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."[108] 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,[109] 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."[110]
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 fills 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,[111] 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,[112] 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
oldest 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 Duesseldorf, 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[113] 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,[114]
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.[115] 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[116] have referred to _Homo
primigenius_, and which has lately been examined in detail by
Sollas,[117] 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.[118]
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 structural 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 humourous sketch.[119] 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 his _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 man, 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[120] 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."[121] 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,[122]
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.