In the rock shelter of Cro-Magnon, France, were found the bones of three
men, one woman, and one child, of more advanced character. These,
however, are of late date and may have been early neolithic. At Engis,
near Liege, Belgium, a deeply buried skull, associated with many remains
of extinct animals, has been dug up, which is by no means ape-like in
character. A still superior example of palaeolithic man is the skeleton
found in a cavern at Mentone, east of Nice, France, which represents a
man six feet in height, with rather large head, high forehead, and very
large facial angle (85 deg.). The cave contained bones of extinct animals,
but no trace of the reindeer.
There is no occasion to speak here of the many remains of neolithic man
that have been exhumed. Sparse in the early part of the age of polished
stone weapons, they gradually became numerous, and merged into the human
remains of late prehistoric times. The American continent is not without
its relics of ancient man, the most famous of which is the Calaveras
skull, found in 1886 in the auriferous gravels of Calaveras County,
California, at an extraordinary depth. The miners, in excavating a
shaft, passed through several layers of lava and gravel, forming a total
thickness of seventy-nine feet of lava and a considerable thickness of
gravel, making nearly one hundred and thirty feet in all. At this depth
a skull was found imbedded in the gravel, which, if authentic, must have
been overflowed by several successive thick outpours of lava in the
ancient volcanic era of that region. As its authenticity is, however,
still a matter of controversy, nothing further need here be said about
it.
Leaving these evidences of human antiquity, we come to the most
remarkable and significant of all the known relics of man, if indeed it
is man, for it seems to many a link between man and the ape,--not yet
human, while no longer simian. This is the fossil find made by Dr.
Eugene Dubois in 1891 on the banks of the Bengawan River, Java, and
named by him _Pithecanthropus erectus_, he maintaining that it
represents a new genus of upright animals, or even a new family. The
remains found by him consisted of the upper part of a skull, a molar
tooth, and a femur, possibly not belonging to a single individual, as
they were somewhat separated. These were exhumed from a stratum of
volcanic tufa, claimed to be of Tertiary age, but perhaps Quaternary,
and lay at a depth of some forty feet beneath the surface.
The femur very closely resembles that of a human being of average size,
and its shape, articulating surface, and other characters show clearly
that the animal stood habitually erect. The principal significance lies
in the tooth and the cranium. The former is like that of the chimpanzee
in shape, but less rugose on its grinding surface. It seems to lie
between the ape and the human type of dentition. The cranium has a low,
depressed arch, with a very narrow frontal region and highly developed
superciliary ridges. The cranial capacity was apparently about one
thousand, that of man being from thirteen hundred to fourteen hundred.
It is therefore said to be "the lowest human cranium yet described, very
nearly as much below the Neanderthal as that is below the normal
European."
Professor O. C. Marsh, in a paper on the subject in the _American
Journal of Science_, for February, 1895, agrees with Dr. Dubois in his
view of the distinct position of this form in the animal kingdom, and
says that the discoverer "has proved the existence of a new prehistoric
anthropoid form, not human, indeed, but in size, brain power, and erect
posture much nearer man than any animal hitherto discovered, living or
extinct."
We have here given a short review of a long story. The evidences of
man's former existence upon the earth are multitudinous, but any
extended consideration of them is aside from our purpose, which is
merely to show that the proofs of man's descent found in his physical
structure are strengthened by evidences which he has left strewn behind
him in his long march down the ages. Only a single conclusion can be
drawn from these vestiges of man excavated from caves and gravels,
namely, that they indicate a gradual and steady progression upward from
a very low condition, while they nowhere give evidence of the
traditional fall of man.
This is certainly the case with the relics of human workmanship. They
begin with the rudest chipped stones, and very slowly improve in form
and finish and become more varied, as we move upward in our search. The
ground and polished stones follow, and the variety of implements
considerably increases, until at length the age of metal, with its
developed industries, is reached. The only seeming evidence of superior
intellect to be found in this gradual progress is that of the drawings
and carvings left us by one group of palaeolithic men. But the actual
mental development indicated by these becomes problematical when we
consider that similar drawings are made to-day by the Bushmen of South
Africa, a race of men occupying a very low mental stage. From this fact
we may fairly conclude that the possession of a simple graphic art does
not necessarily indicate any considerable intellectual advance.
If we consider the remains of man himself, the few bones which mark his
early pathway through time, a similar conclusion must be drawn.
Beginning with Pithecanthropus, which science is yet in doubt whether to
class with the apes or with men, we pass upward to the bestial
Neanderthal man and his fellows of the same low type. Of the sparse
remains of palaeolithic man that exist, the most are of this degraded
type. The cranial capacity is usually not small. They had the full brain
development of man. But this simply assimilates them with the low races
of existing savages, many of whom have not developed the simple art of
chipping stone to form weapons and yet have brains of normal human
weight.
