellect, articulate
language has been evolved; and on this his wonderful advancement has
mainly depended. As Mr. Chauncey Wright remarks (66. Limits of Natural
Selection, ‘North American Review,’ Oct. 1870, p. 295.): “a
psychological analysis of the faculty of language shews, that even the
smallest proficiency in it might require more brain power than the
greatest proficiency in any other direction.” He has invented and is
able to use various weapons, tools, traps, etc., with which he defends
himself, kills or catches prey, and otherwise obtains food. He has made
rafts or canoes for fishing or crossing over to neighbouring fertile
islands. He has discovered the art of making fire, by which hard and
stringy roots can be rendered digestible, and poisonous roots or herbs
innocuous. This discovery of fire, probably the greatest ever made by
man, excepting language, dates from before the dawn of history. These
several inventions, by which man in the rudest state has become so
pre-eminent, are the direct results of the development of his powers of
observation, memory, curiosity, imagination, and reason. I cannot,
therefore, understand how it is that Mr. Wallace (67. ‘Quarterly
Review,’ April 1869, p. 392. This subject is more fully discussed in
Mr. Wallace’s ‘Contributions to the Theory of Natural Selection,’ 1870,
in which all the essays referred to in this work are re-published. The
‘Essay on Man,’ has been ably criticised by Prof. Claparede, one of the
most distinguished zoologists in Europe, in an article published in the
‘Bibliotheque Universelle,’ June 1870. The remark quoted in my text
will surprise every one who has read Mr. Wallace’s celebrated paper on
‘The Origin of Human Races Deduced from the Theory of Natural
Selection,’ originally published in the ‘Anthropological Review,’ May
1864, p. clviii. I cannot here resist quoting a most just remark by Sir
J. Lubbock (‘Prehistoric Times,’ 1865, p. 479) in reference to this
paper, namely, that Mr. Wallace, “with characteristic unselfishness,
ascribes it (i.e. the idea of natural selection) unreservedly to Mr.
Darwin, although, as is well known, he struck out the idea
independently, and published it, though not with the same elaboration,
at the same time.”) maintains, that “natural selection could only have
endowed the savage with a brain a little superior to that of an ape.”

Although the intellectual powers and social habits of man are of
paramount importance to him, we must not underrate the importance of
his bodily structure, to which subject the remainder of this chapter
will be devoted; the development of the intellectual and social or
moral faculties being discussed in a later chapter.

Even to hammer with precision is no easy matter, as every one who has
tried to learn carpentry will admit. To throw a stone with as true an
aim as a Fuegian in defending himself, or in killing birds, requires
the most consummate perfection in the correlated action of the muscles
of the hand, arm, and shoulder, and, further, a fine sense of touch. In
throwing a stone or spear, and in many other actions, a man must stand
firmly on his feet; and this again demands the perfect co-adaptation of
numerous muscles. To chip a flint into the rudest tool, or to form a
barbed spear or hook from a bone, demands the use of a perfect hand;
for, as a most capable judge, Mr. Schoolcraft (68. Quoted by Mr. Lawson
Tait in his ‘Law of Natural Selection,’ ‘Dublin Quarterly Journal of
Medical Science,’ Feb. 1869. Dr. Keller is likewise quoted to the same
effect.), remarks, the shaping fragments of stone into knives, lances,
or arrow-heads, shews “extraordinary ability and long practice.” This
is to a great extent proved by the fact that primeval men practised a
division of labour; each man did not manufacture his own flint tools or
rude pottery, but certain individuals appear to have devoted themselves
to such work, no doubt receiving in exchange the produce of the chase.
Archaeologists are convinced that an enormous interval of time elapsed
before our ancestors thought of grinding chipped flints into smooth
tools. One can hardly doubt, that a man-like animal who possessed a
hand and arm sufficiently perfect to throw a stone with precision, or
to form a flint into a rude tool, could, with sufficient practice, as
far as mechanical skill alone is concerned, make almost anything which
a civilised man can make. The structure of the hand in this respect may
be compared with that of the vocal organs, which in the apes are used
for uttering various signal-cries, or, as in one genus, musical
cadences; but in man the closely similar vocal organs have become
adapted through the inherited effects of use for the utterance of
articulate language.

Turning now to the nearest allies of men, and therefore to the best
representatives of our early progenitors, we find that the hands of the
Quadrumana are constructed on the same general pattern as our own, but
are far less perfectly adapted for diversified uses. Their hands do not
serve for locomotion so well as the feet of a dog; as may be seen in
such monkeys as the chimpanzee and orang, which walk on the outer
margins of the palms, or on the knuckles. (69. Owen, ‘Anatomy of
Vertebrates,’ vol. iii. p. 71.) Their hands, however, are admirably
adapted for climbing trees. Monkeys seize thin branches or ropes, with
the thumb on one side and the fingers and palm on the other, in the
same manner as we do. They can thus also lift rather large objects,
such as the neck of a bottle, to their mouths. Baboons turn over
stones, and scratch up roots with their hands. They seize nuts,
insects, or other small objects with the thumb in opposition to the
fingers, and no doubt they thus extract eggs and young from the nests
of birds. American monkeys beat the wild oranges on the branches until
the rind is cracked, and then tear it off with the fingers of the two
hands. In a wild state they break open hard fruits with stones. Other
monkeys open mussel-shells with the two thumbs. With their fingers they
pull out thorns and burs, and hunt for each other’s parasites. They
roll down stones, or throw them at their enemies: nevertheless, they
are clumsy in these various actions, and, as I have myself seen, are
quite unable to throw a stone with precision.

