cerebral lobes overlap and extend much further behind the cerebellum, in
proportion, than they do in man (Fig. 16)--and it is quite certain that,
in all, the cerebellum is completely covered behind, by well-developed
posterior lobes. The fact can be verified by every one who possesses the
skull of any old or new world monkey. For, inasmuch as the brain in all
mammals completely fills the cranial cavity, it is obvious that a cast
of the interior of the skull will reproduce the general form of the
brain, at any rate with such minute and, for the present purpose,
utterly unimportant differences as may result from the absence of the
enveloping membranes of the brain in the dry skull. But if such a cast
be made in plaster, and compared with a similar cast of the interior of
a human skull, it will be obvious that the cast of the cerebral chamber,
representing the cerebrum of the ape, as completely covers over
and overlaps the cast of the cerebellar chamber, representing the
cerebellum, as it does in the man (Fig. 20). A careless observer,
forgetting that a soft structure like the brain loses its proper
shape the moment it is taken out of the skull, may indeed mistake the
uncovered condition of the cerebellum of an extracted and distorted
brain for the natural relations of the parts; but his error must become
patent even to himself if he try to replace the brain within the cranial
chamber. To suppose that the cerebellum of an ape is naturally uncovered
behind is a miscomprehension comparable only to that of one who should
imagine that a man's lungs always occupy but a small portion of the
thoracic cavity--because they do so when the chest is opened, and their
elasticity is no longer neutralized by the pressure of the air.
And the error is the less excusable, as it must become apparent to
every one who examines a section of the skull of any ape above a Lemur,
without taking the trouble to make a cast of it. For there is a
very marked groove in every such skull, as in the human skull--which
indicates the line of attachment of what is termed the 'tentorium'--a
sort of parchment-like shelf, or partition, which, in the recent state,
is interposed between the cerebrum and cerebellum, and prevents the
former from pressing upon the latter. (See Fig. 16.)
This groove, therefore, indicates the line of separation between that
part of the cranial cavity which contains the cerebrum, and that which
contains the cerebellum; and as the brain exactly fills the cavity of
the skull, it is obvious that the relations of these two parts of the
cranial cavity at once informs us of the relations of their contents.
Now in man, in all the old-world, and in all the new-world Simiae,
with one exception, when the face is directed forwards, this line of
attachment of the tentorium, or impression for the lateral sinus, as it
is technically called, is nearly horizontal, and the cerebral chamber
invariably overlaps or projects behind the cerebellar chamber. In the
Howler Monkey or 'Mycetes' (see Fig. 16), the line passes obliquely
upwards and backwards, and the cerebral overlap is almost nil; while in
the Lemurs, as in the lower mammals, the line is much more inclined in
the same direction, and the cerebellar chamber projects considerably
beyond the cerebral.
When the gravest errors respecting points so easily settled as
this question respecting the posterior lobes can be authoritatively
propounded, it is no wonder that matters of observation, of no very
complex character, but still requiring a certain amount of care, should
have fared worse. Any one who cannot see the posterior lobe in an ape's
brain is not likely to give a very valuable opinion respecting the
posterior cornu or the hippocampus minor. If a man cannot see a church,
it is preposterous to take his opinion about its altar-piece or painted
window--so that I do not feel bound to enter upon any discussion of
these points, but content myself with assuring the reader that the
posterior cornu and the hippocampus minor, have now been seen--usually,
at least as well developed as in man, and often better--not only in the
Chimpanzee, the Orang, and the Gibbon, but in all the genera of the old
world baboons and monkeys, and in most of the new world forms, including
the Marmosets.
[Illustration: FIG. 21.--Drawings of the cerebral hemispheres of a Man
and of a Chimpanzee of the same length, in order to show the relative
proportions of the parts: the former taken from a specimen, which Mr.
