THE SKELETON OF APES AND OF MAN
THE upright carriage of man has entailed remarkable changes in the
proportions and shapes of parts of his body, as well as leading to
special skill in the use of his hands. The vertebral column of man has
not the single curve of a bow, as it has (practically) in the higher
apes, but as he stands it curves (slightly, it is true, but definitely)
forward at the neck, backward at the chest, forward at the loins, and
backward again at the hips, an arrangement which appears to protect to
some extent the brain from the transmission to it along the vertebral
column of the shock caused by the sudden impact of the feet on the
ground in jumping. The head is balanced on the top of this slightly
elastic curvilinear column, the joint by which the skull rests on the
vertebræ being placed beneath the brain-box and near the middle region
of the skull. The ligaments which hold the skull in place are smaller
than those in monkeys. In the higher apes the skull is not so balanced,
but is held by very strong ligaments and muscles braced, as it were,
on to the end of the forwardly sloping, nearly straight, backbone,
from which it projects, and has further to be held in position by a
great ligament attached to it and the dorsal processes of the neck
vertebræ. As an adaptation to the upright carriage of man, the shape
of his pelvic bones is that of a basin upon which his coiled mass
of intestines can rest when he stands erect. The pelvic bones of the
higher apes are flat, nearly parallel with the broad plane of the back,
and give no such support; the viscera have to rest against the wall
of the abdomen in the stooping position assumed by these animals in
walking. The abdominal walls are consequently strong and thick, and the
abdomen protrudes, as does that of a very young child. One result of
man's upright carriage, showing that it is a recent acquirement and one
to which he is not completely adapted, is the frequent occurrence in
him of "hernia," or protrusion of the intestine through certain spaces
in the deep fibrous wall of the abdomen. There would be no excessive
pressure upon these spaces (near the groin), and therefore little
danger of hernia, were it not for man's newly-acquired habit of erect
gait. He is still incompletely adapted to the upright pose.
The arms of man are relatively shorter and his legs much longer than
in the man-like apes. The Neandermen were more ape-like in these
proportions than are modern races of man, and show also an "ape-like"
curvature of the thigh bone which in man is straight. Whilst the arm
and hand of man has gradually become a more delicate thing than that
of the apes, and capable of much greater variety and efficiency in the
movements of its parts, this condition has come about by alteration
in proportions and to some extent shape, and not by any great change
in construction. Only two muscles exist in connexion with man's hand
not found in that of the higher apes. They are small slips adding to
the efficiency of the fingers and thumb, whilst in the foot there is
in man a small muscle connected with its outer border--"the peroneus
tertius"--which helps to keep the sole of the foot turned downwards,
and is not present in the apes. The general shape and proportionate
size of the muscles of the leg in man give it a very different
appearance from that of the ape; but there are no muscles or bones
present which are not found in the apes. The beautiful outline and form
of the human leg and buttocks are directly the result of the increased
size of certain muscles used in maintaining the upright position,
and in the peculiarly human swing of the leg in walking and running.
Their beauty, like that of the other specially human features which we
consider beautiful, depends upon the fact that their development, in
due proportion, is a necessary condition of efficiency, activity, and
strength in movements and attitudes which have gradually been acquired
by man, and distinguish him from the apes. Our admiration for them is
a sort of self-love, a worship of an ideal of efficiency and balance
which is specifically "human," and is more or less fully realized in
every individual. Probably sexual selection has had a large share in
thus moulding the human form. The apes do not present the development
of the gluteal region characteristic of man, and the muscles of both
the arms and legs in them are, though very powerful, less fleshy and
more "stringy" than those of man. There is, indeed, a difference
of "quality" in the muscles of apes and men, especially civilized
men, which needs investigation by the microscopist and experimental
physiologist.
