SIMIAN ORIGIN OF MAN
Relationship of the human species with anthropoid apes—Analogies in
the dentition, in the organisation of the limbs and of the
brain—Resemblance of the vermiform appendage of man and
anthropoids—Analogy between the placenta and fœtus of man and
anthropoid apes—Blood relationship of man and monkeys shown by serums
and precipitates—Transmutation of species—Sudden transition from
monkey to man—J. Inaudi, the calculator, as an example of the sudden
appearance of characters in the human species—Rudimentary organs in
man—Proportion of progressive and retrogressive organs in the
organisation of man
To understand human nature it is necessary first to give an account of
the origin of man. This question has preoccupied mankind for ages, and
for a long time it was believed that a solution of the problem was to be
found in religious dogmas. Man was regarded as being of supernatural
origin, the result of a special creation. Scientific criticism has now
shown that there are no grounds for such a conclusion.
Nearly half a century ago Darwin applied to man his discovery of the
principle of natural selection, and of the part played by that in the
origin and transmutation of species. Soon after the publication of the
“Origin of Species,” attention was given to the special case of man. In
1863 Huxley[48] gave an admirable review of the problem in his work on
“Man’s Place in Nature.” He brought forward arguments of the highest
scientific validity in support of the thesis that man is descended from
animals, and that he is a mammal most nearly related to monkeys, and
among these to the anthropoid apes. In spite of this masterly
exposition, there are still persons of high intelligence and superior
education who declare that science has not yet answered the question as
to whence he came, and that the theory of evolution will never provide
an answer.[49] Close examination of the structure of man has proved, in
the most definite fashion, the existence of a near kinship with the
higher monkeys, or anthropoids. When the chimpanzee and the
ourang-outang were discovered, comparison became inevitable, and many
naturalists, including the great Linnæus, saw that the human race must
find its place in classification near the anthropoids.
Now that all the details of the human organisation have been studied,
and the anatomical structures of man and large monkeys without tails
have been compared, bone with bone and muscle with muscle, a truly
astonishing analogy between these organisms is made manifest, an analogy
apparent in every detail. It is known that in the natural history of
mammals the teeth play an important part as a means of determining
differences and relationships. The dentition of man bears a very great
resemblance to that of anthropoids. Every one knows the _milk teeth_ and
the _permanent teeth_ of man. The anthropoid apes bear in this respect
an astonishing likeness to man. The number (thirty-two in the adult),
the form and general arrangement of the crown, are identical in man and
anthropoid apes. The differences are to be found only in minor details,
such as the exact shape and relative dimensions and the number of cusps.
It can be said in a general way that in the anthropoid apes the teeth
are more strongly developed than in man. The canines are much longer and
the roots of the pre-molars are more complex in the gorilla than in man.
But the fact must not be lost sight of, that all these differences are
less pronounced than those which exist between the dentition of
anthropoid apes and that of all other monkeys. Even in the cynocephalous
monkeys, those that most nearly approach the anthropoids, the teeth
exhibit marked differences. Thus, the forms of the upper molars are
quite different in the baboon and in the gorilla. The canines are
longer, and the pre-molars and molars are still more complex in the
baboon.
In the monkeys of the New World, the dentition differs still more from
that of man and anthropoids. Instead of thirty-two teeth, they possess
thirty-six in the adult condition. The number of pre-molars is twelve
instead of eight. The general form and the crowns of the molars are very
different from those of anthropoid apes.
These considerations led Huxley to conclude that “it is obvious that,
greatly as the dentition of the highest ape differs from that of man, it
differs far more widely from that of the lower and lowest apes.”[50]
Another character which shows that anthropoids are nearer man than other
monkeys is furnished by the anatomy of the sacrum. In monkeys as a whole
the sacrum is composed of three, or rarely four, vertebræ, while in
anthropoid apes it contains five, that is to say just as many as in man.