Flower, Conservator of the Museum of the Royal College of Surgeons,
was good enough to dissect for me; the latter, from the photograph of
a similarly dissected Chimpanzee's brain, given in Mr. Marshall's paper
above referred to. 'a', posterior lobe; 'b', lateral ventricle; 'c',
posterior cornu; 'x', the hippocampus minor.]
In fact, all the abundant and trustworthy evidence (consisting of the
results of careful investigations directed to the determination of these
very questions, by skilled anatomists) which we now possess, leads
to the conviction that, so far from the posterior lobe, the posterior
cornu, and the hippocampus minor, being structures peculiar to and
characteristic of man, as they have been over and over again asserted
to be, even after the publication of the clearest demonstration of the
reverse, it is precisely these 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.
As to the convolutions, the brains of the apes exhibit every stage of
progress, from the almost smooth brain of the Marmoset, to the Orang
and the Chimpanzee, which fall but little below Man. And it is most
remarkable that, as soon as all the principal sulci appear, the pattern
according to which they are arranged is identical with that of the
corresponding sulci of man. The surface of the brain of a monkey
exhibits a sort of skeleton map of man's, and in the man-like apes
the details become more and more filled in, until it is only in minor
characters, such as the greater excavation of the anterior lobes, the
constant presence of fissures usually absent in man, and the different
disposition and proportions of some convolutions, that the Chimpanzee's
or the Orang's brain can be structurally distinguished from Man's.
So far as cerebral structure goes, therefore, it is clear that Man
differs less from the Chimpanzee or the Orang, than these do even
from the Monkeys, and that the difference between the brains of the
Chimpanzee and of Man is almost insignificant, when compared with that
between the Chimpanzee brain and that of a Lemur.
It must not be overlooked, however, that there is a very striking
difference in absolute mass and weight between the lowest human
brain and that of the highest ape--a difference which is all the more
remarkable when we recollect that a full grown Gorilla is probably
pretty nearly twice as heavy as a Bosjes man, or as many an European
woman. It may be doubted whether a healthy human adult brain ever
weighed less than thirty-one or two ounces, or that the heaviest Gorilla
brain has exceeded twenty ounces.
This is a very noteworthy circumstance, and doubtless will one day help
to furnish an explanation of the great gulf which intervenes between
the lowest man and the highest ape in intellectual power; [6] but it has
little systematic value, for the simple reason that, as may be concluded
from what has been already said respecting cranial capacity, the
difference in weight of brain between the highest and the lowest men
is far greater, both relatively and absolutely, than that between
the lowest man and the highest ape. The latter, as has been seen, is
represented by, say twelve ounces of cerebral substance absolutely, or
by 32:20 relatively; but as the largest recorded human brain weighed
between 65 and 66 ounces, the former difference is represented by
more than 33 ounces absolutely, or by 65:32 relatively. Regarded
systematically, the cerebral differences of man and apes are not of
more than generic value; his Family distinction resting chiefly on his
dentition, his pelvis, and his lower limbs.
A man born dumb, notwithstanding his great cerebral mass and his
inheritance of strong intellectual instincts, would be capable of few
higher intellectual manifestations than an Orang or a Chimpanzee, if he
were confined to the society of dumb associates. And yet there might not
be the slightest discernible difference between his brain and that of
a highly intelligent and cultivated person. The dumbness might be the
result of a defective structure of the mouth, or of the tongue, or
a mere defective innervation of these parts; or it might result from
congenital deafness, caused by some minute defect of the internal ear,
which only a careful anatomist could discover.
The argument, that because there is an immense difference between a
Man's intelligence and an Ape's, therefore, there must be an equally
immense difference between their brains, appears to me to be about as
well based as the reasoning by which one should endeavour to prove that,
because there is a "great gulf" between a watch that keeps accurate
time and another that will not go at all, there is therefore a great
structural hiatus between the two watches. A hair in the balance-wheel,
a little rust on a pinion, a bend in a tooth of the escapement, a
something so slight that only the practised eye of the watchmaker can
discover it, may be the source of all the difference.
