Professor of Anatomy in the University of Strassburg.
The problem of the origin of the human race, of the descent of man, is
ranked by Huxley in his epoch-making book "Man's Place in Nature", as
the deepest with which biology has to concern itself, "the question
of questions,"--the problem which underlies all others. In the same
brilliant and lucid exposition, which appeared in 1863, soon after the
publication of Darwin's "Origin of Species", Huxley stated his own views
in regard to this great problem. He tells us how the idea of a natural
descent of man gradually grew up in his mind, it was especially the
assertions of Owen in regard to the total difference between the human
and the simian brain that called forth strong dissent from the great
anatomist Huxley, and he easily succeeded in showing that Owen's
supposed differences had no real existence; he even established, on the
basis of his own anatomical investigations, the proposition that the
anatomical differences between the Marmoset and the Chimpanzee are much
greater than those between the Chimpanzee and Man.
But why do we thus introduce the study of Darwin's "Descent of Man",
which is to occupy us here, by insisting on the fact that Huxley had
taken the field in defence of the descent of man in 1863, while Darwin's
book on the subject did not appear till 1871? It is in order that we may
clearly understand how it happened that from this time onwards Darwin
and Huxley followed the same great aim in the most intimate association.
Huxley and Darwin working at the same Problema maximum! Huxley fiery,
impetuous, eager for battle, contemptuous of the resistance of a dull
world, or energetically triumphing over it. Darwin calm, weighing every
problem slowly, letting it mature thoroughly,--not a fighter, yet having
the greater and more lasting influence by virtue of his immense mass of
critically sifted proofs. Darwin's friend, Huxley, was the first to do
him justice, to understand his nature, and to find in it the reason why
the detailed and carefully considered book on the descent of man made
its appearance so late. Huxley, always generous, never thought of
claiming priority for himself. In enthusiastic language he tells how
Darwin's immortal work, "The Origin of Species", first shed light for
him on the problem of the descent of man; the recognition of a vera
causa in the transformation of species illuminated his thoughts as with
a flash. He was now content to leave what perplexed him, what he could
not yet solve, as he says himself, "in the mighty hands of Darwin."
Happy in the bustle of strife against old and deep-rooted prejudices,
against intolerance and superstition, he wielded his sharp weapons on
Darwin's behalf; wearing Darwin's armour he joyously overthrew adversary
after adversary. Darwin spoke of Huxley as his "general agent." ("Life
and Letters of Thomas Henry Huxley", Vol. I. page 171, London, 1900.)
Huxley says of himself "I am Darwin's bulldog." (Ibid. page 363.)
Thus Huxley openly acknowledged that it was Darwin's "Origin of Species"
that first set the problem of the descent of man in its true light, that
made the question of the origin of the human race a pressing one. That
this was the logical consequence of his book Darwin himself had long
felt. He had been reproached with intentionally shirking the application
of his theory to Man. Let us hear what he says on this point in his
autobiography: "As soon as I had become, in the year 1837 or 1838,
convinced that species were mutable productions, I could not avoid the
belief that man must come under the same law. Accordingly I collected
notes on the subject for my own satisfaction, and not for a long time
with any intention of publishing. Although in the 'Origin of Species'
the derivation of any particular species is never discussed, yet I
thought it best, in order THAT NO HONOURABLE MAN SHOULD ACCUSE ME OF
CONCEALING MY VIEWS (No italics in original.), to add that by the work
'light would be thrown on the origin of man and his history.' It would
have been useless and injurious to the success of the book to have
paraded, without giving any evidence, my conviction with respect to his
origin." ("Life and Letters of Charles Darwin", Vol. 1. page 93.)
In a letter written in January, 1860, to the Rev. L. Blomefield, Darwin
expresses himself in similar terms. "With respect to man, I am very far
from wishing to obtrude my belief; but I thought it dishonest to quite
conceal my opinion." (Ibid. Vol. II. page 263.)
The brief allusion in the "Origin of Species" is so far from prominent
and so incidental that it was excusable to assume that Darwin had not
touched upon the descent of man in this work. It was solely the desire
to have his mass of evidence sufficiently complete, solely Darwin's
great characteristic of never publishing till he had carefully weighed
all aspects of his subject for years, solely, in short, his most
fastidious scientific conscience that restrained him from challenging
the world in 1859 with a book in which the theory of the descent of man
was fully set forth. Three years, frequently interrupted by ill-health,
were needed for the actual writing of the book ("Life and Letters", Vol.
I. page 94.): the first edition, which appeared in 1871, was followed in
1874 by a much improved second edition, the preparation of which he very
reluctantly undertook. (Ibid. Vol. III. page 175.)
This, briefly, is the history of the work, which, with the "Origin of
Species", marks an epoch in the history of biological sciences--the work
with which the cautious, peace-loving investigator ventured forth from
his contemplative life into the arena of strife and unrest, and
laid himself open to all the annoyances that deep-rooted belief and
prejudice, and the prevailing tendency of scientific thought at the time
could devise.
Darwin did not take this step lightly. Of great interest in this
connection is a letter written to Wallace on Dec. 22, 1857 (Ibid. Vol.
II. page 109.), in which he says "You ask whether I shall discuss
'man.' I think I shall avoid the whole subject, as so surrounded
with prejudices; though I fully admit that it is the highest and most
interesting problem for the naturalist." But his conscientiousness
compelled him to state briefly his opinion on the subject in the "Origin
of Species" in 1859. Nevertheless he did not escape reproaches for
having been so reticent. This is unmistakably apparent from a letter to
Fritz Muller dated February 22 (1869?), in which he says: "I am thinking
of writing a little essay on the Origin of Mankind, as I have been
taunted with concealing my opinions." (Ibid. Vol. III. page 112.)
It might be thought that Darwin behaved thus hesitatingly, and was so
slow in deciding on the full publication of his collected material in
regard to the descent of man, because he had religious difficulties to
overcome.
But this was not the case, as we can see from his admirable confession
of faith, the publication of which we owe to his son Francis. (Ibid.
Vol. I. pages 304-317.) Whoever wishes really to understand the lofty
character of this great man should read these immortal lines in which he
unfolds to us in simple and straightforward words the development of his
conception of the universe. He describes how, though he was still quite
orthodox during his voyage round the world on board the "Beagle", he
came gradually to see, shortly afterwards (1836-1839) that the Old
Testament was no more to be trusted than the Sacred Books of the
Hindoos; the miracles by which Christianity is supported, the
discrepancies between the accounts in the different Gospels, gradually
led him to disbelieve in Christianity as a divine revelation. "Thus," he
writes ("Life and Letters", Vol. 1. page 309.), "disbelief crept over me
at a very slow rate, but was at last complete. The rate was so slow that
I felt no distress." But Darwin was too modest to presume to go beyond
the limits laid down by science. He wanted nothing more than to be able
to go, freely and unhampered by belief in authority or in the Bible, as
far as human knowledge could lead him. We learn this from the concluding
words of his chapter on religion: "The mystery of the beginning of all
things is insoluble by us; and I for one must be content to remain an
Agnostic." (Loc. cit. page 313.)