Though we necessarily compare man with the highest existing apes, we
must not suppose that the man-like ape from which the earliest ape-like
men developed was in fact a gorilla or a chimpanzee. The survival
of the gorilla and chimpanzee at this day necessarily implies that
they were not the actual ancestral forms which became modified and
superseded in the course of man's development. Very probably the ape
(the creature more ape-like than man-like, of which more anon) from
which man took his direct descent had already developed a plantigrade
foot--that is a foot of which the sole is placed on the ground for
support, as it is in gibbons, baboons, and bears, but not in most apes,
nor in cats, dogs, sheep, and horses! And probably the hands of that
ancestral ape were already used more dexterously in consequence, and
the dog teeth were less needed either in fighting or in breaking up
food and so had become smaller.
This reflection brings us to the differences between the teeth of a
man and those of apes. The face of apes is drawn forward so as to
approach in form the "muzzle" of a dog. It is far less muzzle-like
in the more man-like apes than in the dog-faced baboons, and in the
least civilized living races of man is much less prominent--what is
called "prognathous"--than in the highest existing apes. In civilized
living races of man it is markedly reduced, so that in the habitual
carriage of the head, with the eyes looking forward over a horizontal
plane at right angles to the vertical or upright body, the front
border of the jaws, in which the chisel-like incisor teeth are set,
usually projects but very little beyond the brow or forehead. In Greek
sculpture and other examples regarded by us as types of "beauty," the
jaws do not project at all. Such a face is called "orthognathous."
This modification of the shape of the face is due to the progressive
dwindling in the size of the front part of the jaw and its teeth in
the series dog, ape, less-civilized man, highly-civilized man, and is
accompanied by an increase in the size of the front part of the brain.
The number of the teeth and their arrangement in groups are identical
in man and the apes. The most important difference is in the size of
the front teeth, and especially in the size of the "corner" teeth (one
on each side above and below), also called eye-teeth, dog-teeth, or
"canines." In the highest apes, as in all monkeys, the canine teeth
are very large, and even tusk-like in the males, projecting above the
horizonal line formed by the crowns of the other teeth. This projecting
of the canine teeth results in their not meeting one another point
to point when the jaws are closed, but necessitates one, the lower,
shutting in front of the other, and a space is left in the row of
teeth, both in the upper and the lower jaw, for this interlocking of
the great canines. It is called a "diastema." Man stands in strong
contrast to the apes in this respect. His canines do not project beyond
the level of the neighbouring teeth, and there is no "diastema" or gap
in either the upper or lower row of his teeth.[9] There is no trace of
such a gap nor any excess of size of the canines in any living race of
men, and what is more remarkable, the jaws of very ancient prehistoric
men which have been found in the Middle Pleistocene--the Neander or
Moustierian men as well as the more ancient jaw from Heidelberg (see p.
286)--do not show any difference in this respect from the most advanced
European race. On the other hand, it is one of the most remarkable
features presented by the recently discovered "Piltdown" lower jaw that
it had a larger canine tooth than that of any recent or fossil man, and
consequently a gap or "diastema" in the row of teeth (see Chap. XXX).
This difference between men and apes is all the more marked since the
grinders or cheek teeth (called also molars) of man and the higher
apes agree very closely, each to each in order of their position, in
the pattern formed by the irregular surface of the crown. There are
some slight differences in relative size and in the order of their
"cutting" or growth, but these are trivial. The jaws of man show their
derivation by gradual dwindling from the larger projecting jaws seen
in apes and monkeys, in the close setting (that is to say, "crowding")
of the teeth, and also in the dwindling and late "cutting" of the last
tooth, in each jaw above and below, which we call the wisdom tooth.
The "wisdom teeth" are in the higher races of men on their way to
total disappearance. In lower races of men they are larger than in the
higher, and in the man-like apes are of full size, and there is plenty
of room in the jaw for them.
[9] See Plates VII. and VIII., p. 166, in "Science from an Easy Chair,"
Second Series, for careful drawings of the complete series of teeth in
both the upper and lower jaw of Man and of an Ape.