The whole skeleton, and particularly the skull of man, and the higher
monkeys, present certainly some marked differences; but here again the
differences are less than those between the anthropoid apes and other
monkeys. As regards the osteology the proposition laid down by Huxley is
just. “So that, for the skull, no less than for the skeleton in general,
the proposition holds good, that the differences between man and the
gorilla are of smaller value than those between the gorilla and some
other apes.”[51]
The believers in the doctrine that the human species is essentially
distinct from all the known monkeys have laid great stress on the
difference between the foot of man and that of anthropoid apes. This
difference cannot be denied. Man assumes the direct posture habitually,
while monkeys, even the highest of them, walk on two legs only
occasionally. There has followed from this a greater development of the
feet in monkeys. Yet this difference ought not to be exaggerated. It has
been sought to prove that monkeys are “quadrumanous,” and that their
hind legs terminate in “hind-hands.” But it is clearly shown that in all
essential respects the hinder limb of the gorilla terminates in as true
a foot as that of man.[52] “The hind limb of the gorilla, therefore,
ends in a true foot, with a very movable great toe. It is a prehensile
foot, indeed, but is in no sense a hand; it is a foot which differs from
that of man not in any fundamental character, but in mere proportions,
in the degree of mobility, and in the secondary arrangement of its
parts.”[53]
In all these cases the argument is confirmed, “that be the differences
between the hand and foot of man and those of the gorilla what they may,
the differences between those of the gorilla and those of the lower apes
are much greater.”[54]
The comparison of muscles and of other internal organs leads to the same
conclusion; the differences between monkeys are more varied and greater
than those between anthropoids and man. The anatomy of the brain has
been much discussed with regard to this. Several distinguished
zoologists, amongst them Owen in particular, have insisted on the
absence in all monkeys of certain parts of the brain peculiarly
characteristic of man. Such are the posterior lobe, the posterior cornu,
and the lesser hippocampus. Controversy on this topic has been animated;
but, ultimately, the opinion of Owen did not triumph, and now it is
unanimously accepted that the parts of the brain in question are
“precisely those structures which are the most marked cerebral
characters common to man with the apes. They are among the most
distinctly simian peculiarities which the human organism exhibits.”[55]
[Illustration:
FIG. 6.—Cæcum and vermiform appendage of man (after Ewald).
]
As regards the brain, the differences between man and anthropoid apes
are certainly less marked than those that exist between the higher and
lower monkeys.
The digestive tract affords another argument in favour of the affinity
of anthropoid apes to man. The human cæcum is furnished with the very
remarkable and strange vermiform appendage which often is the cause of a
grave and prevalent illness known as _appendicitis_. Now, it is quite
remarkable that this organ is practically identical with the vermiform
appendage of anthropoid apes. A glance at the accompanying figures (6
and 7) will convince the reader of this. Yet none of the other monkeys
present any such resemblance with man.
[Illustration:
FIG. 7.—Cæcum and vermiform appendage of the chimpanzee (from a
preparation in the Paris Museum of Natural History).
]
It is not surprising, in the face of resemblances so numerous, that
forty years’ science has proclaimed the existence of a close affinity
between man and the anthropoid apes. The view has become an established
doctrine, now that no single fact has been brought against it. Since the
theory was enunciated we have learned much regarding the natural history
of these apes. Generally, when a theory is false, a new set of facts
overthrows it. Attempts may be made to trim the new facts to the
existing theory, but such attempts are doomed to failure, and the theory
disappears. It is of special interest, then, to confront the simian
theory of the origin of man with a series of facts gathered by science
since the theory was propounded.
When Huxley wrote, the embryological history of anthropoid apes was
practically unknown. Darwin, Vogt, and Haeckel, in their attempts to
support the theory of the animal origin of man, had not sufficient
knowledge of the embryology of monkeys. It is only recently that
important work on this subject has been published.
It is known that the history of development is very often an excellent
guide in tracing the relationship of organisms. It is therefore
interesting to examine the established facts concerning the embryology
of anthropoid apes. The material for these studies is very difficult to
obtain, and it is not astonishing that even our present state of
knowledge is still imperfect.
[Illustration:
FIG. 8.—Fœtus of gibbon (after Selenka).