In truth, the influences under which the development of the brain took
place were not what we now call intellectual. Developing man used his
mental powers actively in his dealings with the hostile forces of
surrounding nature, and nearly all the forces of evolution were brought
to bear upon the organ of the mind, the body remaining practically
unchanged. His senses became acute, his cunning and alertness high, his
use of weapons skilful, but his field of mental exercise was still the
outer world, and the inner world of thought remained in its embryo
state. The more recent development of the mind has been in its
intellectual powers, while its physical aptitudes have somewhat
declined. This has not yielded any marked increase in the dimensions of
the brain, but it may have had a decided effect upon the proportion of
its parts, the regions of the cerebrum devoted to intellectual activity
probably increasing at the expense of the motor and sensory regions,
while the convolutions may have grown considerably more complicated.
IV
FROM QUADRUPED TO BIPED
In the question which now confronts us, that of the evolution of man
from the lower world of animals, it is necessary first to state in what
particulars he has evolved, what are the conditions which distinguish
him from the lower animals. Four marked distinctions may be named: his
erect attitude, with the freeing of the fore limbs from use as agents in
locomotion; his employment of natural objects, instead of his bodily
organs, as tools and weapons; his development of vocal language; and his
great mental superiority, with the general use of the mind in his
dealings with nature.
In none of these particulars does man stand quite alone; in all of them
an affinity with the lower animals exists. Steps of progress in these
directions have been made by many animals, though none of them have
gained any considerable advance. In man's strikingly developed social
habit and organization he has no close counterpart among the
vertebrates, but several among the insects. And it is of much interest
to find that in the highest field of man's progress, his employment of
the mind in his dealings with nature, he is chiefly emulated by such
lowly-organized creatures as the ants and the bees.
We do not need to look far among the lower animals for the species which
come nearest to man in structure and which seem to have immediately
preceded him in the line of descent. We find these forms in the monkeys
or apes, and especially in their highest representatives, the anthropoid
apes. These possess in a partial degree all the special characteristics
of man. They are social in habit; some of them are semi-erect in
posture, and their fore limbs partly freed from use in locomotion; they
possess some imperfect means of vocal communication; they employ the
mind to some extent in place of the body; in short, they seem arrested
forms on the road from brute to man, signal-posts on the highway of
evolution. In physical organization their approach to man is singularly
close. In anatomy man and the higher apes are in most respects
counterparts of each other. The principal anatomical distinction has
been considered to be in the foot, which from the opposable character of
the great toe was classed by Cuvier with the hand, the apes being named
Quadrumana, or four-handed, and man Bimana, or two-handed. Fuller
research has shown that this distinction does not exist, the foot of the
ape being found to agree far more closely with the foot than with the
hand of man. Estimated according to use, the hand is, in the whole
order, the special prehensile organ; the foot, however prehensile it
may be, is predominantly a walking organ. And the opposability of the
great toe is approached in some men, who have great mobility in this
organ, and can use it for grasping.
In regard to the brain, the organ of the mind, the difference between
the higher apes and man is almost solely one of comparative size, the
lower intelligence of the apes being indicated by the smaller size of
their brains. The largest ape brain is scarcely half the size of the
smallest human brain. But anatomically they are nearly identical. All
the structural features of the brain are common to both, and the details
are largely filled out in the anthropoid apes, the convolutions being
all present and the pattern of arrangement the same. The brain of the
orang may be said to be like that of man in all respects except size and
the greater symmetry of its convolutions, which are less complicated
with minor convolutions than in man. In truth, the difference between
the brains of man and the orang is almost insignificant as compared with
the difference between those of the orang and the lowest apes. Mr. E. W.
Taylor, who has recently made an exhaustive study of the minute anatomy
of the brain of the chimpanzee, remarks, "The similarity between the
brain of the anthropoid apes and of man is one of the most singular and
interesting facts of which we have knowledge."
In any attempt, then, to consider the origin of man from the point of
view of evolution, we are irresistibly drawn to the ape tribe as the
next lower link in the long chain of development, and are led to
consider the characteristics of the apes as the intermediate stage
between the quadruped and the biped, the bridge crossing this great gulf
in organic development. This is by no means to suggest that some one of
the existing anthropoid apes is the direct ancestor of man. Such an idea
has never been entertained by scientists. These animals cannot even
fairly be considered as brothers to man's ancestor, but must be looked
upon as more or less distant cousins, with a physical organization less
favorable to high development than that of man. Man's ancestry lies much
farther back in time, and his progenitor must have been constituted
differently from any of the existing large apes.