It seems to me far from true that because “objects are grasped
clumsily” by monkeys, “a much less specialised organ of prehension”
would have served them (70. ‘Quarterly Review,’ April 1869, p. 392.)
equally well with their present hands. On the contrary, I see no reason
to doubt that more perfectly constructed hands would have been an
advantage to them, provided that they were not thus rendered less
fitted for climbing trees. We may suspect that a hand as perfect as
that of man would have been disadvantageous for climbing; for the most
arboreal monkeys in the world, namely, Ateles in America, Colobus in
Africa, and Hylobates in Asia, are either thumbless, or their toes
partially cohere, so that their limbs are converted into mere grasping
hooks. (71. In Hylobates syndactylus, as the name expresses, two of the
toes regularly cohere; and this, as Mr. Blyth informs me, is
occasionally the case with the toes of H. agilis, lar, and leuciscus.
Colobus is strictly arboreal and extraordinarily active (Brehm,
‘Thierleben,’ B. i. s. 50), but whether a better climber than the
species of the allied genera, I do not know. It deserves notice that
the feet of the sloths, the most arboreal animals in the world, are
wonderfully hook-like.

As soon as some ancient member in the great series of the Primates came
to be less arboreal, owing to a change in its manner of procuring
subsistence, or to some change in the surrounding conditions, its
habitual manner of progression would have been modified: and thus it
would have been rendered more strictly quadrupedal or bipedal. Baboons
frequent hilly and rocky districts, and only from necessity climb high
trees (72. Brehm, ‘Thierleben,’ B. i. s. 80.); and they have acquired
almost the gait of a dog. Man alone has become a biped; and we can, I
think, partly see how he has come to assume his erect attitude, which
forms one of his most conspicuous characters. Man could not have
attained his present dominant position in the world without the use of
his hands, which are so admirably adapted to act in obedience to his
will. Sir C. Bell (73. ‘The Hand,’ etc., ‘Bridgewater Treatise,’ 1833,
p. 38.) insists that “the hand supplies all instruments, and by its
correspondence with the intellect gives him universal dominion.” But
the hands and arms could hardly have become perfect enough to have
manufactured weapons, or to have hurled stones and spears with a true
aim, as long as they were habitually used for locomotion and for
supporting the whole weight of the body, or, as before remarked, so
long as they were especially fitted for climbing trees. Such rough
treatment would also have blunted the sense of touch, on which their
delicate use largely depends. From these causes alone it would have
been an advantage to man to become a biped; but for many actions it is
indispensable that the arms and whole upper part of the body should be
free; and he must for this end stand firmly on his feet. To gain this
great advantage, the feet have been rendered flat; and the great toe
has been peculiarly modified, though this has entailed the almost
complete loss of its power of prehension. It accords with the principle
of the division of physiological labour, prevailing throughout the
animal kingdom, that as the hands became perfected for prehension, the
feet should have become perfected for support and locomotion. With some
savages, however, the foot has not altogether lost its prehensile
power, as shewn by their manner of climbing trees, and of using them in
other ways. (74. Haeckel has an excellent discussion on the steps by
which man became a biped: ‘Natürliche Schöpfungsgeschichte,’ 1868, s.
507. Dr. Buchner (‘Conférences sur la Théorie Darwinienne,’ 1869, p.
135) has given good cases of the use of the foot as a prehensile organ
by man; and has also written on the manner of progression of the higher
apes, to which I allude in the following paragraph: see also Owen
(‘Anatomy of Vertebrates,’ vol. iii. p. 71) on this latter subject.)

If it be an advantage to man to stand firmly on his feet and to have
his hands and arms free, of which, from his pre-eminent success in the
battle of life there can be no doubt, then I can see no reason why it
should not have been advantageous to the progenitors of man to have
become more and more erect or bipedal. They would thus have been better
able to defend themselves with stones or clubs, to attack their prey,
or otherwise to obtain food. The best built individuals would in the
long run have succeeded best, and have survived in larger numbers. If
the gorilla and a few allied forms had become extinct, it might have
been argued, with great force and apparent truth, that an animal could
not have been gradually converted from a quadruped into a biped, as all
the individuals in an intermediate condition would have been miserably
ill-fitted for progression. But we know (and this is well worthy of
reflection) that the anthropomorphous apes are now actually in an
intermediate condition; and no one doubts that they are on the whole
well adapted for their conditions of life. Thus the gorilla runs with a
sidelong shambling gait, but more commonly progresses by resting on its
bent hands. The long-armed apes occasionally use their arms like
crutches, swinging their bodies forward between them, and some kinds of
Hylobates, without having been taught, can walk or run upright with
tolerable quickness; yet they move awkwardly, and much less securely
than man. We see, in short, in existing monkeys a manner of progression
intermediate between that of a quadruped and a biped; but, as an
unprejudiced judge (75. Prof. Broca, La Constitution des Vertèbres
caudales; ‘La Revue d’Anthropologie,’ 1872, p. 26, (separate copy).)
insists, the anthropomorphous apes approach in structure more nearly to
the bipedal than to the quadrupedal type.

As the progenitors of man became more and more erect, with their hands
and arms more and more modified for prehension and other purposes, with
their feet and legs at the same time transformed for firm support and
progression, endless other changes of structure would have become
necessary. The pelvis would have to be broadened, the spine peculiarly
curved, and the head fixed in an altered position, all which changes
have been attained by man. Prof. Schaaffhausen (76. ‘On the Primitive
Form of the Skull,’ translated in ‘Anthropological Review,’ Oct. 1868,
p. 428. Owen (‘Anatomy of Vertebrates,’ vol. ii. 1866, p. 551) on the
mastoid processes in the higher apes.) maintains that “the powerful
mastoid processes of the human skull are the result of his erect
position;” and these processes are absent in the orang, chimpanzee,
etc., and are smaller in the gorilla than in man. Various other
structures, which appear connected with man’s erect position, might
here have been added. It is very difficult to decide how far these
correlated modifications are the result of natural selection, and how
far of the inherited effects of the increased use of certain parts, or
of the action of one part on another. No doubt these means of change
often co-operate: thus when certain muscles, and the crests of bone to
which they are attached, become enlarged by habitual use, this shews
that certain actions are habitually performed and must be serviceable.
Hence the individuals which performed them best, would tend to survive
in greater numbers.

