The Riddle of the Universe at the close of the nineteenth century
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Title: The Riddle of the Universe at the close of the nineteenth century
Author: Ernst Haeckel
Translator: Joseph McCabe
Release date: June 17, 2013 [eBook #42968]
Most recently updated: October 23, 2024
Language: English
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*** START OF THE PROJECT GUTENBERG EBOOK THE RIDDLE OF THE UNIVERSE AT THE CLOSE OF THE NINETEENTH CENTURY ***
Transcriber's Note:
Every effort has been made to replicate this text as faithfully as
possible, including inconsistencies in hyphenation. It seems that
the italic typeface used in this book did not have an ae ligature.
Names of genera and higher taxonomic groups are not capitalized in
the printed book: they have bee left unchanged. Some changes have
been made. They are listed at the end of the text.
Italic text has been marked with _underscores_.
OE ligatures have been expanded.
THE RIDDLE OF THE UNIVERSE
[Illustration: ERNST HAECKEL]
THE RIDDLE
OF THE UNIVERSE
_AT THE CLOSE OF
THE NINETEENTH CENTURY_
BY
ERNST HAECKEL
(Ph.D., M.D., LL.D., Sc.D., and Professor at the
University of Jena)
AUTHOR OF "THE HISTORY OF CREATION"
"THE EVOLUTION OF MAN" ETC.
TRANSLATED BY
JOSEPH McCABE
[Illustration]
HARPER & BROTHERS PUBLISHERS
NEW YORK AND LONDON
1905
Copyright, 1900, by HARPER & BROTHERS.
_All rights reserved._
CONTENTS
PAGE
AUTHOR'S PREFACE v
TRANSLATOR'S PREFACE xi
CHAPTER I
THE NATURE OF THE PROBLEM 1
CHAPTER II
OUR BODILY FRAME 22
CHAPTER III
OUR LIFE 39
CHAPTER IV
OUR EMBRYONIC DEVELOPMENT 53
CHAPTER V
THE HISTORY OF OUR SPECIES 71
CHAPTER VI
THE NATURE OF THE SOUL 88
CHAPTER VII
PSYCHIC GRADATIONS 108
CHAPTER VIII
THE EMBRYOLOGY OF THE SOUL 132
CHAPTER IX
THE PHYLOGENY OF THE SOUL 148
CHAPTER X
CONSCIOUSNESS 170
CHAPTER XI
THE IMMORTALITY OF THE SOUL 188
CHAPTER XII
THE LAW OF SUBSTANCE 211
CHAPTER XIII
THE EVOLUTION OF THE WORLD 233
CHAPTER XIV
THE UNITY OF NATURE 254
CHAPTER XV
GOD AND THE WORLD 275
CHAPTER XVI
KNOWLEDGE AND BELIEF 292
CHAPTER XVII
SCIENCE AND CHRISTIANITY 308
CHAPTER XVIII
OUR MONISTIC RELIGION 331
CHAPTER XIX
OUR MONISTIC ETHICS 347
CHAPTER XX
SOLUTION OF THE WORLD-PROBLEMS 365
CONCLUSION 380
INDEX 385
AUTHOR'S PREFACE
The present study of the monistic philosophy is intended for thoughtful
readers of every condition who are united in an honest search for the
truth. An intensification of this effort of man to attain a knowledge
of the truth is one of the most salient features of the nineteenth
century. That is easily explained, in the first place, by the immense
progress of science, especially in its most important branch, the
history of humanity; it is due, in the second place, to the open
contradiction that has developed during the century between science
and the traditional "Revelation"; and, finally, it arises from the
inevitable extension and deepening of the rational demand for an
elucidation of the innumerable facts that have been recently brought to
light, and for a fuller knowledge of their causes.
Unfortunately, this vast progress of empirical knowledge in our
"Century of Science" has not been accompanied by a corresponding
advancement of its theoretical interpretation--that higher knowledge of
the causal nexus of individual phenomena which we call philosophy. We
find, on the contrary, that the abstract and almost wholly metaphysical
science which has been taught in our universities for the last hundred
years under the name of "philosophy" is far from assimilating our
hard-earned treasures of experimental research. On the other hand, we
have to admit, with equal regret, that most of the representatives
of what is called "exact science" are content with the special care
of their own narrow branches of observation and experiment, and
deem superfluous the deeper study of the universal connection of
the phenomena they observe--that is, philosophy. While these pure
empiricists "do not see the wood for the trees," the metaphysicians, on
the other hand, are satisfied with the mere picture of the wood, and
trouble not about its individual trees. The idea of a "philosophy of
nature," to which both those methods of research, the empirical and the
speculative, naturally converge, is even yet contemptuously rejected by
large numbers of representatives of both tendencies.
This unnatural and fatal opposition between science and philosophy,
between the results of experience and of thought, is undoubtedly
becoming more and more onerous and painful to thoughtful people. That
is easily proved by the increasing spread of the immense popular
literature of "natural philosophy" which has sprung up in the course
of the last half-century. It is seen, too, in the welcome fact that,
in spite of the mutual aversion of the scientific observer and the
speculative philosopher, nevertheless eminent thinkers from both
camps league themselves in a united effort to attain the solution
of that highest object of inquiry which we briefly denominate the
"world-riddles." The studies of these "world-riddles" which I offer in
the present work cannot reasonably claim to give a perfect solution of
them; they merely offer to a wide circle of readers a critical inquiry
into the problem, and seek to answer the question as to how nearly we
have approached that solution at the present day. What stage in the
attainment of truth have we actually arrived at in this closing year of
the nineteenth century? What progress have we really made during its
course towards that immeasurably distant goal?
The answer which I give to these great questions must, naturally, be
merely subjective and only partly correct; for my knowledge of nature
and my ability to interpret its objective reality are limited, as are
those of every man. The one point that I can claim for it, and which,
indeed, I must ask of my strongest opponents, is that my Monistic
Philosophy is sincere from beginning to end--it is the complete
expression of the conviction that has come to me, after many years of
ardent research into Nature and unceasing reflection, as to the true
basis of its phenomena. For fully half a century has my mind's work
proceeded, and I now, in my sixty-sixth year, may venture to claim
that it is mature; I am fully convinced that this "ripe fruit" of the
tree of knowledge will receive no important addition and suffer no
substantial modification during the brief spell of life that remains to
me.
I presented all the essential and distinctive elements of my monistic
and genetic philosophy thirty-three years ago, in my _General
Morphology of Organisms_, a large and laborious work, which has had but
a limited circulation. It was the first attempt to apply in detail the
newly established theory of evolution to the whole science of organic
forms. In order to secure the acceptance of at least one part of the
new thought which it contained, and to kindle a wider interest in the
greatest advancement of knowledge that our century has witnessed, I
published my _Natural History of Creation_ two years afterwards.
As this less complicated work, in spite of its great defects, ran
into nine large editions and twelve different translations, it has
contributed not a little to the spread of monistic views. The same
may be said of the less known _Anthropogeny_[1] (1874), in which I
set myself the difficult task of rendering the most important facts
of the theory of man's descent accessible and intelligible to the
general reader; the fourth, enlarged, edition of that work appeared in
1891. In the paper which I read at the fourth International Congress
of Zoology at Cambridge, in 1898, on "Our Present Knowledge of the
Descent of Man"[2] (a seventh edition of which appeared in 1899), I
treated certain significant and particularly valuable advances which
this important branch of anthropology has recently made. Other isolated
questions of our modern natural philosophy, which are peculiarly
interesting, have been dealt with in my _Collected Popular Lectures on
the Subject of Evolution_ (1878). Finally, I have briefly presented
the broad principles of my monistic philosophy and its relation to the
dominant faith in my _Confession of Faith of a Man of Science: Monism
as a Connecting Link between Religion and Science_[3] (1892, eighth
edition, 1899).
The present work on _The Riddle of the Universe_ is the continuation,
confirmation, and integration of the views which I have urged for a
generation in the aforesaid volumes. It marks the close of my studies
on the monistic conception of the universe. The earlier plan, which
I projected many years ago, of constructing a complete "System of
Monistic Philosophy" on the basis of evolution will never be carried
into effect now. My strength is no longer equal to the task, and many
warnings of approaching age urge me to desist. Indeed, I am wholly a
child of the nineteenth century, and with its close I draw the line
under my life's work.
The vast extension of human knowledge which has taken place during
the present century, owing to a happy division of labor, makes
it impossible to-day to range over all its branches with equal
thoroughness, and to show their essential unity and connection.
Even a genius of the highest type, having an equal command of every
branch of science, and largely endowed with the artistic faculty of
comprehensive presentation, would be incapable of setting forth a
complete view of the cosmos in the space of a moderate volume. My own
command of the various branches of science is uneven and defective,
so that I can attempt no more than to sketch the general plan of such
a world-picture, and point out the pervading unity of its parts,
however imperfect be the execution. Thus it is that this work on the
world-enigma has something of the character of a sketch-book, in which
studies of unequal value are associated. As the material of the book
was partly written many years ago, and partly produced for the first
time during the last few years, the composition is, unfortunately,
uneven at times; repetitions, too, have proved unavoidable. I trust
those defects will be overlooked.
In taking leave of my readers, I venture the hope that, through my
sincere and conscientious work--in spite of its faults, of which I am
not unconscious--I have contributed a little towards the solution
of the great enigma. Amid the clash of theories, I trust that I have
indicated to many a reader who is absorbed in the zealous pursuit of
purely rational knowledge that path which, it is my firm conviction,
alone leads to the truth--the path of empirical investigation and of
the Monistic Philosophy which is based upon it.
ERNST HAECKEL.
JENA, GERMANY.
PREFACE
The hour is close upon us when we shall commence our retrospect of one
of the most wonderful sections of time that was ever measured by the
sweep of the earth. Already the expert is at work, dissecting out and
studying his particular phase of that vast world of thought and action
we call the nineteenth century. Art, literature, commerce, industry,
politics, ethics--all have their high interpreters among us; but in
the chance of life it has fallen out that there is none to read aright
for us, in historic retrospect, what after ages will probably regard
as the most salient feature of the nineteenth century--the conflict
of theology with philosophy and science. The pens of our Huxleys,
and Tyndalls, and Darwins lie where they fell; there is none left in
strength among us to sum up the issues of that struggle with knowledge
and sympathy.
In these circumstances it has been thought fitting that we should
introduce to English readers the latest work of Professor Haeckel.
Germany, as the reader will quickly perceive, is witnessing the same
strange reaction of thought that we see about us here in England,
yet _Die Welträthsel_ found an immediate and very extensive circle
of readers. One of the most prominent zoologists of the century,
Professor Haeckel, has a unique claim to pronounce with authority, from
the scientific side, on what is known as "the conflict of science and
religion." In the contradictory estimates that are urged on us--for
the modern ecclesiastic is as emphatic in his assurance that the
conflict has ended favorably to theology as the rationalist is with his
counter-assertion--the last words of one of the leading combatants of
the second half of the century, still, happily, in full vigor of mind,
will be heard with respect and close attention.
A glance at the index of the work suffices to indicate its comprehensive
character. The judgment of the distinguished scientist cannot fail
to have weight on all the topics included; yet the reader will soon
discover a vein of exceptionally interesting thought in the chapters
on evolution. The evolution of the human body is no longer a matter
of serious dispute. It has passed the first two tribunals--those of
theology and of an _à priori_ philosophy--and is only challenged at the
third and last--that of empirical proof--by the decorative heads of
scientific bodies and a few isolated thinkers.
"_Apparent rari nantes in gurgite vasto._"
But the question of the evolution of the human mind, or soul, has been
successfully divorced from that of the body. Roman Catholic advanced
theologians, whose precise terminology demanded a clear position, admit
the latter and deny the former categorically. Other theologians, and
many philosophers, have still a vague notion that the evidence for
the one does not impair their sentimental objection to the other. Dr.
Haeckel's work summarizes the evidence for the evolution of mind in
a masterly and profoundly interesting fashion. It seems impossible to
follow his broad survey of the psychic world, from protist to man,
without bearing away a conviction of the natural origin of every power
and content of the human soul.
TRANSLATOR.
_October, 1900._
THE RIDDLE OF THE UNIVERSE
CHAPTER I
THE NATURE OF THE PROBLEM
The Condition of Civilization and of Thought at the Close of
the Nineteenth Century--Progress of Our Knowledge of Nature,
of the Organic and Inorganic Sciences--The Law of Substance
and the Law of Evolution--Progress of Technical Science and
of Applied Chemistry--Stagnancy in other Departments of
Life: Legal and Political Administration, Education, and the
Church--Conflict of Reason and Dogma--Anthropism--Cosmological
Perspective--Cosmological Theorems--Refutation of the Delusion
of Man's Importance--Number of "World-Riddles"--Criticism of
the "Seven" Enigmas--The Way to Solve Them--Function of the
Senses and of the Brain--Induction and Deduction--Reason,
Sentiment, and Revelation--Philosophy and Science--Experience and
Speculation--Dualism and Monism
The close of the nineteenth century offers one of the most remarkable
spectacles to the thoughtful observer. All educated people are
agreed that it has in many respects immeasurably outstripped its
predecessors, and has achieved tasks that were deemed impracticable at
its commencement. An entirely new character has been given to the whole
of our modern civilization, not only by our astounding theoretical
progress in sound knowledge of nature, but also by the remarkably
fertile practical application of that knowledge in technical science,
industry, commerce, and so forth. On the other hand, however, we have
made little or no progress in moral and social life, in comparison with
earlier centuries; at times there has been serious reaction. And from
this obvious conflict there have arisen, not only an uneasy sense of
dismemberment and falseness, but even the danger of grave catastrophes
in the political and social world. It is, then, not merely the right,
but the sacred duty, of every honorable and humanitarian thinker to
devote himself conscientiously to the settlement of that conflict,
and to warding off the dangers that it brings in its train. In our
conviction this can only be done by a courageous effort to attain the
truth, and by the formation of a clear view of the world--a view that
shall be based on truth and conformity to reality.
If we recall to mind the imperfect condition of science at the
beginning of the century, and compare this with the magnificent
structure of its closing years, we are compelled to admit that
marvellous progress has been made during its course. Every single
branch of science can boast that it has, especially during the latter
half of the century, made numerous acquisitions of the utmost value.
Both in our microscopic knowledge of the little and in our telescopic
investigation of the great we have attained an invaluable insight
that seemed inconceivable a hundred years ago. Improved methods of
microscopic and biological research have not only revealed to us an
invisible world of living things in the kingdom of the protists, full
of an infinite wealth of forms, but they have taught us to recognize in
the tiny cell the all-pervading "elementary organism" of whose social
communities--the tissues--the body of every multicellular plant and
animal, even that of man, is composed. This anatomical knowledge is
of extreme importance; and it is supplemented by the embryological
discovery that each of the higher multicellular organisms is developed
out of one simple cell, the impregnated ovum. The "cellular theory,"
which has been founded on that discovery, has given us the first true
interpretation of the physical, chemical, and even the psychological
processes of life--those mysterious phenomena for whose explanation
it had been customary to postulate a supernatural "vital force" or
"immortal soul." Moreover, the true character of disease has been made
clear and intelligible to the physician for the first time by the
cognate science of Cellular Pathology.
The discoveries of the nineteenth century in the inorganic world are no
less important. Physics has made astounding progress in every section
of its province--in optics and acoustics, in magnetism and electricity,
in mechanics and thermo-dynamics; and, what is still more important,
it has proved the unity of the forces of the entire universe. The
mechanical theory of heat has shown how intimately they are connected,
and how each can, in certain conditions, transform itself directly
into another. Spectral analysis has taught us that the same matter
which enters into the composition of all bodies on earth, including
its living inhabitants, builds up the rest of the planets, the sun,
and the most distant stars. Astro-physics has considerably enlarged
our cosmic perspective in revealing to us, in the immeasurable depths
of space, millions of circling spheres larger than our earth, and,
like it, in endless transformation, in an eternal rhythm of life and
death. Chemistry has introduced us to a multitude of new substances,
all of which arise from the combination of a few (about seventy)
elements that are incapable of further analysis; some of them play a
most important part in every branch of life. It has been shown that one
of these elements--carbon--is the remarkable substance that effects
the endless variety of organic syntheses, and thus may be considered
"the chemical basis of life." All the particular advances, however, of
physics and chemistry yield in theoretical importance to the discovery
of the great law which brings them all to one common focus, the "Law
of Substance." As this fundamental cosmic law establishes the eternal
persistence of matter and force, their unvarying constancy throughout
the entire universe, it has become the pole-star that guides our
Monistic Philosophy through the mighty labyrinth to a solution of the
world-problem.
Since we intend to make a general survey of the actual condition of
our knowledge of nature and its progress during the present century in
the following chapters, we shall delay no longer with the review of
its particular branches. We would only mention one important advance,
which was contemporary with the discovery of the law of substance, and
which supplements it--the establishment of the theory of evolution.
It is true that there were philosophers who spoke of the evolution
of things a thousand years ago; but the recognition that such a law
dominates the entire universe, and that the world is nothing else than
an eternal "evolution of substance," is a fruit of the nineteenth
century. It was not until the second half of this century that it
attained to perfect clearness and a universal application. The immortal
merit of establishing the doctrine on an empirical basis, and pointing
out its world-wide application, belongs to the great scientist Charles
Darwin; he it was who, in 1859, supplied a solid foundation for the
theory of descent, which the able French naturalist Jean Lamarck had
already sketched in its broad outlines in 1809, and the fundamental
idea of which had been almost prophetically enunciated in 1799 by
Germany's greatest poet and thinker, Wolfgang Goethe. In that theory we
have the key to "the question of all questions," to the great enigma
of "the place of man in nature," and of his natural development. If we
are in a position to-day to recognize the sovereignty of the law of
evolution--and, indeed, of a monistic evolution--in every province of
nature, and to use it, in conjunction with the law of substance, for a
simple interpretation of all natural phenomena, we owe it chiefly to
those three distinguished naturalists; they shine as three stars of the
first magnitude amid all the great men of the century.
This marvellous progress in a theoretical knowledge of nature has
been followed by a manifold practical application in every branch
of civilized life. If we are to-day in the "age of commerce," if
international trade and communication have attained dimensions beyond
the conception of any previous age, if we have transcended the limits
of space and time by our telegraph and telephone, we owe it, in the
first place, to the technical advancement of physics, especially in
the application of steam and electricity. If, in photography, we can,
with the utmost ease, compel the sunbeam to create for us in a moment's
time a correct picture of any object we like; if we have made enormous
progress in agriculture, and in a variety of other pursuits; if, in
surgery, we have brought an infinite relief to human pain by our
chloroform and morphia, our antiseptics and serous therapeutics, we
owe it all to applied chemistry. But it is so well known how much we
have surpassed all earlier centuries through these and other scientific
discoveries that we need linger over the question no longer.
While we look back with a just pride on the immense progress of the
nineteenth century in a knowledge of nature and in its practical
application, we find, unfortunately, a very different and far from
agreeable picture when we turn to another and not less important
province of modern life. To our great regret we must endorse the words
of Alfred Wallace: "Compared with our astounding progress in physical
science and its practical application, our system of government, of
administrative justice, and of national education, and our entire
social and moral organization, remain in a state of barbarism." To
convince ourselves of the truth of this grave indictment we need only
cast an unprejudiced glance at our public life, or look into the mirror
that is daily offered to us by the press, the organ of public sentiment.
We begin our review with justice, the _fundamentum regnorum_. No one
can maintain that its condition to-day is in harmony with our advanced
knowledge of man and the world. Not a week passes in which we do not
read of judicial decisions over which every thoughtful man shakes his
head in despair; many of the decisions of our higher and lower courts
are simply unintelligible. We are not referring in the treatment of
this particular "world-problem" to the fact that many modern states, in
spite of their paper constitutions, are really governed with absolute
despotism, and that many who occupy the bench give judgment less in
accordance with their sincere conviction than with wishes expressed
in higher quarters. We readily admit that the majority of judges and
counsel decide conscientiously, and err simply from human frailty.