]
The placenta often gives information of great importance in the
classification of mammals. It is sufficient to glance at the zonary
placenta of dogs and seals to be convinced of the relationship of these
two species, which at first sight seem so different. Now, the placentas
of all the anthropoid apes examined up to the present are of the same
discoid type as that of man. The arrangement of the umbilical cord of
man, which was formerly considered as quite peculiar to him, is found in
anthropoid apes, as has been established by Deniker[56] and Selenka[57]
It is striking that the anthropoids resemble man rather than the lower
monkeys in the relation of the fœtus to the fœtal membranes.
[Illustration:
FIG. 9.—Human fœtus of three months and a half.
]
With regard to the embryos themselves, the similarity between those of
monkeys and of man is very great. Selenka insists on the fact that the
youngest stages of human development that have been obtained can hardly
be distinguished from those of the lower monkeys either in position or
in shape. More advanced stages exhibit greater differentiation, and the
later embryos of man resemble those of anthropoids much more closely
than those of the lower monkeys. The fœtus of the gibbon, figured by
Selenka (Fig. 8), presents the most striking likeness to a corresponding
human fœtus (Fig. 9).
Later on, the characters that distinguish man from even the highest of
the apes become more and more pronounced. In the anthropoids the facial
portion becomes more and more prominent, and betrays a bestiality absent
from the human form. None the less the resemblance between the nearly
mature fœtus of anthropoids and human embryos of about the sixth month
is evident enough. M. Deniker had the good fortune to obtain the late
fœtus of a gorilla—a very rare piece of fortune—and he has made an
elaborate investigation of its structure. The general appearance (Fig.
10) is quite enough to show the close relationship with a human fœtus of
a corresponding age (Fig. 11). It is plain, moreover, that the young
gorilla is more human-like than is the adult. Detailed anatomical
investigation only confirms this conclusion.
The skulls of the young stages of anthropoids are much more human in
their character than the adult skulls. Selenka states that such young
skulls of different anthropoids not only resemble one another more
closely, but are more human. As soon as the teeth begin to appear, the
individual characters are assumed so rapidly, and become so marked,
that, in the absence of the intermediate stages, it would be difficult
to establish the kinships.
The data derived from embryology do not point to any one of the existing
genera of monkeys as the ancestor of man. They lead us to infer, rather,
that man and the anthropoid apes had a common origin, and
palæontological evidence must be scanned to find this ancestor. The
greatest importance has been attached to a discovery in Java, made in
1894 by Eugène Dubois. The remains, consisting of the crown of a skull,
two teeth and a femur, belonging to a creature for which the name
_Pithecanthropus erectus_[58] has been invented, have been interpreted
by several anatomists as those of a form intermediate between man and
the anthropoid apes. However, as the facts about this creature are
meagre and have been interpreted differently, I shall not make use of
them in my argument. Even apart from them, the simian origin of man may
be taken as proved.
The series of facts that I have been employing as evidence of the
relationship between men and anthropoid apes has been drawn from the
observations of anatomists and embryologists. Darwin, seeking to broaden
the basis of the argument, called attention to the resemblances of the
parasites of men and apes, as evidence of a close similarity of
physiological processes in the creatures. In the last few years,
investigations in a very different field seem capable of throwing a
novel light on the question.
When the blood of one mammal is injected into the body of another, the
latter shows remarkable modifications. When there is added to a serum,
prepared from the blood of a rabbit and consisting of a colourless
transparent liquid, a few drops of blood drawn from another rodent (for
instance a guinea-pig), nothing unusual happens. The blood of the
guinea-pig preserves its normal colour, and its corpuscles remain
practically unaltered. If, instead of adding guinea-pig’s blood to the
serum of rabbit’s blood, we add a serum drawn from the blood of the
guinea-pig, still no special change occurs.
[Illustration:
FIG. 10.—Fœtus of gorilla (after Deniker).
]
If, however, a serum be prepared from the blood of a rabbit into which
there had first been injected the blood of a guinea-pig, the serum shows
new and striking qualities. The addition to it of some drops of
guinea-pig’s blood brings about, in a very short time, a changed
appearance. The red liquid, at first opaque, becomes transparent. The
mixture of the prepared serum of the rabbit with the blood of the
guinea-pig will assume the colour of claret mixed with water. The change
is due to solution of the red corpuscles of the guinea-pig in the blood
serum of the rabbit.