The free use of the arms and hands, partly the cause and partly the
result of man’s erect position, appears to have led in an indirect
manner to other modifications of structure. The early male forefathers
of man were, as previously stated, probably furnished with great canine
teeth; but as they gradually acquired the habit of using stones, clubs,
or other weapons, for fighting with their enemies or rivals, they would
use their jaws and teeth less and less. In this case, the jaws,
together with the teeth, would become reduced in size, as we may feel
almost sure from innumerable analogous cases. In a future chapter we
shall meet with a closely parallel case, in the reduction or complete
disappearance of the canine teeth in male ruminants, apparently in
relation with the development of their horns; and in horses, in
relation to their habit of fighting with their incisor teeth and hoofs.

In the adult male anthropomorphous apes, as Rutimeyer (77. ‘Die Grenzen
der Thierwelt, eine Betrachtung zu Darwin’s Lehre,’ 1868, s. 51.), and
others, have insisted, it is the effect on the skull of the great
development of the jaw-muscles that causes it to differ so greatly in
many respects from that of man, and has given to these animals “a truly
frightful physiognomy.” Therefore, as the jaws and teeth in man’s
progenitors gradually become reduced in size, the adult skull would
have come to resemble more and more that of existing man. As we shall
hereafter see, a great reduction of the canine teeth in the males would
almost certainly affect the teeth of the females through inheritance.

As the various mental faculties gradually developed themselves the
brain would almost certainly become larger. No one, I presume, doubts
that the large proportion which the size of man’s brain bears to his
body, compared to the same proportion in the gorilla or orang, is
closely connected with his higher mental powers. We meet with closely
analogous facts with insects, for in ants the cerebral ganglia are of
extraordinary dimensions, and in all the Hymenoptera these ganglia are
many times larger than in the less intelligent orders, such as beetles.
(78. Dujardin, ‘Annales des Sciences Nat.’ 3rd series, Zoolog., tom.
xiv. 1850, p. 203. See also Mr. Lowne, ‘Anatomy and Phys. of the Musca
vomitoria,’ 1870, p. 14. My son, Mr. F. Darwin, dissected for me the
cerebral ganglia of the Formica rufa.) On the other hand, no one
supposes that the intellect of any two animals or of any two men can be
accurately gauged by the cubic contents of their skulls. It is certain
that there may be extraordinary mental activity with an extremely small
absolute mass of nervous matter: thus the wonderfully diversified
instincts, mental powers, and affections of ants are notorious, yet
their cerebral ganglia are not so large as the quarter of a small pin’s
head. Under this point of view, the brain of an ant is one of the most
marvellous atoms of matter in the world, perhaps more so than the brain
of a man.

The belief that there exists in man some close relation between the
size of the brain and the development of the intellectual faculties is
supported by the comparison of the skulls of savage and civilised
races, of ancient and modern people, and by the analogy of the whole
vertebrate series. Dr. J. Barnard Davis has proved (79. ‘Philosophical
Transactions,’ 1869, p. 513.), by many careful measurements, that the
mean internal capacity of the skull in Europeans is 92.3 cubic inches;
in Americans 87.5; in Asiatics 87.1; and in Australians only 81.9 cubic
inches. Professor Broca (80. ‘Les Selections,’ M. P. Broca, ‘Revue
d’Anthropologies,’ 1873; see also, as quoted in C. Vogt’s ‘Lectures on
Man,’ Engl. translat., 1864, pp. 88, 90. Prichard, ‘Physical History of
Mankind,’ vol. i. 1838, p. 305.) found that the nineteenth century
skulls from graves in Paris were larger than those from vaults of the
twelfth century, in the proportion of 1484 to 1426; and that the
increased size, as ascertained by measurements, was exclusively in the
frontal part of the skull—the seat of the intellectual faculties.
Prichard is persuaded that the present inhabitants of Britain have
“much more capacious brain-cases” than the ancient inhabitants.
Nevertheless, it must be admitted that some skulls of very high
antiquity, such as the famous one of Neanderthal, are well developed
and capacious. (81. In the interesting article just referred to, Prof.
Broca has well remarked, that in civilised nations, the average
capacity of the skull must be lowered by the preservation of a
considerable number of individuals, weak in mind and body, who would
have been promptly eliminated in the savage state. On the other hand,
with savages, the average includes only the more capable individuals,
who have been able to survive under extremely hard conditions of life.
Broca thus explains the otherwise inexplicable fact, that the mean
capacity of the skull of the ancient Troglodytes of Lozere is greater
than that of modern Frenchmen.) With respect to the lower animals, M.E.
Lartet (82. ‘Comptes-rendus des Sciences,’ etc., June 1, 1868.), by
comparing the crania of tertiary and recent mammals belonging to the
same groups, has come to the remarkable conclusion that the brain is
generally larger and the convolutions are more complex in the more
recent forms. On the other hand, I have shewn (83. The ‘Variation of
Animals and Plants under Domestication,’ vol. i. pp. 124-129.) that the
brains of domestic rabbits are considerably reduced in bulk, in
comparison with those of the wild rabbit or hare; and this may be
attributed to their having been closely confined during many
generations, so that they have exerted their intellect, instincts,
senses and voluntary movements but little.