Most of their errors, indeed, are due to defective preparation. It is
popularly supposed that these are just the men of highest education,
and that on that very account they have the preference in nominations
to different offices. However, this famed "legal education" is for the
most part rather of a formal and technical character. They have but a
superficial acquaintance with that chief and peculiar object of their
activity, the human organism, and its most important function, the
mind. That is evident from the curious views as to the liberty of the
will, responsibility, etc., which we encounter daily. I once told an
eminent jurist that the tiny spherical ovum from which every man is
developed is as truly endowed with life as the embryo of two, or seven,
or even nine months; he laughed incredulously. Most of the students
of jurisprudence have no acquaintance with anthropology, psychology,
and the doctrine of evolution--the very first requisites for a correct
estimate of human nature. They have "no time" for it; their time is
already too largely bespoken for an exhaustive study of beer and wine
and for the noble art of fencing. The rest of their valuable study-time
is required for the purpose of learning some hundreds of paragraphs of
law books, a knowledge of which is supposed to qualify the jurist for
any position whatever in our modern civilized community.
We shall touch but lightly on the unfortunate province of politics, for
the unsatisfactory condition of the modern political world is only too
familiar. In a great measure its evils are due to the fact that most of
our officials are jurists--that is, men of high technical education,
but utterly devoid of that thorough knowledge of human nature which is
only obtained by the study of comparative anthropology and the monistic
psychology--men without an acquaintance with those social relations of
which we find the earlier types in comparative zoology and the theory
of evolution, in the cellular theory, and the study of the protists. We
can only arrive at a correct knowledge of the structure and life of the
social body, the state, through a scientific knowledge of the structure
and life of the individuals who compose it, and the cells of which they
are in turn composed. If our political rulers and our "representatives
of the people" possessed this invaluable biological and anthropological
knowledge, we should not find our journals so full of the sociological
blunders and political nonsense which at present are far from adorning
our parliamentary reports, and even many of our official documents.
Worst of all is it when the modern state flings itself into the arms
of the reactionary Church, and when the narrow-minded self-interest
of parties and the infatuation of short-sighted party-leaders lend
their support to the hierarchy. Then are witnessed such sad scenes
as the German Reichstag puts before our eyes even at the close of
the nineteenth century. We have the spectacle of the educated German
people in the power of the ultramontane Centre, under the rule of the
Roman papacy, which is its bitterest and most dangerous enemy. Then
superstition and stupidity reign instead of right and reason. Never
will our government improve until it casts off the fetters of the
Church and raises the views of the citizens on man and the world to a
higher level by a general scientific education. That does not raise
the question of any special form of constitution. Whether a monarchy
or a republic be preferable, whether the constitution should be
aristocratic or democratic, are subordinate questions in comparison
with the supreme question: Shall the modern civilized state be
spiritual or secular? Shall it be _theocratic_--ruled by the irrational
formulæ of faith and by clerical despotism--or _nomocratic_--under the
sovereignty of rational laws and civic right? The first task is to
kindle a rational interest in our youth, and to uplift our citizens
and free them from superstition. That can only be achieved by a timely
reform of our schools.
Our education of the young is no more in harmony with modern scientific
progress than our legal and political world. Physical science, which
is so much more important than all other sciences, and which, properly
understood, really embraces all the so-called moral sciences, is still
regarded as a mere accessory in our schools, if not treated as the
Cinderella of the curriculum. Most of our teachers still give the
most prominent place to that dead learning which has come down from
the cloistral schools of the Middle Ages. In the front rank we have
grammatical gymnastics and an immense waste of time over a "thorough
knowledge" of classics and of the history of foreign nations. Ethics,
the most important object of practical philosophy, is entirely
neglected, and its place is usurped by the ecclesiastical creed. Faith
must take precedence over knowledge--not that scientific faith which
leads to a monistic religion, but the irrational superstition that
lays the foundation of a perverted Christianity. The valuable teaching
of modern cosmology and anthropology, of biology and evolution, is
most inadequately imparted, if not entirely unknown, in our higher
schools; while the memory is burdened with a mass of philological and
historical facts which are utterly useless, either from the point of
view of theoretical education or for the practical purposes of life.
Moreover, the antiquated arrangements and the distribution of faculties
in the universities are just as little in harmony with the point we
have reached in monistic science as the curriculum of the primary and
secondary schools.
The climax of the opposition to modern education and its foundation,
advanced natural philosophy, is reached, of course, in the Church. We
are not speaking here of ultramontane papistry, nor of the orthodox
evangelical tendencies, which do not fall far short of it in ignorance
and in the crass superstition of their dogmas. We are imagining
ourselves for the moment to be in the church of a liberal Protestant
minister, who has a good average education, and who finds room for
"the rights of reason" by the side of his faith. There, besides
excellent moral teaching, which is in perfect harmony with our own
monistic ethics, and humanitarian discussion of which we cordially
approve, we hear ideas on the nature of God, of the world, of man, and
of life which are directly opposed to all scientific experience. It
is no wonder that physicists and chemists, doctors and philosophers,
who have made a thorough study of nature, refuse a hearing to such
preachers. Our theologians and our politicians are just as ignorant
as our philosophers and our jurists of that elementary knowledge of
nature which is based on the monistic theory of evolution, and which is
already far exceeded in the triumph of our modern learning.
From this opposition, which we can only briefly point out at present,
there arise grave conflicts in our modern life which urgently demand
a settlement. Our modern education, the outcome of our great advance
in knowledge, has a claim upon every department of public and private
life; it would see humanity raised, by the instrumentality of
reason, to that higher grade of culture, and, consequently, to that
better path towards happiness which has been opened out to us by the
progress of modern science. That aim, however, is vigorously opposed
by the influential parties who would detain the mind in the exploded
views of the Middle Ages with regard to the most important problems
of life; they linger in the fold of traditional dogma, and would
have reason prostrate itself before their "higher revelation." That
is the condition of things, to a very large extent, in theology and
philosophy, in sociology and jurisprudence. It is not that the motives
of the latter are to be attributed, as a rule, to pure self-interest;
they spring partly from ignorance of the facts, and partly from an
indolent acquiescence in tradition. The most dangerous of the three
great enemies of reason and knowledge is not malice; but ignorance, or,
perhaps, indolence. The gods themselves still strive in vain against
these two latter influences when they have happily vanquished the first.
One of the main supports of that reactionary system is still what
we may call "anthropism." I designate by this term "that powerful
and world-wide group of erroneous opinions which opposes the human
organism to the whole of the rest of nature, and represents it to be
the preordained end of the organic creation, an entity essentially
distinct from it, a godlike being." Closer examination of this group of
ideas shows it to be made up of three different dogmas, which we may
distinguish as the _anthropocentric_, the _anthropomorphic_, and the
_anthropolatrous_.[4]
I. The _anthropocentric_ dogma culminates in the idea that man
is the preordained centre and aim of all terrestrial life--or, in
a wider sense, of the whole universe. As this error is extremely
conducive to man's interest, and as it is intimately connected with the
creation-myth of the three great Mediterranean religions, and with the
dogmas of the Mosaic, Christian, and Mohammedan theologies, it still
dominates the greater part of the civilized world.
II. The _anthropomorphic_ dogma is likewise connected with the
creation-myth of the three aforesaid religions, and of many others. It
likens the creation and control of the world by God to the artificial
creation of a talented engineer or mechanic, and to the administration
of a wise ruler. God, as creator, sustainer, and ruler of the world,
is thus represented after a purely human fashion in his thought and
work. Hence it follows, in turn, that man is godlike. "God made man
to His own image and likeness." The older, naïve mythology is pure
"homotheism," attributing human shape, flesh, and blood to the gods.
It is more intelligible than the modern mystic theosophy that adores
a personal God as an invisible--properly speaking, gaseous--being,
yet makes him think, speak, and act in human fashion; it gives us the
paradoxical picture of a "gaseous vertebrate."
III. The _anthropolatric_ dogma naturally results from this comparison
of the activity of God and man; it ends in the apotheosis of the human
organism. A further result is the belief in the personal immortality of
the soul, and the dualistic dogma of the twofold nature of man, whose
"immortal soul" is conceived as but the temporary inhabitant of the
mortal frame. Thus these three anthropistic dogmas, variously adapted
to the respective professions of the different religions, came at
length to be vested with an extraordinary importance, and proved the
source of the most dangerous errors. The anthropistic view of the world
which springs from them is in irreconcilable opposition to our monistic
system; indeed, it is at once disproved by our new cosmological
perspective.
Not only the three anthropistic dogmas, but many other notions of the
dualistic philosophy and orthodox religion, are found to be untenable
as soon as we regard them critically from the cosmological perspective
of our monistic system. We understand by that the comprehensive view
of the universe which we have from the highest point of our monistic
interpretation of nature. From that stand-point we see the truth of the
following "cosmological theorems," most of which, in our opinion, have
already been amply demonstrated:
(1) The universe, or the cosmos, is eternal, infinite, and illimitable.
(2) Its substance, with its two attributes (matter and energy), fills
infinite space, and is in eternal motion. (3) This motion runs on
through infinite time as an unbroken development, with a periodic
change from life to death, from evolution to devolution. (4) The
innumerable bodies which are scattered about the space-filling ether
all obey the same "law of substance;" while the rotating masses slowly
move towards their destruction and dissolution in one part of space
others are springing into new life and development in other quarters
of the universe. (5) Our sun is one of these unnumbered perishable
bodies, and our earth is one of the countless transitory planets that
encircle them. (6) Our earth has gone through a long process of cooling
before water, in liquid form (the first condition of organic life),
could settle thereon. (7) The ensuing biogenetic process, the slow
development and transformation of countless organic forms, must have
taken many millions of years--considerably over a hundred.[5] (8) Among
the different kinds of animals which arose in the later stages of the
biogenetic process on earth the vertebrates have far outstripped all
other competitors in the evolutionary race. (9) The most important
branch of the vertebrates, the mammals, were developed later (during
the triassic period) from the lower amphibia and the reptilia. (10) The
most perfect and most highly developed branch of the class mammalia is
the order of primates, which first put in an appearance, by development
from the lowest prochoriata, at the beginning of the Tertiary
period--at least three million years ago. (11) The youngest and most
perfect twig of the branch primates is man, who sprang from a series of
manlike apes towards the end of the Tertiary period. (12) Consequently,
the so-called "history of the world"--that is, the brief period of a
few thousand years which measures the duration of civilization--is an
evanescently short episode in the long course of organic evolution,
just as this, in turn, is merely a small portion of the history of
our planetary system; and as our mother-earth is a mere speck in the
sunbeam in the illimitable universe, so man himself is but a tiny grain
of protoplasm in the perishable framework of organic nature.
Nothing seems to me better adapted than this magnificent cosmological
perspective to give us the proper standard and the broad outlook
which we need in the solution of the vast enigmas that surround us.
It not only clearly indicates the true place of man in nature, but it
dissipates the prevalent illusion of man's supreme importance, and
the arrogance with which he sets himself apart from the illimitable
universe, and exalts himself to the position of its most valuable
element. This boundless presumption of conceited man has misled him
into making himself "the image of God," claiming an "eternal life" for
his ephemeral personality, and imagining that he possesses unlimited
"freedom of will." The ridiculous imperial folly of Caligula is but
a special form of man's arrogant assumption of divinity. Only when
we have abandoned this untenable illusion, and taken up the correct
cosmological perspective, can we hope to reach the solution of the
"riddles of the universe."
The uneducated member of a civilized community is surrounded with
countless enigmas at every step, just as truly as the savage. Their
number, however, decreases with every stride of civilization and of
science; and the monistic philosophy is ultimately confronted with but
one simple and comprehensive enigma--the "problem of substance." Still,
we may find it useful to include a certain number of problems under
that title. In the famous speech which Emil du Bois-Reymond delivered
in 1880, in the Leibnitz session of the Berlin Academy of Sciences,
he distinguished seven world-enigmas, which he enumerated as follows:
(1) The nature of matter and force. (2) The origin of motion. (3) The
origin of life. (4) The (apparently preordained) orderly arrangement
of nature. (5) The origin of simple sensation and consciousness. (6)
Rational thought, and the origin of the cognate faculty, speech. (7)
The question of the freedom of the will. Three of these seven enigmas
are considered by the orator of the Berlin Academy to be entirely
transcendental and insoluble--they are the first, second, and fifth;
three others (the third, fourth, and sixth) he considers to be capable
of solution, though extremely difficult; as to the seventh and last
"world-enigma," the freedom of the will, which is the one of the
greatest practical importance, he remains undecided.
As my monism differs materially from that of the Berlin orator, and as
his idea of the "seven great enigmas" has been very widely accepted,
it may be useful to indicate their true position at once. In my
opinion, the three transcendental problems (1, 2, and 5) are settled
by our conception of substance (_vide_ chap. xii.); the three which
he considers difficult, though soluble, (3, 4, and 6), are decisively
answered by our modern theory of evolution; the seventh and last, the
freedom of the will, is not an object for critical, scientific inquiry
at all, for it is a pure dogma, based on an illusion, and has no real
existence.
The means and methods we have chosen for attaining the solution of the
great enigma do not differ, on the whole, from those of all purely
scientific investigation--firstly, experience; secondly, inference.
Scientific experience comes to us by observation and experiment, which
involve the activity of our sense-organs in the first place, and,
secondly, of the inner sense-centres in the cortex of the brain. The
microscopic elementary organs of the former are the sense-cells; of the
latter, groups of ganglionic cells. The experiences which we derive
from the outer world by these invaluable instruments of our mental life
are then moulded into ideas by other parts of the brain, and these,
in their turn, are united in a chain of reasoning by association. The
construction of this chain may take place in two different ways, which
are, in my opinion, equally valuable and indispensable: _induction_
and _deduction_. The higher cerebral operations, the construction
of complicated chains of reasoning, abstraction, the formation of
concepts, the completion of the perceptive faculty by the plastic
faculty of the imagination--in a word, consciousness, thought, and
speculation--are functions of the ganglionic cells of the cortex of the
brain, just like the preceding simpler mental functions. We unite them
all in the supreme concept of _reason_.[6]
By reason only can we attain to a correct knowledge of the world and a
solution of its great problems. Reason is man's highest gift, the only
prerogative that essentially distinguishes him from the lower animals.
Nevertheless, it has only reached this high position by the progress of
culture and education, by the development of knowledge. The uneducated
man and the savage are just as little (or just as much) "rational"
as our nearest relatives among the mammals (apes, dogs, elephants,
etc.). Yet the opinion still obtains in many quarters that, besides
our godlike reason, we have two further (and even surer!) methods of
receiving knowledge--emotion and revelation. We must at once dispose
of this dangerous error. Emotion has nothing whatever to do with the
attainment of truth. That which we prize under the name of "emotion"
is an elaborate activity of the brain, which consists of feelings of
like and dislike, motions of assent and dissent, impulses of desire and
aversion. It may be influenced by the most diverse activities of the
organism, by the cravings of the senses and the muscles, the stomach,
the sexual organs, etc. The interests of truth are far from promoted
by these conditions and vacillations of emotion; on the contrary, such
circumstances often disturb that reason which alone is adapted to the
pursuit of truth, and frequently mar its perceptive power. No cosmic
problem is solved, or even advanced, by the cerebral function we call
emotion. And the same must be said of the so-called "revelation," and
of the "truths of faith" which it is supposed to communicate; they are
based entirely on a deception, consciously or unconsciously, as we
shall see in the sixteenth chapter.
We must welcome as one of the most fortunate steps in the direction
of a solution of the great cosmic problems the fact that of recent
years there is a growing tendency to recognize the two paths which
alone lead thereto--_experience_ and _thought_, or _speculation_--to
be of equal value, and mutually complementary. Philosophers have come
to see that pure speculation--such, for instance, as Plato and Hegel
employed for the construction of their _idealist_ systems--does not
lead to knowledge of reality. On the other hand, scientists have been
convinced that mere experience--such as Bacon and Mill, for example,
made the basis of their _realist_ systems--is insufficient of itself
for a complete philosophy. For these two great paths of knowledge,
sense-experience and rational thought, are two distinct cerebral
functions; the one is elaborated by the sense-organs and the inner
sense-centres, the other by the thought-centres, the great "centres
of association in the cortex of the brain," which lie between the
sense-centres. (Cf. cc. vii. and x.) True knowledge is only acquired
by combining the activity of the two. Nevertheless, there are still
many philosophers who would construct the world out of their own
inner consciousness, and who reject our empirical science precisely
because they have no knowledge of the real world. On the other hand,
there are many scientists who still contend that the sole object of
science is "the knowledge of facts, the objective investigation of
isolated phenomena"; that "the age of philosophy" is past, and science
has taken its place.[7] This one-sided over-estimation of experience
is as dangerous an error as the converse exaggeration of the value of
speculation. Both channels of knowledge are mutually indispensable.
The greatest triumphs of modern science--the cellular theory, the
dynamic theory of heat, the theory of evolution, and the law of
substance--are _philosophic achievements_; not, however, the fruit of
pure speculation, but of an antecedent experience of the widest and
most searching character.
At the commencement of the nineteenth century the great idealistic
poet, Schiller, gave his counsel to both groups of combatants, the
philosophers and the scientists:
"Does strife divide your efforts--no union bless your toil?
Will truth e'er be delivered if ye your forces rend?"
Since then the situation has, happily, been profoundly modified; while
both schools, in their different paths, have pressed onward towards the
same high goal, they have recognized their common aspiration, and they
draw nearer to a knowledge of the truth in mutual covenant. At the end
of the nineteenth century we have returned to that monistic attitude
which our greatest realistic poet, Goethe, had recognized from its very
commencement to be alone correct and fruitful.[8]
All the different philosophical tendencies may, from the point of
view of modern science, be ranged in two antagonistic groups; they
represent either a _dualistic_ or a _monistic_ interpretation of
the cosmos. The former is usually bound up with teleological and
idealistic dogmas, the latter with mechanical and realistic theories.
Dualism, in the widest sense, breaks up the universe into two entirely
distinct substances--the material world and an immaterial God, who
is represented to be its creator, sustainer, and ruler. Monism, on
the contrary (likewise taken in its widest sense), recognizes one
sole substance in the universe, which is at once "God and nature";
body and spirit (or matter and energy) it holds to be inseparable.
The extramundane God of dualism leads necessarily to theism; and the
intra-mundane God of the monist leads to pantheism.
The different ideas of _monism_ and _materialism_, and likewise
the essentially distinct tendencies of theoretical and practical
materialism, are still very frequently confused. As this and other
similar cases of confusion of ideas are very prejudicial, and give rise
to innumerable errors, we shall make the following brief observations,
in order to prevent misunderstanding:
I. Pure monism is identical neither with the theoretical materialism
that denies the existence of spirit, and dissolves the world into a
heap of dead atoms, nor with the theoretical spiritualism (lately
entitled "energetic" spiritualism by Ostwald) which rejects the notion
of matter, and considers the world to be a specially arranged group of
"energies" or immaterial natural forces.
II. On the contrary, we hold, with Goethe, that "matter cannot exist
and be operative without spirit, nor spirit without matter." We
adhere firmly to the pure, unequivocal monism of Spinoza: Matter, or
infinitely extended substance, and spirit (or energy), or sensitive and
thinking substance, are the two fundamental attributes or principal
properties of the all-embracing divine essence of the world, the
universal substance. (Cf. chap. xii.)