In the ape tribe we are able to trace nearly every step by which the
gulf between quadruped and biped has been crossed, from the quadrupedal
baboon to the nearly erect gibbon. And in seeking to follow this
development through its successive stages, the first point to be
considered is how the apes gained their special power of grasping, that
characteristic to which they undoubtedly owe the partial freedom of
their hands and their tendency to assume the erect attitude.
The most distinguishing characteristic of the apes and of the nearly
related lemurs has not hitherto been definitely pointed out. This is
that they form the only group of strictly arboreal animals. The tree is
not alone their native habitat, but they are specially adapted to it in
their organs of motion, a fact which cannot be affirmed of any other
animal group. If we consider, for instance, the squirrels, one of the
best-known groups of tree-living animals, we find them to be members of
the great order of rodents, whose native habitat is the land surface.
Though the squirrels have taken to the trees, there has been no adaptive
change in the structure of their limbs and feet. The same may be said of
almost all tree-dwellers except the lemurs and apes. The sloth, indeed,
is specially adapted in organization to an arboreal residence, but this
change is individual, not tribal, this animal being an aberrant form of
the ground-dwelling edentata. In the apes and lemurs, on the contrary,
the ground-dwellers are the aberrant forms, stray wanderers from the
host. Nearly all the species live in trees, to which they are specially
adapted by the formation of their feet. It remains to inquire how this
deviation in structure arose, what were the steps of development of the
grasping foot and hand, the special characteristic of this group.
In considering this question, the first fact to appear is that the apes
and lemurs are plantigrade animals. Their natural tendency is to walk on
the sole of the foot, a habit which few other tribes of animals
possess. Most of the larger animals walk on the knuckles or the toes,
and develop claws or hoofs, but the ancestral form of the ape, ages in
the past, was doubtless a sole-walking quadruped, its toes apparently
provided with nails instead of claws. What the story of this very
ancient quadruped was we are quite unable to say. It may, in the
exigencies of existence, have come to a parting of the ways; a section
of the group, drawn by a love of fruit, developing the climbing habit;
the remaining section continuing on the ground and following a separate
line of evolution. Perhaps only a single species took to the trees; for
it is quite possible for a single form, in a new and advantageous
habitat, to vary in time into a great number of species.
Of all this we can know nothing: but of one thing we may feel assured,
which is that the plantigrade foot is the only one that could have
developed into a grasping organ; such a development being impossible to
the digitigrade or the hoofed animals. One can readily see how the habit
of walking on the sole might tend to a spreading of the toes, in order
to obtain a wider and firmer footing. And it is equally easy to see how
a free and wide motion in the great toe would aid in this result. The
animal may have been at first light in weight and able to support itself
on its unchanged foot, but as it increased in size and weight it would
need a firmer grasp, and the final result of spreading its toes for
this purpose may well have been the opposable great toe.
It must be borne in mind, in this consideration, that the apes differ
from the other tree-dwellers in being destitute of claws. The squirrels,
the opossums, and other arboreal animals have sharp claws, by whose aid
they can easily cling to the surface of the bark-covered boughs. The
nails of the apes are incapable of affording them this service, and it
is not easy to perceive how a foot like theirs could become adapted to
locomotion in the trees otherwise than by the gaining of mobile action
and grasping power in the toes.
The existing habits of the ape tribe lead us to the conclusion that the
ancestral animal may have soon begun to seek support from upper limbs.
The plantigrade foot is one capable of readily curving into an organ of
support, and in the case of the forefoot the toes would tend to spread
and gain flexibility of motion, and the first toe to become opposable to
the others and yield a more complete grasping power. It does not seem
difficult to comprehend, from this point of view, how the feet of a
five-toed plantigrade animal may in time have developed into grasping
organs, since there would be required only an increased flexibility of
the joints, and a wider and fuller movement of the great toes. That such
a change took place in this instance the facts appear to indicate, the
most simple and probable explanation of the development of the grasping
power in the hands and feet of the ape being seemingly that given above.
The relation of the lemurs to the apes is not clearly defined. It may be
an ancestral one, or the two animals may represent distinct lines of
descent. In the latter case we would have two lines of animal evolution
in which the grasping power was gained and adaptation to arboreal life
completed. Whatever their relationship, they both possess the opposable
thumb as the hall-mark of their arboreal habitat, and whenever found
walking on the ground they may be looked upon as estrays from their
native place of residence.
Once the grasping power was gained, the first step of change from the
quadrupedal to the semi-erect attitude was completed. The process may
have begun in the effort to fit the sole of the foot to the rounded
surface of boughs; or its first stage may have been in the seizing of
overhead branches with the flexible hand; or both influences may have
acted simultaneously. We see the result only, we cannot trace the exact
process; but we have as an outcome the adoption of a method of
locomotion different from that of all other tree-dwellers, the forefoot
developing into the hand with its opposable thumb, and the hindfoot
gaining a similar grasping power in the toes.
