the most valuable amplification of his theory of selection is, in my
opinion, the work of Richard Semon: _Die Mneme als erhaltendes Prinzip
im Wechsel des organischen Geschehens_.[133] He offers a psychological
explanation of the facts of heredity by reducing them to a process of
(unconscious) memory. The physiologist Ewald Hering had shown in 1870
that memory must be regarded as a general function of organic matter,
and that we are quite unable to explain the chief vital phenomena,
especially those of reproduction and inheritance, unless we admit this
unconscious memory. In my essay _Die Perigenesis der Plastidule_[134]
I elaborated this far-reaching idea, and applied the physical
principle of transmitted motion to the plastidules, or active
molecules of plasm. I concluded that "heredity is the memory of the
plastidules, and variability their power of comprehension." This
"provisional attempt to give a mechanical explanation of the
elementary processes of evolution" I afterwards extended by showing
that sensitiveness is (as Carl Naegeli, Ernst Mach, and Albrecht Rau
express it) a general quality of matter. This form of panpsychism
finds its simplest expression in the "trinity of substance."
To the two fundamental attributes that Spinoza ascribed to
substance--Extension (matter as occupying space) and Cogitation
(energy, force)--we now add the third fundamental quality of Psychoma
(sensitiveness, soul). I further elaborated this trinitarian
conception of substance in the nineteenth chapter of my _Die
Lebenswunder_ (1904),[135] and it seems to me well calculated to
afford a monistic solution of many of the antitheses of philosophy.
This important Mneme-theory of Semon and the luminous physiological
experiments and observations associated with it not only throw
considerable light on transformative inheritance, but provide a sound
physiological foundation for the biogenetic law. I had endeavoured to
show in 1874, in the first chapter of my _Anthropogenie_,[136] that
this fundamental law of organic evolution holds good generally, and
that there is everywhere a direct causal connection between ontogeny
and phylogeny. "Phylogenesis is the mechanical cause of ontogenesis;"
in other words, "The evolution of the stem or race is--in accordance
with the laws of heredity and adaptation--the real cause of all the
changes that appear, in a condensed form, in the development of the
individual organism from the ovum, in either the embryo or the larva."
It is now fifty years since Charles Darwin pointed out, in the
thirteenth chapter of his epoch-making _Origin of Species_, the
fundamental importance of embryology in connection with his theory of
descent:
"The leading facts in embryology, which are second to none in
importance, are explained on the principle of variations in the many
descendants from some one ancient progenitor, having appeared at a not
very early period of life, and having been inherited at a
corresponding period."[137]
He then shows that the striking resemblance of the embryos and larvae
of closely related animals, which in the mature stage belong to widely
different species and genera, can only be explained by their descent
from a common progenitor. Fritz Mueller made a closer study of these
important phenomena in the instructive instance of the Crustacean
larva, as given in his able work _Fuer Darwin_[138] (1864). I then, in
1872, extended the range so as to include all animals (with the
exception of the unicellular Protozoa) and showed, by means of the
theory of the Gastraea, that all multicellular, tissue-forming
animals--all the Metazoa--develop in essentially the same way from the
primary germ-layers.
I conceived the embryonic form, in which the whole structure consists of
only two layers of cells, and is known as the gastrula, to be the
ontogenetic recapitulation, maintained by tenacious heredity, of a
primitive common progenitor of all the Metazoa, the Gastraea. At a later
date (1895) Monticelli discovered that this conjectural ancestral form is
still preserved in certain primitive Coelenterata--Pemmatodiscus,
Kunstleria, and the nearly-related Orthonectida.
The general application of the biogenetic law to all classes of
animals and plants has been proved in my _Systematische
Phylogenie_.[139] It has, however, been frequently challenged, both by
botanists and zoologists, chiefly owing to the fact that many have
failed to distinguish its two essential elements, palingenesis and
cenogenesis. As early as 1874 I had emphasised, in the first chapter
of my _Evolution of Man_, the importance of discriminating carefully
between these two sets of phenomena:
"In the evolutionary appreciation of the facts of embryology we must
take particular care to distinguish sharply and clearly between the
primary, palingenetic evolutionary processes and the secondary,
cenogenetic processes. The palingenetic phenomena, or embryonic
_recapitulations_, are due to heredity, to the transmission of
characters from one generation to another. They enable us to draw
direct inferences in regard to corresponding structures in the
development of the species (e.g. the chorda or the branchial arches in
all vertebrate embryos). The cenogenetic phenomena, on the other hand,
or the embryonic _variations_, cannot be traced to inheritance from a
mature ancestor, but are due to the adaption of the embryo or the
larva to certain conditions of its individual development (e.g. the
amnion, the allantois, and the vitelline arteries in the embryos of
the higher vertebrates). These cenogenetic phenomena are later
additions; we must not infer from them that there were corresponding
processes in the ancestral history, and hence they are apt to
mislead."