CHAPTER II
OUR BODILY FRAME
Fundamental Importance of Anatomy--Human Anatomy--Hippocrates,
Aristotle, Galen, Vesalius--Comparative Anatomy--Georges
Cuvier--Johannes Müller--Karl Gegenbaur--Histology--The Cellular
Theory--Schleiden and Schwann--Kölliker--Virchow--Man a
Vertebrate, a Tetrapod, a Mammal, a Placental, a Primate--Prosimiæ
and Simiæ--The Catarrhinæ--Papiomorphic and Anthropomorphic
Apes--Essential Likeness of Man and the Ape in Corporal Structure
All biological research, all investigation into the forms and vital
activities of organisms, must first deal with the visible body, in
which the morphological and physiological phenomena are observed. This
fundamental rule holds good for man just as much as for all other
living things. Moreover, the inquiry must not confine itself to mere
observation of the outer form; it must penetrate to the interior, and
study both the general plan and the minute details of the structure.
The science which pursues this fundamental investigation in the
broadest sense is anatomy.
The first stimulus to an inquiry into the human frame arose, naturally,
in medicine. As it was usually practised by the priests in the older
civilizations, we may assume that these highest representatives of
the education of the time had already acquired a certain amount
of anatomical knowledge two thousand years before Christ, or even
earlier. We do not, however, find more exact observations, founded
on the dissection of mammals, and applied, by analogy, to the human
frame, until we come to the Greek scientists of the sixth and fifth
centuries before Christ--Empedocles (of Agrigentum) and Democritus
(of Abdera), and especially the most famous physician of classic
antiquity, Hippocrates (of Cos). It was from these and other sources
that the great Aristotle, the renowned "father of natural history,"
equally comprehensive as investigator and philosopher, derived his
first knowledge. After him only one anatomist of any consequence is
found in antiquity, the Greek physician Claudius Galenus (of Pergamus),
who developed a wealthy practice in Rome in the second century after
Christ, under the Emperor Marcus Aurelius. All these ancient anatomists
acquired their knowledge, as a rule, not by the dissection of the human
body itself--which was then sternly forbidden--but by a study of the
bodies of the animals which most closely resembled man, especially the
apes; they were all, indeed, comparative anatomists.
The triumph of Christianity and its mystic theories meant retrogression
to anatomy, as it did to all the other sciences. The popes were
resolved above all things to detain humanity in ignorance; they rightly
deemed a knowledge of the human organism to be a dangerous source
of enlightenment as to our true nature. During the long period of
thirteen centuries the writings of Galen were almost the only source
of human anatomy, just as the works of Aristotle were for the whole
of natural history. It was not until the sixteenth century, when the
spiritual tyranny of the papacy was broken by the Reformation, and the
geocentric theory, so intimately connected with papal doctrine, was
destroyed by the new cosmic system of Copernicus, that the knowledge
of the human frame entered upon a new period of progress. The great
anatomists, Vesalius (of Brussels), and Eustachius and Fallopius
(of Modena), advanced the knowledge of our bodily structure so much
by their own thorough investigations that little remained for their
numerous followers to do, with regard to the more obvious phenomena,
except the substantiation of details. Andreas Vesalius, as courageous
as he was talented and indefatigable, was the pioneer of the movement;
he completed in his twenty-eighth year (1543) that great and systematic
work _De humani corporis fabrica_; he gave to the whole of human
anatomy a new and independent scope and a more solid foundation. On
that account he was, at a later date, at Madrid--where he was physician
to Charles V. and Philip II.--condemned to death by the Inquisition as
a magician. He only escaped by undertaking a pilgrimage to Jerusalem;
in returning he suffered shipwreck on the Isle of Zante, and died there
in misery and destitution.
The great merit of the nineteenth century, as far as our knowledge of
the human frame is concerned, lies in the founding of two new lines
of research of immense importance--comparative anatomy and histology,
or microscopic anatomy. The former was intimately associated with
human anatomy from the very beginning; indeed, it had to supply the
place of the latter so long because the dissection of human corpses
was a crime visited with capital punishment--that was the case even
in the fifteenth century! But the many anatomists of the next three
centuries devoted themselves mainly to a more accurate study of the
human organism. The elaborate science which we now call comparative
anatomy was born in the year 1803, when the great French zoologist
Georges Cuvier (a native of Mömpelgard, in Alsace) published his
profound _Leçons sur l'anatomie comparée_, and endeavored to formulate,
for the first time, definite laws as to the organism of man and the
beasts. While his predecessors--among whom was Goethe in 1790--had
mainly contented themselves with comparing the skeleton of man with
those of other animals, Cuvier's broader vision took in the whole
of the animal organization. He distinguished therein four great and
mutually independent types: Vertebrata, Articulata, Mollusca, and
Radiata. This advance was of extreme consequence for our "question
of all questions," since it clearly brought out the fact that man
belonged to the vertebral type, and differed fundamentally from all
the other types. It is true that the keen-sighted Linné had already,
in his _Systema Natuae_, made a great step in advance by assigning
man a definite place in the class of mammals; he had even drawn up
the three groups of half-apes, apes, and men (_Lemur_, _simia_, and
_homo_) in the order of primates. But his keen, systematic mind was
not furnished with that profound empirical foundation, supplied by
comparative anatomy, which Cuvier was the first to attain. Further
developments were added by the great comparative anatomists of our own
century--Friedrich Meckel (Halle), Johannes Müller (Berlin), Richard
Owen, T. Huxley, and Karl Gegenbaur (Jena, subsequently Heidelberg).
The last-named, in applying the evolutionary theory, which Darwin had
just established, to comparative anatomy, raised his science to the
front rank of biological studies. The numerous comparative anatomical
works of Gegenbaur are, like his well-known _Manual of Human Anatomy_,
equally distinguished by a thorough empirical acquaintance with their
immense multitudes of facts, and by a comprehensive control of his
material, and its philosophic appreciation in the evolutionary sense.
His recent _Comparative Anatomy of the Vertebrata_ establishes the
solid foundation on which our conviction of the vertebral character of
man in every aspect is chiefly based.
Microscopic anatomy has been developed, in the course of the present
century, in a very different fashion from comparative anatomy. At
the beginning of the century (1802) a French physician, Bichat, made
an attempt to dissect the organs of the human body into their finer
constituents by the aid of the microscope, and to show the connection
of these various _tissues_ (_hista_, or _tela_). This first attempt
led to little result, because the scientist was ignorant of the one
common element of all the different tissues. This was first discovered
(1838) in the shape of the _cell_, in the plant world, by Matthias
Schleiden, and immediately afterwards proved to be the same in the
animal world by Theodor Schwann, the pupil and assistant of Johannes
Müller at Berlin. Two other distinguished pupils of this great master,
who are still living, Albert Kölliker and Rudolph Virchow, took up
the cellular theory, and the theory of tissues which is founded on
it, in the sixties, and applied them to the human organism in all its
details, both in health and disease; they proved that, in man and
all other animals, every tissue is made up of the same microscopic
particles, the _cells_, and these "elementary organisms" are the real,
self-active citizens which, in combinations of millions, constitute
the "cellular state," our body. All these cells spring from one simple
cell, the _cytula_, or impregnated ovum, by continuous subdivision.
The general structure and combination of the tissues are the same in
man as in the other vertebrates. Among these the mammals, the youngest
and most highly developed class take precedence, in virtue of certain
special features which were acquired late. Such are, for instance, the
microscopic texture of the hair, of the glands of the skin, and of the
breasts, and the corpuscles of the blood, which are quite peculiar to
mammals, and different from those of the other vertebrates; man, even
in these finest histological relations, is a _true mammal_.
The microscopic researches of Albert Kölliker and Franz Leydig (at
Würzburg) not only enlarged our knowledge of the finer structure of man
and the beasts in every direction, but they were especially important
in the light of their connection with the evolution of the cell and
the tissue; they confirmed the great theory of Carl Theodor Siebold
(1845) that the lowest animals, the Infusoria and the Rhizopods, are
unicellular organisms.
Our whole frame, both in its general plan and its detailed structure,
presents the characteristic type of the vertebrates. This most
important and most highly developed group in the animal world was
first recognized in its natural unity in 1801 by the great Lamarck;
he embraced under that title the four higher animal groups of
Linné--mammals, birds, amphibia, and fishes. To these he opposed the
two lower classes, insects and worms, as invertebrates. Cuvier (1812)
established the unity of the vertebrate type on a firmer basis by
his comparative anatomy. It is quite true that all the vertebrates,
from the fish up to man, agree in every essential feature; they all
have a firm internal skeleton, a framework of cartilage and bone,
consisting principally of a vertebral column and a skull; the advanced
construction of the latter presents many variations, but, on the whole,
all may be reduced to the same fundamental type. Further, in all
vertebrates the "organ of the mind," the central nervous system, in
the shape of a spinal cord and a brain, lies at the back of this axial
skeleton. Moreover, what we said of its bony environment, the skull,
is also true of the brain--the instrument of consciousness and all the
higher functions of the mind; its construction and size present very
many variations in detail, but its general characteristic structure
remains always the same.
We meet the same phenomenon when we compare the rest of our organs with
those of the other vertebrates; everywhere, in virtue of heredity,
the original plan and the relative distribution of the organs remain
the same, although, through adaptation to different environments,
the size and the structure of particular sections offer considerable
variation. Thus we find that in all cases the blood circulates in
two main blood-vessels, of which one--the aorta--passes over the
intestine, and the other--the principal vein--passes underneath, and
that by the broadening out of the latter in a very definite spot a
heart has arisen; this "ventral heart" is just as characteristic of all
vertebrates as the "dorsal heart" is of the articulata and mollusca.
Equally characteristic of all vertebrates is the early division of
the intestinal tube into a "head-gut" (or gill-gut), which serves in
respiration, and a "body-gut" (or liver-gut), which co-operates with
the liver in digestion; so are, likewise, the ramification of the
muscular system, the peculiar structure of the urinary and sexual
organs, and so forth. In all these anatomical relations _man is a true
vertebrate_.
Aristotle gave the name of four-footed, or tetrapoda, to all the higher
warm-blooded animals which are distinguished by the possession of two
pairs of legs. The category was enlarged subsequently, and its title
changed into the Latin "quadrupeda," when Cuvier proved that even
"two-legged" birds and men are really "four-footed"; he showed that the
internal skeleton of the four legs in all the higher land-vertebrates,
from the amphibia up to man, was originally constructed after the same
pattern out of a definite number of members. The "arm" of man and the
"wing" of bats and birds have the same typical skeleton as the foreleg
of the animals which are conspicuously "four-footed."
The anatomical unity of the fully developed skeleton in the four limbs
of all tetrapods is very important. In order to appreciate it fully
one has only to compare carefully the skeleton of a salamander or a
frog with that of a monkey or a man. One perceives at once that the
humeral zone in front and the pelvic zone behind are made up of the
same principal parts as in the rest of the quadrupeds. We find in all
cases that the first section of the leg proper consists of one strong
marrow-bone (the _humerus_, in the forearm; the _femur_, behind);
the second part, on the contrary, originally always consists of two
bones (the _ulna_ and _radius_, in front; the _fibula_ and _tibia_,
behind). When we further compare the developed structure of the foot
proper we are surprised to find that the small bones of which it is
made up are also similarly arranged and distributed in every case: in
the front limb the three groups of bones of the forefoot (or "hand")
correspond in all classes of the tetrapoda: (1) the _carpus_, (2)
the _metacarpus_, (3) the five fingers (_digiti anteriores_); in the
rear limb, similarly, we have always the same three osseous groups of
the hind foot: (1) the _tarsus_, (2) the _metatarsus_, and (3) the
five toes (_digiti posteriores_). It was a very difficult task to
reduce all these little bones to one primitive type, and to establish
the equivalence (or homology) of the separate parts in all cases;
they present extreme variations of form and construction in detail,
sometimes being partly fused together and losing their individuality.
This great task was first successfully achieved by the most eminent
comparative anatomist of our day, Karl Gegenbaur. He pointed out,
in his _Researches into the Comparative Anatomy of the Vertebrata_
(1864), how this characteristic "five-toed leg" of the land tetrapods
originally (not before the Carboniferous period) arose out of the
radiating fin (the breast-fin, or the belly-fin) of the ancient
fishes. He had also, in his famous _Researches into the Skull of the
Vertebrata_ (1872), deduced the younger skull of the tetrapods from the
oldest cranial form among the fishes, that of the shark.
It is especially remarkable that the original number of the toes (five)
on each of the four feet, which first appeared in the old amphibia
of the Carboniferous period, has, in virtue of a strict heredity,
been preserved even to the present day in man. Also, naturally and
harmoniously, the typical construction of the joints, ligaments,
muscles, and nerves of the two pairs of legs has, in the main, remained
the same as in the rest of the "four-footed." In all these important
relations _man is a true tetrapod_.
The mammals are the youngest and most advanced class of the vertebrates.
It is true they are derived from the older class of amphibia, like
birds and reptiles: yet they are distinguished from all the other
tetrapods by a number of very striking anatomical features. Externally,
there is the clothing of the skin with hair, and the possession of
two kinds of skin glands--the sweat glands and the sebaceous glands.
A local development of these glands on the abdominal skin gave
rise (probably during the Triassic period) to the organ which is
especially characteristic of the class, and from which it derives its
name--the _mammarium_. This important instrument of lactation is made
up of milk glands (_mammae_) and the "mammar-pouches" (folds of the
abdominal skin); in its development the teats appear, through which
the young mammal sucks its mother's milk. In internal structure the
most remarkable feature is the possession of a complete diaphragm, a
muscular wall which, in all mammals--and _only_ in mammals--separates
the thoracic from the abdominal cavity; in all other vertebrates
there is no such separation. The skull of mammals is distinguished
by a number of remarkable formations, especially in the maxillary
apparatus (the upper and lower jaws, and the temporal bones). Moreover,
the brain, the olfactory organ, the heart, the lungs, the internal
and external sexual organs, the kidneys, and other parts of the body
present special peculiarities, both in general and detailed structure,
in the mammals; all these, taken collectively, point unequivocally
to an early derivation of the mammals from the older groups of the
reptiles and amphibia, which must have taken place, at the latest, in
the Triassic period--at least twelve million years ago! In all these
important characteristics _man is a true mammal_.
The numerous orders (12-33) which modern systematic zoology
distinguishes in the class of mammals had been arranged in 1816
(by Blainville) in three natural groups, which still hold good as
sub-classes: (1) the monotrema, (2) the marsupialia, and (3) the
placentalia. These three sub-classes not only differ in the important
respect of bodily structure and development, but they correspond, also,
to three different historical stages in the formation of the class,
as we shall see later on. The monotremes of the Triassic period were
followed by the marsupials of the Jurassic, and these by the placentals
of the Cretaceous. Man belongs to this, the youngest, sub-class; for
he presents in his organization all the features which distinguish
the placentals from the marsupials and the still older monotremes.
First of all, there is the peculiar organ which gives a name to the
placentals--the _placenta_. It serves the purpose of nourishing the
young mammal embryo for a long time during its enclosure in the
mother's womb; it consists of blood-bearing tufts which grow out of the
chorion surrounding the embryo, and penetrate corresponding cavities in
the mucous membrane of the maternal uterus; the delicate skin between
the two structures is so attenuated in this spot that the nutriment in
the mother's blood can pass directly into the blood of the child. This
excellent contrivance for nourishing the embryo, which makes its first
appearance at a somewhat late date, gives the foetus the opportunity
of a longer maintenance and a higher development in the protecting
womb; it is wanting in the _implacentalia_, the two older sub-classes
of the marsupials and the monotremes. There are, likewise, other
anatomical features, particularly the higher development of the brain
and the absence of the marsupial bone, which raise the placentals above
all their implacental ancestors. In all these important particulars
_man is a true placental_.
The very varied sub-class of the placentals has been recently
subdivided into a great number of orders; they are usually put at from
ten to sixteen, but when we include the important extinct forms which
have been recently discovered the number runs up to from twenty to
twenty-six. In order to facilitate the study of these numerous orders,
and to obtain a deeper insight into their kindred construction, it
is very useful to form them into great natural groups, which I have
called "legions." In my latest attempt[9] to arrange the advanced
system of placentals in phylogenetic order I have substituted eight
of these legions for the twenty-six orders, and shown that these may
be reduced to four main groups. These, in turn, are traceable to one
common ancestral group of all the placentals, their fossil ancestors,
the _prochoriata_ of the Cretaceous period. These are directly
connected with the marsupial ancestors of the Jurassic period. We
will only specify here, as the most important living representatives
of these four main groups, the rodentia, the ungulata, the carnivora,
and the primates. To the legion of the primates belong the prosimiæ
(half-apes), the simiæ (real apes), and man. All the members of these
three orders agree in many important features, and are at the same
time distinguished by these features from the other twenty-three
orders of placentals. They are especially conspicuous for the length
of their bones, which were originally adapted to their arboreal manner
of life. Their hands and feet are five-fingered, and the long fingers
are excellently suited for grasping and embracing the branches of
trees; they are provided, either partially or completely, with nails,
but have no claws. The dentition is complete, containing all four
classes--incisors, canine, premolars, and molars. Primates are also
distinguished from all the other placentals by important features in
the special construction of the skull and the brain; and these are the
more striking in proportion to their development and the lateness of
their appearance in the history of the earth. In all these important
anatomical features our human organism agrees with that of all the
other primates: _man is a true primate_.
An impartial and thorough comparison of the bodily structure of the
primates forces us to distinguish two orders in this most advanced
legion of the mammalia--half-apes (_prosimiae_ or _hemipitheci_) and
apes (_simiae_ or _pitheci_). The former seem in every respect to be
the lower and older, the latter to be the higher and younger order. The
womb of the half-ape is still double, or two-horned, as it is in all
the other mammals. In the true ape, on the contrary, the right and left
wombs have completely amalgamated; they blend into a pear-shaped womb,
which the human mother possesses besides the ape. In the skull of the
apes, just as in that of man, the orbits of the eyes are completely
separated from the temporal cavities by an osseous partition; in
the _prosimiae_ this is either entirely wanting or very imperfect.
Finally, the cerebrum of the _prosimia_ is either quite smooth or very
slightly furrowed, and proportionately small; that of the true ape is
much larger, and the gray bed especially, the organ of higher psychic
activity, is much more developed; the characteristic convolutions
and furrows appear on its surface exactly in proportion as the ape
approaches to man. In these and other important respects, particularly
in the construction of the face and the hands, _man presents all the
anatomical marks of a true ape_.
The extensive order of apes was divided by Geoffroi, in 1812, into
two sub-orders, which are still universally accepted in systematic
zoology--New World and Old World monkeys, according to the hemisphere
they respectively inhabit. The American "New World" monkeys are called
_Platyrrhinae_ (flat-nosed); their nose is flat, and the nostrils
divergent, with a broad partition. The "Old World" monkeys, on the
contrary, are called collectively _Catarrhinae_ (narrow-nosed); their
nostrils point downward, like man's, and the dividing cartilage is
narrow. A further difference between the two groups is that the
tympanum is superficial in the _platyrrhinae_, but lies deeper,
inside the petrous bone, in the _catarrhinae_; in the latter a long
and narrow bony passage has been formed, while in the former it is
still short and wide, or even altogether wanting. Finally, we have a
much more important and decisive difference between the two groups in
the circumstance that all the Old World monkeys have the same teeth
as man--_i. e._, twenty deciduous and thirty-two permanent teeth
(two incisors, one canine, two premolars, and three molars in each
half of the jaw). The New World monkeys, on the other hand, have an
additional premolar in each half-jaw, or thirty-six teeth altogether.