The gradually increasing weight of the brain and skull in man must have
influenced the development of the supporting spinal column, more
especially whilst he was becoming erect. As this change of position was
being brought about, the internal pressure of the brain will also have
influenced the form of the skull; for many facts shew how easily the
skull is thus affected. Ethnologists believe that it is modified by the
kind of cradle in which infants sleep. Habitual spasms of the muscles,
and a cicatrix from a severe burn, have permanently modified the facial
bones. In young persons whose heads have become fixed either sideways
or backwards, owing to disease, one of the two eyes has changed its
position, and the shape of the skull has been altered apparently by the
pressure of the brain in a new direction. (84. Schaaffhausen gives from
Blumenbach and Busch, the cases of the spasms and cicatrix, in
‘Anthropological Review,’ Oct. 1868, p. 420. Dr. Jarrold
(‘Anthropologia,’ 1808, pp. 115, 116) adduces from Camper and from his
own observations, cases of the modification of the skull from the head
being fixed in an unnatural position. He believes that in certain
trades, such as that of a shoemaker, where the head is habitually held
forward, the forehead becomes more rounded and prominent.) I have shewn
that with long-eared rabbits even so trifling a cause as the lopping
forward of one ear drags forward almost every bone of the skull on that
side; so that the bones on the opposite side no longer strictly
correspond. Lastly, if any animal were to increase or diminish much in
general size, without any change in its mental powers, or if the mental
powers were to be much increased or diminished, without any great
change in the size of the body, the shape of the skull would almost
certainly be altered. I infer this from my observations on domestic
rabbits, some kinds of which have become very much larger than the wild
animal, whilst others have retained nearly the same size, but in both
cases the brain has been much reduced relatively to the size of the
body. Now I was at first much surprised on finding that in all these
rabbits the skull had become elongated or dolichocephalic; for
instance, of two skulls of nearly equal breadth, the one from a wild
rabbit and the other from a large domestic kind, the former was 3.15
and the latter 4.3 inches in length. (85. ‘Variation of Animals and
Plants under Domestication,’ vol. i. p. 117, on the elongation of the
skull; p. 119, on the effect of the lopping of one ear.) One of the
most marked distinctions in different races of men is that the skull in
some is elongated, and in others rounded; and here the explanation
suggested by the case of the rabbits may hold good; for Welcker finds
that short “men incline more to brachycephaly, and tall men to
dolichocephaly” (86. Quoted by Schaaffhausen, in ‘Anthropological
Review,’ Oct. 1868, p. 419.); and tall men may be compared with the
larger and longer-bodied rabbits, all of which have elongated skulls or
are dolichocephalic.

From these several facts we can understand, to a certain extent, the
means by which the great size and more or less rounded form of the
skull have been acquired by man; and these are characters eminently
distinctive of him in comparison with the lower animals.

Another most conspicuous difference between man and the lower animals
is the nakedness of his skin. Whales and porpoises (Cetacea), dugongs
(Sirenia) and the hippopotamus are naked; and this may be advantageous
to them for gliding through the water; nor would it be injurious to
them from the loss of warmth, as the species, which inhabit the colder
regions, are protected by a thick layer of blubber, serving the same
purpose as the fur of seals and otters. Elephants and rhinoceroses are
almost hairless; and as certain extinct species, which formerly lived
under an Arctic climate, were covered with long wool or hair, it would
almost appear as if the existing species of both genera had lost their
hairy covering from exposure to heat. This appears the more probable,
as the elephants in India which live on elevated and cool districts are
more hairy (87. Owen, ‘Anatomy of Vertebrates,’ vol. iii. p. 619.) than
those on the lowlands. May we then infer that man became divested of
hair from having aboriginally inhabited some tropical land? That the
hair is chiefly retained in the male sex on the chest and face, and in
both sexes at the junction of all four limbs with the trunk, favours
this inference—on the assumption that the hair was lost before man
became erect; for the parts which now retain most hair would then have
been most protected from the heat of the sun. The crown of the head,
however, offers a curious exception, for at all times it must have been
one of the most exposed parts, yet it is thickly clothed with hair. The
fact, however, that the other members of the order of Primates, to
which man belongs, although inhabiting various hot regions, are well
clothed with hair, generally thickest on the upper surface (88. Isidore
Geoffroy St.-Hilaire remarks (‘Histoire Nat. Generale,’ tom. ii. 1859,
pp. 215-217) on the head of man being covered with long hair; also on
the upper surfaces of monkeys and of other mammals being more thickly
clothed than the lower surfaces. This has likewise been observed by
various authors. Prof. P. Gervais (‘Histoire Nat. des Mammifères,’ tom.
i. 1854, p. 28), however, states that in the Gorilla the hair is
thinner on the back, where it is partly rubbed off, than on the lower
surface.), is opposed to the supposition that man became naked through
the action of the sun. Mr. Belt believes (89. The ‘Naturalist in
Nicaragua,’ 1874, p. 209. As some confirmation of Mr. Belt’s view, I
may quote the following passage from Sir W. Denison (‘Varieties of
Vice-Regal Life,’ vol. i. 1870, p. 440): “It is said to be a practice
with the Australians, when the vermin get troublesome, to singe
themselves.”) that within the tropics it is an advantage to man to be
destitute of hair, as he is thus enabled to free himself of the
multitude of ticks (acari) and other parasites, with which he is often
infested, and which sometimes cause ulceration. But whether this evil
is of sufficient magnitude to have led to the denudation of his body
through natural selection, may be doubted, since none of the many
quadrupeds inhabiting the tropics have, as far as I know, acquired any
specialised means of relief. The view which seems to me the most
probable is that man, or rather primarily woman, became divested of
hair for ornamental purposes, as we shall see under Sexual Selection;
and, according to this belief, it is not surprising that man should
differ so greatly in hairiness from all other Primates, for characters,
gained through sexual selection, often differ to an extraordinary
degree in closely related forms.

According to a popular impression, the absence of a tail is eminently
distinctive of man; but as those apes which come nearest to him are
destitute of this organ, its disappearance does not relate exclusively
to man. The tail often differs remarkably in length within the same
genus: thus in some species of Macacus it is longer than the whole
body, and is formed of twenty-four vertebrae; in others it consists of
a scarcely visible stump, containing only three or four vertebrae. In
some kinds of baboons there are twenty-five, whilst in the mandrill
there are ten very small stunted caudal vertebrae, or, according to
Cuvier (90. Mr. St. George Mivart, ‘Proc. Zoolog. Soc.’ 1865, pp. 562,
583. Dr. J.E. Gray, ‘Cat. Brit. Mus.: ‘Skeletons.’ Owen, ‘Anatomy of
Vertebrates,’ vol. ii. p. 517. Isidore Geoffroy, ‘Hist. Nat. Gen.’ tom.
ii. p. 244.), sometimes only five. The tail, whether it be long or
short, almost always tapers towards the end; and this, I presume,
results from the atrophy of the terminal muscles, together with their
arteries and nerves, through disuse, leading to the atrophy of the
terminal bones. But no explanation can at present be given of the great
diversity which often occurs in its length. Here, however, we are more
specially concerned with the complete external disappearance of the
tail. Professor Broca has recently shewn (91. ‘Revue d’Anthropologie,’
1872; ‘La Constitution des vertèbres caudales.’) that the tail in all
quadrupeds consists of two portions, generally separated abruptly from
each other; the basal portion consists of vertebrae, more or less
perfectly channelled and furnished with apophyses like ordinary
vertebrae; whereas those of the terminal portion are not channelled,
are almost smooth, and scarcely resemble true vertebrae. A tail, though
not externally visible, is really present in man and the
anthropomorphous apes, and is constructed on exactly the same pattern
in both. In the terminal portion the vertebrae, constituting the os
coccyx, are quite rudimentary, being much reduced in size and number.
In the basal portion, the vertebrae are likewise few, are united firmly
together, and are arrested in development; but they have been rendered
much broader and flatter than the corresponding vertebrae in the tails
of other animals: they constitute what Broca calls the accessory sacral
vertebrae. These are of functional importance by supporting certain
internal parts and in other ways; and their modification is directly
connected with the erect or semi-erect attitude of man and the
anthropomorphous apes. This conclusion is the more trustworthy, as
Broca formerly held a different view, which he has now abandoned. The
modification, therefore, of the basal caudal vertebrae in man and the
higher apes may have been effected, directly or indirectly, through
natural selection.