Darwin was always very unwilling to give publicity to his views in
regard to religion. In a letter to Asa Gray on May 22, 1860 (Ibid. Vol.
II. page 310.), he declares that it is always painful to him to have
to enter into discussion of religious problems. He had, he said, no
intention of writing atheistically.
Finally, let us cite one characteristic sentence from a letter from
Darwin to C. Ridley (Ibid. Vol. III. page. 236. ("C. Ridley," Mr Francis
Darwin points out to me, should be H.N. Ridley. A.C.S.)) (Nov. 28,
1878.) A clergyman, Dr Pusey, had asserted that Darwin had written
the "Origin of Species" with some relation to theology. Darwin writes
emphatically, "Many years ago, when I was collecting facts for the
'Origin', my belief in what is called a personal God was as firm as that
of Dr Pusey himself, and as to the eternity of matter I never troubled
myself about such insoluble questions." The expression "many years ago"
refers to the time of his voyage round the world, as has already been
pointed out. Darwin means by this utterance that the views which had
gradually developed in his mind in regard to the origin of species were
quite compatible with the faith of the Church.
If we consider all these utterances of Darwin in regard to religion and
to his outlook on life (Weltanschauung), we shall see at least so much,
that religious reflection could in no way have influenced him in regard
to the writing and publishing of his book on "The Descent of Man".
Darwin had early won for himself freedom of thought, and to this freedom
he remained true to the end of his life, uninfluenced by the customs and
opinions of the world around him.
Darwin was thus inwardly fortified and armed against the host of
calumnies, accusations, and attacks called forth by the publication of
the "Origin of Species", and to an even greater extent by the appearance
of the "Descent of Man". But in his defence he could rely on the aid of
a band of distinguished auxiliaries of the rarest ability. His faithful
confederate, Huxley, was joined by the botanist Hooker, and, after
longer resistance, by the famous geologist Lyell, whose "conversion"
afforded Darwin peculiar satisfaction. All three took the field with
enthusiasm in defence of the natural descent of man. From Wallace, on
the other hand, though he shared with him the idea of natural selection,
Darwin got no support in this matter. Wallace expressed himself in a
strange manner. He admitted everything in regard to the morphological
descent of man, but maintained, in a mystic way, that something else,
something of a spiritual nature must have been added to what man
inherited from his animal ancestors. Darwin, whose esteem for Wallace
was extraordinarily high, could not understand how he could give
utterance to such a mystical view in regard to man; the idea seemed
to him so "incredibly strange" that he thought some one else must have
added these sentences to Wallace's paper.
Even now there are thinkers who, like Wallace, shrink from applying to
man the ultimate consequences of the theory of descent. The idea
that man is derived from ape-like forms is to them unpleasant and
humiliating.
So far I have been depicting the development of Darwin's work on the
descent of man. In what follows I shall endeavour to give a condensed
survey of the contents of the book.
It must at once be said that the contents of Darwin's work fall into two
parts, dealing with entirely different subjects. "The Descent of Man"
includes a very detailed investigation in regard to secondary sexual
characters in the animal series, and on this investigation Darwin
founded a new theory, that of sexual selection. With astonishing
patience he gathered together an immense mass of material, and showed,
in regard to Arthropods and Vertebrates, the wide distribution of
secondary characters, which develop almost exclusively in the male, and
which enable him, on the one hand, to get the better of his rivals in
the struggle for the female by the greater perfection of his weapons,
and on the other hand, to offer greater allurements to the female
through the higher development of decorative characters, of song, or of
scent-producing glands. The best equipped males will thus crowd out the
less well-equipped in the matter of reproduction, and thus the relevant
characters will be increased and perfected through sexual selection.
It is, of course, a necessary assumption that these secondary sexual
characters may be transmitted to the female, although perhaps in
rudimentary form.
As we have said, this theory of sexual selection takes up a great deal
of space in Darwin's book, and it need only be considered here in so far
as Darwin applied it to the descent of man. To this latter problem the
whole of Part I is devoted, while Part III contains a discussion of
sexual selection in relation to man, and a general summary. Part II
treats of sexual selection in general, and may be disregarded in our
present study. Moreover, many interesting details must necessarily be
passed over in what follows, for want of space.
The first part of the "Descent of Man" begins with an enumeration of
the proofs of the animal descent of man taken from the structure of
the human body. Darwin chiefly emphasises the fact that the human body
consists of the same organs and of the same tissues as those of the
other mammals; he shows also that man is subject to the same diseases
and tormented by the same parasites as the apes. He further dwells
on the general agreement exhibited by young, embryonic forms, and
he illustrates this by two figures placed one above the other, one
representing a human embryo, after Eaker, the other a dog embryo, after
Bischoff. ("Descent of Man" (Popular Edition, 1901), fig. 1, page 14.)
Darwin finds further proofs of the animal origin of man in the
reduced structures, in themselves extremely variable, which are either
absolutely useless to their possessors, or of so little use that they
could never have developed under existing conditions. Of such vestiges
he enumerates: the defective development of the panniculus carnosus
(muscle of the skin) so widely distributed among mammals, the
ear-muscles, the occasional persistence of the animal ear-point in man,
the rudimentary nictitating membrane (plica semilunaris) in the human
eye, the slight development of the organ of smell, the general hairiness
of the human body, the frequently defective development or entire
absence of the third molar (the wisdom tooth), the vermiform appendix,
the occasional reappearance of a bony canal (foramen supracondyloideum)
at the lower end of the humerus, the rudimentary tail of man (the
so-called taillessness), and so on. Of these rudimentary structures
the occasional occurrence of the animal ear-point in man is most fully
discussed. Darwin's attention was called to this interesting structure
by the sculptor Woolner. He figures such a case observed in man, and
also the head of an alleged orang-foetus, the photograph of which he
received from Nitsche.
Darwin's interpretation of Woolner's case as having arisen through a
folding over of the free edge of a pointed ear has been fully borne out
by my investigations on the external ear. (G. Schwalbe, "Das Darwin'sche
Spitzohr beim menschlichen Embryo", "Anatom. Anzeiger", 1889, pages
176-189, and other papers.) In particular, it was established by these
investigations that the human foetus, about the middle of its embryonic
life, possesses a pointed ear somewhat similar to that of the monkey
genus Macacus. One of Darwin's statements in regard to the head of the
orang-foetus must be corrected. A LARGE ear with a point is shown in
the photograph ("Descent of Man", fig.3, page 24.), but it can easily be
demonstrated--and Deniker has already pointed this out--that the figure
is not that of an orang-foetus at all, for that form has much smaller
ears with no point; nor can it be a gibbon-foetus, as Deniker supposes,
for the gibbon ear is also without a point. I myself regard it as that
of a Macacus-embryo. But this mistake, which is due to Nitsche, in no
way affects the fact recognised by Darwin, that ear-forms showing the
point characteristic of the animal ear occur in man with extraordinary
frequency.