The fact that these anatomical differences of the two simian groups
are universal and conspicuous, and that they harmonize with their
geographical distribution in the two hemispheres, fully authorizes
a sharp systematic division of the two, as well as the phylogenetic
conclusion that for a very long period (for more than a million years)
the two sub-orders have been developing quite independently of each
other in the western and eastern hemispheres. That is a most important
point in view of the genealogy of our race; for man bears all the marks
of a _true catarrhina_; he has descended from some extinct member of
this sub-order in the Old World.
The numerous types of _catarrhinae_ which still survive in Asia and
Africa have been formed into two sections for some time--the tailed,
doglike apes (the _cynopitheci_) and the tailless, manlike apes (the
_anthropomorpha_). The latter are much nearer to man than the former,
not only in the absence of a tail and in the general build of the body
(especially of the head), but also on account of certain features
which are unimportant in themselves but very significant in their
constancy. The sacrum of the anthropoid ape, like that of man, is made
up of the fusion of five vertebræ; that of the _cynopithecus_ consists
of three (more rarely four) sacral vertebræ. The premolar teeth of
the _cynopitheci_ are greater in length than breadth; those of the
_anthropomorpha_ are broader than they are long; and the first molar
has four protuberances in the former, five in the latter. Furthermore,
the outer incisor of the lower jaw is broader than the inner one
in the manlike apes and man; in the doglike ape it is the smaller.
Finally, there is a special significance in the fact, established by
Selenka in 1890, that the anthropoid apes share with man the peculiar
structure of the discoid _placenta_, the _decidua reflexa_, and the
pedicle of the allantois. In fact, even a superficial comparison of
the bodily structure of the _anthropomorpha_ which still survive makes
it clear that both the Asiatic (the orang-outang and the gibbous ape)
and the African (the gorilla and chimpanzee) representatives of this
group are nearer to man in build than any of the _cynopitheci_. Under
the latter group we include the dog-faced papiomorpha, the baboon,
and the long-tailed monkey, at a very low stage. The anatomical
difference between these low papiomorpha and the most highly developed
anthropoid apes is greater in every respect, whatever organ we take
for comparison, than the difference between the latter and man.
This instructive fact was established with great penetration by the
anatomist Robert Hartmann, in his work on _The Anthropoid Apes_;[10]
he proposed to divide the order of _Simiae_ in a new way--namely, into
the two great groups of _primaria_ (man and the anthropoid ape) and the
_simiae_ proper, or _pitheci_ (the rest of the catarrhinæ and all the
platyrrhinæ). In any case, we have a clear proof of _the close affinity
of man and the anthropoid ape_.
Thus comparative anatomy proves to the satisfaction of every
unprejudiced and critical student the significant fact that the body of
man and that of the anthropoid ape are not only peculiarly similar, but
they are practically one and the same in every important respect. The
same two hundred bones, in the same order and structure, make up our
inner skeleton; the same three hundred muscles effect our movements;
the same hair clothes our skin; the same groups of ganglionic cells
build up the marvellous structure of our brain; the same four chambered
heart is the central pulsometer in our circulation; the same thirty-two
teeth are set in the same order in our jaws; the same salivary,
hepatic, and gastric glands compass our digestive process; the same
reproductive organs insure the maintenance of our race.
It is true that we find, on close examination, certain minor
differences in point of size and shape in most of the organs of man
and the ape; but we discover the same, or similar, differences
between the higher and lower races of men, when we make a careful
comparison--even, in fact, in a minute comparison of the various
individuals of our own race. We find no two persons who have exactly
the same size and form of nose, ears, eyes, and so forth. One has
only to compare attentively these special features in many different
persons in any large company to convince one's self of the astonishing
diversity of their construction and the infinite variability of
specific forms. Not infrequently even two sisters are so much unlike
as to make their origin from the same parents almost incredible. Yet
all these individual variations do not weaken the significance of the
fundamental similarity of structure; they are traceable to certain
minute differences in the growth of the individual features.
CHAPTER III
OUR LIFE
Development of Physiology in Antiquity and the Middle Ages:
Galen--Experiment and Vivisection--Discovery of the Circulation
of the Blood by Harvey--Vitalism: Haller--Teleological and
Vitalistic Conception of Life--Mechanical and Monistic View
of the Physiological Processes--Comparative Physiology in the
Nineteenth Century: Johannes Müller--Cellular Physiology: Max
Verworn--Cellular Pathology: Virchow--Mammal Physiology--Similarity
of all Vital Activity in Man and the Ape
It is only in the nineteenth century that our knowledge of human life
has attained the dignity of a genuine, independent science; during the
course of the century it has developed into one of the highest, most
interesting, and most important branches of knowledge. This "science
of the vital functions," physiology, had, it is true, been regarded
at a much earlier date as a desirable, if not a necessary, condition
of success in medical treatment, and had been constantly associated
with anatomy, the science of the structure of the body. But it was
only much later, and much more slowly, than the latter that it could
be thoroughly studied, as it had to contend with much more serious
difficulties.
The idea of life, as the opposite of death, naturally became the
subject of speculation at a very early age. In the living man, just
as in other living animals, there were certain peculiar changes,
especially movements, which were wanting in lifeless nature:
spontaneous locomotion, the beat of the heart, the drawing of the
breath, speech, and so forth. But the discrimination of such "organic
movements" from similar phenomena in inorganic bodies was by no means
easy, and was frequently impossible; the flowing stream, the flickering
flame, the rushing wind, the falling rock, seemed to man to exhibit
the same movements. It was quite natural that primitive man should
attribute an independent life to these "dead" bodies. He knew no more
of the real sources of movement in the one case than in the other.
We find the earliest scientific observations on the nature of man's
vital functions (as well as on his structure) in the Greek natural
philosophers and physicians of the sixth and fifth centuries before
Christ. The best collection of the physiological facts which were known
at that time is to be found in the _Natural History_ of Aristotle; a
great number of his assertions were probably taken from Democritus
and Hippocrates. The school of the latter had already made attempts
to explain the mystery; it postulated as the ultimate source of life
in man and the beasts a volatile "spirit of life" (Pneuma); and
Erasistratus (280 B.C.) already drew a distinction between the lower
and the higher "spirit of life," the _pneuma zoticon_ in the heart and
the _pneuma psychicon_ in the brain.
The credit of gathering these scattered truths into unity, and of
making the first attempt at a systematic physiology, belongs to the
great Greek physician Galen; we have already recognized in him the
first great anatomist of antiquity (cf. p. 23). In his researches
into the organs of the body he never lost sight of the question of
their vital activity, their functions; and even in this direction he
proceeded by the same comparative method, taking for his principal
study the animals which approach nearest to man. Whatever he learned
from these he applied directly to man. He recognized the value of
physiological experiment; in his vivisection of apes, dogs, and
swine he made a number of interesting experiments. Vivisection has
been made the object of a violent attack in recent years, not only
by the ignorant and narrow-minded, but by theological enemies of
knowledge and by perfervid sentimentalists; it is, however, one of the
_indispensable_ methods of research into the nature of life, and has
given us invaluable information on the most important questions. This
was recognized by Galen seventeen hundred years ago.
Galen reduces all the different functions of the body to three
groups, which correspond to the three forms of the _pneuma_, or vital
spirit. The _pneuma psychicon_--the soul--which resides in the brain
and nerves, is the cause of thought, sensation, and will (voluntary
movement); the _pneuma zoticon_--the heart--is responsible for the beat
of the heart, the pulse, and the temperature; the _pneuma physicon_,
seated in the liver, is the source of the so-called vegetative
functions, digestion and assimilation, growth and reproduction.
He especially emphasized the renewal of the blood in the lungs,
and expressed a hope that we should some day succeed in isolating
the permanent element in the atmosphere--the _pneuma_, as he calls
it--which is taken into the blood in respiration. More than fifteen
centuries elapsed before this _pneuma_--oxygen--was discovered by
Lavoisier.
In human physiology, as well as in anatomy, the great system of Galen
was for thirteen centuries the _Codex aureus_, the inviolable source of
all knowledge. The influence of Christianity, so fatal to scientific
culture, raised the same insuperable obstacles in this as in every
other branch of secular knowledge. Not a single scientist appeared
from the third to the sixteenth century who dared to make independent
research into man's vital activity, and transcend the limits of the
Galenic system. It was not until the sixteenth century that experiments
were made in that direction by a number of distinguished physicians
and anatomists (Paracelsus, Servetus, Vesalius, and others). In 1628
Harvey published his great discovery of the circulation of the blood,
and showed that the heart is a pump, which drives the red stream
unceasingly through the connected system of arteries and veins by a
rhythmic, unconscious contraction of its muscles. Not less important
were Harvey's researches into the procreation of animals, as a result
of which he formulated the well-known law: "Every living thing comes
from an egg" (_omne vivum ex ovo_).
The powerful impetus which Harvey gave to physiological observation and
experiment led to a great number of discoveries in the sixteenth and
seventeenth centuries. These were co-ordinated for the first time by
the learned Albrecht Haller about the middle of the last century; in
his great work, _Elementa Physiologiae_, he established the inherent
importance of the science, independently of its relation to practical
medicine. In postulating, however, a special "sensitive force or
sensibility" for neural action, and a special "irritability" for
muscular movement, Haller gave strong support to the erroneous idea of
a specific "vital force" (_vis vitalis_).
For more than a century afterwards, from the middle of the eighteenth
until the middle of the nineteenth century, medicine and (especially)
physiology were dominated by the old idea that a certain number of the
vital processes may be traced to physical and chemical causes, but that
others are the outcome of a special vital force which is independent
of physical agencies. However much scientists differed in their
conceptions of its nature and its relation to the "soul," they were all
agreed as to its independence of, and essential distinction from, the
chemico-physical forces of ordinary "matter"; it was a self-contained
force (_archaeus_), unknown in inorganic nature, which compelled
ordinary forces into its service. Not only the distinctly psychical
activity, the sensibility of the nerves and the irritability of the
muscles, but even the phenomena of sense activity, of reproduction,
and of development seemed so wonderful and so mysterious in their
sources that it was impossible to attribute them to simple physical
and chemical processes. As the free activity of the vital force
was purposive and conscious, it led, in philosophy, to a complete
_teleology_; especially did this seem indisputable when even the
"critical" philosopher Kant had acknowledged, in his famous critique
of the teleological position, that, though the mind's authority to
give a mechanical interpretation of all phenomena is theoretically
unlimited, yet its actual capacity for such interpretation does not
extend to the phenomena of organic life; here we are compelled to have
recourse to a _purposive_--therefore _supernatural_--principle. This
divergence of the _vital_ phenomena from the _mechanical_ processes of
life became, naturally, more conspicuous as science advanced in the
chemical and physical explanation of the latter. The circulation of the
blood and a number of other phenomena could be traced to mechanical
agencies; respiration and digestion were attributable to chemical
processes like those we find in inorganic nature. On the other hand,
it seemed impossible to do this with the wonderful performances of the
nerves and muscles, and with the characteristic life of the mind; the
co-ordination of all the different forces in the life of the individual
seemed also beyond such a mechanical interpretation. Hence there arose
a complete physiological dualism--an essential distinction was drawn
between inorganic and organic nature, between mechanical and vital
processes, between material force and life force, between the body and
the soul. At the beginning of the nineteenth century this vitalism was
firmly established in France by Louis Dumas, and in Germany by Reil.
Alexander Humboldt had already published a poetical presentation of it
in 1795, in his narrative of the _Legend of Rhodes_; it is repeated,
with critical notes, in his _Views of Nature_.
In the first half of the seventeenth century the famous philosopher
Descartes, starting from Harvey's discovery of the circulation of the
blood, put forward the idea that the body of man, like that of other
animals, is merely an intricate machine, and that its movements take
place under the same mechanical laws as the movements of an automaton
of human construction. It is true that Descartes, at the same time,
claimed for man the exclusive possession of a perfectly independent,
immaterial soul, and held that its subjective experience, thought,
was the only thing in the world of which we have direct and certain
cognizance ("_Cogito, ergo sum_"). Yet this dualism did not prevent
him from doing much to advance our knowledge of the mechanical life
processes in detail. Borelli followed (1660) with a reduction of the
movements of the animal body to purely physical laws, and Sylvius
endeavored, about the same time, to give a purely chemical explanation
of the phenomena of digestion and respiration; the former founded the
_iatromechanical_, the latter the _iatrochemical_, school of medicine.
However, these rational tendencies towards a natural, mechanical
explanation of the phenomena of life did not attain to a universal
acceptance and application; in the course of the eighteenth century
they fell entirely away before the advance of teleological vitalism.
The final disproof of the latter and a return to mechanism only became
possible with the happy growth of the new science of comparative
physiology in the forties of the present century.
Our knowledge of the vital functions, like our knowledge of the
structure of the human body, was originally obtained, for the most
part, not by direct observation of the human organism itself, but by
a study of the more closely related animals among the vertebrates,
especially the mammals. In this sense the very earliest beginning
of human anatomy and physiology was "comparative." But the distinct
science of "comparative physiology," which embraces the whole sphere
of life phenomena, from the lowest animal up to man, is a triumph of
the nineteenth century. Its famous creator was Johannes Müller, of
Berlin (born, the son of a shoemaker, at Coblentz, in 1801). For fully
twenty-five years--from 1833 to 1858--this most versatile and most
comprehensive biologist of our age evinced an activity at the Berlin
University, as professor and investigator, which is only comparable
with the associated work of Haller and Cuvier. Nearly every one of the
great biologists who have taught and worked in Germany for the last
sixty years was, directly or indirectly, a pupil of Johannes Müller.
Starting from the anatomy and physiology of man, he soon gathered all
the chief groups of the higher and lower animals within his sphere
of comparison. As, moreover, he compared the structure of extinct
animals with the living, and the healthy organism with the diseased,
endeavoring to bring together all the phenomena of life in a truly
philosophic fashion, he attained a biological knowledge far in advance
of his predecessors.
The most valuable fruit of these comprehensive studies of Johannes
Müller was his _Manual of Human Physiology_. This classical work
contains much more than the title indicates; it is the sketch of
a comprehensive "comparative biology." It is still unsurpassed in
respect of its contents and range of investigation. In particular,
we find the methods of observation and experiment applied in it as
masterfully as the philosophic processes of induction and deduction.
Müller was originally a vitalist, like all the physiologists of his
time. Nevertheless, the current idea of a vital force took a novel
form in his speculations, and gradually transformed itself into the
very opposite. For he attempted to explain the phenomena of life
mechanically in every department of physiology. His "transfigured"
vital force was not _above_ the physical and chemical laws of the rest
of nature but entirely bound up with them. It was, in a word, nothing
more than life itself--that is, the sum of all the movements which we
perceive in the living organism. He sought especially to give them
the same mechanical interpretation in the life of the senses and of
the mind as in the working of the muscles; the same in the phenomena
of circulation, respiration, and digestion as in generation and
development. Müller's success was chiefly due to the fact that he
always began with the simplest life phenomena of the lowest animals,
and followed them step by step in their gradual development up to the
very highest, to man. In this his method of _critical comparison_
proved its value both from the physiological and from the anatomical
point of view. Johannes Müller is, moreover, the only great scientist
who has equally cultivated these two branches of research, and combined
them with equal brilliancy. Immediately after his death his vast
scientific kingdom fell into four distinct provinces, which are now
nearly always represented by four or more chairs--human and comparative
anatomy, pathological anatomy, physiology, and the history of
evolution. This sudden division of Müller's immense realm of learning
in 1858 has been compared to the dissolution of the empire which
Alexander the Great had consolidated and ruled.
Among the many pupils of Johannes Müller who, either during his
lifetime or after his death, labored hard for the advancement of the
various branches of biology, one of the most fortunate--if not the
most important--was Theodor Schwann. When the able botanist Schleiden,
in 1838, indicated the cell as the common elementary organ of all
plants, and proved that all the different tissues of the plant are
merely combinations of cells, Johannes Müller recognized at once the
extraordinary possibilities of this important discovery. He himself
sought to point out the same composition in various tissues of the
animal body--for instance, in the spinal cord of vertebrates--and
thus led his pupil, Schwann, to extend the discovery to all the
animal tissues. This difficult task was accomplished by Schwann in
his _Microscopic Researches into the Accordance in the Structure and
Growth of Plants and Animals_ (1839). Thus was the foundation laid
of the "cellular theory," the profound importance of which, both in
physiology and anatomy, has become clearer and more widely recognized
in each subsequent year. Moreover, it was shown by two other pupils
of Johannes Müller that the activity of all organisms is, in the
ultimate analysis, the activity of the components of their tissues, the
microscopic cells--these were the able physiologist Ernst Brücke, of
Vienna, and the distinguished histologist Albert Kölliker, of Würzburg.
Brücke correctly denominated the cells the "elementary organisms," and
showed that, in the body of man and of all other animals, they are the
only actual, independent factors of the life process. Kölliker earned
special distinction, not only in the construction of the whole science
of histology, but particularly by showing that the animal ovum and its
products are simple cells.
Still, however widely the immense importance of the cellular theory for
all biological research was acknowledged, the "cellular physiology"
which is based on it only began an independent development very
recently. In this Max Verworn (of Jena) earned a twofold distinction.
In his _Psycho-physiological Studies of the Protistae_ (1889) he
showed, as a result of an ingenious series of experimental researches,
that the "theory of a cell-soul" which I put forward in 1866[11]
is completely established by an accurate study of the unicellular
protozoa, and that "the psychic phenomena of the protistæ form the
bridge which unites the chemical processes of inorganic nature with
the mental life of the highest animals." Verworn has further developed
these views, and based them on the modern theory of evolution, in
his _General Physiology_. This distinguished work returns to the
comprehensive point of view of Johannes Müller, in opposition to the
one-sided and narrow methods of those modern physiologists who think
to discover the nature of the vital phenomena by the exclusive aid of
chemical and physical experiments. Verworn showed that it is only by
Müller's comparative method and by a profound study of the physiology
of the cell that we can reach the higher stand-point which will give us
a comprehensive survey of the wonderful realm of the phenomena of life.
Only thus do we become convinced that the vital processes in man are
subject to the same physical and chemical laws as those of all other
animals.
The fundamental importance of the cellular theory for all branches of
biology was made clear in the second half of the nineteenth century,
not only by the rapid progress of morphology and physiology, but also
by the entire reform of that biological science which has always
been deemed most important on account of its relation to practical
medicine--pathology, or the science of disease. Many even of the
older physicians were convinced that human diseases were natural
phenomena, like all other manifestations of life, and should be studied
scientifically, like other vital functions. Particular schools of
medicine--the Iatrophysical and the Iatrochemical--had already, in
the seventeenth century, attempted to trace the sources of disease to
certain physical and chemical changes. However, the imperfect condition
of science at that period precluded any lasting results of these
efforts. Many of the older theories, which sought the nature of disease
in supernatural and mystical causes, were almost universally accepted
down to the middle of the nineteenth century.
It was then that Rudolf Virchow, another pupil of Müller, conceived
the happy idea of transferring the cellular theory from the healthy to
the diseased organism; he sought in the more minute metamorphoses of
the diseased cells and the tissues they composed the true source of
those larger changes which, in the form of disease, threaten the living
organism with peril and death. Especially during the seven years of
his professorship at Würzburg (1849-56) Virchow pursued his great task
with such brilliant results that his _Cellular Pathology_ (published in
1858) turned, at one stroke, the whole of pathology and the dependent
science of practical medicine into new and eminently fruitful paths.
This reform of medicine is significant for our present purpose in that
it led us to a monistic and purely scientific conception of disease. In
sickness, no less than in health, man is subject to the same eternal
"iron laws" of physics and chemistry as all the rest of the organic
world.