[Illustration:
FIG. 11.—Human fœtus of about five months.
]
This serum has still another property not less worthy of attention. If
there is added to it not pure blood but only blood serum of the
guinea-pig, a disturbance in the mixture occurs almost at once, and
leads to the forming of a precipitate more or less abundant.
The injection of the blood of the guinea-pig into a rabbit has therefore
changed the serum of the latter by introducing new properties: that of
dissolving the red corpuscles of the guinea-pig and of giving a
precipitate with the blood serum of the same animal.
Frequently the blood serum of animals prepared by previous injections of
the blood of other species of animals is strictly specific. In such
cases the serum only gives a precipitate with the serum of the species
which has furnished the blood for the injections, and only dissolves the
red corpuscles of this same species. But there are some instances in
which a serum of a prepared animal dissolves, not only the red
corpuscles of the species which has furnished the injected blood, but
those of allied species. Thus the blood serum of the rabbit, after some
injections of blood of the chicken, becomes capable of dissolving not
only the red corpuscles of the chicken but also those of the pigeon,
although in a less degree.
It has been suggested that assistance could be rendered to forensic
medicine by making use of this property of serums, to discover the
origin of a certain blood. As is well known, it is often very important
to decide whether a stain was caused by the blood of man or of another
animal. Until quite recently it was not known how to distinguish human
blood from that of other mammals. Experiments have been made to discover
if the red corpuscles found in the blood stain could be dissolved by the
serum of animals which had previously been injected with the blood of
man. In a certain case the human origin of the stain in question was
shown. But it was soon discovered that this method was not infallible.
It is now found that the method of precipitates gives much more
conclusive results. It is done in this way: Human blood is injected
several times into any animal (rabbit, dog, sheep, horse). Some time
afterwards the animal is bled, and a clear and limpid serum, quite
devoid of corpuscles, is prepared. When there is added to this serum one
or several drops of human serum, it forms immediately a precipitate
which falls to the bottom. In this way it is discovered whether the
prepared serum is sufficiently active. It then becomes possible to
recognise even dried human blood. A little of such blood is dissolved in
normal salt solution, and placed in a tube containing the serum of an
animal prepared by means of the injections of human blood. If a
precipitate forms in the liquid in a short time, the fact indicates that
the stain is really human blood. This method is being practised in
forensic medicine.
This reaction is of great interest to us because it is of assistance in
revealing the relationship between species. The serum of an animal
prepared with the blood of the fowl gives a precipitate, not only with
the serum of the fowl itself, but also with that of the pigeon; on the
other hand, it remains undisturbed when the serum of mammals is added.
The reaction indicates then that there is a sufficiently marked degree
of relationship between the fowl and the pigeon. Here is another
example: the serum of an animal prepared with the blood of an ox gives
an abundant precipitate when there is added to it a little blood serum
of the ox, but it does not produce this reaction with the serum of any
of the other mammals, not even with that of the sheep, stag and
deer.[59] The relationship between the _Bovidæ_ and these other
ruminants is then not so close as that between the fowl and the pigeon.
How does the serum of animals which has been injected with human blood
behave? The serum capable of giving a precipitate with human serum does
not produce the same reaction except with the serum of some monkeys (the
small _Papio_).[60]
Gruenbaum, of Liverpool,[61] has been fortunate enough to procure a
considerable quantity of the blood of three large anthropoid apes—the
gorilla, chimpanzee, and ourang-outang. He has been able to prove that
the serum of animals injected with man’s blood gives a precipitate not
only with this blood but also with that of the above-mentioned apes. It
was impossible for him “to distinguish this precipitate as regards
quality and quantity from that which is obtained with human blood.”
To verify this result, Gruenbaum prepared the serum of animals injected
with the blood of the gorilla, chimpanzee, and ourang-outang. These
three kinds of serum gave precipitates with the blood of these three
apes, and to the same extent with the blood of man. It is therefore
evident that there exists between the human species and the anthropoid
apes not only a superficial analogy of body and of the principal organs,
but a close blood relationship.