Finally, there is a discussion of those rudimentary structures which
occur only in ONE sex, such as the rudimentary mammary glands in the
male, the vesicula prostatica, which corresponds to the uterus of the
female, and others. All these facts tell in favour of the common descent
of man and all other vertebrates. The conclusion of this section is
characteristic: "IT IS ONLY OUR NATURAL PREJUDICE, AND THAT ARROGANCE
WHICH MADE OUR FOREFATHERS DECLARE THAT THEY WERE DESCENDED FROM
DEMI-GODS, WHICH LEADS US TO DEMUR TO THIS CONCLUSION. BUT THE TIME WILL
BEFORE LONG COME, WHEN IT WILL BE THOUGHT WONDERFUL THAT NATURALISTS,
WHO WERE WELL ACQUAINTED WITH THE COMPARATIVE STRUCTURE AND DEVELOPMENT
OF MAN, AND OTHER MAMMALS, SHOULD HAVE BELIEVED THAT EACH WAS THE WORK
OF A SEPARATE ACT OF CREATION." (Ibid. page 36.)
In the second chapter there is a more detailed discussion, again based
upon an extraordinary wealth of facts, of the problem as to the manner
in which, and the causes through which, man evolved from a lower form.
Precisely the same causes are here suggested for the origin of man, as
for the origin of species in general. Variability, which is a necessary
assumption in regard to all transformations, occurs in man to a high
degree. Moreover, the rapid multiplication of the human race creates
conditions which necessitate an energetic struggle for existence, and
thus afford scope for the intervention of natural selection. Of the
exercise of ARTIFICIAL selection in the human race, there is nothing
to be said, unless we cite such cases as the grenadiers of Frederick
William I, or the population of ancient Sparta. In the passages already
referred to and in those which follow, the transmission of acquired
characters, upon which Darwin does not dwell, is taken for granted.
In man, direct effects of changed conditions can be demonstrated (for
instance in regard to bodily size), and there are also proofs of the
influence exerted on his physical constitution by increased use or
disuse. Reference is here made to the fact, established by Forbes,
that the Quechua-Indians of the high plateaus of Peru show a striking
development of lungs and thorax, as a result of living constantly at
high altitudes.
Such special forms of variation as arrests of development
(microcephalism) and reversion to lower forms are next discussed. Darwin
himself felt ("Descent of Man", page 54.) that these subjects are so
nearly related to the cases mentioned in the first chapter, that many
of them might as well have been dealt with there. It seems to me that it
would have been better so, for the citation of additional instances
of reversion at this place rather disturbs the logical sequence of his
ideas as to the conditions which have brought about the evolution of
man from lower forms. The instances of reversion here discussed
are microcephalism, which Darwin wrongly interpreted as atavistic,
supernumerary mammae, supernumerary digits, bicornuate uterus, the
development of abnormal muscles, and so on. Brief mention is also made
of correlative variations observed in man.
Darwin next discusses the question as to the manner in which man
attained to the erect position from the state of a climbing quadruped.
Here again he puts the influence of Natural Selection in the first
rank. The immediate progenitors of man had to maintain a struggle for
existence in which success was to the more intelligent, and to those
with social instincts. The hand of these climbing ancestors, which
had little skill and served mainly for locomotion, could only undergo
further development when some early member of the Primate series came to
live more on the ground and less among trees.
A bipedal existence thus became possible, and with it the liberation
of the hand from locomotion, and the one-sided development of the human
foot. The upright position brought about correlated variations in the
bodily structure; with the free use of the hand it became possible
to manufacture weapons and to use them; and this again resulted in a
degeneration of the powerful canine teeth and the jaws, which were then
no longer necessary for defence. Above all, however, the intelligence
immediately increased, and with it skull and brain. The nakedness of
man, and the absence of a tail (rudimentariness of the tail vertebrae)
are next discussed. Darwin is inclined to attribute the nakedness of
man, not to the action of natural selection on ancestors who originally
inhabited a tropical land, but to sexual selection, which, for aesthetic
reasons, brought about the loss of the hairy covering in man, or
primarily in woman. An interesting discussion of the loss of the tail,
which, however, man shares with the anthropoid apes, some other monkeys
and lemurs, forms the conclusion of the almost superabundant material
which Darwin worked up in the second chapter. His object was to
show that some of the most distinctive human characters are in all
probability directly or indirectly due to natural selection. With
characteristic modesty he adds ("Descent of Man", page 92.): "Hence, if
I have erred in giving to natural selection great power, which I am
very far from admitting, or in having exaggerated its power, which is in
itself probable, I have at least, as I hope, done good service in aiding
to overthrow the dogma of separate creations." At the end of the chapter
he touches upon the objection as to man's helpless and defenceless
condition. Against this he urges his intelligence and social instincts.
The two following chapters contain a detailed discussion of the
objections drawn from the supposed great differences between the mental
powers of men and animals. Darwin at once admits that the differences
are enormous, but not that any fundamental difference between the two
can be found. Very characteristic of him is the following passage:
"In what manner the mental powers were first developed in the
lowest organisms, is as hopeless an enquiry as how life itself first
originated. These are problems for the distant future, if they are ever
to be solved by man." (Ibid. page 100.)
After some brief observations on instinct and intelligence, Darwin
brings forward evidence to show that the greater number of the emotional
states, such as pleasure and pain, happiness and misery, love and hate
are common to man and the higher animals. He goes on to give various
examples showing that wonder and curiosity, imitation, attention, memory
and imagination (dreams of animals), can also be observed in the higher
mammals, especially in apes. In regard even to reason there are
no sharply defined limits. A certain faculty of deliberation is
characteristic of some animals, and the more thoroughly we know an
animal the more intelligence we are inclined to credit it with. Examples
are brought forward of the intelligent and deliberate actions of apes,
dogs and elephants. But although no sharply defined differences exist
between man and animals, there is, nevertheless, a series of other
mental powers which are characteristics usually regarded as absolutely
peculiar to man. Some of these characteristics are examined in detail,
and it is shown that the arguments drawn from them are not conclusive.
Man alone is said to be capable of progressive improvement; but against
this must be placed as something analogous in animals, the fact that
they learn cunning and caution through long continued persecution. Even
the use of tools is not in itself peculiar to man (monkeys use sticks,
stones and twigs), but man alone fashions and uses implements DESIGNED
FOR A SPECIAL PURPOSE. In this connection the remarks taken from Lubbock
in regard to the origin and gradual development of the earliest
flint implements will be read with interest; these are similar to the
observations on modern eoliths, and their bearing on the development of
the stone-industry. It is interesting to learn from a letter to Hooker
("Life and Letters", Vol. II. page 161, June 22, 1859.), that Darwin
himself at first doubted whether the stone implements discovered
by Boucher de Perthes were really of the nature of tools. With the
relentless candour as to himself which characterised him, he writes four
years later in a letter to Lyell in regard to this view of Boucher de
Perthes' discoveries: "I know something about his errors, and looked at
his book many years ago, and am ashamed to think that I concluded the
whole was rubbish! Yet he has done for man something like what Agassiz
did for glaciers." (Ibid. Vol. III. page 15, March 17, 1863.)