Among the numerous classes of animals which modern zoology
distinguishes the mammals occupy a pre-eminent position, not only on
morphological grounds, but also for physiological reasons. As man
belongs to the class of mammals (see p. 27) by every portion of his
frame, we must expect him to share his characteristic functions with
the rest of the mammals. Such we find to be the case. The circulation
of the blood and respiration are accomplished in man under precisely
the same laws and in the same manner as in all the other mammals--_and
in these alone_; they are determined by the peculiar structure of
their heart and lungs. In mammals only is all the arterial blood
conducted from the left ventricle of the heart to the body by one,
the _left_, branch of the aorta, while in birds it passes along the
_right_ branch, and in reptiles along both branches. The blood of
mammals is distinguished from that of any other vertebrate by the
circumstance that its red cells have lost their nucleus (by reversion).
The respiratory movements are effected largely by the diaphragm in
this class of animals alone, because only in them does it form a
complete partition between the pectoral and abdominal cavities. Special
importance, however, in this highest class of animals, attaches to
the production of milk in the breasts (_mammae_), and to the peculiar
method of the rearing of the young, which entails the supplying of the
offspring with the mother's milk. As this nutritive process reacts most
powerfully on the other vital functions, and the maternal affection of
mammals must have arisen from this intimate form of rearing, the name
of the class justly reminds us of its great importance. In millions of
pictures, most of them produced by painters of the highest rank, the
"madonna with the child" is revered as the purest and noblest type of
maternal love--the instinct which is found in its extreme form in the
exaggerated tenderness of the mother-ape.
As the apes approach nearest to man of all the mammals in point of
structure, we shall expect to hear the same of their vital functions;
and that we find to be the case. Everybody knows how closely the
habits, the movements, the sense activity, the mental life, and the
parental customs of apes resemble those of man. Scientific physiology
proves the same significant resemblance in other less familiar
processes, particularly in the working of the heart, the division
of the breasts, and the sexual life. In the latter connection it is
especially noteworthy that the mature females of many kinds of apes
suffer a periodical discharge of blood from the womb, which corresponds
to the menstruation of the human female. The secretion of the milk in
the glands and the suctorial process also take place in the female ape
in precisely the same fashion as in women.
Finally, it is of especial interest that the speech of apes seems on
physiological comparison to be a stage in the formation of articulate
human speech. Among living apes there is an Indian species which is
musical; the _hylobates syndactylus_ sings a full octave in perfectly
pure, harmonious half-tones. No impartial philologist can hesitate any
longer to admit that our elaborate rational language has been slowly
and gradually developed out of the imperfect speech of our Pliocene
simian ancestors.
CHAPTER IV
OUR EMBRYONIC DEVELOPMENT
The Older Embryology--The Theory of Preformation--The Theory of
Scatulation: Haller and Leibnitz--The Theory of Epigenesis: C. F.
Wolff--The Theory of Germinal Layers: Carl Ernst Baer--Discovery
of the Human Ovum: Remak, Kölliker--The Egg-Cell and the
Sperm-Cell--The Theory of the Gastræa--Protozoa and Metazoa--The
Ova and the Spermatozoa: Oscar Hertwig--Conception--Embryonic
Development in Man--Uniformity of the Vertebrate Embryo--The
Germinal Membranes in Man--The Amnion, the Serolemma, and the
Allantois--The Formation of the Placenta and the "After-Birth"--The
_Decidua_ and the _Funiculus Umbilicalis_--The Discoid Placenta of
Man and the Ape
Comparative ontogeny, or the science of the development of the
individual animal, is a child of the nineteenth century in even a truer
sense than comparative anatomy and physiology. How is the child formed
in the mother's womb? How do animals evolve from ova? How does the
plant come forth from the seed? These pregnant questions have occupied
the thoughtful mind for thousands of years. Yet it is only seventy
years since the embryologist Baer pointed out the correct means and
methods for penetrating into the mysteries of embryonic life; it is
only forty years since Darwin, by his reform of the theory of descent,
gave us the key which should open the long-closed door, and lead to
a knowledge of embryonic agencies. As I have endeavored to give a
complete, popular presentation of this very interesting but difficult
study in the first section of my _Anthropogeny_, I will confine myself
here to a brief survey and discussion of the most important phenomena.
Let us first cast a historical glance at the older ontogeny, and the
theory of preformation which is connected with it.
The classical works of Aristotle, the many-sided "father of science,"
are the oldest known scientific sources of embryology, as we found them
to be for comparative anatomy. Not only in his great natural history,
but also in a special small work, _Five Books on the Generation and
Development of Animals_, the great philosopher gives us a host of
interesting facts, adding many observations on their significance; it
was not until our own days that many of them were fully appreciated,
and, indeed, we may say, discovered afresh. Naturally, many fables and
errors are mixed up with them; it was all that was known at that time
of the hidden growth of the human germ. Yet during the long space of
the next two thousand years the slumbering science made no further
progress. It was not until the commencement of the seventeenth century
that there was a renewal of activity. In 1600 the Italian anatomist
Fabricius ab Aquapendente published at Padua the first pictures and
descriptions of the embryos of man and some of the higher animals; in
1687 the famous Marcello Malpighi, of Bologna, a distinguished pioneer
alike in zoology and botany, published the first consistent exposition
of the growth of the chick in the hatched egg.
All these older scientists were possessed with the idea that the
complete body, with all its parts, was already contained in the ovum
of animals, only it was so minute and transparent that it could not
be detected; that, therefore, the whole development was nothing more
than a _growth_, or an "unfolding," of the parts that were already
"infolded" (_involutae_). This erroneous notion, almost universally
accepted until the beginning of the present century, is called the
"preformation theory"; sometimes it is called the "evolution theory"
(in the literal sense of "unfolding"); but the latter title is accepted
by modern scientists for the very different theory of "transformation."
Closely connected with the preformation theory, and as a logical
consequence of it, there arose in the last century a further theory
which keenly interested all thoughtful biologists--the curious
"theory of scatulation." As it was thought that the outline of the
entire organism, with all its parts, was present in the egg, the
ovary of the embryo had to be supposed to contain the ova of the
following generation; these, again, the ova of the next, and so on
_in infinitum_! On that basis the distinguished physiologist Haller
calculated that God had created together, 6000 years ago--on the sixth
day of his creatorial labors--the germs of 200,000,000,000 men, and
ingeniously packed them all in the ovary of our venerable mother Eve.
Even the gifted philosopher Leibnitz fully accepted this conclusion,
and embodied it in his monadist theory; and as, on his theory, soul and
body are in eternal, inseparable companionship, the consequence had to
be accepted for the soul; "the souls of men have existed in organized
bodies in their ancestors from Adam downward--that is, from the very
beginning of things."
In the month of November, 1759, a young doctor of twenty-six years,
Caspar Friedrich Wolff (son of a Berlin tailor), published his
dissertation for the degree at Halle, under the title, _Theoria
Generationis_. Supported by a series of most laborious and painstaking
observations, he proved the entire falsity of the dominant theories of
preformation and scatulation. In the hatched egg there is at first no
trace of the coming chick and its organs; instead of it we find on top
of the yolk a small, circular, white disk. This thin "germinal disk"
becomes gradually round, and then breaks up into four folds, lying
upon each other, which are the rudiments of the four chief systems of
organs--the nervous system above, the muscular system underneath, the
vascular system (with the heart), and, finally, the alimentary canal.
Thus, as Wolff justly remarked, the embryonic development does not
consist in an unfolding of the preformed organs, but in a series of
new constructions; it is a true _epigenesis_. One part arises after
another, and all make their appearance in a simple form, which is very
different from the later structure. This only appears after a series of
most remarkable formations. Although this great discovery--one of the
most important of the eighteenth century--could be directly proved by a
verification of the facts Wolff had observed, and although the "theory
of generation" which was founded on it was in reality not a theory at
all, but a simple fact, it met with no sympathy whatever for half a
century. It was particularly retarded by the high authority of Haller,
who fought it strenuously with the dogmatic assertion that "there is
no such thing as development: no part of the animal body is formed
before another; all were created together." Wolff, who had to go to St.
Petersburg, was long in his grave before the forgotten facts he had
observed were discovered afresh by Oken at Jena, in 1806.
After Wolff's "epigenesis theory" had been established by Oken and
Neckel (whose important work on the development of the alimentary
canal was translated from Latin into German), a number of young German
scientists devoted themselves eagerly to more accurate embryological
research. The most important and successful of these was Carl Ernst
Baer. His principal work appeared in 1828, with the title, _History of
the Development of Animals: Observations and Reflections_. Not only
the phenomena of the formation of the germ are clearly illustrated
and fully described in it, but it adds a number of very pregnant
speculations. In particular, the form of the embryo of man and the
mammals is correctly presented, and the vastly different development
of the lower invertebrate animals is also considered. The two leaflike
layers which appear in the round germ disk of the higher vertebrates
first divide, according to Baer, into two further layers, and these
four germinal layers are transformed into four tubes, which represent
the fundamental organs--the skin layer, the muscular layer, the
vascular layer, and the mucous layer. Then, by very complicated
evolutionary processes, the later organs arise, in substantially the
same manner, in man and all the other vertebrates. The three chief
groups of invertebrates, which in their turn differ widely from each
other, have a very different development.
One of the most important of Baer's many discoveries was the finding of
the human ovum. Up to that time the little vesicles which are found in
great numbers in the human ovary and in that of all other mammals had
been taken for the ova. Baer was the first to prove, in 1827, that the
real ova are enclosed in these vesicles--the "Graafian follicles"--and
much smaller, being tiny spheres 1-120th inch in diameter, visible
to the naked eye as minute specks under favorable conditions. He
discovered likewise that from this tiny ovum of the mammal there
develops first a characteristic germ globule, a hollow sphere with
liquid contents, the wall of which forms the slender germinal membrane,
or blastoderm.
Ten years after Baer had given a firm foundation to embryological
science by his theory of germ layers a new task confronted it on the
establishment of the cellular theory in 1838. What is the relation of
the ovum and the layers which arise from it to the tissues and cells
which compose the fully developed organism? The correct answer to this
difficult question was given about the middle of this century by two
distinguished pupils of Johannes Müller--Robert Remak, of Berlin, and
Albert Kölliker, of Würzburg. They showed that the ovum is at first one
simple cell, and that the many germinal globules, or granules, which
arise from it by repeated segmentation, are also simple cells. From
this mulberry-like group of cells are constructed first the germinal
layers, and subsequently by differentiation, or division of labor,
all the different organs. Kölliker has the further merit of showing
that the seminal fluid of male animals is also a mass of microscopic
cells. The active pin-shaped "seed-animalcules," or _spermatozoa_, in
it are merely ciliated cells, as I first proved in the case of the
seed-filaments of the sponge in 1866. Thus it was proved that both
the materials of generation, the male sperm and the female ova, fell
in with the cellular theory. That was a discovery of which the great
philosophic significance was not appreciated until a much later date,
on a close study of the phenomena of conception in 1875.
All the older studies in embryonic development concern man and the
higher vertebrates, especially the embryonic bird, since hens' eggs
are the largest and most convenient objects for investigation, and
are plentiful enough to facilitate experiment; we can hatch them in
the incubator, as well as by the natural function of the hen, and
so observe from hour to hour, during the space of three weeks, the
whole series of formations, from the simple germ cell to the complete
organism. Even Baer had only been able to gather from such observations
the fact that the different classes of vertebrates agreed in the
characteristic form of the germ layers and the growth of particular
organs. In the innumerable classes of invertebrates, on the other
hand--that is, in the great majority of animals--the embryonic
development seemed to run quite a different course, and most of them
seemed to be altogether without true germinal layers. It was not until
about the middle of the century that such layers were found in some of
the invertebrates. Huxley, for instance, found them in the medusæ in
1849, and Kölliker in the cephalopods in 1844. Particularly important
was the discovery of Kowalewsky (1886) that the lowest vertebrate--the
lancelot, or amphioxus--is developed in just the same manner (and a
very original fashion it is) as an invertebrate, apparently quite
remote, tunicate, the sea-squirt, or ascidian. Even in some of the
worms, the radiata and the articulata, a similar formation of the
germinal layers was pointed out by the same observer. I myself was
then (since 1886) occupied with the embryology of the sponges, corals,
medusæ, and siphonophoræ, and, as I found the same formation of two
primary germ layers everywhere in these lowest classes of multicellular
animals, I came to the conclusion that this important embryonic
feature is common to the entire animal world. The circumstance that
in the sponges and the cnidaria (polyps, medusæ, etc.) the body
consists for a long time, sometimes throughout life, merely of two
simple layers of cells, seemed to me especially significant. Huxley
had already (1849) compared these, in the case of the medusæ, with the
two primary germinal layers of the vertebrates. On the ground of these
observations and comparisons I then, in 1872, in my _Philosophy of the
Calcispongiae_, published the "theory of the gastræa," of which the
following are the essential points:
I. The whole animal world falls into two essentially different groups,
the unicellular primitive animals (Protozoa) and the multicellular
animals with complex tissues (Metazoa). The entire organism of the
protozoon (the rhizopods of the infusoria) remains throughout life a
single simple cell (or occasionally a loose colony of cells without
the formation of tissue, a _coenobium_). The organism of the metazoon,
on the contrary, is only unicellular at the commencement, and is
subsequently built up of a number of cells which form tissues.
II. Hence the method of reproduction and development is very different
in each of these great categories of animals. The protozoa usually
multiply by _non-sexual_ means, by fission, gemmation, or spores;
they have no real ova and no sperm. The metazoa, on the contrary, are
divided into male and female sexes, and generally propagate sexually,
by means of true ova, which are fertilized by the male sperm.
III. Hence, further, true germinal layers, and the tissues which are
formed from them, are found only in the metazoa; they are entirely
wanting in the protozoa.
IV. In all the metazoa only two primary layers appear at first, and
these have always the same essential significance; from the _outer_
layer the external skin and the nervous system are developed; from the
_inner_ layer are formed the alimentary canal and all the other organs.
V. I called the germ, which always arises first from the impregnated
ovum, and which consists of these two primary layers, the "gut-larva,"
or the _gastrula_; its cup-shaped body with the two layers encloses
originally a simple digestive cavity, the primitive gut (the
_progaster_ or _archenteron_), and its simple opening is the primitive
mouth (the _prostoma_ or _blastoporus_). These are the earliest organs
of the multicellular body, and the two cell layers of its enclosing
wall, simple epithelia, are its earliest tissues; all the other organs
and tissues are a later and secondary growth from these.
VI. From this similarity, or _homology_, of the gastrula in all classes
of compound animals I drew the conclusion, in virtue of the biogenetic
law (p. 81), that all the metazoa come originally from one simple
ancestral form, the _gastraea_, and that this ancient (Laurentian),
long-extinct form had the structure and composition of the actual
gastrula, in which it is preserved by heredity.
VII. This phylogenetic conclusion, based on the comparison of
ontogenetic facts, is confirmed by the circumstance that there are
several of these gastræades still in existence (_gastraemaria_,
_cyemaria_, _physemaria_, etc.), and also some ancient forms of
other animal groups whose organization is very little higher (the
_olynthus_ of the sponges, the _hydra_, or common fresh-water polyp,
of the cnidaria, the _convoluta_ and other cryptocæla, or worms of the
simplest type, of the _platodes_).
VIII. In the further development of the various tissue-forming animals
from the gastrula we have to distinguish two principal groups. The
earlier and _lower_ types (the _coelenteria_ or _acoelomia_) have
no body cavity, no vent, and no blood; such is the case with the
gastræades, sponges, cnidaria, and platodes. The later and _higher_
types (the _caelomaria_ or _bilateria_), on the other hand, have a
true body cavity, and generally blood and a vent; to these we must
refer the worms and the higher types of animals which were evolved from
these later on, the echinodermata, mollusca, articulata, tunicata, and
vertebrata.
Those are the main points of my "gastræa theory"; I have since
enlarged the first sketch of it (given in 1872), and have endeavored
to substantiate it in a series of "Studies on the gastræa theory"
(1873-84). Although it was almost universally rejected at first, and
fiercely combated for ten years by many authorities, it is now (and has
been for the last fifteen years) accepted by nearly all my colleagues.
Let us now see what far-reaching consequences follow from it, and
from the evolution of the germ, especially with regard to our great
question, "the place of man in nature."
The human ovum, like that of all other animals, is a single cell, and
this tiny globular egg cell (about the 120th of an inch in diameter)
has just the same characteristic appearance as that of all other
viviparous organisms. The little ball of protoplasm is surrounded
by a thick, transparent, finely reticulated membrane, called the
_zona pellucida_; even the little, globular, germinal vesicle (the
cell-nucleus), which is enclosed in the protoplasm (the cell-body),
is of the same size and the same qualities as in the rest of the
mammals. The same applies to the active spermatozoa of the male,
the minute, threadlike, ciliated cells of which millions are found
in every drop of the seminal fluid; on account of their lifelike
movements they were previously taken to be forms of life, as the name
indicates (spermatozoa--sperm animals). Moreover, the origin of both
these important sexual cells in their respective organs is the same in
man as in the other mammals; both the ova in the ovary of the female
and the spermatozoa in the spermarium of the male arise in the same
fashion--they always come from cells, which are originally derived from
the coelous epithelium, the layer of cells which clothes the cavity
of the body.
The most important moment in the life of every man, as in that of all
other complex animals, is the moment in which he begins his individual
existence; it is the moment when the sexual cells of both parents meet
and coalesce for the formation of a single simple cell. This new cell,
the impregnated egg cell, is the individual stem cell (the _cytula_),
the continued segmentation of which produces the cells of the germinal
layers and the gastrula. With the formation of this cytula, hence in
the process of conception itself, the existence of the personality, the
independent individual, commences. This ontogenic fact is supremely
important, for the most far-reaching conclusions may be drawn from
it. In the first place, we have a clear perception that man, like all
the other complex animals, inherits all his personal characteristics,
bodily and mental, from his parents; and, further, we come to the
momentous conclusion that the new personality which arises thus can lay
no claim to "immortality."
Hence the minute processes of conception and sexual generation are
of the first importance. We are, however, only familiar with their
details since 1875, when Oscar Hertwig, my pupil and fellow-traveller
at that time, began his researches into the impregnation of the egg
of the sea-urchin at Ajaccio, in Corsica. The beautiful capital of
the island in which Napoleon the Great was born, in 1769, was also
the spot in which the mysteries of animal conception were carefully
studied for the first time in their most important aspects. Hertwig
found that the one essential element in conception is the coalescence
of the two sexual cells and their nuclei. Only one out of the millions
of male ciliated cells which press round the ovum penetrates to its
nucleus. The nuclei of both cells, of the spermatozoon and of the ovum,
drawn together by a mysterious force, which we take to be a chemical
sense-activity, related to smell, approach each other and melt into
one. Thus, by the sensitive perception of the sexual nuclei, following
upon a kind of "erotic chemicotropism," a new cell is formed, which
unites in itself the inherited qualities of both parents; the nucleus
of the spermatozoon conveys the paternal features, the nucleus of the
ovum those of the mother, to the stem cell, from which the child is
to be developed. That applies both to the bodily and to the mental
characteristics.
The formation of the germinal layers by the repeated division of
the stem cell, the growth of the gastrula and of the later germ
structures which succeed it, take place in man in just the same manner
as in the other higher mammals, under the peculiar conditions which
differentiate this group from the lower vertebrates. In the earlier
stages of development these special characters of the placentalia are
not to be detected. The significant embryonic or larval form of the
chordula, which succeeds the gastrula, has substantially the same
structure in all vertebrates; a simple straight rod, the dorsal cord,
lies lengthways along the main axis of the shield-shaped body--the
"embryonic shield"; above the cord the spinal marrow develops out
of the outer germinal layer, while the gut makes its appearance
underneath. Then, on both sides, to the right and left of the axial
rod, appear the segments of the "pro-vertebræ" and the outlines of
the muscular plates, with which the formation of the members of the
vertebrate body begins. The gill-clefts appear on either side of the
fore-gut; they are the openings of the gullet, through which, in our
primitive fish-ancestors, the water which had entered at the mouth
for breathing purposes made its exit at the sides of the head. By a
tenacious heredity these gill-clefts, which have no meaning except for
our fish-like aquatic ancestors, are still preserved in the embryo of
man and all the other vertebrates. They disappear after a time. Even
after the five vesicles of the embryonic brain appear in the head,
and the rudiments of the eyes and ears at the sides, and after the
legs sprout out at the base of the fish-like embryo, in the form of
two roundish, flat buds, the foetus is still so like that of other
vertebrates that it is indistinguishable from them.
