Of the many evidences of the kinship of all animals including man only
a few can be mentioned in this book. All animals, man included, are
constructed on the same general plan. They have the same organs--brain,
heart, lungs, digestive tract, nerves, skin--performing the same
functions for the same purposes. The skeleton of man can be compared,
bone for bone, with that of a monkey, bat or seal. The bat’s membranous
wing is ribbed with bones corresponding to the bones of a monkey’s or a
man’s hand. The wing of both the bat and the bird has one bone from the
shoulder to the first joint, and two bones from the first to the second
joint, like the fore leg of quadrupeds and the arm of man--thus proving
that the fore leg, the arm and the wing are only modifications of the
same limb. The biped bird and biped man are modified quadrupeds.
All the five hundred muscles of the human body correspond with the
muscles of other mammals. Even the brain, wherein man differs most
from the lower animals, has the same chief fissures and folds in both
man and the animal nearest man, the orang-outang. Man and the other
animals have the same five senses and the same sense organs. They in
common have the same basic emotions, such as surprise, jealousy, pride,
hatred, shame, anger, grief, affection, and a sense of the ludicrous.
Bucks says, “So is man’s so-called human mind rooted in the senses and
the instincts of all his ancestral species; and not only so, but these
senses and instincts still live in him, making up, indeed, far the
larger part of his current everyday life; while his higher psychical
life is merely the outgrowth and flower of them.”
The old formula was: “Man is governed by reason; brutes by instinct.”
But science has proved that lower animals are not guided altogether
by instinct, that many of their actions are the results of mental
activities remarkably similar to reasoning. On the other hand man
himself has instinct--and well for him that he has, for his reason, as
yet, is only partially developed. If we will but subtract from the sum
of man’s actions, not only those prompted by instinct, but those also
that result from habit, custom, prejudice, and the emotions of anger,
revenge, vanity, and other elemental passions, we will not feel like
crying from the housetops that “man is governed by reason.”
Man and the lower animals have similar diseases. He is liable to
contract from, or communicate to them, such diseases as glanders,
hydrophobia, cholera, tuberculosis. Drugs, tobacco and alcohol have the
same effects on animals as on us.
Of course the dog, the ape, the horse and man do not perfectly agree in
their corresponding parts and in their natures--if they did they would
belong to the same species--but their similarities are so remarkable
that they have a profound meaning for the thoughtful, however
meaningless they may be to the thoughtless and the prejudiced.
In embryonic development are found evidences not only of man’s close
relationship with all animals but of the long, long route he and they
have travelled in their common descent from the simpler forms of life.
Darwin says that the whole process of reproduction, from the first act
of courtship by the male to the birth and nurturing of the young, is
very much the same in all mammals.
The lowest forms of animal life, the one-celled animals, are without
sex, and multiply by dividing into half, each half developing into
a complete cell, which in turn is subjected to the same dividing
process. Many species of these lowly organisms still exist, never
having developed further than the unicellular stage. All higher forms,
as of fishes, reptiles, birds, mammals, begin life at this point--as
a single cell. The cell, germ, or ovum of an embryo (the young of a
mammal before birth) when fertilized divides, forming two cells, the
two divide into four, the four into eight, and so on, until there is a
colony of similar cells enmassed, and with a little rod of tissue--the
beginnings of the spinal column--running through. The embryo at this
stage is passing beyond the lowest grand division, the invertebrates.
Entering the vertebrate division the embryo passes into the fish group.
Deep grooves, gill slits, appear on the side of the neck of the embryo
and six pairs of arched branches of arteries arise, just as in fishes,
as if to give blood to the gills. Later all but one of these pairs
disappear. The arms and legs of the child, like the legs of all other
embryos, begin to develop, and continue to do so for some time, on the
same plan as the fins of fishes.
Further along in its development the embryo assumes all the
characteristics of the quadruped even to the tail which in the human
embryo at this stage is longer than its legs. During the sixth month
the entire body of the human foetus, except the palms and soles, is
covered with fine, woolly hair.
Thus far the human embryo has developed in the same way, has undergone
the same changes, has passed through precisely the same stages as the
embryo of other animals. In its further development it leaves them all
behind except those nearest man. Its tail disappears, and it now has
an opposable or thumb-like great toe which with the monkey and the
ape is a permanent characteristic. It is only in the latest stages of
development that the human embryo presents marked differences from the
embryonic ape.
Of the fact that the embryo in its development from a single fertilized
cell passes through all the stages representative of the principal
animal divisions, and in a progressive order from the simple to the
complex and highly developed, there is no explanation but that of
heredity and descent--of descent of the higher animals from the lower
with heredity transmitting the records of the remote ancestral stages.
Each stage, as of the fish, the quadruped, the ape, is a sign board
along the route of man’s descent. The nine months’ embryonic period of
each of us is an epitome of the history of the race down to the human
period.