But what are we to say about the rudimentary and variable vertebrae of
the terminal portion of the tail, forming the os coccyx? A notion which
has often been, and will no doubt again be ridiculed, namely, that
friction has had something to do with the disappearance of the external
portion of the tail, is not so ridiculous as it at first appears. Dr.
Anderson (92. ‘Proceedings Zoological Society,’ 1872, p. 210.) states
that the extremely short tail of Macacus brunneus is formed of eleven
vertebrae, including the imbedded basal ones. The extremity is
tendinous and contains no vertebrae; this is succeeded by five
rudimentary ones, so minute that together they are only one line and a
half in length, and these are permanently bent to one side in the shape
of a hook. The free part of the tail, only a little above an inch in
length, includes only four more small vertebrae. This short tail is
carried erect; but about a quarter of its total length is doubled on to
itself to the left; and this terminal part, which includes the
hook-like portion, serves “to fill up the interspace between the upper
divergent portion of the callosities;” so that the animal sits on it,
and thus renders it rough and callous. Dr. Anderson thus sums up his
observations: “These facts seem to me to have only one explanation;
this tail, from its short size, is in the monkey’s way when it sits
down, and frequently becomes placed under the animal while it is in
this attitude; and from the circumstance that it does not extend beyond
the extremity of the ischial tuberosities, it seems as if the tail
originally had been bent round by the will of the animal, into the
interspace between the callosities, to escape being pressed between
them and the ground, and that in time the curvature became permanent,
fitting in of itself when the organ happens to be sat upon.” Under
these circumstances it is not surprising that the surface of the tail
should have been roughened and rendered callous, and Dr. Murie (93.
‘Proceedings Zoological Society,’ 1872, p. 786.), who carefully
observed this species in the Zoological Gardens, as well as three other
closely allied forms with slightly longer tails, says that when the
animal sits down, the tail “is necessarily thrust to one side of the
buttocks; and whether long or short its root is consequently liable to
be rubbed or chafed.” As we now have evidence that mutilations
occasionally produce an inherited effect (94. I allude to Dr.
Brown-Sequard’s observations on the transmitted effect of an operation
causing epilepsy in guinea-pigs, and likewise more recently on the
analogous effects of cutting the sympathetic nerve in the neck. I shall
hereafter have occasion to refer to Mr. Salvin’s interesting case of
the apparently inherited effects of mot-mots biting off the barbs of
their own tail-feathers. See also on the general subject ‘Variation of
Animals and Plants under Domestication,’ vol. ii. pp. 22-24.), it is
not very improbable that in short-tailed monkeys, the projecting part
of the tail, being functionally useless, should after many generations
have become rudimentary and distorted, from being continually rubbed
and chafed. We see the projecting part in this condition in the Macacus
brunneus, and absolutely aborted in the M. ecaudatus and in several of
the higher apes. Finally, then, as far as we can judge, the tail has
disappeared in man and the anthropomorphous apes, owing to the terminal
portion having been injured by friction during a long lapse of time;
the basal and embedded portion having been reduced and modified, so as
to become suitable to the erect or semi-erect position.

I have now endeavoured to shew that some of the most distinctive
characters of man have in all probability been acquired, either
directly, or more commonly indirectly, through natural selection. We
should bear in mind that modifications in structure or constitution
which do not serve to adapt an organism to its habits of life, to the
food which it consumes, or passively to the surrounding conditions,
cannot have been thus acquired. We must not, however, be too confident
in deciding what modifications are of service to each being: we should
remember how little we know about the use of many parts, or what
changes in the blood or tissues may serve to fit an organism for a new
climate or new kinds of food. Nor must we forget the principle of
correlation, by which, as Isidore Geoffroy has shewn in the case of
man, many strange deviations of structure are tied together.
Independently of correlation, a change in one part often leads, through
the increased or decreased use of other parts, to other changes of a
quite unexpected nature. It is also well to reflect on such facts, as
the wonderful growth of galls on plants caused by the poison of an
insect, and on the remarkable changes of colour in the plumage of
parrots when fed on certain fishes, or inoculated with the poison of
toads (95. The ‘Variation of Animals and Plants under Domestication,’
vol. ii. pp. 280, 282.); for we can thus see that the fluids of the
system, if altered for some special purpose, might induce other
changes. We should especially bear in mind that modifications acquired
and continually used during past ages for some useful purpose, would
probably become firmly fixed, and might be long inherited.