And believing, as I do, with Cuvier, that the possession of articulate
speech is the grand distinctive character of man (whether it be
absolutely peculiar to him or not), I find it very easy to comprehend,
that some equally inconspicuous structural difference may have been the
primary cause of the immeasurable and practically infinite divergence of
the Human from the Simian Stirps.
Thus, whatever system of organs be studied, the comparison of their
modifications in the ape series leads to one and the same result--that
the structural differences which separate Man from the Gorilla and the
Chimpanzee are not so great as those which separate the Gorilla from the
lower apes.
But in enunciating this important truth I must guard myself against a
form of misunderstanding, which is very prevalent. I find, in fact, that
those who endeavour to teach what nature so clearly shows us in this
matter, are liable to have their opinions misrepresented and their
phraseology garbled, until they seem to say that the structural
differences between man and even the highest apes are small and
insignificant. Let me take this opportunity then of distinctly
asserting, on the contrary, that they are great and significant; that
every bone of a Gorilla bears marks by which it might be distinguished
from the corresponding bone of a Man; and that, in the present creation,
at any rate, no intermediate link bridges over the gap between 'Homo'
and 'Troglodytes'.
It would be no less wrong than absurd to deny the existence of this
chasm; but it is at least equally wrong and absurd to exaggerate its
magnitude, and, resting on the admitted fact of its existence, to refuse
to inquire whether it is wide or narrow. Remember, if you will, that
there is no existing link between Man and the Gorilla, but do not forget
that there is a no less sharp line of demarcation, a no less complete
absence of any transitional form, between the Gorilla and the Orang, or
the Orang and the Gibbon. I say, not less sharp, though it is somewhat
narrower. The structural differences between Man and the Man-like apes
certainly justify our regarding him as constituting a family apart from
them; though, inasmuch as he differs less from them than they do from
other families of the same order, there can be no justification for
placing him in a distinct order.
And thus the sagacious foresight of the great lawgiver of systematic
zoology, Linnaeus, becomes justified, and a century of anatomical
research brings us back to his conclusion, that man is a member of the
same order (for which the Linnaean term PRIMATES ought to be retained)
as the Apes and Lemurs. This order is now divisible into seven families,
of about equal systematic value: the first, the ANTHROPINI, contains
Man alone; the second, the CATARHINI, embraces the old-world apes; the
third, the PLATYRHINI, all new-world apes, except the Marmosets; the
fourth, the ARCTOPITHECINI, contains the Marmosets; the fifth, the
LEMURINI, the Lemurs--from which 'Cheiromys' should probably be excluded
to form a sixth distinct family, the CHEIROMYINI; while the seventh,
the GALEOPITHECINI, contains only the flying Lemur 'Galeopithecus',--a
strange form which almost touches on the Bats, as the 'Cheiromys' puts
on a rodent clothing, and the Lemurs simulate Insectivora.
Perhaps no order of mammals presents us with so extraordinary a series
of gradations as this--leading us insensibly from the crown and summit
of the animal creation down to creatures, from which there is but a
step, as it seems, to the lowest, smallest, and least intelligent of
the placental Mammalia. It is as if nature herself had foreseen
the arrogance of man, and with Roman severity had provided that his
intellect, by its very triumphs, should call into prominence the slaves,
admonishing the conqueror that he is but dust.
These are the chief facts, this the immediate conclusion from them
to which I adverted in the commencement of this Essay. The facts, I
believe, cannot be disputed; and if so, the conclusion appears to me to
be inevitable.
But if Man be separated by no greater structural barrier from the brutes
than they are from one another--then it seems to follow that if any
process of physical causation can be discovered by which the genera
and families of ordinary animals have been produced, that process of
causation is amply sufficient to account for the origin of Man. In other
words, if it could be shown that the Marmosets, for example, have
arisen by gradual modification of the ordinary Platyrhini, or that
both Marmosets and Platyrhini are modified ramifications of a primitive
stock--then, there would be no rational ground for doubting that man
might have originated, in the one case, by the gradual modification of
a man-like ape; or, in the other case, as a ramification of the same
primitive stock as those apes.