The power of walking on a lower limb and grasping an upper one once
attained, a succeeding step in evolution quickly appeared, and one of
prime importance to our inquiry. The animal had ceased to be in a full
sense a quadruped, while not yet a biped, and a variation in the length
of its limbs was almost sure to take place. This is an ordinary result
when animals cease to walk on all fours. In the leaping kangaroo and
jerboa a shortening of the arms and lengthening of the legs appear. Here
the arms are relieved from duty and a double duty is laid on the legs,
with the consequence stated. In the ancient dinosaurian reptiles,
upright walkers, the same was the case. Those varied from quite small to
very large animals, but in all known instances the fore limbs were
greatly reduced in size. A similar condition may be seen in the birds,
the bones of whose fore-limbs have largely aborted from lack of
employment as walking organs.
In the case of the apes and lemurs, while a similar effect has taken
place, an interesting difference appears, due to the difference in
conditions. In these animals the fore limbs are not freed from duty as
organs of locomotion. In many cases, on the contrary, they have an extra
duty put upon them, with the result that they have grown longer instead
of shorter. Very likely these animals differed considerably in the past,
as they do to-day, in the degree of use of their legs and arms. Many of
them walk in the quadruped manner, either on the ground or in trees.
Others make much use of their hands and arms in grasping and swinging.
Great differences in the use of the arms and legs may have arisen in
different species. In some, the legs may have been mainly trusted to for
support, and the hands used for steadying. In others the arms may have
been the chief locomotive organs and the feet have given steadiness.
Here the legs may have grown the longer, there the arms, the limbs
developing in accordance with their degree of employment. In the lower
monkeys and the lemurs, the bones of the pelvis are altogether
quadrupedal in character. This is not the case in the higher forms, and
in the highest apes the pelvic bones approach those of man.
Highly interesting examples of these varied results may be seen in the
existing anthropoid apes. In all of them it would appear that the arm
was a prominent factor in locomotion, for in each instance it is longer
than the leg,--but it differs in proportional length in every instance.
It is shortest in the chimpanzee, somewhat longer in the gorilla, still
longer in the orang, and remarkably long in the gibbon. In all these
instances the fact that the arms exceed the legs in length indicates
that they must have played a large and important part in the work of
locomotion, and especially so in the case of the gibbon. It is well
known, in fact, that the gibbons progress very largely by the aid of
their arms, swinging from limb to limb and from tree to tree with
extraordinary strength and facility. The legs lend their aid in this,
but the arms are the principal organs of motion, and seem to have
developed in length accordingly.
As regards the other anthropoid species, Wallace's observations on the
habits of the orang are of interest. This animal usually walks on all
fours on the branches in a semi-erect crouching attitude, but our
naturalist saw one moving by the use of its arms alone. In passing from
tree to tree the arms come actively into play. The animal seizes a
handful of the overlapping boughs of the two trees and swings easily
across the intervening space. While seeming to move very deliberately,
its actual speed was found to be about six miles an hour.
The organization of man, as he now exists, shows an interesting and
important deviation from that of the manlike apes, and one which serves
as strong evidence that none of these apes occupied a place in his line
of descent. This is that he is a long-legged and short-armed animal, a
condition the reverse of that seen in the anthropoid apes. While man's
hands reach barely to the middle of the thigh, those of the chimpanzee
reach below the knee, of the gorilla to the middle of the leg, of the
orang to the ankle, and of the gibbon to the ground. All these apes have
short legs and long arms. Man, on the contrary, has long legs and short
arms.
The natural presumption from this interesting fact is that man's
ancestor, which we may provisionally call the man-ape, differed
essentially in its mode of progression from the other apes. The smaller
forms of these usually move on all fours in the trees, though the arms
are always ready for a swing or a climb. The anthropoid apes also show a
tendency to a similar mode of progression, though with a difference in
their mode of walking, which, as we shall see later on, is never that of
the quadruped. As for the man-ape, it may have originally walked in the
same manner as the related species, if we surmise that the variation in
the length of the limbs was a subsequent development. Certainly after
its limbs attained the proportions of those of man, its facility of
swinging from tree to tree must have been diminished, while it would
have found it inconvenient to move in the crouching attitude of the
orang and its fellows. Its easiest attitude must then have been the
erect one, and its motion a true biped walk, not the swinging and
jumping movement of the other anthropoids. In short, the development of
man's ancestor into a short-armed animal, however and whenever it took
place, could not but have interfered seriously with its ease of motion
in the trees. Though this change may have begun in the trees, it
probably had its full development only after the animal made the ground
its habitual place of residence.