Thus a large yet undefined extension may safely be given to the direct
and indirect results of natural selection; but I now admit, after
reading the essay by Nageli on plants, and the remarks by various
authors with respect to animals, more especially those recently made by
Professor Broca, that in the earlier editions of my ‘Origin of Species’
I perhaps attributed too much to the action of natural selection or the
survival of the fittest. I have altered the fifth edition of the
‘Origin’ so as to confine my remarks to adaptive changes of structure;
but I am convinced, from the light gained during even the last few
years, that very many structures which now appear to us useless, will
hereafter be proved to be useful, and will therefore come within the
range of natural selection. Nevertheless, I did not formerly consider
sufficiently the existence of structures, which, as far as we can at
present judge, are neither beneficial nor injurious; and this I believe
to be one of the greatest oversights as yet detected in my work. I may
be permitted to say, as some excuse, that I had two distinct objects in
view; firstly, to shew that species had not been separately created,
and secondly, that natural selection had been the chief agent of
change, though largely aided by the inherited effects of habit, and
slightly by the direct action of the surrounding conditions. I was not,
however, able to annul the influence of my former belief, then almost
universal, that each species had been purposely created; and this led
to my tacit assumption that every detail of structure, excepting
rudiments, was of some special, though unrecognised, service. Any one
with this assumption in his mind would naturally extend too far the
action of natural selection, either during past or present times. Some
of those who admit the principle of evolution, but reject natural
selection, seem to forget, when criticising my book, that I had the
above two objects in view; hence if I have erred in giving to natural
selection great power, which I am very far from admitting, or in having
exaggerated its power, which is in itself probable, I have at least, as
I hope, done good service in aiding to overthrow the dogma of separate
creations.

It is, as I can now see, probable that all organic beings, including
man, possess peculiarities of structure, which neither are now, nor
were formerly of any service to them, and which, therefore, are of no
physiological importance. We know not what produces the numberless
slight differences between the individuals of each species, for
reversion only carries the problem a few steps backwards, but each
peculiarity must have had its efficient cause. If these causes,
whatever they may be, were to act more uniformly and energetically
during a lengthened period (and against this no reason can be
assigned), the result would probably be not a mere slight individual
difference, but a well-marked and constant modification, though one of
no physiological importance. Changed structures, which are in no way
beneficial, cannot be kept uniform through natural selection, though
the injurious will be thus eliminated. Uniformity of character would,
however, naturally follow from the assumed uniformity of the exciting
causes, and likewise from the free intercrossing of many individuals.
During successive periods, the same organism might in this manner
acquire successive modifications, which would be transmitted in a
nearly uniform state as long as the exciting causes remained the same
and there was free intercrossing. With respect to the exciting causes
we can only say, as when speaking of so-called spontaneous variations,
that they relate much more closely to the constitution of the varying
organism, than to the nature of the conditions to which it has been
subjected.

—CONCLUSION—

In this chapter we have seen that as man at the present day is liable,
like every other animal, to multiform individual differences or slight
variations, so no doubt were the early progenitors of man; the
variations being formerly induced by the same general causes, and
governed by the same general and complex laws as at present. As all
animals tend to multiply beyond their means of subsistence, so it must
have been with the progenitors of man; and this would inevitably lead
to a struggle for existence and to natural selection. The latter
process would be greatly aided by the inherited effects of the
increased use of parts, and these two processes would incessantly react
on each other. It appears, also, as we shall hereafter see, that
various unimportant characters have been acquired by man through sexual
selection. An unexplained residuum of change must be left to the
assumed uniform action of those unknown agencies, which occasionally
induce strongly marked and abrupt deviations of structure in our
domestic productions.

Judging from the habits of savages and of the greater number of the
Quadrumana, primeval men, and even their ape-like progenitors, probably
lived in society. With strictly social animals, natural selection
sometimes acts on the individual, through the preservation of
variations which are beneficial to the community. A community which
includes a large number of well-endowed individuals increases in
number, and is victorious over other less favoured ones; even although
each separate member gains no advantage over the others of the same
community. Associated insects have thus acquired many remarkable
structures, which are of little or no service to the individual, such
as the pollen-collecting apparatus, or the sting of the worker-bee, or
the great jaws of soldier-ants. With the higher social animals, I am
not aware that any structure has been modified solely for the good of
the community, though some are of secondary service to it. For
instance, the horns of ruminants and the great canine teeth of baboons
appear to have been acquired by the males as weapons for sexual strife,
but they are used in defence of the herd or troop. In regard to certain
mental powers the case, as we shall see in the fifth chapter, is wholly
different; for these faculties have been chiefly, or even exclusively,
gained for the benefit of the community, and the individuals thereof
have at the same time gained an advantage indirectly.

It has often been objected to such views as the foregoing, that man is
one of the most helpless and defenceless creatures in the world; and
that during his early and less well-developed condition, he would have
been still more helpless. The Duke of Argyll, for instance, insists
(96. ‘Primeval Man,’ 1869, p. 66.) that “the human frame has diverged
from the structure of brutes, in the direction of greater physical
helplessness and weakness. That is to say, it is a divergence which of
all others it is most impossible to ascribe to mere natural selection.”
He adduces the naked and unprotected state of the body, the absence of
great teeth or claws for defence, the small strength and speed of man,
and his slight power of discovering food or of avoiding danger by
smell. To these deficiencies there might be added one still more
serious, namely, that he cannot climb quickly, and so escape from
enemies. The loss of hair would not have been a great injury to the
inhabitants of a warm country. For we know that the unclothed Fuegians
can exist under a wretched climate. When we compare the defenceless
state of man with that of apes, we must remember that the great canine
teeth with which the latter are provided, are possessed in their full
development by the males alone, and are chiefly used by them for
fighting with their rivals; yet the females, which are not thus
provided, manage to survive.

In regard to bodily size or strength, we do not know whether man is
descended from some small species, like the chimpanzee, or from one as
powerful as the gorilla; and, therefore, we cannot say whether man has
become larger and stronger, or smaller and weaker, than his ancestors.
We should, however, bear in mind that an animal possessing great size,
strength, and ferocity, and which, like the gorilla, could defend
itself from all enemies, would not perhaps have become social: and this
would most effectually have checked the acquirement of the higher
mental qualities, such as sympathy and the love of his fellows. Hence
it might have been an immense advantage to man to have sprung from some
comparatively weak creature.