In the highest apes as well as the lower, the bony lower jaw slopes
gradually backwards and downwards from the _palisade_ of front
chisel-like teeth or incisors (see Fig. 23 C, p. 277). There is no
bony projection below the front teeth--in fact, no bony "chin." But
in all modern races of men the front part of the semicircle arch of
teeth has shrunk or "withdrawn" considerably or more than has the
bony jaw in which the teeth are set. Consequently the bone projects
in front of the front teeth as the bony chin (see Fig. 23 A, p. 277,
and also "Science from an Easy Chair," 1910, pp. 404, 405). This is
characteristic of modern races of man and occurs in no other animal.
The very remarkable fact has recently been established that in the
ancient species of man from the Middle and Lower Pleistocene--the
Neander man and the Heidelberg man (Homo Neanderthalensis)--this extra
or excessive shrinking of the dental arch (the half-circle formed by
the complete row of teeth) had not taken place. Though the teeth are
placed closely side by side and have the same shape as in modern man,
they are a little bigger and form a larger and longer arch--more like a
horse-shoe than a semicircle, and have not shrunk back so as to leave a
projecting bony chin. The bony jaw _recedes_ in these early races of
men from the line of the front teeth as it does in the apes. _They have
no chin_ (see Fig. 25, p. 286).
Since we are all accustomed to regard a well-marked chin as a necessary
feature of a beautiful human face, and to deplore or disapprove the
receding or evanescent chin, it is not improbable that sexual selection
has favoured the recession of the dental arch with the retention of the
original bulk of the lower front margin of the jaw and chin, though
why the chin should be thus appreciated is a matter of speculation. It
is remarkable that in many of the monkeys the hair grows forward as
a projecting beard on the front of the jaw, so as to resemble a chin
although no chin is there. It is also the fact that some uncivilized
races of men trim the beard and train it in a forward growth so as to
suggest the possession of a very prominent chin, when in reality their
solid chins of flesh and bone are not especially large.
It is not easy to suggest how the reduction in size of the canines and
front teeth and of the length of the jaw could be of such advantage
to incipient man as to lead to the survival of those individuals
in which these parts were least developed, and so gradually to the
crowding of the teeth, reduced in size, into a jaw of reduced length,
whilst at a late stage, long after man was man and no ape, the teeth
became so reduced in volume as to leave the lower margin of the lower
jaw--projecting far in front of them as the "chin," the eminently
human chin. The nutrition of these parts placed in the head near the
brain, the great canine having so vast a fang that it reaches up to the
eye-socket, whence it is called the "eye-tooth," renders it probable
that there is a relation depending on nutrition and blood supply
between them and that all-important organ contained in the neighbouring
bony box, the brain. As the great teeth and long jaw have dwindled, the
brain has increased in volume, and, what is more important, in activity.
Other neighbouring bony structures have dwindled whilst the brain
has increased. The great longitudinal and transverse crests of bone
seen on the skull of the gorilla may never have existed in that form
of ape from which man is derived, but a tendency to such ridge-like
outgrowth and to a greater thickness of the bony wall of the brain-case
characterizes apes as distinguished from men, and its disappearance
is one of the changes which have accompanied the expansion of the
brain-case and the increased size of brain in man. Lower races of
existing men have frequently thicker skulls than the higher races.
The bony development of the skull in the higher apes is especially
remarkable in the region just above the eye. The upper border of the
orbit is greatly thickened, and projects as a bony arch overhanging the
eye. But the extent of this growth, as also of crests on the skull,
varies in individuals, and is much smaller in females than in males. In
the young these ridges and prominences are absent. It is accordingly no
very great change that they should disappear altogether in man, even
were they as large in the ape-like ancestor of man, which probably
they were not. But the existence of a considerable thickening and
forward growth of the eyebrow region of the skull is noticed in many
human skulls. It is particularly large in some skulls of Australian
"black-fellows," and is still larger in and characteristic of the
ancient species of men of the Moustierian period in Europe, Homo
Neanderthalensis.