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.[90] 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,[91]
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._"[92]
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[93] 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:[94] "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."[95]
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,[96] 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."[97]
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 Mueller:[98]
"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:[99] "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."[100]
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."[101]
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:[102] "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
Monotrems, 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."[103]
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,"[104] and of Lamarck's "absurd, though clever
work"[105] and expressly declaring, "I attribute very little to the
direct action of climate, etc."[106] 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 a natural selection."[107]
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.