To return to Darwin's further comparisons between the higher mental
powers of man and animals. He takes much of the force from the argument
that man alone is capable of abstraction and self-consciousness by his
own observations on dogs. One of the main differences between man and
animals, speech, receives detailed treatment. He points out that various
animals (birds, monkeys, dogs) have a large number of different sounds
for different emotions, that, further, man produces in common with
animals a whole series of inarticulate cries combined with gestures, and
that dogs learn to understand whole sentences of human speech. In regard
to human language, Darwin expresses a view contrary to that held by Max
Muller ("Descent of Man", page 132.): "I cannot doubt that language owes
its origin to the imitation and modification of various natural sounds,
the voices of other animals, and man's own instinctive cries, aided by
signs and gestures." The development of actual language presupposes a
higher degree of intelligence than is found in any kind of ape. Darwin
remarks on this point (Ibid. pages 136, 137.): "The fact of the higher
apes not using their vocal organs for speech no doubt depends on their
intelligence not having been sufficiently advanced."
The sense of beauty, too, has been alleged to be peculiar to man. In
refutation of this assertion Darwin points to the decorative colours of
birds, which are used for display. And to the last objection, that man
alone has religion, that he alone has a belief in God, it is answered
"that numerous races have existed, and still exist, who have no idea of
one or more gods, and who have no words in their languages to express
such an idea." (Ibid. page 143.)
The result of the investigations recorded in this chapter is to show
that, great as the difference in mental powers between man and the
higher animals may be, it is undoubtedly only a difference "of degree
and not of kind." ("Descent of Man", page 193.)
In the fourth chapter Darwin deals with the MORAL SENSE or CONSCIENCE,
which is the most important of all differences between man and animals.
It is a result of social instincts, which lead to sympathy for other
members of the same society, to non-egoistic actions for the good
of others. Darwin shows that social tendencies are found among many
animals, and that among these love and kin-sympathy exist, and he gives
examples of animals (especially dogs) which may exhibit characters that
we should call moral in man (e.g. disinterested self-sacrifice for the
sake of others). The early ape-like progenitors of the human race were
undoubtedly social. With the increase of intelligence the moral sense
develops farther; with the acquisition of speech public opinion arises,
and finally, moral sense becomes habit. The rest of Darwin's detailed
discussions on moral philosophy may be passed over.
The fifth chapter may be very briefly summarised. In it Darwin shows
that the intellectual and moral faculties are perfected through natural
selection. He inquires how it can come about that a tribe at a low level
of evolution attains to a higher, although the best and bravest among
them often pay for their fidelity and courage with their lives without
leaving any descendants. In this case it is the sentiment of glory,
praise and blame, the admiration of others, which bring about the
increase of the better members of the tribe. Property, fixed dwellings,
and the association of families into a community are also indispensable
requirements for civilisation. In the longer second section of the
fifth chapter Darwin acts mainly as recorder. On the basis of numerous
investigations, especially those of Greg, Wallace, and Galton, he
inquires how far the influence of natural selection can be demonstrated
in regard to civilised nations. In the final section, which deals with
the proofs that all civilised nations were once barbarians, Darwin again
uses the results gained by other investigators, such as Lubbock and
Tylor. There are two sets of facts which prove the proposition in
question. In the first place, we find traces of a former lower state
in the customs and beliefs of all civilised nations, and in the second
place, there are proofs to show that savage races are independently able
to raise themselves a few steps in the scale of civilisation, and that
they have thus raised themselves.
In the sixth chapter of the work, Morphology comes into the foreground
once more. Darwin first goes back, however, to the argument based on the
great difference between the mental powers of the highest animals and
those of man. That this is only quantitative, not qualitative, he has
already shown. Very instructive in this connection is the reference to
the enormous difference in mental powers in another class. No one
would draw from the fact that the cochineal insect (Coccus) and the ant
exhibit enormous differences in their mental powers, the conclusion that
the ant should therefore be regarded as something quite distinct, and
withdrawn from the class of insects altogether.
Darwin next attempts to establish the SPECIFIC genealogical tree of
man, and carefully weighs the differences and resemblances between the
different families of the Primates. The erect position of man is an
adaptive character, just as are the various characters referable to
aquatic life in the seals, which, notwithstanding these, are ranked as
a mere family of the Carnivores. The following utterance is very
characteristic of Darwin ("Descent of Man", page 231.): "If man had
not been his own classifier, he would never have thought of founding
a separate order for his own reception." In numerous characters not
mentioned in systematic works, in the features of the face, in the form
of the nose, in the structure of the external ear, man resembles the
apes. The arrangement of the hair in man has also much in common with
the apes; as also the occurrence of hair on the forehead of the human
embryo, the beard, the convergence of the hair of the upper and under
arm towards the elbow, which occurs not only in the anthropoid apes, but
also in some American monkeys. Darwin here adopts Wallace's explanation
of the origin of the ascending direction of the hair in the forearm of
the orang,--that it has arisen through the habit of holding the hands
over the head in rain. But this explanation cannot be maintained when we
consider that this disposition of the hair is widely distributed among
the most different mammals, being found in the dog, in the sloth, and in
many of the lower monkeys.
After further careful analysis of the anatomical characters Darwin
reaches the conclusion that the New World monkeys (Platyrrhine) may
be excluded from the genealogical tree altogether, but that man is
an offshoot from the Old World monkeys (Catarrhine) whose progenitors
existed as far back as the Miocene period. Among these Old World monkeys
the forms to which man shows the greatest resemblance are the anthropoid
apes, which, like him, possess neither tail nor ischial callosities. The
platyrrhine and catarrhine monkeys have their primitive ancestor among
extinct forms of the Lemuridae. Darwin also touches on the question of
the original home of the human race and supposes that it may have been
in Africa, because it is there that man's nearest relatives, the gorilla
and the chimpanzee, are found. But he regards speculation on this point
as useless. It is remarkable that, in this connection, Darwin regards
the loss of the hair-covering in man as having some relation to a
warm climate, while elsewhere he is inclined to make sexual selection
responsible for it. Darwin recognises the great gap between man and
his nearest relatives, but similar gaps exist at other parts of the
mammalian genealogical tree: the allied forms have become extinct. After
the extermination of the lower races of mankind, on the one hand, and of
the anthropoid apes on the other, which will undoubtedly take place, the
gulf will be greater than ever, since the baboons will then bound it on
the one side, and the white races on the other. Little weight need be
attached to the lack of fossil remains to fill up this gap, since the
discovery of these depends upon chance. The last part of the chapter is
devoted to a discussion of the earlier stages in the genealogy of
man. Here Darwin accepts in the main the genealogical tree, which had
meantime been published by Haeckel, who traces the pedigree back through
Monotremes, Reptiles, Amphibians, and Fishes, to Amphioxus.
Then follows an attempt to reconstruct, from the atavistic characters,
a picture of our primitive ancestor who was undoubtedly an arboreal
animal. The occurrence of rudiments of parts in one sex which only come
to full development in the other is next discussed. This state of things
Darwin regards as derived from an original hermaphroditism. In regard to
the mammary glands of the male he does not accept the theory that they
are vestigial, but considers them rather as not fully developed.
The last chapter of Part I deals with the question whether the different
races of man are to be regarded as different species, or as sub-species
of a race of monophyletic origin. The striking differences between
the races are first emphasised, and the question of the fertility or
infertility of hybrids is discussed. That fertility is the more usual
is shown by the excessive fertility of the hybrid population of Brazil.