At the present moment, but one such process of physical causation
has any evidence in its favour; or, in other words, there is but one
hypothesis regarding the origin of species of animals in general
which has any scientific existence--that propounded by Mr. Darwin. For
Lamarck, sagacious as many of his views were, mingled them with so much
that was crude and even absurd, as to neutralize the benefit which his
originality might have effected, had he been a more sober and cautious
thinker; and though I have heard of the announcement of a formula
touching "the ordained continuous becoming of organic forms," it is
obvious that it is the first duty of a hypothesis to be intelligible,
and that a qua-qua-versal proposition of this kind, which may be read
backwards, or forwards, or sideways, with exactly the same amount of
signification, does not really exist, though it may seem to do so.
At the present moment, therefore, the question of the relation of man to
the lower animals resolves itself, in the end, into the larger question
of the tenability, or untenability of Mr. Darwin's views. But here
we enter upon difficult ground, and it behoves us to define our exact
position with the greatest care.
It cannot be doubted, I think, that Mr. Darwin has satisfactorily proved
that what he terms selection, or selective modification, must occur, and
does occur, in nature; and he has also proved to superfluity that such
selection is competent to produce forms as distinct, structurally, as
some genera even are. If the animated world presented us with none but
structural differences, I should have no hesitation in saying that Mr.
Darwin had demonstrated the existence of a true physical cause, amply
competent to account for the origin of living species, and of man among
the rest.
But, in addition to their structural distinctions, the species of
animals and plants, or at least a great number of them, exhibit
physiological characters--what are known as distinct species,
structurally, being for the most part either altogether incompetent to
breed one with another; or if they breed, the resulting mule, or hybrid,
is unable to perpetuate its race with another hybrid of the same kind.
A true physical cause is, however, admitted to be such only on one
condition--that it shall account for all the phenomena which come
within the range of its operation. If it is inconsistent with any
one phenomenon, it must be rejected; if it fails to explain any one
phenomenon, it is so far weak, so far to be suspected; though it may
have a perfect right to claim provisional acceptance.
Now, Mr. Darwin's hypothesis is not, so far as I am aware, inconsistent
with any known biological fact; on the contrary, if admitted, the facts
of Development, of Comparative Anatomy, of Geographical Distribution,
and of Palaeontology, become connected together, and exhibit a meaning
such as they never possessed before; and I, for one, am fully convinced,
that if not precisely true, that hypothesis is as near an approximation
to the truth as, for example, the Copernican hypothesis was to the true
theory of the planetary motions.
But, for all this, our acceptance of the Darwinian hypothesis must be
provisional so long as one link in the chain of evidence is wanting; and
so long as all the animals and plants certainly produced by selective
breeding from a common stock are fertile, and their progeny are fertile
with one another, that link will be wanting. For, so long, selective
breeding will not be proved to be competent to do all that is required
of it to produce natural species.
I have put this conclusion as strongly as possible before the reader,
because the last position in which I wish to find myself is that of
an advocate for Mr. Darwin's, or any other views--if by an advocate is
meant one whose business it is to smooth over real difficulties, and to
persuade where he cannot convince.
In justice to Mr. Darwin, however, it must be admitted that the
conditions of fertility and sterility are very ill understood, and that
every day's advance in knowledge leads us to regard the hiatus in his
evidence as of less and less importance, when set against the multitude
of facts which harmonize with, or receive an explanation from, his
doctrines.
I adopt Mr. Darwin's hypothesis, therefore, subject to the production of
proof that physiological species may be produced by selective breeding;
just as a physical philosopher may accept the undulatory theory of
light, subject to the proof of the existence of the hypothetical ether;
or as the chemist adopts the atomic theory, subject to the proof of the
existence of atoms; and for exactly the same reasons, namely, that it
has an immense amount of prima facie probability: that it is the only
means at present within reach of reducing the chaos of observed facts
to order; and lastly, that it is the most powerful instrument of
investigation which has been presented to naturalists since the
invention of the natural system of classification, and the commencement
of the systematic study of embryology.