The substantial similarity in outer form and inner structure which
characterizes the embryo of man and other vertebrates in this early
stage of development is an embryological fact of the first importance;
from it, by the fundamental law of biogeny, we may draw the most
momentous conclusions. There is but one explanation of it--heredity
from a common parent form. When we see that, at a certain stage,
the embryos of man and the ape, the dog and the rabbit, the pig and
the sheep, although recognizable as higher vertebrates, cannot be
distinguished from each other, the fact can only be elucidated by
assuming a common parentage. And this explanation is strengthened when
we follow the subsequent divergence of these embryonic forms. The
nearer two animals are in their bodily structure, and, therefore, in
the scheme of nature, so much the longer do we find their embryos to
retain this resemblance, and so much the closer do they approach each
other in the ancestral tree of their respective group, so much the
closer is their genetic relationship. Hence it is that the embryos of
man and the anthropoid ape retain the resemblance much later, at an
advanced stage of development, when their distinction from the embryos
of other mammals can be seen at a glance. I have illustrated this
significant fact by a juxtaposition of corresponding stages in the
development of a number of different vertebrates in my _Natural History
of Creation_ and in my _Anthropogeny_.
The great phylogenetic significance of the resemblance we have
described is seen, not only in the comparison of the embryos of
vertebrates, but also in the comparison of their protective membranes.
All vertebrates of the three higher classes--reptiles, birds, and
mammals--are distinguished from the lower classes by the possession
of certain special foetal membranes, the amnion and the serolemma.
The embryo is enclosed in these membranes, or bags, which are full of
water, and is thus protected from pressure or shock. This provident
arrangement probably arose during the Permian period, when the oldest
reptiles, the _proreptilia_, the common ancestors of all the amniotes
(animals with an _amnion_), completely adapted themselves to a life on
land. Their direct ancestors, the amphibia, and the fishes are devoid
of these foetal membranes; they would have been superfluous to these
inhabitants of the water. With the inheritance of these protective
coverings are closely connected two other changes in the amniotes:
firstly, the entire disappearance of the gills (while the gill arches
and clefts continue to be inherited as "rudimentary organs"); secondly,
the construction of the _allantois_. This vesicular bag, filled with
water, grows out of the hind-gut in the embryo of all the amniotes,
and is nothing else than an enlargement of the bladder of their
amphibious ancestors. From its innermost and inferior section is formed
subsequently the permanent bladder of the amniotes, while the larger
outer part shrivels up. Usually this has an important part to play for
a long time as the respiratory organ of the embryo, a number of large
blood-vessels spreading out over its inner surface. The formation of
the membranes, the amnion and the serolemma, and of the allantois,
is just the same, and is effected by the same complicated process of
growth, in man as in all the other amniotes; _man is a true amniote_.
The nourishment of the foetus in the maternal womb is effected, as
is well known, by a peculiar organ, richly supplied with blood at its
surface, called the _placenta_. This important nutritive organ is a
spongy, round disk, from six to eight inches in diameter, about an
inch thick, and one or two pounds in weight; it is separated after
the birth of the child, and issues as the "after-birth." The placenta
consists of two very different parts, the foetal and the maternal
part. The latter contains highly developed sinuses, which retain the
blood conveyed to them by the arteries of the mother. On the other
hand, the foetal placenta is formed by innumerable branching tufts or
villi, which grow out of the outer surface of the allantois, and derive
their blood from the umbilical vessels. The hollow, blood-filled villi
of the foetal placenta protrude into the sinuses of the maternal
placenta, and the slender membrane between the two is so attenuated
that it offers no impediment to the direct interchange of material
through the nutritive blood-stream (by osmosis).
In the older and lower groups of the placentals the entire surface
of the chorion is covered with a number of short villi; these
"chorion-villi" take the form of pit-like depressions of the mucous
membrane of the mother, and are easily detached at birth. That
happens in most of the ungulata (the sow, camel, mare, etc.), the
cetacea, and the prosimiæ; these "mallo-placentalia" (with a _diffuse_
placenta) have been denominated the _indeciduata_. The same formation
is present in man and the other placentals in the beginning. It is
soon modified, however, as the villi on one part of the chorion are
withdrawn; while on the other part they grow proportionately stronger,
and unite intimately with the mucous membrane of the womb. It is in
consequence of this intimate blending that a portion of the uterus is
detached at birth, and carried away with loss of blood. This detachable
membrane--the _decidua_--is a characteristic of the higher placentalia,
which have, consequently, been grouped under the title of _deciduata_;
to that category belong the carnassia, rodentia, simiæ, and man. In
the carnassia and some of the ungulata (the elephant, for instance)
the placenta takes the form of a girdle, hence they are known as the
_zonoplacentalia_; in the rodentia, the insectivora (the mole and the
hedge-hog), the apes, and man, it takes the form of a disk.
Even ten years ago the majority of embryologists thought that man
was distinguished by certain peculiarities in the form of the
placenta--namely, by the possession of what is called the _decidua
reflexa_, and by a special formation of the umbilical chord which
unites the _decidua_ to the foetus. It was supposed that the rest
of the placentals, including the apes, were without these special
embryonic structures. The _funiculus umbilicalis_ is a smooth,
cylindrical cord, from sixteen to twenty-three inches long, and as
thick as the little finger. It forms the connecting link between the
foetus and the maternal placenta, since it conducts the nutritive
vessels from the body of the foetus to the placenta; it comprises,
besides, the pedicle of the allantois and the yelk-sac. The yelk-sac in
the human case forms the greater portion of the germinal vesicle during
the third week of gestation; but it shrivels up afterwards so that it
was formerly entirely missed in the mature foetus. Yet it remains all
the time in a rudimentary condition, and may be detected even after
birth as the little umbilical vesicle. Moreover, even the vesicular
structure of the allantois disappears at an early stage in the human
case; with a deflection of the amnion, it gives rise to the pedicle.
We cannot enter here into a discussion of the complicated anatomical
and embryological relations of these structures. I have described and
illustrated them in my _Anthropogeny_ (twenty-third chapter).
The opponents of evolution still appealed to these "special features"
of human embryology, which were supposed to distinguish man from all
the other mammals, even so late as ten years ago. But in 1890 Emil
Selenka proved that the same features are found in the anthropoid apes,
especially in the orang (_satyrus_), while the lower apes are without
them. Thus Huxley's pithecometra thesis was substantiated once more:
"The differences between man and the great apes are not so great as
are those between the manlike apes and the lower monkeys." The supposed
"evidences _against_ the near blood-relationship of man and the apes"
proved, on a closer examination of the real circumstances, to be strong
reasons in favor of it.
Every scientist who penetrates with open eyes into this dark but
profoundly interesting labyrinth of our embryonic development, and who
is competent to compare it critically with that of the rest of the
mammals, will find in it a most important aid towards the elucidation
of the descent of our species. For the various stages of our embryonic
development, in the character of _palingenetic_ phenomena of heredity,
cast a brilliant light on the corresponding stages of our ancestral
tree, in accordance with the great law of biogeny. But even the
_cenogenetic_ phenomena of adaptation, the formation of the temporary
foetal organs--the characteristic foetal membranes, and especially
the placenta--gives us sufficiently definite indications of our _close
genetic relationship with the primates_.
CHAPTER V
THE HISTORY OF OUR SPECIES
Origin of Man--Mythical History of Creation--Moses and Linné--The
Creation of Permanent Species--The Catastrophic Theory:
Cuvier--Transformism: Goethe--Theory of Descent: Lamarck--Theory
of Selection: Darwin--Evolution (Phylogeny)--Ancestral
Trees--General Morphology--Natural History of Creation--Systematic
Phylogeny--Fundamental Law of Biogeny--Anthropogeny--Descent of Man
from the Ape--Pithecoid Theory--The Fossil Pithecanthropus of Dubois
The youngest of the great branches of the living tree of biology is
the science we call biological evolution, or _phylogeny_. It came into
existence much later, and under much more difficult circumstances, than
its natural sister, embryonic evolution or _ontogeny_. The object of
the latter was to attain a knowledge of the mysterious processes by
which the individual organism, plant or animal, developed from the egg.
Phylogeny has to answer the much more obscure and difficult question:
"What is the origin of the different organic species of plants and
animals?"
Ontogeny (embryology and metamorphism) could follow the empirical
method of direct observation in the solution of its not remote problem;
it needed but to follow, day by day and hour by hour, the visible
changes which the foetus experiences during a brief period in the
course of its development from the ovum. Much more difficult was
the remote problem of phylogeny; for the slow processes of gradual
construction, which effect the rise of new species of animals and
plants, go on imperceptibly during thousands and even millions of
years. Their direct observation is possible only within very narrow
limits; the vast majority of these historical processes can only be
known by direct inference--by critical reflection, and by a comparative
use of empirical sciences which belong to very different fields of
thought, palæontology, ontogeny, and morphology. To this we must
add the immense opposition which was everywhere made to biological
evolution on account of the close connection between questions of
organic creation and supernatural myths and religious dogmas. For these
reasons it can easily be understood how it is that the scientific
existence of a true theory of origins was only secured, amid fierce
controversy, in the course of the last forty years.
Every serious attempt that was made before the beginning of the
nineteenth century to solve the problem of the origin of species
lost its way in the mythological labyrinth of the supernatural
stories of creation. The efforts of a few distinguished thinkers to
emancipate themselves from this tyranny and attain to a naturalistic
interpretation proved unavailing. A great variety of creation myths
arose in connection with their religion in all the ancient civilized
nations. During the Middle Ages triumphant Christendom naturally
arrogated to itself the sole right of pronouncing on the question; and,
the Bible being the basis of the structure of the Christian religion,
the whole story of creation was taken from the book of Genesis. Even
Carl Linné, the famous Swedish scientist, started from that basis
when, in 1735, in his classical _Systema Naturae_, he made the first
attempt at a systematic arrangement, nomenclature, and classification
of the innumerable objects in nature. As the best practical aid in that
attempt he introduced the well-known double or binary nomenclature; to
each kind of animals and plants he gave a particular specific name,
and added to it the wider-reaching name of the genus. A _genus_ served
to unite the nearest related _species_; thus, for instance, Linné
grouped under the genus "dog" (_canis_), as different species, the
house-dog (_canis familiaris_), the jackal (_canis aureus_), the wolf
(_canis lupus_) the fox (_canis vulpes_), etc. This binary nomenclature
immediately proved of such great practical assistance that it was
universally accepted, and is still always followed in zoological and
botanical classification.
But the theoretical dogma which Linné himself connected with his
practical idea of species was fraught with the gravest peril to
science. The first question which forced itself on the mind of the
thoughtful scientist was the question as to the nature of the concept
of species, its contents, and its range. And the creator of the idea
answered this fundamental question by a naïve appeal to the dominant
Mosaic legend of creation: "_Species tot sunt diversae, quot diversas
formas ab initio creavit infinitum ens_"--(There are just so many
distinct species as there were distinct types created in the beginning
by the Infinite). This theosophic dogma cut short all attempt at a
natural explanation of the origin of species. Linné was acquainted only
with the plant and animal worlds that exist to-day; he had no suspicion
of the much more numerous extinct species which had peopled the earth
with their varying forms in the earlier period of its development.
It was not until the beginning of the nineteenth century that we were
introduced to these fossil animals by Cuvier. In his famous work on
the fossil bones of the four-footed vertebrates he gave (1812) the
first correct description and true interpretation of many of these
fossil remains. He showed, too, that a series of very different animal
populations have succeeded each other in the various stages of the
earth's history. Since Cuvier held firmly to Linné's idea of the
absolute permanency of species, he thought their origin could only be
explained by the supposition that a series of great cataclysms and new
creations had marked the history of the globe; he imagined that all
living creatures were destroyed at the commencement of each of these
terrestrial revolutions, and an entirely new population was created
at its close. Although this "catastrophic theory" of Cuvier's led to
the most absurd consequences, and was nothing more than a bald faith
in miracles, it obtained almost universal recognition, and reigned
triumphant until the coming of Darwin.
It is easy to understand that these prevalent ideas of the absolute
unchangeability and supernatural creation of organic species could not
satisfy the more penetrating thinkers. We find several eminent minds
already, in the second half of the last century, busy with the attempt
to find a natural explanation of the "problem of creation." Pre-eminent
among them was the great German poet and philosopher, Wolfgang Goethe,
who, by his long and assiduous study of morphology, obtained, more than
a hundred years ago, a clear insight into the intimate connection of
all organic forms, and a firm conviction of a common natural origin.
In his famed _Metamorphosis of Plants_ (1790) he derived all the
different species of plants from one primitive type, and all their
different organs from one primitive organ--the leaf. In his vertebral
theory of the skull he endeavored to prove that the skulls of the
vertebrates--including man--were all alike made up of certain groups
of bones, arranged in a definite structure, and that these bones are
nothing else than transformed vertebræ. It was his penetrating study
of comparative osteology that led Goethe to a firm conviction of the
unity of the animal organization; he had recognized that the human
skeleton is framed on the same fundamental type as that of all other
vertebrates--"built on a primitive plan that only deviates more or less
to one side or other in its very constant features, and still develops
and refashions itself daily." This remodelling, or transformation,
is brought about, according to Goethe, by the constant interaction
of two powerful constructive forces--a centripetal force within the
organism, the "tendency to specification," and a centrifugal force
without, the tendency to variation, or the "idea of metamorphosis";
the former corresponds to what we now call heredity, the latter to
the modern idea of adaptation. How deeply Goethe had penetrated into
their character by these philosophic studies of the "construction and
reconstruction of organic natures," and how far, therefore, he must be
considered the most important precursor of Darwin and Lamarck,[12] may
be gathered from the interesting passages from his works which I have
collected in the fourth chapter of my _Natural History of Creation_.
These evolutionary ideas of Goethe, however, like analogous ideas of
Kant, Owen, Treviranus, and other philosophers of the commencement of
the century (which we have quoted in the above work), did not amount to
more than certain general conclusions. They had not that great lever
which the "natural history of creation" needed for its firm foundation
on a criticism of the dogma of fixed species; this lever was first
supplied by Lamarck.
The first thorough attempt at a scientific establishment of transformism
was made at the beginning of the nineteenth century by the great
French scientist Jean Lamarck, the chief opponent of his colleague,
Cuvier, at Paris. He had already, in 1802, in his _Observations on
Living Organisms_, expressed the new ideas as to the mutability and
formation of species, which he thoroughly established in 1809 in the
two volumes of his profound work, _Philosophie Zoologique_. In this
work he first gave expression to the correct idea, in opposition to
the prevalent dogma of fixed species, that the organic "species" is
an _artificial abstraction_, a concept of only relative value, like
the wider-ranging concepts of genus, family, order, and class. He
went on to affirm that all species are changeable, and have arisen
from older species in the course of very long periods of time. The
common parent forms from which they have descended were originally
very simple and lowly organisms. The first and oldest of them arose
by abiogenesis. While the type is preserved by _heredity_ in the
succession of generations, _adaptation_, on the other hand, effects
a constant modification of the species by change of habits and the
exercise of the various organs. Even our human organism has arisen in
the same natural manner, by gradual transformation, from a group of
pithecoid mammals. For all these phenomena--indeed, for all phenomena
both in nature and in the mind--Lamarck takes exclusively mechanical,
physical, and chemical activities to be the true efficient causes. His
magnificent _Philosophie Zoologique_ contains all the elements of a
purely monistic system of nature on the basis of evolution. I have
fully treated these achievements of Lamarck in the fourth chapter of my
_Anthropogeny_, and in the fourth chapter of the _Natural History of
Creation_.
Science had now to wait until this great effort to give a scientific
foundation to the theory of evolution should shatter the dominant myth
of a "specific creation, and open out the path of natural" development.
In this respect Lamarck was not more successful in resisting the
conservative authority of his great opponent, Cuvier, than was his
colleague and sympathizer, Geoffrey St. Hilaire, twenty years later.
The famous controversies which he had with Cuvier in the Parisian
Academy in 1830 ended with the complete triumph of the latter. I have
elsewhere fully described these conflicts, in which Goethe took so
lively an interest. The great expansion which the study of biology
experienced at that time, the abundance of interesting discoveries
in comparative anatomy and physiology, the establishment of the
cellular theory, and the progress of ontogeny, gave zoologists and
botanists so overwhelming a flood of welcome material to deal with
that the difficult and obscure question of the origin of species was
easily forgotten for a time. People rested content with the old dogma
of creation. Even when Charles Lyell refuted Cuvier's extraordinary
"catastrophic theory" in his _Principles of Geology_, in 1830, and
vindicated a natural, continuous evolution for the inorganic structure
of our planet, his simple principle of continuity found no one to
apply it to the inorganic world. The rudiments of a natural phylogeny
which were buried in Lamarck's works were as completely forgotten as
the germ of a natural ontogeny which Caspar Friedrich Wolff had given
fifty years earlier in his _Theory of Generation_. In both cases a full
half-century elapsed before the great idea of a natural development
won a fitting recognition. Only when Darwin (in 1859) approached the
solution of the problem from a different side altogether, and made
a happy use of the rich treasures of empirical knowledge which had
accumulated in the mean time, did men begin to think once more of
Lamarck as his great precursor.
The unparalleled success of Charles Darwin is well known. It shows him
to-day, at the close of the century, to have been, if not the greatest,
at least the most effective of its distinguished scientists. No other
of the many great thinkers of our time has achieved so magnificent, so
thorough, and so far-reaching a success with a single classical work as
Darwin did in 1859 with his famous _Origin of Species_. It is true that
the reform of comparative anatomy and physiology by Johannes Müller
had inaugurated a new and fertile epoch for the whole of biology, that
the establishment of the cellular theory by Schleiden and Schwann, the
reform of ontogeny by Baer, and the formulation of the law of substance
by Robert Mayer and Helmholtz were scientific facts of the first
importance; but no one of them has had so profound an influence on the
whole structure of human knowledge as Darwin's theory of the natural
origin of species. For it at once gave us the solution of the mystic
"problem of creation," the great "question of all questions"--the
problem of the true character and origin of man himself.
If we compare the two great founders of transformism, we find in
Lamarck a preponderant inclination to _deduction_, and to forming a
completely monistic scheme of nature; in Darwin we have a predominant
application of _induction_, and a prudent concern to establish the
different parts of the theory of selection as firmly as possible on a
basis of observation and experiment. While the French scientist far
outran the then limits of empirical knowledge, and rather sketched the
programme of future investigation, the English empiricist was mainly
preoccupied about securing a unifying principle of interpretation for
a mass of empirical knowledge which had hitherto accumulated without
being understood. We can thus understand how it was that the success
of Darwin was just as overwhelming as that of Lamarck was evanescent.
Darwin, however, had not only the signal merit of bringing all the
results of the various biological sciences to a common focus in the
principle of descent, and thus giving them a harmonious interpretation,
but he also discovered, in the principle of selection, that direct
cause of transformation which Lamarck had missed. In applying, as a
practical breeder, the experience of artificial selection to organisms
in a state of nature, and in recognizing in the "struggle for life" the
selective principle of natural selection, Darwin created his momentous
"theory of selection," which is what we properly call Darwinism.