This, and the great variability of the distinguishing characters of
the different races, as well as the fact that all grades of transition
stages are found between these, while considerable general agreement
exists, tell in favour of the unity of the races and lead to the
conclusion that they all had a common primitive ancestor.
Darwin therefore classifies all the different races as sub-species of
ONE AND THE SAME SPECIES. Then follows an interesting inquiry into the
reasons for the extinction of human races. He recognises as the ultimate
reason the injurious effects of a change of the conditions of life,
which may bring about an increase in infantile mortality, and a
diminished fertility. It is precisely the reproductive system, among
animals also, which is most susceptible to changes in the environment.
The final section of this chapter deals with the formation of the races
of mankind. Darwin discusses the question how far the direct effect of
different conditions of life, or the inherited effects of increased use
or disuse may have brought about the characteristic differences between
the different races. Even in regard to the origin of the colour of the
skin he rejects the transmitted effects of an original difference of
climate as an explanation. In so doing he is following his tendency to
exclude Lamarckian explanations as far as possible. But here he makes
gratuitous difficulties from which, since natural selection fails, there
is no escape except by bringing in the principle of sexual selection, to
which, he regarded it as possible, skin-colouring, arrangement of
hair, and form of features might be traced. But with his characteristic
conscientiousness he guards himself thus: "I do not intend to assert
that sexual selection will account for all the differences between the
races." ("Descent of Man", page 308.)
I may be permitted a remark as to Darwin's attitude towards Lamarck.
While, at an earlier stage, when he was engaged in the preliminary
labours for his immortal work, "The Origin of Species", Darwin expresses
himself very forcibly against the views of Lamarck, speaking of
Lamarckian "nonsense," ("Life and Letters", Vol. II. page 23.), and
of Lamarck's "absurd, though clever work" (Loc. cit. page 39.) and
expressly declaring, "I attribute very little to the direct action of
climate, etc." (Loc. cit. (1856), page 82.) yet in later life he became
more and more convinced of the influence of external conditions. In
1876, that is, two years after the appearance of the second edition of
"The Descent of Man", he writes with his usual candid honesty: "In my
opinion the greatest error which I have committed, has been not allowing
sufficient weight to the direct action of the environment, i.e. food,
climate, etc. independently of natural selection." (Ibid. Vol. III. page
159.) It is certain from this change of opinion that, if he had been
able to make up his mind to issue a third edition of "The Descent of
Man", he would have ascribed a much greater influence to the effect of
external conditions in explaining the different characters of the races
of man than he did in the second edition. He would also undoubtedly have
attributed less influence to sexual selection as a factor in the origin
of the different bodily characteristics, if indeed he would not have
excluded it altogether.
In Part III of the "Descent" two additional chapters are devoted to the
discussion of sexual selection in relation to man. These may be very
briefly referred to. Darwin here seeks to show that sexual selection has
been operative on man and his primitive progenitor. Space fails me to
follow out his interesting arguments. I can only mention that he is
inclined to trace back hairlessness, the development of the beard in
man, and the characteristic colour of the different human races to
sexual selection. Since bareness of the skin could be no advantage, but
rather a disadvantage, this character cannot have been brought about by
natural selection. Darwin also rejected a direct influence of climate as
a cause of the origin of the skin-colour. I have already expressed the
opinion, based on the development of his views as shown in his letters,
that in a third edition Darwin would probably have laid more stress on
the influence of external environment. He himself feels that there are
gaps in his proofs here, and says in self-criticism: "The views here
advanced, on the part which sexual selection has played in the history
of man, want scientific precision." ("Descent of Man", page 924.) I
need here only point out that it is impossible to explain the graduated
stages of skin-colour by sexual selection, since it would have produced
races sharply defined by their colour and not united to other races
by transition stages, and this, it is well known, is not the case.
Moreover, the fact established by me ("Die Hautfarbe des Menschen",
"Mitteilungen der Anthropologischen Gesellschaft in Wien", Vol. XXXIV.
pages 331-352.), that in all races the ventral side of the trunk is
paler than the dorsal side, and the inner surface of the extremities
paler than the outer side, cannot be explained by sexual selection in
the Darwinian sense.
With this I conclude my brief survey of the rich contents of Darwin's
book. I may be permitted to conclude by quoting the magnificent final
words of "The Descent of Man": "We must, however, acknowledge, as it
seems to me, that man, with all his noble qualities, with sympathy which
feels for the most debased, with benevolence which extends not only
to other men but to the humblest living creature, with his god-like
intellect which has penetrated into the movements and constitution of
the solar system--with all these exalted powers--Man still bears in his
bodily frame the indelible stamp of his lowly origin." (Ibid. page 947.)
What has been the fate of Darwin's doctrines since his great
achievement? How have they been received and followed up by the
scientific and lay world? And what do the successors of the mighty hero
and genius think now in regard to the origin of the human race?
At the present time we are incomparably more favourably placed than
Darwin was for answering this question of all questions. We have at our
command an incomparably greater wealth of material than he had at his
disposal. And we are more fortunate than he in this respect, that we
now know transition-forms which help to fill up the gap, still great,
between the lowest human races and the highest apes. Let us consider
for a little the more essential additions to our knowledge since the
publication of "The Descent of Man".
Since that time our knowledge of animal embryos has increased
enormously. While Darwin was obliged to content himself with comparing
a human embryo with that of a dog, there are now available the youngest
embryos of monkeys of all possible groups (Orang, Gibbon, Semnopithecus,
Macacus), thanks to Selenka's most successful tour in the East Indies in
search of such material. We can now compare corresponding stages of
the lower monkeys and of the Anthropoid apes with human embryos, and
convince ourselves of their great resemblance to one another, thus
strengthening enormously the armour prepared by Darwin in defence of his
view on man's nearest relatives. It may be said that Selenka's material
fils up the blanks in Darwin's array of proofs in the most satisfactory
manner.
The deepening of our knowledge of comparative anatomy also gives us much
surer foundations than those on which Darwin was obliged to build. Just
of late there have been many workers in the domain of the anatomy of
apes and lemurs, and their investigations extend to the most different
organs. Our knowledge of fossil apes and lemurs has also become much
wider and more exact since Darwin's time: the fossil lemurs have been
especially worked up by Cope, Forsyth Major, Ameghino, and others.
Darwin knew very little about fossil monkeys. He mentions two or three
anthropoid apes as occurring in the Miocene of Europe ("Descent of
Man", page 240.), but only names Dryopithecus, the largest form from
the Miocene of France. It was erroneously supposed that this form was
related to Hylobates. We now know not only a form that actually stands
near to the gibbon (Pliopithecus), and remains of other anthropoids
(Pliohylobates and the fossil chimpanzee, Palaeopithecus), but also
several lower catarrhine monkeys, of which Mesopithecus, a form nearly
related to the modern Sacred Monkeys (a species of Semnopithecus) and
found in strata of the Miocene period in Greece, is the most important.
Quite recently, too, Ameghino's investigations have made us acquainted
with fossil monkeys from South America (Anthropops, Homunculus), which,
according to their discoverer, are to be regarded as in the line of
human descent.