Nor do the evidences of race-history as revealed by the child cease
with its birth. The babe is nearer the lower mammals than is the
adult man. When it acquires the use of its limbs it begins life as
a quadruped. Its blundering attempts in learning to stand erect and
walk is evidence of the fact that man’s peculiar mode of locomotion is
a late acquirement. Like the lower animals the babe makes known its
wants by means of natural language; it later acquires artificial or
spoken language in the same slow, laborious way that it was acquired
by the race. At the average age of three years the child has become
self-conscious; his mind has passed the mental stage of all animals
below man. Psychically he has become man.
In certain periods of youth the child is a tree-climber, a cave-digger,
childish sports that hark back to periods passed through hundreds of
thousands of years ago in the childhood of the race. At a certain
stage his emotional nature has developed to the point that he is
conscious of wrong-doing. This is what the old theologians called
“the age of accountability.” If there is a grain of truth in the
chaff-heap of Mosaic mythology the fall of Adam indicates the point in
the development of the race when conscience had dawned and feelings
of remorse had begun to stir within. Man had reached the age of
accountability. But prior to the “fall” there was a rise.
Rudiments or vestiges are also evidences of the descent (or ascent) of
the higher forms of life from the lower. Rudiments are incomplete parts
of the body which have become arrested in their development, and which
are now of no use, nor would now be of use if fully developed. They are
relics handed down to us by the laws of heredity from a long-past age
when they were well developed and useful to our lowly ancestors. Though
we outgrow primitive conditions and stages of development we can not
get rid of the past, but must drag it around with us as the snail drags
its shell.
All the higher animals bear within their bodies the reminders of
a humble origin, some of which are: The incisor teeth of certain
grass-eating animals, so rudimentary as never to cut through; the
small hoof points of the cow which do not touch the ground, and the
rudimentary fifth and sixth teats on the hinder part of her udder;
the splint bones in the horse’s leg--vestiges of toes when he was a
three-toed animal; the scanty, downy hair that covers the human body.
Certain muscles by which animals can twitch the skin are inherited by
some persons who can move the scalp and the ears. The sense of smell in
civilized man has become almost rudimentary. The vermiform appendix is
not only useless but often injurious. It points back to the time when
our ancestors were strict vegetarians--grass-eaters. In the _os coccyx_
man carries about with him the rudimentary bones of a tail. This, with
the fact that the human embryo at one stage has a tail longer than its
legs, is Nature’s everlasting reminder that proud man’s remote ancestor
was adorned with a tail.
In order to get as clear an idea as possible of man’s exact place in
the animal scale we should note the points wherein man differs from
his nearest relatives--the orang, the gorilla, the chimpanzee, the
gibbon--as well as the points wherein he agrees with them. Here are the
most obvious points of dissimilarity. Man walks erect, though in his
first year he goes on all fours, while apes only occasionally walk,
and that in a semi-erect position, their arms, longer than their legs,
reaching the ground, knuckles touching. The nose of the ape is small,
undeveloped; the canine teeth are very large; the mouth projects, and
there is no chin. The entire body except the palms and soles is covered
with hair. The brain capacity of the ape is less than half that of man.
On the other hand there are more points of similarity than of
dissimilarity between man and the apes; and if the points wherein they
differ be examined they will be found to be differences in degree
rather than in kind. The higher apes are entirely without tails; the
embryo of the ape, like the human foetus, loses its tail sometime
before birth. The young ape (monkey also) is born in almost as helpless
a condition as is the human babe. The female ape has two mammary glands
(udders) and they are always on the chest. Adult apes have the same
teeth as man--thirty-two in number, incisors, canines, premolars,
molars. They have the same 200 bones, the same 500 muscles, the same
organs and glands. On their toes and fingers they have flat nails, like
man, instead of claws. On account of the ape’s opposable great toe they
were formerly classed as four-handed; but this was an error. In all
essential respects their legs terminate in feet. Like man they are
bipeds, and like man they have two hands. The brain of the ape, though
much smaller than man’s, as we would expect it to be, is constructed on
the same general plan as his with the same main fissures and the same
groups of cells. There is no “missing link” in the plan and structure
of man’s brain, whatever difference there may be between his and the
ape’s in capacity.
No scientist has ever been so foolish as to say that man and the apes
belong to the same species. There are four species of the higher apes
and one of man, though the one species of man is divided into five
varieties, called “races.” Varieties differ less widely than species.
Individuals within a variety also differ. Differences are no bar to
unity if they are nullified and outweighed by similarities.
Finally, let us keep in mind that while man has departed from the
ancestral type, developing in one direction, the apes have gone off
in another and have acquired characteristics peculiarly their own.
Resemblance in a babe and a young ape is far greater than in a man and
an adult ape. The same is true of the young of all allied species. This
divergence from birth of the adults of different species is strong
evidence of a common origin.
These are only a few of the hundreds of evidences proving that man fits
into the same creative scheme with the lower animals--proving that he,
in common with them, has developed from still lower forms, and that, as
a product of the creative forces of Nature, he is wholly subject to her
laws.