The fundamental importance of these facts of comparative anatomy,
atavism, and the rudimentary organs, was pointed out by Darwin in the
first part of his classic work, _The Descent of Man and Selection in
Relation to Sex_ (1871).[140] In the "General summary and conclusion"
(chap. xxi.) he was able to say, with perfect justice: "He who is not
content to look, like a savage, at the phenomena of nature as
disconnected, cannot any longer believe that man is the work of a
separate act of creation. He will be forced to admit that the close
resemblance of the embryo of man to that, for instance, of a dog--the
construction of his skull, limbs, and whole frame on the same plan
with that of other mammals, independently of the uses to which the
parts may be put--the occasional reappearance of various structures,
for instance of several muscles, which man does not normally possess,
but which are common to the Quadrumana--and a crowd of analogous
facts--all point in the plainest manner to the conclusion that man is
the co-descendant with other mammals of a common progenitor."
These few lines of Darwin's have a greater scientific value than
hundreds of those so-called "anthropological treatises," which give
detailed descriptions of single organs, or mathematical tables with
series of numbers and what are claimed to be "exact analyses," but are
devoid of synoptic conclusions and a philosophical spirit.
Charles Darwin is not generally recognised as a great anthropologist,
nor does the school of modern anthropologists regard him as a leading
authority. In Germany, especially, the great majority of the members
of the anthropological societies took up an attitude of hostility to
him from the very beginning of the controversy in 1860. _The Descent
of Man_ was not merely rejected, but even the discussion of it was
forbidden on the ground that it was "unscientific."
The centre of this inveterate hostility for thirty years--especially
after 1877--was Rudolph Virchow of Berlin, the leading investigator
in pathological anatomy, who did so much for the reform of medicine by
his establishment of cellular pathology in 1858. As a prominent
representative of "exact" or "descriptive" anthropology, and lacking a
broad equipment in comparative anatomy and ontogeny, he was unable to
accept the theory of descent. In earlier years, and especially during
his splendid period of activity at Wuerzburg (1848-1856), he had been a
consistent free-thinker, and had in a number of able articles
(collected in his _Gesammelte Abhandlungen_)[141] upheld the unity of
human nature, the inseparability of body and spirit. In later years at
Berlin, where he was more occupied with political work and sociology
(especially after 1866), he abandoned the positive monistic position
for one of agnosticism and scepticism, and made concessions to the
dualistic dogma of a spiritual world apart from the material frame.
In the course of a Scientific Congress at Munich in 1877 the conflict
of these antithetic views of nature came into sharp relief. At this
memorable Congress I had undertaken to deliver the first address
(September 18th) on the subject of "Modern evolution in relation to
the whole of science." I maintained that Darwin's theory not only
solved the great problem of the origin of species, but that its
implications, especially in regard to the nature of man, threw
considerable light on the whole of science, and on anthropology in
particular. The discovery of the real origin of man by evolution from
a long series of mammal ancestors threw light on his place in nature
in every respect, as Huxley had already shown in his excellent
lectures of 1863. Just as all the organs and tissues of the human body
had originated from those of the nearest related mammals, certain
ape-like forms, so we were bound to conclude that his mental qualities
also had been derived from those of his extinct primate ancestor.
This monistic view of the origin and nature of man, which is now admitted
by nearly all who have the requisite acquaintance with biology, and
approach the subject without prejudice, encountered a sharp opposition at
that time. The opposition found its strongest expression in an address that
Virchow delivered at Munich four days afterwards (September 22nd), on "The
freedom of science in the modern State." He spoke of the theory of
evolution as an unproved hypothesis, and declared that it ought not to be
taught in the schools, because it was dangerous to the State. "We must
not," he said, "teach that man has descended from the ape or any other
animal." When Darwin, usually so lenient in his judgment, read the English
translation of Virchow's speech, he expressed his disapproval in strong
terms. But the great authority that Virchow had--an authority well founded
in pathology and sociology--and his prestige as president of the German
Anthropological Society, had the effect of preventing any member of the
Society from raising serious opposition to him for thirty years. Numbers of
journals and treatises repeated his dogmatic statement: "It is quite
certain that man has descended neither from the ape nor from any other
animal." In this he persisted till his death in 1902. Since that time the
whole position of German anthropology has changed. The question is no
longer whether man was created by a distinct supernatural act or evolved
from other mammals, but to which line of the animal hierarchy we must look
for the actual series of ancestors. The interested reader will find an
account of this "battle of Munich" (1877) in my three Berlin lectures
(April, 1905), _Der Kampf um die Entwickelungs-Gedanken_.[142]
The main points in our genealogical tree were clearly recognised by
Darwin in the sixth chapter of the _Descent of Man_. Lowly organised
fishes, like the lancelot (Amphioxus), are descended from lower
invertebrates resembling the larvae of an existing Tunicate
(Appendicularia). From these primitive fishes were evolved higher
fishes of the ganoid type and others of the type of Lepidosiren
(Dipneusta). It is a very small step from these to the Amphibia:
"In the class of animals the steps are not difficult to conceive which
led from the ancient Monotremata to the ancient Marsupials; and from
these to the early progenitors of the placental mammals. We may thus
ascend to the Lemuridae; and the interval is not very wide from these
to the Simiadae. The Simiadae then branched off into two great stems,
the New World and Old World monkeys; and from the latter, at a remote
period, Man, the wonder and glory of the Universe, proceeded."[143]
In these few lines Darwin clearly indicated the way in which we were
to conceive our ancestral series within the vertebrates. It is fully
confirmed by all the arguments of comparative anatomy and embryology,
of palaeontology and physiology; and all the research of the
subsequent forty years have gone to establish it. The deep interest in
geology which Darwin maintained throughout his life and his complete
knowledge of palaeontology enabled him to grasp the fundamental
importance of the palaeontological record more clearly than
anthropologists and zoologists usually do.