What Darwin missed most of all--intermediate forms between apes
and man--has been recently furnished. (E. Dubois, as is well known,
discovered in 1893, near Trinil in Java, in the alluvial deposits of
the river Bengawan, an important form represented by a skull-cap, some
molars, and a femur. His opinion--much disputed as it has been--that in
this form, which he named Pithecanthropus, he has found a long-desired
transition-form is shared by the present writer. And although the
geological age of these fossils, which, according to Dubois, belong to
the uppermost Tertiary series, the Pliocene, has recently been fixed
at a later date (the older Diluvium)), the MORPHOLOGICAL VALUE of
these interesting remains, that is, the intermediate position of
Pithecanthropus, still holds good. Volz says with justice ("Das
geologische Alter der Pithecanthropus-Schichten bei Trinil, Ost-Java".
"Neues Jahrb. f.Mineralogie". Festband, 1907.), that even if
Pithecanthropus is not THE missing link, it is undoubtedly _A_ missing
link.
As on the one hand there has been found in Pithecanthropus a form which,
though intermediate between apes and man, is nevertheless more closely
allied to the apes, so on the other hand, much progress has been made
since Darwin's day in the discovery and description of the older
human remains. Since the famous roof of a skull and the bones of the
extremities belonging to it were found in 1856 in the Neandertal near
Dusseldorf, the most varied judgments have been expressed in regard
to the significance of the remains and of the skull in particular.
In Darwin's "Descent of Man" there is only a passing allusion to them
("Descent of Man", page 82.) in connection with the discussion of the
skull-capacity, although the investigations of Schaaffhausen, King, and
Huxley were then known. I believe I have shown, in a series of papers,
that the skull in question belongs to a form different from any of the
races of man now living, and, with King and Cope, I regard it as at
least a different species from living man, and have therefore designated
it Homo primigenius. The form unquestionably belongs to the older
Diluvium, and in the later Diluvium human forms already appear, which
agree in all essential points with existing human races.
As far back as 1886 the value of the Neandertal skull was greatly
enhanced by Fraipont's discovery of two skulls and skeletons from Spy in
Belgium. These are excellently described by their discoverer ("La race
humaine de Neanderthal ou de Canstatt en Belgique". "Arch. de Biologie",
VII. 1887.), and are regarded as belonging to the same group of forms
as the Neandertal remains. In 1899 and the following years came the
discovery by Gorjanovic-Kramberger of different skeletal parts of
at least ten individuals in a cave near Krapina in Croatia.
(Gorjanovic-Kramberger "Der diluviale Mensch von Krapina in Kroatien",
1906.) It is in particular the form of the lower jaw which is different
from that of all recent races of man, and which clearly indicates
the lowly position of Homo primigenius, while, on the other hand, the
long-known skull from Gibraltar, which I ("Studien zur Vorgeschichte des
Menschen", 1906, pages 154 ff.) have referred to Homo primigenius, and
which has lately been examined in detail by Sollas ("On the cranial and
facial characters of the Neandertal Race". "Trans. R. Soc." London, vol.
199, 1908, page 281.), has made us acquainted with the surprising shape
of the eye-orbit, of the nose, and of the whole upper part of the face.
Isolated lower jaws found at La Naulette in Belgium, and at Malarnaud
in France, increase our material which is now as abundant as could be
desired. The most recent discovery of all is that of a skull dug up in
August of this year (1908) by Klaatsch and Hauser in the lower grotto
of the Le Moustier in Southern France, but this skull has not yet
been fully described. Thus Homo primigenius must also be regarded as
occupying a position in the gap existing between the highest apes and
the lowest human races, Pithecanthropus, standing in the lower part of
it, and Homo primigenius in the higher, near man. In order to prevent
misunderstanding, I should like here to emphasise that in arranging this
structural series--anthropoid apes, Pithecanthropus, Homo primigenius,
Homo sapiens--I have no intention of establishing it as a direct
genealogical series. I shall have something to say in regard to the
genetic relations of these forms, one to another, when discussing the
different theories of descent current at the present day. ((Since
this essay was written Schoetensack has discovered near Heidelberg
and briefly described an exceedingly interesting lower jaw from rocks
between the Pliocene and Diluvial beds. This exhibits interesting
differences from the forms of lower jaw of Homo primigenius.
(Schoetensack "Der Unterkiefer des Homo heidelbergensis". Leipzig,
1908.) G.S.))
In quite a different domain from that of morphological relationship,
namely in the physiological study of the blood, results have recently
been gained which are of the highest importance to the doctrine of
descent. Uhlenhuth, Nuttall, and others have established the fact
that the blood-serum of a rabbit which has previously had human blood
injected into it, forms a precipitate with human blood. This biological
reaction was tried with a great variety of mammalian species, and it was
found that those far removed from man gave no precipitate under these
conditions. But as in other cases among mammals all nearly related forms
yield an almost equally marked precipitate, so the serum of a rabbit
treated with human blood and then added to the blood of an anthropoid
ape gives ALMOST as marked a precipitate as in human blood; the reaction
to the blood of the lower Eastern monkeys is weaker, that to the Western
monkeys weaker still; indeed in this last case there is only a slight
clouding after a considerable time and no actual precipitate. The blood
of the Lemuridae (Nuttall) gives no reaction or an extremely weak one,
that of the other mammals none whatever. We have in this not only a
proof of the literal blood-relationship between man and apes, but the
degree of relationship with the different main groups of apes can be
determined beyond possibility of mistake.
Finally, it must be briefly mentioned that in regard to remains of human
handicraft also, the material at our disposal has greatly increased of
late years, that, as a result of this, the opinions of archaeologists
have undergone many changes, and that, in particular, their views in
regard to the age of the human race have been greatly influenced. There
is a tendency at the present time to refer the origin of man back to
Tertiary times. It is true that no remains of Tertiary man have been
found, but flints have been discovered which, according to the opinion
of most investigators, bear traces either of use, or of very primitive
workmanship. Since Rutot's time, following Mortillet's example,
investigators have called these "eoliths," and they have been traced
back by Verworn to the Miocene of the Auvergne, and by Rutot even to the
upper Oligocene. Although these eoliths are even nowadays the subject of
many different views, the preoccupation with them has kept the problem
of the age of the human race continually before us.
Geology, too, has made great progress since the days of Darwin and
Lyell, and has endeavoured with satisfactory results to arrange the
human remains of the Diluvial period in chronological order (Penck). I
do not intend to enter upon the question of the primitive home of the
human race; since the space at my disposal will not allow of my
touching even very briefly upon all the departments of science which are
concerned in the problem of the descent of man. How Darwin would have
rejoiced over each of the discoveries here briefly outlined! What use
he would have made of the new and precious material, which would have
prevented the discouragement from which he suffered when preparing the
second edition of "The Descent of Man"! But it was not granted to him to
see this progress towards filling up the gaps in his edifice of which he
was so painfully conscious.
