Darwin and Modern Science (1909)
Edited by A.C. Seward
VII. "THE DESCENT OF MAN"
By G. SCHWALBE.
Professor of Anatomy in the University of Strassburg.
he 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.
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