But even leaving Mr. Darwin's views aside, the whole analogy of natural
operations furnishes so complete and crushing an argument against
the intervention of any but what are termed secondary causes, in the
production of all the phenomena of the universe; that, in view of the
intimate relations between Man and the rest of the living world, and
between the forces exerted by the latter and all other forces, I can see
no excuse for doubting that all are co-ordinated terms of Nature's great
progression, from the formless to the formed--from the inorganic to the
organic--from blind force to conscious intellect and will.
Science has fulfilled her function when she has ascertained and
enunciated truth; and were these pages addressed to men of science only,
I should now close this essay, knowing that my colleagues have learned
to respect nothing but evidence, and to believe that their highest duty
lies in submitting to it, however it may jar against their inclinations.
But desiring, as I do, to reach the wider circle of the intelligent
public, it would be unworthy cowardice were I to ignore the repugnance
with which the majority of my readers are likely to meet the conclusions
to which the most careful and conscientious study I have been able to
give to this matter, has led me.
On all sides I shall hear the cry--"We are men and women, not a mere
better sort of apes, a little longer in the leg, more compact in the
foot, and bigger in brain than your brutal Chimpanzees and Gorillas.
The power of knowledge--the conscience of good and evil--the pitiful
tenderness of human affections, raise us out of all real fellowship with
the brutes, however closely they may seem to approximate us."
To this I can only reply that the exclamation would be most just and
would have my own entire sympathy, if it were only relevant. But, it is
not I who seek to base Man's dignity upon his great toe, or insinuate
that we are lost if an Ape has a hippocampus minor. On the contrary, I
have done my best to sweep away this vanity. I have endeavoured to show
that no absolute structural line of demarcation, wider than that between
the animals which immediately succeed us in the scale, can be drawn
between the animal world and ourselves; and I may add the expression of
my belief that the attempt to draw a psychical distinction is equally
futile, and that even the highest faculties of feeling and of intellect
begin to germinate in lower forms of life. [7] At the same time, no one
is more strongly convinced than I am of the vastness of the gulf between
civilized man and the brutes; or is more certain that whether 'from'
them or not, he is assuredly not 'of' them. No one is less disposed
to think lightly of the present dignity, or desparingly of the future
hopes, of the only consciously intelligent denizen of this world.
We are indeed told by those who assume authority in these matters, that
the two sets of opinions are incompatible, and that the belief in
the unity of origin of man and brutes involves the brutalization and
degradation of the former. But is this really so? Could not a sensible
child confute by obvious arguments, the shallow rhetoricians who would
force this conclusion upon us? Is it, indeed, true, that the Poet, or
the Philosopher, or the Artist whose genius is the glory of his age, is
degraded from his high estate by the undoubted historical probability,
not to say certainty, that he is the direct descendant of some naked
and bestial savage, whose intelligence was just sufficient to make him a
little more cunning than the Fox, and by so much more dangerous than
the Tiger? Or is he bound to howl and grovel on all fours because of the
wholly unquestionable fact, that he was once an egg, which no ordinary
power of discrimination could distinguish from that of a Dog? Or is the
philanthropist or the saint to give up his endeavours to lead a noble
life, because the simplest study of man's nature reveals, at its
foundations, all the selfish passions and fierce appetites of the merest
quadruped? Is mother-love vile because a hen shows it, or fidelity base
because dogs possess it?
The common sense of the mass of mankind will answer these questions
without a moment's hesitation. Healthy humanity, finding itself hard
pressed to escape from real sin and degradation, will leave the brooding
over speculative pollution to the cynics and the 'righteous overmuch'
who, disagreeing in everything else, unite in blind insensibility to
the nobleness of the visible world, and in inability to appreciate the
grandeur of the place Man occupies therein.