He did, however, have the satisfaction of seeing his ideas steadily
gaining ground, notwithstanding much hostility and deep-rooted
prejudice. Even in the years between the appearance of "The Origin
of Species" and of the first edition of the "Descent", the idea of a
natural descent of man, which was only briefly indicated in the work of
1859, had been eagerly welcomed in some quarters. It has been already
pointed out how brilliantly Huxley contributed to the defence and
diffusion of Darwin's doctrines, and how in "Man's Place in Nature"
he has given us a classic work as a foundation for the doctrine of
the descent of man. As Huxley was Darwin's champion in England, so in
Germany Carl Vogt, in particular, made himself master of the Darwinian
ideas. But above all it was Haeckel who, in energy, eagerness for
battle, and knowledge may be placed side by side with Huxley, who took
over the leadership in the controversy over the new conception of the
universe. As far back as 1866, in his "Generelle Morphologie", he had
inquired minutely into the question of the descent of man, and not
content with urging merely the general theory of descent from lower
animal forms, he drew up for the first time genealogical trees showing
the close relationships of the different animal groups; the last of
these illustrated the relationships of Mammals, and among them of all
groups of the Primates, including man. It was Haeckel's genealogical
trees that formed the basis of the special discussion of the
relationships of man, in the sixth chapter of Darwin's "Descent of Man".
In the last section of this essay I shall return to Haeckel's conception
of the special descent of man, the main features of which he still
upholds, and rightly so. Haeckel has contributed more than any one else
to the spread of the Darwinian doctrine.
I can only allow myself a few words as to the spread of the theory
of the natural descent of man in other countries. The Parisian
anthropological school, founded and guided by the genius of Broca, took
up the idea of the descent of man, and made many notable contributions
to it (Broca, Manouvrier, Mahoudeau, Deniker and others). In England
itself Darwin's work did not die. Huxley took care of that, for he, with
his lofty and unprejudiced mind, dominated and inspired English biology
until his death on June 29, 1895. He had the satisfaction shortly before
his death of learning of Dubois' discovery, which he illustrated by a
humorous sketch. ("Life and Letters of Thomas Henry Huxley", Vol. II.
page 394.) But there are still many followers in Darwin's footsteps
in England. Keane has worked at the special genealogical tree of the
Primates; Keith has inquired which of the anthropoid apes has the
greatest number of characters in common with man; Morris concerns
himself with the evolution of man in general, especially with
his acquisition of the erect position. The recent discoveries of
Pithecanthropus and Homo primigenius are being vigorously discussed; but
the present writer is not in a position to form an opinion of the
extent to which the idea of descent has penetrated throughout England
generally.
In Italy independent work in the domain of the descent of man is being
produced, especially by Morselli; with him are associated, in the
investigation of related problems, Sergi and Giuffrida-Ruggeri. From
the ranks of American investigators we may single out in particular the
eminent geologist Cope, who championed with much decision the idea
of the specific difference of Homo neandertalensis (primigenius) and
maintained a more direct descent of man from the fossil Lemuridae. In
South America too, in Argentina, new life is stirring in this department
of science. Ameghino in Buenos Ayres has awakened the fossil primates
of the Pampas formation to new life; he even believes that in
Tetraprothomo, represented by a femur, he has discovered a direct
ancestor of man. Lehmann-Nitsche is working at the other side of the
gulf between apes and men, and he describes a remarkable first cervical
vertebra (atlas) from Monte Hermoso as belonging to a form which
may bear the same relation to Homo sapiens in South America as Homo
primigenius does in the Old World. After a minute investigation he
establishes a human species Homo neogaeus, while Ameghino ascribes this
atlas vertebra to his Tetraprothomo.
Thus throughout the whole scientific world there is arising a new
life, an eager endeavour to get nearer to Huxley's problema maximum,
to penetrate more deeply into the origin of the human race. There are
to-day very few experts in anatomy and zoology who deny the animal
descent of man in general. Religious considerations, old prejudices,
the reluctance to accept man, who so far surpasses mentally all
other creatures, as descended from "soulless" animals, prevent a few
investigators from giving full adherence to the doctrine. But there are
very few of these who still postulate a special act of creation for
man. Although the majority of experts in anatomy and zoology accept
unconditionally the descent of man from lower forms, there is much
diversity of opinion among them in regard to the special line of
descent.
In trying to establish any special hypothesis of descent, whether by
the graphic method of drawing up genealogical trees or otherwise, let us
always bear in mind Darwin's words ("Descent of Man", page 229.) and use
them as a critical guiding line: "As we have no record of the lines of
descent, the pedigree can be discovered only by observing the degrees of
resemblance between the beings which are to be classed." Darwin carries
this further by stating "that resemblances in several unimportant
structures, in useless and rudimentary organs, or not now functionally
active, or in an embryological condition, are by far the most
serviceable for classification." (Loc. cit.) It has also to be
remembered that NUMEROUS separate points of agreement are of much
greater importance than the amount of similarity or dissimilarity in a
few points.
The hypotheses as to descent current at the present day may be divided
into two main groups. The first group seeks for the roots of the human
race not among any of the families of the apes--the anatomically nearest
forms--nor among their very similar but less specialised ancestral
forms, the fossil representatives of which we can know only in part,
but, setting the monkeys on one side, it seeks for them lower down among
the fossil Eocene Pseudo-lemuridae or Lemuridae (Cope), or even among
the primitive pentadactylous Eocene forms, which may either have led
directly to the evolution of man (Adloff), or have given rise to an
ancestral form common to apes and men (Klaatsch (Klaatsch in his last
publications speaks in the main only of an ancestral form common to men
and anthropoid apes.), Giuffrida-Ruggeri). The common ancestral form,
from which man and apes are thus supposed to have arisen independently,
may explain the numerous resemblances which actually exist between
them. That is to say, all the characters upon which the great structural
resemblance between apes and man depends must have been present in their
common ancestor. Let us take an example of such a common character. The
bony external ear-passage is in general as highly developed in the lower
Eastern monkeys and the anthropoid apes as in man. This character must,
therefore, have already been present in the common primitive form. In
that case it is not easy to understand why the Western monkeys have
not also inherited the character, instead of possessing only a tympanic
ring. But it becomes more intelligible if we assume that forms with a
primitive tympanic ring were the original type, and that from these were
evolved, on the one hand, the existing New World monkeys with persistent
tympanic ring, and on the other an ancestral form common to the lower
Old World monkeys, the anthropoid apes and man. For man shares with
these the character in question, and it is also one of the "unimportant"
characters required by Darwin. Thus we have two divergent lines arising
from the ancestral form, the Western monkeys (Platyrrhine) on the one
hand, and an ancestral form common to the lower Eastern monkeys, the
anthropoid apes, and man, on the other. But considerations similar to
those which showed it to be impossible that man should have developed
from an ancestor common to him and the monkeys, yet outside of and
parallel with these, may be urged also against the likelihood of a
parallel evolution of the lower Eastern monkeys, the anthropoid apes,
and man. The anthropoid apes have in common with man many characters
which are not present in the lower Old World monkeys. These characters
must therefore have been present in the ancestral form common to the
three groups. But here, again, it is difficult to understand why the
lower Eastern monkeys should not also have inherited these characters.