One of the most pressing of the many important tasks which Darwin
proposed to modern biology was the reform of the zoological and
botanical system. Since the innumerable species of animals and plants
were not created by a supernatural miracle, but evolved by natural
processes, their ancestral tree is their "natural system." The first
attempt to frame a system in this sense was made by myself in 1866,
in my _General Morphology of Organisms_. The first volume of this
work ("General Anatomy") dealt with the "mechanical science of the
developed forms"; the second volume ("General Evolution") was occupied
with the science of the "developing forms." The systematic introduction
to the latter formed a "genealogical survey of the natural system
of organisms." Until that time the term "evolution" had been taken
to mean exclusively, both in zoology and botany, the development of
individual organisms--embryology, or metamorphic science. I established
the opposite view, that this history of the embryo (ontogeny) must be
completed by a second, equally valuable, and closely connected branch
of thought--the history of the race (phylogeny). Both these branches
of evolutionary science are, in my opinion, in the closest causal
connection; this arises from the reciprocal action of the laws of
heredity and adaptation; it has a precise and comprehensive expression
in my "fundamental law of biogeny."
As the new views I had put forward in my _General Morphology_ met with
very little notice, and still less acceptance, from my scientific
colleagues, in spite of their severely scientific setting, I thought
I would make the most important of them accessible to a wider circle
of informed readers by a smaller work, written in a more popular
style. This was done in 1868, in _The Natural History of Creation_ (a
series of popular scientific lectures on evolution in general, and the
systems of Darwin, Goethe, and Lamarck in particular). If the success
of my _General Morphology_ was far below my reasonable anticipation,
that of _The Natural History of Creation_ went far beyond it. In a
period of thirty years nine editions and twelve different translations
of it have appeared. In spite of its great defects, the book has
contributed much to the popularization of the main ideas of modern
evolution. Still, I could only give the barest outlines in it of my
chief object, the phylogenetic construction of a natural system. I
have, therefore, given the complete proof, which is wanting in the
earlier work, of the phylogenetic system in a subsequent larger work,
my _Systematic Phylogeny_ (outlines of a natural system of organisms
on the basis of their specific development). The first volume of
it deals with the protists and plants (1894), the second with the
invertebrate animals (1896), the third with the vertebrates (1895). The
ancestral tree of both the smaller and the larger groups is carried
on in this work as far as my knowledge of the three great "ancestral
documents"--palæontology, ontogeny, and morphology--qualified me to
extend it.
I had already, in my _General Morphology_ (at the end of the fifth
book), described the close causative connection which exists, in
my opinion, between the two branches of organic evolution as one
of the most important ideas of transformism, and I had framed a
precise formula for it in a number of "theses on the causal nexus of
biontic and phyletic development": "_Ontogenesis is a brief and rapid
recapitulation of phylogenesis_, determined by the physiological
functions of heredity (generation) and adaptation (maintenance)."
Darwin himself had emphasized the great significance of his theory
for the elucidation of embryology in 1859, and Fritz Müller had
endeavored to prove it as regards the Crustacea in the able little
work, _Facts and Arguments for Darwin_ (1864). My own task has been
to prove the universal application and the fundamental importance of
the biogenetic law in a series of works, especially in the _Biology
of the Calcispongiae_ (1872), and in _Studies on the Gastraea Theory_
(1873-1884). The theory of the homology of the germinal layers and of
the relations of _palingenesis_ to _cenogenesis_ which I have exposed
in them has been confirmed subsequently by a number of works of other
zoologists. That theory makes it possible to follow nature's law of
unity in the innumerable variations of animal embryology; it gives us
for their ancestral history a common derivation from a simple primitive
stem form.
The far-seeing founder of the theory of descent, Lamarck, clearly
recognized in 1809 that it was of universal application; that even man
himself, the most highly developed of the mammals, is derived from the
same stem as all the other mammals; and that this in its turn belongs
to the same older branch of the ancestral tree as the rest of the
vertebrates. He had even indicated the agencies by which it might be
possible to explain man's descent from the apes as the nearest related
mammals. Darwin, who was, naturally, of the same conviction, purposely
avoided this least acceptable consequence of his theory in his chief
work in 1859, and put it forward for the first time in his _Descent of
Man_ in 1871. In the mean time (1863) Huxley had very ably discussed
this most important consequence of evolution in his famous _Place of
Man in Nature_. With the aid of comparative anatomy and ontogeny,
and the support of the facts of palæontology, Huxley proved that the
"descent of man from the ape" is a necessary consequence of Darwinism,
and that no other scientific explanation of the origin of the human
race is possible. Of the same opinion was Karl Gegenbaur, the most
distinguished representative of comparative anatomy, who lifted his
science to a higher level by a consistent and ingenious application of
the theory of descent.
As a further consequence of the "pithecoid theory" (the theory of the
descent of man from the ape) there now arose the difficult task of
investigating, not only the nearest related mammal ancestors of man
in the Tertiary epoch, but also the long series of the older animal
ancestors which had lived in earlier periods of the earth's history and
been developed in the course of countless millions of years. I had made
a start with the hypothetical solution of this great historic problem
in my _General Morphology_; a further development of it appeared in
1874 in my _Anthropogeny_ (first section, Origin of the Individual;
second section, Origin of the Race). The fourth, enlarged, edition of
this work (1891) contains that theory of the development of man which
approaches nearest, in my own opinion, to the still remote truth, in
the light of our present knowledge of the documentary evidence. I was
especially preoccupied in its composition to use the three empirical
"documents"--palæontology, ontogeny, and morphology (or comparative
anatomy)--as evenly and harmoniously as possible. It is true that my
hypotheses were in many cases supplemented and corrected in detail by
later phylogenetic research; yet I am convinced that the ancestral tree
of human origin which I have sketched therein is substantially correct.
For the historical succession of vertebrate fossils corresponds
completely with the morphological evolutionary scale which is revealed
to us by comparative anatomy and ontogeny. After the Silurian fishes
come the _dipnoi_ of the Devonian period--the Carboniferous amphibia,
the Permian reptilia, and the Mesozoic mammals. Of these, again, the
lowest forms, the monotremes, appear first in the Triassic period,
the marsupials in the Jurassic, and then the oldest placentals in
the Cretaceous. Of the placentals, in turn, the first to appear in
the oldest Tertiary period (the Eocene) are the lowest primates,
the prosimiæ, which are followed by the simiæ in the Miocene. Of the
catarrhinæ, the cynopitheci precede the anthropomorpha; from one branch
of the latter, during the Pliocene period, arises the ape-man without
speech (the _pithecanthropus alalus_); and from him descends, finally,
speaking man.
The chain of our earlier invertebrate ancestors is much more difficult
to investigate and much less safe than this tree of our vertebrate
predecessors; we have no fossilized relics of their soft, boneless
structures, so palæontology can give us no assistance in this case.
The evidence of comparative anatomy and ontogeny, therefore, becomes
all the more important. Since the human embryo passes through the
same _chordula_-stage as the germs of all other vertebrates, since
it evolves, similarly, out of two germinal layers of a _gastrula_,
we infer, in virtue of the biogenetic law, the early existence of
corresponding ancestral forms--vermalia, gastræada, etc. Most important
of all is the fact that the human embryo, like that of all other
animals, arises originally from a single cell; for this "stem-cell"
(_cytula_)--the impregnated egg cell--points indubitably to a
corresponding unicellular ancestor, a primitive, Laurentian protozoon.
For the purpose of our monistic philosophy, however, it is a matter of
comparative indifference how the succession of our animal predecessors
may be confirmed in detail. Sufficient for us, as an incontestable
historical fact, is the important thesis that man descends immediately
from the ape, and secondarily from a long series of lower vertebrates.
I have laid stress on the logical proof of this "pithecometra-thesis"
in the seventh book of the _General Morphology_: "The thesis that
man has been evolved from lower vertebrates, and immediately from the
_simiae_, is a special inference which results with absolute necessity
from the general inductive law of the theory of descent."
For the definitive proof and establishment of this fundamental
pithecometra-thesis the palæontological discoveries of the last
thirty years are of the greatest importance; in particular, the
astonishing discoveries of a number of extinct mammals of the Tertiary
period have enabled us to draw up clearly in its main outlines the
evolutionary history of this most important class of animals, from
the lowest oviparous monotremes up to man. The four chief groups
of the placentals, the heterogeneous legions of the carnassia, the
rodentia, the ungulata, and the primates, seem to be separated by
profound gulfs, when we confine our attention to their representatives
of to-day. But these gulfs are completely bridged, and the sharp
distinctions of the four legions are entirely lost, when we compare
their extinct predecessors of the Tertiary period, and when we go
back into the Eocene twilight of history, in the oldest part of the
Tertiary period--at least three million years ago. There we find the
great sub-class of the placentals, which to-day comprises more than
two thousand five hundred species, represented by only a small number
of little, insignificant "proplacentals"; and in these _prochoriata_
the characters of the four divergent legions are so intermingled and
toned down that we cannot in reason do other than consider them as the
precursors of those features. The oldest carnassia (the _ictopsales_),
the oldest rodentia (the _esthonychales_), the oldest ungulata (the
_condylarthrales_) and the oldest primates (the _lemuravales_), all
have the same fundamental skeletal structure, and the same typical
dentition of the primitive placentals, consisting of forty-four teeth
(three incisors, one canine, four premolars, and three molars in each
half of the jaw); all are characterized by the small size and the
imperfect structure of the brain (especially of its chief part, the
cortex, which does not become a true "organ of thought" until later on
in the Miocene and Pliocene representatives); they have all short legs
and five-toed, flat-soled feet (_plantigrada_). In many cases among
these oldest placentals of the Eocene period it was very difficult
to say at first whether they should be classed with the carnassia,
rodentia, ungulata, or primates; so very closely, even to confusion,
do these four groups of the placentals, which diverge so widely
afterwards, approach each other at that time. Their common origin from
a single ancestral group follows incontestably. These _prochoriata_
lived in the preceding Cretaceous period (more than three million years
ago), and were probably developed in the Jurassic period from a group
of insectivorous marsupials (_amphitheria_) by the formation of a
primitive _placenta diffusa_, a placenta of the simplest type.
But the most important of all the recent palaeontological discoveries
which have served to elucidate the origin of the placentals relate
to our own stem, the legion of primates. Formerly fossil remains of
the primates were very scarce. Even Cuvier, the great founder of
palaeontology, maintained until his last day (1832) that there were no
fossilized primates; he had himself, it is true, described the skull
of an Eocene prosimiæ (_adapis_), but he had wrongly classed it with
the ungulata. However, during the last twenty years a fair number of
well-preserved fossilized skeletons of prosimiæ and simiæ have been
discovered; in them we find all the chief intermediate members which
complete the connecting chain of ancestors from the oldest prosimiæ to
man.
The most famous and most interesting of these discoveries is the
fossil ape-man of Java, the much-talked-of _pithecanthropus erectus_,
found by a Dutch military doctor, Eugen Dubois, in 1894. It is in
truth the much-sought "missing link," supposed to be wanting in
the chain of primates, which stretches unbroken from the lowest
catarrhinæ to the highest-developed man. I have dealt exhaustively
with the significance of this discovery in the paper which I read on
August 26, 1898, at the Fourth International Zoological Congress at
Cambridge.[13] The palæontologist, who knows the conditions of the
formation and preservation of fossils, will think the discovery of the
pithecanthropus an unusually lucky accident. The apes, being arboreal,
seldom came into the circumstances (unless they happened to fall into
the water) which would secure the preservation and petrifaction of
their skeleton. Thus, by the discovery of this fossil man-monkey of
Java the descent of man from the ape has become just as clear and
certain from the palæontological side as it was previously from the
evidence of comparative anatomy and ontogeny. We now have all the
principal documents which tell the history of our race.
CHAPTER VI
THE NATURE OF THE SOUL
Fundamental Importance of Psychology--Its Definition and
Methods--Divergence of Views Thereon--Dualistic and Monistic
Psychology--Relation to the Law of Substance--Confusion
of Ideas--Psychological Metamorphoses: Kant, Virchow,
Du Bois-Reymond--Methods of Research of Psychic
Science--Introspective Method (Self-Observation)--Exact
Method (Psycho-Physics)--Comparative Method (Animal
Psychology)--Psychological Change of Principles:
Wundt--Folk-Psychology and Ethnography: Bastian--Ontogenetic
Psychology: Preyer--Phylogenetic Psychology: Darwin, Romanes
The phenomena which are comprised under the title of the "life of
the soul," or the psychic activity, are, on the one hand, the most
important and interesting, on the other the most intricate and
problematical, of all the phenomena we are acquainted with. As the
knowledge of nature, the object of the present philosophic study,
is itself a part of the life of the soul, and as anthropology, and
even cosmology, presuppose a correct knowledge of the "psyche," we
may regard psychology, the scientific study of the soul, both as the
foundation and the postulate of all other sciences. From another
point of view it is itself a part of philosophy, or physiology, or
anthropology.
The great difficulty of establishing it on a naturalistic basis
arises from the fact that psychology, in turn, presupposes a correct
acquaintance with the human organism, especially the brain, the chief
organ of psychic activity. The great majority of "psychologists" have
little or no acquaintance with these anatomical foundations of the
soul, and thus it happens that in no other science do we find such
contradictions and untenable notions as to its proper meaning and
its essential object as are current in psychology. This confusion
has become more and more palpable during the last thirty years, in
proportion as the immense progress of anatomy and physiology has
increased our knowledge of the structure and the functions of the chief
psychic organ.
What we call the soul is, in my opinion, a natural phenomenon; I
therefore consider psychology to be a branch of natural science--a
section of physiology. Consequently, I must emphatically assert
from the commencement that we have no different methods of research
for that science than for any of the others; we have in the first
place observation and experiment, in the second place the theory of
evolution, and in the third place metaphysical speculation, which
seek to penetrate as far as possible into the cryptic nature of the
phenomena by inductive and deductive reasoning. However, with a view
to a thorough appreciation of the question, we must first of all put
clearly before the reader the antithesis of the dualistic and the
monistic theories.
The prevailing conception of the psychic activity, which we contest,
considers soul and body to be two distinct entities. These two
entities can exist independently of each other; there is no intrinsic
necessity for their union. The organized body is a mortal, material
nature, chemically composed of living protoplasm and its compounds
(plasma-products). The soul, on the other hand, is an immortal,
immaterial being, a spiritual agent, whose mysterious activity
is entirely incomprehensible to us. This trivial conception is,
as such, spiritualistic, and its contradictory is, in a certain
sense, materialistic. It is, at the same time, supernatural and
transcendental, since it affirms the existence of forces which can
exist and operate without a material basis; it rests on the assumption
that outside of and beyond nature there is a "spiritual," immaterial
world, of which we have no experience, and of which we can learn
nothing by natural means.
This hypothetical "spirit world," which is supposed to be entirely
independent of the material universe, and on the assumption of which
the whole artificial structure of the dualistic system is based, is
purely a product of poetic imagination; the same must be said of the
parallel belief in the "immortality of the soul," the scientific
impossibility of which we must prove more fully later on (chap. xi.).
If the beliefs which prevail in these credulous circles had a sound
foundation, the phenomena they relate to could not be subject to the
"law of substance"; moreover, this single exception to the highest
law of the cosmos must have appeared very late in the history of the
organic world, since it only concerns the "soul" of man and of the
higher animals. The dogma of "free will," another essential element
of the dualistic psychology, is similarly irreconcilable with the
universal law of substance.
Our own naturalistic conception of the psychic activity sees in it a
group of vital phenomena, which are dependent on a definite material
substratum, like all other phenomena. We shall give to this material
basis of all psychic activity, without which it is inconceivable,
the provisional name of "psychoplasm"; and for this good reason--that
chemical analysis proves it to be a body of the group we call
protoplasmic bodies the albuminoid carbon-combinations which are at
the root of all vital processes. In the higher animals, which have a
nervous system and sense-organs, "neuroplasm," the nerve-material,
has been differentiated out of psychoplasm. Our conception is, in
this sense, materialistic. It is at the same time empirical and
naturalistic, for our scientific experience has never yet taught us the
existence of forces that can dispense with a material substratum, or of
a spiritual world over and above the realm of nature.
Like all other natural phenomena, the psychic processes are subject to
the supreme, all-ruling law of substance; not even in this province
is there a single exception to this highest cosmological law (compare
chap. xii.). The phenomena of the lowly psychic life of the unicellular
protist and the plant, and of the lowest animal forms--their
irritability, their reflex movements, their sensitiveness and instinct
of self-preservation--are directly determined by physiological action
in the protoplasm of their cells--that is, by physical and chemical
changes which are partly due to heredity and partly to adaptation.
And we must say just the same of the higher psychic activity of the
higher animals and man, of the formation of ideas and concepts, of
the marvellous phenomena of reason and consciousness; for the latter
have been phylogenetically evolved from the former, and it is merely
a higher degree of integration or centralization, of association
or combination of functions which were formerly isolated, that has
elevated them in this manner.
The first task of every science is the clear definition of the object
it has to investigate. In no science, however, is this preliminary
task so difficult as in psychology; and this circumstance is the
more remarkable since logic, the science of defining, is itself a
part of psychology. When we compare all that has been said by the
most distinguished philosophers and scientists of all ages on the
fundamental idea of psychology, we find ourselves in a perfect chaos
of contradictory notions. What, really, is the "soul"? What is its
relation to the "mind"? What is the inner meaning of "consciousness"?
What is the difference between "sensation" and "sentiment"? What is
"instinct"? What is the meaning of "free will"? What is "presentation"?
What is the difference between "intellect" and "reason"? What is the
true nature of "emotion"? What is the relation between all these
"psychic phenomena" and the "body"? The answers to these and many other
cognate questions are infinitely varied; not only are the views of the
most eminent thinkers on these questions widely divergent, but even the
same scientific authority has often completely changed his views in the
course of his psychological development. Indeed, this "psychological
metamorphosis" of so many thinkers has contributed not a little to the
_colossal confusion of ideas_ which prevails in psychology more than in
any other branch of knowledge.
The most interesting example of such an entire change of objective
and subjective psychological opinions is found in the case of the
most influential leader of German philosophy, Immanuel Kant. The
young, severely _critical_ Kant came to the conclusion that the three
great buttresses of mysticism--"God, freedom, and immortality"--were
untenable in the light of "pure reason"; the older, _dogmatic_ Kant
found that these three great hallucinations were postulates of
"practical reason," and were, as such, indispensable. The more the
distinguished modern school of "Neokantians" urges a "return to Kant"
as the only possible salvation from the frightful jumble of modern
metaphysics, the more clearly do we perceive the undeniable and fatal
contradiction between the fundamental opinions of the young and the
older Kant. We shall return to this point later on.