There has been much debate in subsequent decades whether Darwin
himself maintained that man was descended from the ape, and many
writers have sought to deny it. But the lines I have quoted _verbatim_
from the conclusion of the sixth chapter of the _Descent of Man_
(1871) leave no doubt that he was as firmly convinced of it as was his
great precursor Jean Lamarck in 1809. Moreover, Darwin adds, with
particular explicitness, in the "general summary and conclusion"
(chap. xxi.) of that standard work:[144]
"By considering the embryological structure of man--the homologies
which he presents with the lower animals,--the rudiments which he
retains,--and the reversions to which he is liable, we can partly
recall in imagination the former condition of our early progenitors;
and can approximately place them in their proper place in the
zoological series. We thus learn that man is descended from a hairy,
tailed quadruped, probably arboreal in its habits, and an inhabitant
of the Old World. This creature, if its whole structure had been
examined by a naturalist, would have been classed amongst the
Quadrumana, as surely as the still more ancient progenitor of the Old
and New World monkeys."
These clear and definite lines leave no doubt that Darwin--so critical
and cautious in regard to important conclusions--was quite as firmly
convinced of the descent of man from the apes (the Catarrhinae, in
particular) as Lamarck was in 1809 and Huxley in 1863.
It is to be noted particularly that, in these and other observations
on the subject, Darwin decidedly assumes the monophyletic origin of
the mammals, including man. It is my own conviction that this is of
the greatest importance. A number of difficult questions in regard to
the development of man, in respect of anatomy, physiology, psychology,
and embryology, are easily settled if we do not merely extend our
_progonotaxis_ to our nearest relatives, the anthropoid apes and the
tailed monkeys from which these have descended, but go further back
and find an ancestor in the group of the Lemuridae, and still further
back to the Marsupials and Monotremata. The essential identity of all
the Mammals in point of anatomical structure and embryonic
development--in spite of their astonishing differences in external
appearance and habits of life--is so palpably significant that modern
zoologists are agreed in the hypothesis that they have all sprung from
a common root, and that this root may be sought in the earlier
Palaeozoic Amphibia.
The fundamental importance of this comparative morphology of the
Mammals, as a sound basis of scientific anthropology, was recognised
just before the beginning of the nineteenth century, when Lamarck
first emphasised (1794) the division of the animal kingdom into
Vertebrates and Invertebrates. Even thirteen years earlier (1781),
when Goethe made a close study of the mammal skeleton in the
Anatomical Institute at Jena, he was intensely interested to find that
the composition of the skull was the same in man as in the other
mammals. His discovery of the _os inter-maxillare_ in man (1784),
which was contradicted by most of the anatomists of the time, and his
ingenious "vertebral theory of the skull," were the splendid fruit of
his morphological studies. They remind us how Germany's greatest
philosopher and poet was for many years ardently absorbed in the
comparative anatomy of man and the mammals, and how he divined that
their wonderful identity in structure was no mere superficial
resemblance, but pointed to a deep internal connection. In my
_Generelle Morphologie_ (1866), in which I published the first
attempts to construct phylogenetic trees, I have given a number of
remarkable theses of Goethe, which may be called "phyletic
prophecies." They justify us in regarding him as a precursor of
Darwin.
In the ensuing forty years I have made many conscientious efforts to
penetrate further along that line of anthropological research that was
opened up by Goethe, Lamarck, and Darwin. I have brought together the many
valuable results that have constantly been reached in comparative anatomy,
physiology, ontogeny, and palaeontology, and maintained the effort to
reform the classification of animals and plants in an evolutionary sense.