The small strength and speed of man, his want of natural weapons, etc.,
are more than counterbalanced, firstly, by his intellectual powers,
through which he has formed for himself weapons, tools, etc., though
still remaining in a barbarous state, and, secondly, by his social
qualities which lead him to give and receive aid from his fellow-men.
No country in the world abounds in a greater degree with dangerous
beasts than Southern Africa; no country presents more fearful physical
hardships than the Arctic regions; yet one of the puniest of races,
that of the Bushmen, maintains itself in Southern Africa, as do the
dwarfed Esquimaux in the Arctic regions. The ancestors of man were, no
doubt, inferior in intellect, and probably in social disposition, to
the lowest existing savages; but it is quite conceivable that they
might have existed, or even flourished, if they had advanced in
intellect, whilst gradually losing their brute-like powers, such as
that of climbing trees, etc. But these ancestors would not have been
exposed to any special danger, even if far more helpless and
defenceless than any existing savages, had they inhabited some warm
continent or large island, such as Australia, New Guinea, or Borneo,
which is now the home of the orang. And natural selection arising from
the competition of tribe with tribe, in some such large area as one of
these, together with the inherited effects of habit, would, under
favourable conditions, have sufficed to raise man to his present high
position in the organic scale.




CHAPTER III.
COMPARISON OF THE MENTAL POWERS OF MAN AND THE LOWER ANIMALS.


The difference in mental power between the highest ape and the lowest
savage, immense—Certain instincts in common—The
emotions—Curiosity—Imitation—Attention—Memory—
Imagination—Reason—Progressive improvement —Tools and weapons used by
animals—Abstraction, Self-consciousness—Language—Sense of beauty—Belief
in God, spiritual agencies, superstitions.

We have seen in the last two chapters that man bears in his bodily
structure clear traces of his descent from some lower form; but it may
be urged that, as man differs so greatly in his mental power from all
other animals, there must be some error in this conclusion. No doubt
the difference in this respect is enormous, even if we compare the mind
of one of the lowest savages, who has no words to express any number
higher than four, and who uses hardly any abstract terms for common
objects or for the affections (1. See the evidence on those points, as
given by Lubbock, ‘Prehistoric Times,’ p. 354, etc.), with that of the
most highly organised ape. The difference would, no doubt, still remain
immense, even if one of the higher apes had been improved or civilised
as much as a dog has been in comparison with its parent-form, the wolf
or jackal. The Fuegians rank amongst the lowest barbarians; but I was
continually struck with surprise how closely the three natives on board
H.M.S. “Beagle,” who had lived some years in England, and could talk a
little English, resembled us in disposition and in most of our mental
faculties. If no organic being excepting man had possessed any mental
power, or if his powers had been of a wholly different nature from
those of the lower animals, then we should never have been able to
convince ourselves that our high faculties had been gradually
developed. But it can be shewn that there is no fundamental difference
of this kind. We must also admit that there is a much wider interval in
mental power between one of the lowest fishes, as a lamprey or
lancelet, and one of the higher apes, than between an ape and man; yet
this interval is filled up by numberless gradations.

Nor is the difference slight in moral disposition between a barbarian,
such as the man described by the old navigator Byron, who dashed his
child on the rocks for dropping a basket of sea-urchins, and a Howard
or Clarkson; and in intellect, between a savage who uses hardly any
abstract terms, and a Newton or Shakspeare. Differences of this kind
between the highest men of the highest races and the lowest savages,
are connected by the finest gradations. Therefore it is possible that
they might pass and be developed into each other.

My object in this chapter is to shew that there is no fundamental
difference between man and the higher mammals in their mental
faculties. Each division of the subject might have been extended into a
separate essay, but must here be treated briefly. As no classification
of the mental powers has been universally accepted, I shall arrange my
remarks in the order most convenient for my purpose; and will select
those facts which have struck me most, with the hope that they may
produce some effect on the reader.

With respect to animals very low in the scale, I shall give some
additional facts under Sexual Selection, shewing that their mental
powers are much higher than might have been expected. The variability
of the faculties in the individuals of the same species is an important
point for us, and some few illustrations will here be given. But it
would be superfluous to enter into many details on this head, for I
have found on frequent enquiry, that it is the unanimous opinion of all
those who have long attended to animals of many kinds, including birds,
that the individuals differ greatly in every mental characteristic. In
what manner the mental powers were first developed in the lowest
organisms, is as hopeless an enquiry as how life itself first
originated. These are problems for the distant future, if they are ever
to be solved by man.

As man possesses the same senses as the lower animals, his fundamental
intuitions must be the same. Man has also some few instincts in common,
as that of self-preservation, sexual love, the love of the mother for
her new-born offspring, the desire possessed by the latter to suck, and
so forth. But man, perhaps, has somewhat fewer instincts than those
possessed by the animals which come next to him in the series. The
orang in the Eastern islands, and the chimpanzee in Africa, build
platforms on which they sleep; and, as both species follow the same
habit, it might be argued that this was due to instinct, but we cannot
feel sure that it is not the result of both animals having similar
wants, and possessing similar powers of reasoning. These apes, as we
may assume, avoid the many poisonous fruits of the tropics, and man has
no such knowledge: but as our domestic animals, when taken to foreign
lands, and when first turned out in the spring, often eat poisonous
herbs, which they afterwards avoid, we cannot feel sure that the apes
do not learn from their own experience or from that of their parents
what fruits to select. It is, however, certain, as we shall presently
see, that apes have an instinctive dread of serpents, and probably of
other dangerous animals.

The fewness and the comparative simplicity of the instincts in the
higher animals are remarkable in contrast with those of the lower
animals. Cuvier maintained that instinct and intelligence stand in an
inverse ratio to each other; and some have thought that the
intellectual faculties of the higher animals have been gradually
developed from their instincts. But Pouchet, in an interesting essay
(2. ‘L’Instinct chez les Insectes,’ ‘Revue des Deux Mondes,’ Feb. 1870,
p. 690.), has shewn that no such inverse ratio really exists. Those
insects which possess the most wonderful instincts are certainly the
most intelligent. In the vertebrate series, the least intelligent
members, namely fishes and amphibians, do not possess complex
instincts; and amongst mammals the animal most remarkable for its
instincts, namely the beaver, is highly intelligent, as will be
admitted by every one who has read Mr. Morgan’s excellent work. (3.
‘The American Beaver and His Works,’ 1868.)