Other interesting examples of this change of views are found in two of
the most famous living scientists, R. Virchow and E. du Bois-Reymond;
the metamorphoses of their fundamental views on psychology cannot
be overlooked, as both these Berlin biologists have played a most
important part at Germany's greatest university for more than forty
years, and have, therefore, directly and indirectly, had a most
profound influence on the modern mind. Rudolph Virchow, the eminent
founder of cellular pathology, was a _pure monist_ in the best days of
his scientific activity, about the middle of the century; he passed at
that time as one of the most distinguished representatives of the newly
awakened _materialism_, which appeared in 1855, especially through two
famous works, almost contemporaneous in appearance--Ludwig Büchner's
_Matter and Force_ and Carl Vogt's _Superstition and Science_. Virchow
published his general biological views on the vital processes in
man--which he takes to be purely mechanical natural phenomena--in a
series of distinguished papers in the first volumes of the _Archiv
für pathologische Anatomie_, which he founded. The most important of
these articles, and the one in which he most clearly expresses his
monistic views of that period, is that on "The Tendencies Towards
Unity in Scientific Medicine" (1849). It was certainly not without
careful thought, and a conviction of its philosophic value, that
Virchow put this "medical confession of faith" at the head of his
_Collected Essays on Scientific Medicine_ in 1856. He defended in it,
clearly and definitely, the fundamental principles of monism, which I
am presenting here with a view to the solution of the world-problem;
he vindicated the exclusive title of empirical science, of which the
only reliable sources are sense and brain activity; he vigorously
attacked anthropological dualism, the alleged "revelation," and
the transcendental philosophy, with their two methods--"faith and
anthropomorphism." Above all, he emphasized the monistic character of
anthropology, the inseparable connection of spirit and body, of force
and matter. "I am convinced," he exclaims, at the end of his preface,
"that I shall never find myself compelled to deny the thesis of _the
unity_ of human nature." Unhappily, this "conviction" proved to be a
grave error. Twenty-eight years afterwards Virchow represented the
diametrically opposite view; it is to be found in the famous speech on
"The Liberty of Science in Modern States," which he delivered at the
Scientific Congress at Munich in 1877, and which contains attacks that
I have repelled in my _Free Science and Free Teaching_ (1878).
In Emil du Bois-Reymond we find similar contradictions with regard
to the most important and fundamental theses of philosophy. The
more completely the distinguished orator of the Berlin Academy had
defended the main principles of the monistic philosophy, the more he
had contributed to the refutation of vitalism and the transcendental
view of life, so much the louder was the triumphant cry of our
opponents when in 1872, in his famous _Ignorabimus-Speech_, he spoke
of consciousness as an insoluble problem, and opposed it to the other
functions of the brain as a supernatural phenomenon. I return to the
point in the tenth chapter.
The peculiar character of many of the psychic phenomena, especially
of consciousness, necessitates certain modifications of our ordinary
scientific methods. We have, for instance, to associate with the
customary _objective_, external observation, the _introspective_
method, the _subjective_, internal observation which scrutinizes
our own personality in the mirror of consciousness. The majority of
psychologists have started from this "certainty of the ego": "_Cogito
ergo sum_," as Descartes said--I think, therefore I am. Let us first
cast a glance at this way of inquiry, and then deal with the second,
complementary, method.
By far the greater part of the theories of the soul which have been
put forward during the last two thousand years or more are based on
introspective inquiry--that is, on "self-observation," and on the
conclusions which we draw from the association and criticism of these
subjective experiences. Introspection is the only possible method of
inquiry for an important section of psychology, especially for the
study of consciousness. Hence this cerebral function occupies a special
position, and has been a more prolific source of philosophic error than
any of the others (cf. chap. x.). It is, however, most unsatisfactory,
and it leads to entirely false or incomplete notions, to take this
self-observation of the mind to be the chief, or, especially, to be
the only source of mental science, as has happened in the case of
many and distinguished philosophers. A great number of the principal
psychic phenomena, particularly the activity of the senses and speech,
can only be studied in the same way as every other vital function of
the organism--that is, firstly, by a thorough anatomical study of
their organs, and, secondly, by an exact physiological analysis of
the functions which depend on them. In order, however, to complete
this external study of the mental life, and to supplement the results
of _internal_ observation, one needs a thorough knowledge of human
anatomy, histology, ontogeny, and physiology. Most of our so-called
"psychologists" have little or no knowledge of these indispensable
foundations of anthropology; they are, therefore, incompetent to
pronounce on the character even of their own "soul." It must be
remembered, too, that the distinguished personality of one of these
psychologists usually offers a specimen of an educated mind of the
highest civilized races; it is the last link of a long ancestral chain,
and the innumerable older and inferior links are indispensable for
its proper understanding. Hence it is that most of the psychological
literature of the day is so much waste paper. The introspective method
is certainly extremely valuable and indispensable; still it needs the
constant co-operation and assistance of the other methods.
In proportion as the various branches of the human tree of knowledge
have developed during the century, and the methods of the different
sciences have been perfected, the desire has grown to make them
_exact_; that is, to make the study of phenomena as purely empirical
as possible, and to formulate the laws that result as clearly as
the circumstances permit--if possible, _mathematically_. The latter
is, however, only feasible in a small province of human knowledge,
especially in those sciences in which there is question of measurable
quantities; in mathematics, in the first place, and to a greater or
less extent in astronomy, mechanics, and a great part of physics and
chemistry. Hence these studies are called "exact sciences" in the
narrower sense. It is, however, productive only of error to call all
the physical sciences _exact_, and oppose them to the historical,
mental, and moral sciences. The greater part of physical science can
no more be treated as an _exact_ science than history can; this is
especially true of biology and of its subsidiary branch, psychology.
As psychology is a part of physiology, it must, as a general rule,
follow the chief methods of that science. It must establish the facts
of psychic activity by empirical methods as much as possible, by
observation and experiment, and it must then gather the laws of the
mind by inductive and deductive inferences from its observations,
and formulate them with the utmost distinctness. But, for obvious
reasons, it is rarely possible to formulate them mathematically. Such
a procedure is only profitable in one section of the physiology of
the senses; it is not practicable in the greater part of cerebral
physiology.
One small section of physiology, which seems amenable to the "exact"
method of investigation, has been carefully studied for the last
twenty years and raised to the position of a separate science under
the title of _psycho-physics_. Its founders, the physiologists Theodor
Fechner and Ernst Heinrich Weber, first of all closely investigated
the dependence of sensations on the external stimuli that act on the
organs of sense, and particularly the quantitative relation between
the strength of the stimulus and the intensity of the sensation. They
found that a certain minimum strength of stimulus is requisite for
the excitement of a sensation, and that a given stimulus must be
varied to a definite amount before there is any perceptible change
in the sensation. For the highest sensations (of sight, hearing, and
pressure) the law holds good that their variations are proportionate
to the changes in the strength of the stimulus. From this empirical
"law of Weber" Fechner inferred, by mathematical operations, his
"fundamental law of psycho-physics," according to which the intensity
of a sensation increases in arithmetical progression, the strength
of the stimulus in geometrical progression. However, Fechner's law
and other psycho-physical laws are frequently contested, and their
"exactness" is called into question. In any case modern psycho-physics
has fallen far short of the great hopes with which it was greeted
twenty years ago; the field of its applicability is extremely limited.
One important result of its work is that it has proved the application
of physical laws in one, if only a small, branch of the life of the
"soul"--an application which was long ago postulated on principle by
the materialist psychology for the whole province of mental life. In
this, as in many other branches of physiology, the "exact" method has
proved inadequate and of little service. It is the ideal to aim at
everywhere, but it is unattainable in most cases. Much more profitable
are the comparative and genetic methods.
The striking resemblance of man's psychic activity to that of
the higher animals--especially our nearest relatives among the
mammals--is a familiar fact. Most uncivilized races still make no
material distinction between the two sets of mental processes, as
the well-known animal fables, the old legends, and the idea of the
transmigration of souls prove. Even most of the philosophers of
classical antiquity shared the same conviction, and discovered no
essential qualitative difference, but merely a quantitative one,
between the soul of man and that of the brute. Plato himself, who was
the first to draw a fundamental distinction between soul and body,
made one and the same soul (or "idea") pass through a number of animal
and human bodies in his theory of metempsychosis. It was Christianity,
intimately connecting faith in immortality with faith in God, that
emphasized the essential difference of the immortal soul of man from
the mortal soul of the brute. In the dualistic philosophy the idea
prevailed principally through the influence of Descartes (1643);
he contended that man alone had a true "soul," and, consequently,
sensation and free will, and that the animals were mere automata, or
machines, without will or sensibility. Ever since the majority of
psychologists--including even Kant--have entirely neglected the mental
life of the brute, and restricted psychological research to man:
human psychology, mainly introspective, dispensed with the fruitful
comparative method, and so remained at that lower point of view which
human morphology took before Cuvier raised it to the position of a
"philosophic science" by the foundation of comparative anatomy.
Scientific interest in the psychic activity of the brute was revived
in the second half of the last century, in connection with the
advance of systematic zoology and physiology. A strong impulse was
given to it by the work of Reimarus: "General observations on the
instincts of animals" (Hamburg, 1760). At the same time a deeper
scientific investigation had been facilitated by the thorough reform
of physiology by Johannes Müller. This distinguished biologist, having
a comprehensive knowledge of the whole field of organic nature, of
morphology, and of physiology, introduced the "exact methods" of
observation and experiment into the whole province of physiology, and,
with consummate skill, combined them with the comparative methods. He
applied them, not only to mental life in the broader sense (to speech,
senses, and brain-action), but to all the other phenomena of life. The
sixth book of his _Manual of Human Physiology_ treats specially of the
life of the soul, and contains eighty pages of important psychological
observations.
During the last forty years a great number of works on comparative
animal psychology have appeared, principally occasioned by the great
impulse which Darwin gave in 1859 by his work on _The Origin of
Species_, and by the application of the idea of evolution to the
province of psychology. The more important of these works we owe to
Romanes and Sir J. Lubbock, in England; to W. Wundt, L. Büchner, G.
Schneider, Fritz Schultze, and Karl Groos, in Germany; to Alfred
Espinas and E. Jourdan, in France; and to Tito Vignoli, in Italy.
In Germany, Wilhelm Wundt, of Leipzig, is considered to be the ablest
living psychologist; he has the inestimable advantage over most other
philosophers of a thorough zoological, anatomical, and physiological
education. Formerly assistant and pupil of Helmholtz, Wundt had early
accustomed himself to follow the application of the laws of physics and
chemistry through the whole field of physiology, and, consequently,
in the sense of Johannes Müller, in _psychology_, as a subsection
of the latter. Starting from this point of view, Wundt published
his valuable "Lectures on human and animal psychology" in 1863. He
proved, as he himself tells us in the preface, that the theatre of
the most important psychic processes is in the "unconscious soul,"
and he affords us "a view of the mechanism which, in the unconscious
background of the soul, manipulates the impressions which arise
from the external stimuli." What seems to me, however, of special
importance and value in Wundt's work is that he "extends the law of the
persistence of force for the first time to the psychic world, and makes
use of a series of facts of electro-physiology by way of demonstration."
Thirty years afterwards (1892) Wundt published a second, much
abridged and entirely modified, edition of his work. The important
principles of the first edition are entirely abandoned in the second,
and the monistic is exchanged for a purely dualistic stand-point.
Wundt himself says in the preface to the second edition that he has
emancipated himself from the fundamental errors of the first, and
that he "learned many years ago to consider the work a sin of his
youth"; it "weighed on him as a kind of crime, from which he longed
to free himself as soon as possible." In fact, the most important
systems of psychology are completely opposed to each other in the two
editions of Wundt's famous _Observations_. In the first edition he
is purely monistic and materialistic, in the second edition purely
dualistic and spiritualistic. In the one psychology is treated as a
_physical_ science, on the same laws as the whole of physiology, of
which it is only a part; thirty years afterwards he finds psychology
to be a _spiritual_ science, with principles and objects entirely
different from those of physical science. This conversion is most
clearly expressed in his principle of psycho-physical parallelism,
according to which "every psychic event has a corresponding physical
change"; but the two are completely independent, and are not in any
natural causal connection. This complete dualism of body and soul,
of nature and mind, naturally gave the liveliest satisfaction to the
prevailing school-philosophy, and was acclaimed by it as an important
advance, especially seeing that it came from a distinguished scientist
who had previously adhered to the opposite system of monism. As I
myself continue, after more than forty years' study, in this "narrow"
position, and have not been able to free myself from it in spite of
all my efforts, I must naturally consider the "youthful sin" of the
young physiologist Wundt to be a correct knowledge of nature, and
energetically defend it against the antagonistic view of the old
philosopher Wundt.
This entire change of philosophical principles, which we find in Wundt,
as we found it in Kant, Virchow, Du Bois-Reymond, Karl Ernst Baer, and
others, is very interesting. In their youth these able and talented
scientists embrace the whole field of biological research in a broad
survey, and make strenuous efforts to find a unifying, natural basis
for their knowledge; in their later years they have found that this is
not completely attainable, and so they entirely abandon the idea. In
extenuation of these psychological metamorphoses they can, naturally,
plead that in their youth they overlooked the difficulties of the great
task, and misconceived the true goal; with the maturer judgment of age
and the accumulation of experience they were convinced of their errors,
and discovered the true path to the source of truth. On the other hand,
it is possible to think that great scientists approach their task with
less prejudice and more energy in their earlier years--that their
vision is clearer and their judgment purer; the experiences of later
years sometimes have the effect, not of enriching, but of disturbing,
the mind, and with old age there comes a gradual decay of the brain,
just as happens in all other organs. In any case, this change of views
is in itself an instructive psychological fact; because, like many
other forms of change of opinion, it shows that the highest psychic
functions are subject to profound individual changes in the course of
life, like all the other vital processes.
For the profitable construction of comparative psychology it is
extremely important not to confine the critical comparison to man
and the brute in general, but to put side by side the innumerable
gradations of their mental activity. Only thus can we attain a clear
knowledge of the long scale of psychic development which runs unbroken
from the lowest, unicellular forms of life up to the mammals, and to
man at their head. But even within the limits of our own race such
gradations are very noticeable, and the ramifications of the "psychic
ancestral tree" are very numerous. The psychic difference between the
crudest savage of the lowest grade and the most perfect specimen of
the highest civilization is colossal--much greater than is commonly
supposed. By the due appreciation of this fact, especially in the
latter half of the century, the "Anthropology of the uncivilized races"
(Waitz) has received a strong support, and comparative ethnography has
come to be considered extremely important for psychological purposes.
Unfortunately, the enormous quantity of raw material of this science
has not yet been treated in a satisfactory critical manner. What
confused and mystic ideas still prevail in this department may be seen,
for instance, in the _Völkergedanke_ of the famous traveller, Adolf
Bastian, who, though a prolific writer, merely turns out a hopeless
mass of uncritical compilation and confused speculation.
The most neglected of all psychological methods, even up to the present
day, is the evolution of the soul; yet this little-frequented path
is precisely the one that leads us most quickly and securely through
the gloomy primeval forest of psychological prejudices, dogmas, and
errors, to a clear insight into many of the chief psychic problems. As
I did in the other branch of organic evolution, I again put before the
reader the two great branches of the science which I differentiated in
1866--ontogeny and phylogeny. The ontogeny, or embryonic development,
of the soul, individual or biontic psychogeny, investigates the gradual
and hierarchic development of the soul in the individual, and seeks to
learn the laws by which it is controlled. For a great part of the life
of the mind a good deal has been done in this direction for centuries;
rational pedagogy must have set itself the task at an early date of the
theoretical study of the gradual development and formative capacity of
the young mind that was committed to it for education and formation.
Most pedagogues, however, were idealistic or dualistic philosophers,
and so they went to work with all the prejudices of the spiritualistic
psychology. It is only in the last few decades that this dogmatic
tendency has been largely superseded even in the school by scientific
methods; we now find a greater concern to apply the chief laws of
evolution even in the discussion of the soul of the child. The raw
material of the child's soul is already qualitatively determined by
_heredity_ from parents and ancestors; education has the noble task of
bringing it to a perfect maturity by intellectual instruction and moral
training--that is, by _adaptation_. Wilhelm Preyer was the first to
lay the foundation of our knowledge of the early psychic development
in his interesting work on _The Mind of the Child_. Much is still to
be done in the study of the later stages and metamorphoses of the
individual soul, and once more the correct, critical application of the
biogenetic law is proving a guiding star to the scientific mind.
A new and fertile epoch of higher development dawned for psychology
and all other biological sciences when Charles Darwin applied the
principles of evolution to them forty years ago. The seventh chapter
of his epoch-making work on _The Origin of Species_ is devoted to
instinct. It contains the valuable proof that the instincts of animals
are subject, like all other vital processes, to the general laws of
historic development. The special instincts of particular species were
formed by _adaptation_, and the modifications thus acquired were handed
on to posterity by _heredity_; in their formation and preservation
natural selection plays the same part as in the transformation of
every other physiological function. Darwin afterwards developed this
fundamental thought in a number of works, showing that the same laws of
"mental evolution" hold good throughout the entire organic world, not
less in man than in the brute, and even in the plant. Hence the unity
of the organic world, which is revealed by the common origin of its
members, applies also to the entire province of psychic life, from the
simplest unicellular organism up to man.
To George Romanes we owe the further development of Darwin's
psychology and its special application to the different sections of
psychic activity. Unfortunately, his premature decease prevented the
completion of the great work which was to reconstruct every section
of comparative psychology on the lines of monistic evolution. The
two volumes of this work which were completed are among the most
valuable productions of psychological literature. For, conformably
to the principles of our modern monistic research, his first care
was to collect and arrange all the important facts which have been
empirically established in the field of comparative psychology in the
course of centuries; in the second place, these facts are tested with
an _objective criticism_, and systematically distributed; finally, such
rational conclusions are drawn from them on the chief general questions
of psychology as are in harmony with the fundamental principles of
modern monism. The first volume of Romanes's work bears the title
of _Mental Evolution in the Animal World_; it presents, in natural
connection, the entire length of the chain of psychic evolution in the
animal world, from the simplest sensations and instincts of the lowest
animals to the elaborate phenomena of consciousness and reason in the
highest. It contains also a number of extracts from a manuscript which
Darwin left "on instinct," and a complete collection of all that he
wrote in the province of psychology.
The second and more important volume of Romanes's work treats of
"Mental evolution in man and the origin of human faculties." The
distinguished psychologist gives a convincing proof in it "that the
psychological barrier between man and the brute has been overcome."
Man's power of conceptual thought and of abstraction has been gradually
evolved from the non-conceptual stages of thought and ideation in the
nearest related mammals. Man's highest mental powers--reason, speech,
and conscience--have arisen from the lower stages of the same faculties
in our primate ancestors (the simiæ and prosimiæ). Man has no single
mental faculty which is his exclusive prerogative. His whole psychic
life differs from that of the nearest related mammals only in degree,
and not in kind; quantitatively, not qualitatively.
I recommend those of my readers who are interested in these momentous
questions of psychology to study the profound work of Romanes. I am
completely at one with him and Darwin in almost all their views and
convictions. Wherever an apparent discrepancy is found between these
authors and my earlier productions, it is either a case of imperfect
expression on my part or an unimportant difference in application of
principle. For the rest, it is characteristic of this "science of
ideas" that the most eminent philosophers hold entirely antagonistic
views on its fundamental notions.
CHAPTER VII
PSYCHIC GRADATIONS
Psychological Unity of Organic Nature--Material Basis of the
Soul: Psychoplasm--Scale of Sensation--Scale of Movement--Scale
of Reflex Action--Simple and Compound Reflex Action--Reflex
Action and Consciousness--Scale of Perception--Unconscious and
Conscious Perception--Scale of Memory--Unconscious and Conscious
Memory--Association of Perceptions--Instinct--Primary and Secondary
Instincts--Scale of Reason--Language--Emotion and Passion--The
Will--Freedom of the Will
The great progress which psychology has made, with the assistance
of evolution, in the latter half of the century culminates in the
recognition of _the psychological unity of the organic world_.
Comparative psychology, in co-operation with the ontogeny and phylogeny
of the _psyche_, has enforced the conviction that organic life in all
its stages, from the simplest unicellular protozoon up to man, springs
from the same elementary forces of nature, from the physiological
functions of sensation and movement. The future task of scientific
psychology, therefore, is not, as it once was, the exclusively
subjective and introspective analysis of the highly developed mind
of a philosopher, but the objective, comparative study of the long
gradation by which man has slowly arisen through a vast series of lower
animal conditions. This great task of separating the different steps
in the psychological ladder, and proving their unbroken phylogenetic
connection, has only been seriously attempted during the last ten
years, especially in the splendid w
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