Facts of this kind could not be foreseen when the theory of the simian
origin of man was put forward. In spite of this they have arisen to
confirm it in a truly astonishing way.
It is therefore impossible to doubt that man is a member of the group of
primates having a close connection with the higher monkeys of the
present time. This result is of great importance in all questions
relating to human nature.
It would certainly be of considerable interest to know more exactly what
steps were followed in this simian descent of man. On this question our
knowledge is still very imperfect. In his researches on anthropoid apes,
Selenka insists on a more intimate relationship between the chimpanzee
and man. “The great resemblance of the pre-molars and of the molars in
the permanent dentition of the chimpanzee with human teeth appears to
indicate that the chimpanzee and man have a common origin, and descend
from extinct forms like _Dryopithecus_. This conclusion, however, is
contradicted by the fact that the milk teeth of the chimpanzee are much
nearer those of the ourang-outang than those of man.”[62]
It is evident that to clear up this question it would be necessary to
have a greater knowledge of fossil anthropoids such as _Dryopithecus_
and its allies. In the present state of knowledge only a very general
hypothesis can be formulated as to the exact mode of human descent.
We have already shown that the fœtus of man and of the anthropoid
monkeys resemble each other much more than the adult forms, and that the
young of these apes also bear a greater likeness to man than do the
adults. The great development of the skull as compared with the face is
characteristic of young monkeys and of man young or old. The jaws
continue to develop in the anthropoids, while in man there occurs in
this respect a certain arrest of development. The hairs, so small in
man, also show a similar arrest. Generally they remain during the whole
life in a state of incomplete development. It is especially on the back
of man that this feeble development of hairs occurs. As this part of the
body in monkeys, on the contrary, is much more hairy than the under
surface, it has been held to constitute an essential difference between
man and monkeys. But embryological study enables us to settle this
apparent contradiction. The fœtus of the gorilla examined by M. Deniker
possessed an almost entirely smooth back. “The fœtus had true hairs only
on the head, the anterior surface, and around the lips and the genital
organs, and the eyelashes and eyebrows. The remainder of the body was
smooth or covered with down not exceeding a millimetre in length.”[63]
The skin of the under surface, smooth around the navel, was covered with
small hairs more thickly than on the back. The abundance of hairs on the
posterior aspect of the body of monkeys is a later acquisition, which
develops but tardily during fœtal life.
As regards the distribution of these hairs man resembles much more the
embryos of monkeys than adult monkeys. This fact, instead of shaking the
theory of relationship between man and apes, gives us strong evidence as
to the mode of his descent. Putting the known facts together, we may
infer that man is a case of the arrested development of some simian of
ancient days, as it were, a simian monster from the zoological point of
view, although not from the æsthetic. Man may be regarded as a prodigy
sprung from an ape, born with a larger brain and an intelligence more
highly developed than occurred in his parents. Such a view is in
accordance with known facts.
It must be admitted that certain kinds of organisms, instead of evolving
at a very slow pace, spring up suddenly, and that in such a case nature
proceeds with a considerable stride. Darwin foresaw this possibility,
but it has been made plain to us by the remarkable researches of the
botanist Hugo de Vries.[64]
De Vries cultivated for fifteen years the Evening Primrose, a plant of
American origin (_Œnothera lamarckiana_). He obtained, suddenly, a set
of flowers quite distinct from those of the original plant. They
presented such great differences that he could separate them as several
quite distinct species. During the first few years De Vries obtained
three species (_Œnotera lata_, _Œn. nanella_, and sometimes _Œn.
scintillans_), but variation becoming more and more prevalent, he
ultimately distinguished a dozen new species. These were grown from
seed, and transmitted their specific characters to their descendants. De
Vries, in this way, was a witness of the sudden appearance of new
species.