As this is not the case, there remains no alternative but to assume
divergent evolution from an indifferent form. The lower Eastern monkeys
are carrying on the evolution in one direction--I might almost say
towards a blind alley--while anthropoids and men have struck out a
progressive path, at first in common, which explains the many points of
resemblance between them, without regarding man as derived directly
from the anthropoids. Their many striking points of agreement indicate a
common descent, and cannot be explained as phenomena of convergence.
I believe I have shown in the above sketch that a theory which derives
man directly from lower forms without regarding apes as transition-types
leads ad absurdum. The close structural relationship between man and
monkeys can only be understood if both are brought into the same line
of evolution. To trace man's line of descent directly back to the old
Eocene mammals, alongside of, but with no relation to these very similar
forms, is to abandon the method of exact comparison, which, as Darwin
rightly recognised, alone justifies us in drawing up genealogical trees
on the basis of resemblances and differences. The farther down we go the
more does the ground slip from beneath our feet. Even the Lemuridae
show very numerous divergent conditions, much more so the Eocene
mammals (Creodonta, Condylarthra), the chief resemblance of which to man
consists in the possession of pentadactylous hands and feet! Thus the
farther course of the line of descent disappears in the darkness of the
ancestry of the mammals. With just as much reason we might pass by the
Vertebrates altogether, and go back to the lower Invertebrates, but
in that case it would be much easier to say that man has arisen
independently, and has evolved, without relation to any animals, from
the lowest primitive form to his present isolated and dominant position.
But this would be to deny all value to classification, which must after
all be the ultimate basis of a genealogical tree. We can, as Darwin
rightly observed, only infer the line of descent from the degree of
resemblance between single forms. If we regard man as directly derived
from primitive forms very far back, we have no way of explaining the
many points of agreement between him and the monkeys in general, and the
anthropoid apes in particular. These must remain an inexplicable marvel.
I have thus, I trust, shown that the first class of special theories
of descent, which assumes that man has developed, parallel with the
monkeys, but without relation to them, from very low primitive forms
cannot be upheld, because it fails to take into account the close
structural affinity of man and monkeys. I cannot but regard this
hypothesis as lamentably retrograde, for it makes impossible any
application of the facts that have been discovered in the course of
the anatomical and embryological study of man and monkeys, and indeed
prejudges investigations of that class as pointless. The whole method is
perverted; an unjustifiable theory of descent is first formulated with
the aid of the imagination, and then we are asked to declare that all
structural relations between man and monkeys, and between the different
groups of the latter, are valueless,--the fact being that they are the
only true basis on which a genealogical tree can be constructed.
So much for this most modern method of classification, which has
probably found adherents because it would deliver us from the
relationship to apes which many people so much dislike. In contrast
to it we have the second class of special hypotheses of descent, which
keeps strictly to the nearest structural relationships. This is the only
basis that justifies the drawing up of a special hypothesis of descent.
If this fundamental proposition be recognised, it will be admitted that
the doctrine of special descent upheld by Haeckel, and set forth in
Darwin's "Descent of Man", is still valid to-day. In the genealogical
tree, man's place is quite close to the anthropoid apes; these again
have as their nearest relatives the lower Old World monkeys, and their
progenitors must be sought among the less differentiated Platyrrhine
monkeys, whose most important characters have been handed on to the
present day New World monkeys. How the different genera are to be
arranged within the general scheme indicated depends in the main on
the classificatory value attributed to individual characters. This is
particularly true in regard to Pithecanthropus, which I consider as the
root of a branch which has sprung from the anthropoid ape root and has
led up to man; the latter I have designated the family of the Hominidae.
For the rest, there are, as we have said, various possible ways of
constructing the narrower genealogy within the limits of this branch
including men and apes, and these methods will probably continue to
change with the accumulation of new facts. Haeckel himself has modified
his genealogical tree of the Primates in certain details since the
publication of his "Generelle Morphologie" in 1866, but its general
basis remains the same. (Haeckel's latest genealogical tree is to be
found in his most recent work, "Unsere Ahnenreihe". Jena, 1908.) All the
special genealogical trees drawn up on the lines laid down by Haeckel
and Darwin--and that of Dubois may be specially mentioned--are based, in
general, on the close relationship of monkeys and men, although they may
vary in detail. Various hypotheses have been formulated on these lines,
with special reference to the evolution of man. "Pithecanthropus" is
regarded by some authorities as the direct ancestor of man, by others as
a side-track failure in the attempt at the evolution of man. The problem
of the monophyletic or polyphyletic origin of the human race has also
been much discussed. Sergi (Sergi G. "Europa", 1908.) inclines towards
the assumption of a polyphyletic origin of the three main races of man,
the African primitive form of which has given rise also to the
gorilla and chimpanzee, the Asiatic to the Orang, the Gibbon, and
Pithecanthropus. Kollmann regards existing human races as derived from
small primitive races (pigmies), and considers that Homo primigenius
must have arisen in a secondary and degenerative manner.
But this is not the place, nor have I the space to criticise the various
special theories of descent. One, however, must receive particular
notice. According to Ameghino, the South American monkeys (Pitheculites)
from the oldest Tertiary of the Pampas are the forms from which have
arisen the existing American monkeys on the one hand, and on the other,
the extinct South American Homunculidae, which are also small forms.
From these last, anthropoid apes and man have, he believes, been
evolved. Among the progenitors of man, Ameghino reckons the form
discovered by him (Tetraprothomo), from which a South American primitive
man, Homo pampaeus, might be directly evolved, while on the other hand
all the lower Old World monkeys may have arisen from older fossil
South American forms (Clenialitidae), the distribution of which may
be explained by the bridge formerly existing between South America and
Africa, as may be the derivation of all existing human races from Homo
pampaeus. (See Ameghino's latest paper, "Notas preliminares sobre el
Tetraprothomo argentinus", etc. "Anales del Museo nacional de Buenos
Aires", XVI. pages 107-242, 1907.) The fossil forms discovered by
Ameghino deserve the most minute investigation, as does also the fossil
man from South America of which Lehmann-Nitsche ("Nouvelles recherches
sur la formation pampeenne et l'homme fossile de la Republique
Argentine". "Rivista del Museo de la Plata", T. XIV. pages 193-488.) has
made a thorough study.
It is obvious that, notwithstanding the necessity for fitting man's line
of descent into the genealogical tree of the Primates, especially the
apes, opinions in regard to it differ greatly in detail. This could not
be otherwise, since the different Primate forms, especially the fossil
forms, are still far from being exhaustively known. But one thing
remains certain,--the idea of the close relationship between man and
monkeys set forth in Darwin's "Descent of Man". Only those who deny the
many points of agreement, the sole basis of classification, and thus of
a natural genealogical tree, can look upon the position of Darwin and
Haeckel as antiquated, or as standing on an insufficient foundation.
For such a genealogical tree is nothing more than a summarised
representation of what is known in regard to the degree of resemblance
between the different forms.
Darwin's work in regard to the descent of man has not been surpassed;
the more we immerse ourselves in the study of the structural
relationships between apes and man, the more is our path illumined by
the clear light radiating from him, and through his calm and deliberate
investigation, based on a mass of material in the accumulation of which
he has never had an equal. Darwin's fame will be bound up for all time
with the unprejudiced investigation of the question of all questions,
the descent of the human race.