The first rough drafts of pedigrees that were published in the _Generelle
Morphologie_ have been improved time after time in the ten editions of my
_Natuerlich Schoepfungsgeschichte_ (1868-1902).[145] A sounded basis for my
phyletic hypotheses, derived from a discriminating combination of the three
great records--morphology, ontogeny, and palaeontology--was provided in the
three volumes of my _Systematische Phylogenie_[146] (1894 Protists and
Plants, 1895 Vertebrates, 1896 Invertebrates).
In my _Anthropogenie_[147] I endeavoured to employ all the known
facts of comparative ontogeny (embryology) for the purpose of
completing my scheme of human phylogeny (evolution). I attempted to
sketch the historical development of each organ of the body, beginning
with the most elementary structures in the germ-layers of the
Gastraea. At the same time I drew up a corrected statement of the most
important steps in the line of our ancestral series.
At the fourth International Congress of Zoology at Cambridge (August
26th, 1898) I delivered an address on "Our present knowledge of the
Descent of Man." It was translated into English, enriched with many
valuable notes and additions, by my friend and pupil in earlier days
Dr. Hans Gadow (Cambridge), and published under the title: _The Last
Link: our present knowledge of the Descent of Man_[148] The
determination of the chief animal forms that occur in the line of our
ancestry is there restricted to thirty types, and these are
distributed in six main groups.
The first half of this "Progonotaxis hominis," which has no support
from fossil evidence, comprises three groups: (i) Protista
(unicellular organisms, 1-5): (ii) Invertebrate Metazoa (Coelenteria
6-8, Vermalia 9-11): (iii) Monorrhine Vertebrates (Acrania 12-13,
Cyclostoma 14-15). The second half, which is based on fossil records,
also comprises three groups: (iv) Palaeozoic cold-blooded Craniota
(Fishes 16-18, Amphibia 19, Reptiles 20): (v) Mesozoic Mammals
(Monotrema 21, Marsupialia 22, Mallotheria 23): (vi) Cenozoic Primates
(Lemuridae 24-25, Tailed Apes 26-27, Anthropomorpha 28-30). An
improved and enlarged edition of this hypothetic "Progonotaxis
hominis" was published in 1908, in my essay _Unsere Ahnenreihe_.[149]
If I have succeeded in furthering, in some degree, by these
anthropological works, the solution of the great problem of Man's
place in nature, and particularly in helping to trace the definite
stages in our ancestral series, I owe the success, not merely to the
vast progress that biology has made in the last half century, but
largely to the luminous example of the great investigators who have
applied themselves to the problem, with so much assiduity and genius,
for a century and a quarter--I mean Goethe and Lamarck, Gegenbaur and
Huxley, but, above all, Charles Darwin. It was the great genius of
Darwin that first brought together that symmetrical temple of
scientific knowledge, the theory of descent. It was Darwin who put the
crown on the edifice by his theory of natural selection. Not until
this broad inductive law was firmly established was it possible to
vindicate the special conclusion, the descent of man from a series of
other Vertebrates. By his illuminating discovery Darwin did more for
anthropology than thousands of those writers, who are more
specifically titled anthropologists, have done by their technical
treatises. We may, indeed, say that it is not merely as an exact
observer and ingenious experimenter, but as a distinguished
anthropologist and far-seeing thinker, that Darwin takes his place
among the greatest men of science of the nineteenth century.
To appreciate fully the immortal merit of Darwin in connection with
anthropology, we must remember that not only did his chief work, _The
Origin of Species_, which opened up a new era in natural history in
1859, sustain the most virulent and widespread opposition for a
lengthy period, but even thirty years later, when its principles were
generally recognised and adopted, the application of them to man was
energetically contested by many high scientific authorities. Even
Alfred Russel Wallace, who discovered the principle of natural
selection independently in 1858, did not concede that it was
applicable to the higher mental and moral qualities of man. Dr.
Wallace still holds a spiritualist and dualist view of the nature of
man, contending that he is composed of a material frame (descended
from the apes) and an immortal immaterial soul (infused by a higher
power). This dual conception, moreover, is still predominant in the
wide circles of modern theology and metaphysics, and has the general
and influential adherence of the more conservative classes of society.
In strict contradiction to this mystical dualism, which is generally
connected with teleology and vitalism, Darwin always maintained the
complete unity of human nature, and showed convincingly that the
psychological side of man was developed, in the same way as the body,
from the less advanced soul of the anthropoid ape, and, at a still
more remote period, from the cerebral functions of the older
vertebrates. The eighth chapter of the _Origin of Species_, which is
devoted to instinct, contains weighty evidence 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. The higher moral
qualities of civilised man have been derived from the lower mental
functions of the uncultivated barbarians and savages, and these in
turn from the social instincts of the mammals. This natural and
monistic psychology of Darwin's was afterwards more fully developed by
his friend George Romanes in his excellent works _Mental Evolution in
Animals_ and _Mental Evolution in Man_.[150]