It is probable that man owes his origin to a similar phenomenon. Some
anthropoid ape having at a certain period become varied in specific
characters, produced offspring endowed with new properties. The brain,
of abnormal size, placed in a spacious cranium, allowed a rapid
development of intellectual faculties much more advanced than those of
the parent and those of the original species. This peculiarity would be
transmitted to the descendants, and, as it was of very considerable
advantage in the struggle for existence, the new race would hold its
own, propagate and prevail. The extraordinary development of
intelligence necessarily led to perfections in the choice of
nourishment, perfections which approached the art of preparing more
digestible food. The jaws, under these conditions, had not such a
difficult task as before, and, moreover, they were no longer required
for attack or defence. They became less developed than in the true
anthropoid apes.
These suggestions involve a conception of the mind that is in harmony
with known facts. From time to time prodigies are born with some talent
far greater than the gifts possessed by the parents.
About twelve years ago a young native of Piedmont, Jacques Inaudi by
name, became famous in Paris on account of his extraordinary power of
calculation. He had an astonishing memory for figures, and could perform
mathematical calculations with surprising rapidity.[65] Two minutes were
sufficient for him to multiply two numbers composed of seven and six
figures. Other arithmetical calculations, such as the extraction of
roots, gave him but little trouble.
To attain this result, Inaudi made use of his extraordinary memory for
figures, founded on the persistence of auditory images. When he heard
the numbers pronounced, he remembered them. Inaudi declared to the
Commission convened by the Academy of Sciences, that when he tried to
recall the numbers he heard them as if repeated aloud, in the tone of
his own voice, and that he could hear them for the greater part of the
day. “In an hour, or in two hours’ time, if I thought of the number that
was uttered, I should be able to repeat it as exactly as I have done
before the Commission.”
Now this very extraordinary and rare auditory memory was developed in an
altogether abrupt way. Inaudi, the son of poor peasants of Piedmont,
passed the first years of his life as a shepherd. At the age of six his
wonderful faculty of calculating figures appeared. He did not know at
this time how to read or to write. At eleven years of age he astonished
the members of the Anthropological Society of Paris by his phenomenal
memory, and it was only much later, at the age of twenty, that he learnt
to read and write. Neither of the parents of Inaudi had shown in the
slightest degree a calculating faculty like that of little Jacques. It
must then be admitted that it was developed as suddenly as the new
qualities in the Evening Primrose that we have already mentioned.
The first men, also, were probably ingenious children, born of
anthropoid parents. This hypothesis very well explains the fact that man
is more like the fœtus and the young of anthropoid apes than the adult
animals, and exhibits only a trace of many organs which are much more
developed in simian species.
A very distinguished German anatomist, Wiedersheim,[66] has given in a
pamphlet a _resumé_ of our actual knowledge of the organs of man from
the point of view of their descent. He has found fifteen organs which
show in the human species a considerable advance on those of anthropoid
apes. The chief of these are the lower limb, well adapted for a constant
erect carriage of the body; the strengthening of the pelvis and of the
sacrum, as well as the broadening of the more slender pelvis of the
female; the curvature of the lumbar part of the vertebral column; the
development of the buttocks and of the calves; the difference of certain
muscles of the face; the nose; certain strands from the brain to the
spinal cord; the occipital lobe of the brain; the greater development of
the cerebral cortex, and, lastly, the considerable differentiation of
the muscles of the larynx which permit speech.
But besides these progressive organs, Wiedersheim has counted seventeen
decaying organs, still able to fulfil their physiological function in a
more or less incomplete manner (amongst these are the decadent muscles
of the leg and foot; the eleventh and twelfth pairs of ribs, the toes,
the cæcum, etc.), and not less than one hundred and seven rudimentary
organs which serve no useful physiological purpose (to this category
belong the coccyx—the vestige of a tail—the thirteenth pair of ribs in
the adult, the muscles of the ear, the vermiform appendage, etc.).
We have already shown in the preceding chapter the great importance of
rudimentary organs as aids to the tracing of the genealogy of organisms.
These organs, useless at present, are the vestiges of similar but more
developed organs, which fulfilled a useful function in our ancestors.
The extraordinary quantity of rudimentary organs in man furnishes
another proof of his animal origin, and puts at the disposal of science
information of great value for the philosophic conception of human
nature.