Although the first dawnings of intelligence, according to Mr. Herbert
Spencer (4. ‘The Principles of Psychology,’ 2nd edit., 1870, pp.
418-443.), have been developed through the multiplication and
co-ordination of reflex actions, and although many of the simpler
instincts graduate into reflex actions, and can hardly be distinguished
from them, as in the case of young animals sucking, yet the more
complex instincts seem to have originated independently of
intelligence. I am, however, very far from wishing to deny that
instinctive actions may lose their fixed and untaught character, and be
replaced by others performed by the aid of the free will. On the other
hand, some intelligent actions, after being performed during several
generations, become converted into instincts and are inherited, as when
birds on oceanic islands learn to avoid man. These actions may then be
said to be degraded in character, for they are no longer performed
through reason or from experience. But the greater number of the more
complex instincts appear to have been gained in a wholly different
manner, through the natural selection of variations of simpler
instinctive actions. Such variations appear to arise from the same
unknown causes acting on the cerebral organisation, which induce slight
variations or individual differences in other parts of the body; and
these variations, owing to our ignorance, are often said to arise
spontaneously. We can, I think, come to no other conclusion with
respect to the origin of the more complex instincts, when we reflect on
the marvellous instincts of sterile worker-ants and bees, which leave
no offspring to inherit the effects of experience and of modified
habits.

Although, as we learn from the above-mentioned insects and the beaver,
a high degree of intelligence is certainly compatible with complex
instincts, and although actions, at first learnt voluntarily can soon
through habit be performed with the quickness and certainty of a reflex
action, yet it is not improbable that there is a certain amount of
interference between the development of free intelligence and of
instinct,—which latter implies some inherited modification of the
brain. Little is known about the functions of the brain, but we can
perceive that as the intellectual powers become highly developed, the
various parts of the brain must be connected by very intricate channels
of the freest intercommunication; and as a consequence each separate
part would perhaps tend to be less well fitted to answer to particular
sensations or associations in a definite and inherited—that is
instinctive—manner. There seems even to exist some relation between a
low degree of intelligence and a strong tendency to the formation of
fixed, though not inherited habits; for as a sagacious physician
remarked to me, persons who are slightly imbecile tend to act in
everything by routine or habit; and they are rendered much happier if
this is encouraged.

I have thought this digression worth giving, because we may easily
underrate the mental powers of the higher animals, and especially of
man, when we compare their actions founded on the memory of past
events, on foresight, reason, and imagination, with exactly similar
actions instinctively performed by the lower animals; in this latter
case the capacity of performing such actions has been gained, step by
step, through the variability of the mental organs and natural
selection, without any conscious intelligence on the part of the animal
during each successive generation. No doubt, as Mr. Wallace has argued
(5. ‘Contributions to the Theory of Natural Selection,’ 1870, p. 212.),
much of the intelligent work done by man is due to imitation and not to
reason; but there is this great difference between his actions and many
of those performed by the lower animals, namely, that man cannot, on
his first trial, make, for instance, a stone hatchet or a canoe,
through his power of imitation. He has to learn his work by practice; a
beaver, on the other hand, can make its dam or canal, and a bird its
nest, as well, or nearly as well, and a spider its wonderful web, quite
as well (6. For the evidence on this head, see Mr. J. Traherne
Moggridge’s most interesting work, ‘Harvesting Ants and Trap-Door
Spiders,’ 1873, pp. 126, 128.), the first time it tries as when old and
experienced.

To return to our immediate subject: the lower animals, like man,
manifestly feel pleasure and pain, happiness and misery. Happiness is
never better exhibited than by young animals, such as puppies, kittens,
lambs, etc., when playing together, like our own children. Even insects
play together, as has been described by that excellent observer, P.
Huber (7. ‘Recherches sur les Moeurs des Fourmis,’ 1810, p. 173.), who
saw ants chasing and pretending to bite each other, like so many
puppies.

The fact that the lower animals are excited by the same emotions as
ourselves is so well established, that it will not be necessary to
weary the reader by many details. Terror acts in the same manner on
them as on us, causing the muscles to tremble, the heart to palpitate,
the sphincters to be relaxed, and the hair to stand on end. Suspicion,
the offspring of fear, is eminently characteristic of most wild
animals. It is, I think, impossible to read the account given by Sir E.
Tennent, of the behaviour of the female elephants, used as decoys,
without admitting that they intentionally practise deceit, and well
know what they are about. Courage and timidity are extremely variable
qualities in the individuals of the same species, as is plainly seen in
our dogs. Some dogs and horses are ill-tempered, and easily turn sulky;
others are good-tempered; and these qualities are certainly inherited.
Every one knows how liable animals are to furious rage, and how plainly
they shew it. Many, and probably true, anecdotes have been published on
the long-delayed and artful revenge of various animals. The accurate
Rengger, and Brehm (8. All the following statements, given on the
authority of these two naturalists, are taken from Rengger’s
‘Naturgesch. der Säugethiere von Paraguay,’ 1830, s. 41-57, and from
Brehm’s ‘Thierleben,’ B. i. s. 10-87.) state that the American and
African monkeys which they kept tame, certainly revenged themselves.
Sir Andrew Smith, a zoologist whose scrupulous accuracy was known to
many persons, told me the following story of which he was himself an
eye-witness; at the Cape of Good Hope an officer had often plagued a
certain baboon, and the animal, seeing him approaching one Sunday for
parade, poured water into a hole and hastily made some thick mud, which
he skilfully dashed over the officer as he passed by, to the amusement
of many bystanders. For long afterwards the baboon rejoiced and
triumphed whenever he saw his victim.

The love of a dog for his master is notorious; as an old writer
quaintly says (9. Quoted by Dr. Lauder Lindsay, in his ‘Physiology of
Mind in the Lower Animals,’ ‘Journal of Mental Science,’ April 1871, p.
38.), “A dog is the only thing on this earth that luvs you more than he
luvs himself.”

In the agony of death a dog has been known to caress his master, and
every one has heard of the dog suffering under vivisection, who licked
the hand of the operator; this man, unless the operation was fully
justified by an increase of our knowledge, or unless he had a heart of
stone, must have felt remorse to the last hour of his life.

As Wh

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