Photographically reduced from diagrams of the natural size (except that
of the gibbon, which was twice as large as nature) drawn by Mr.
Waterhouse Hawkins from specimens in the Museum of the Royal College of
Surgeons.]
Every human being begins his or her life as a single cell--a fertilised
egg-cell, a treasure-house of all the ages. For in this living
microcosm, only a small fraction (1/125) of an inch in diameter, there
is condensed--who can imagine how?--all the natural inheritance of man,
all the legacy of his parentage, of his ancestry, of his long pre-human
pedigree. Darwin called the pinhead brain of the ant the most marvellous
atom of matter in the world, but the human ovum is more marvellous
still. It has more possibilities in it than any other thing, yet without
fertilisation it will die. The fertilised ovum divides and redivides;
there results a ball of cells and a sack of cells; gradually division of
labour becomes the rule; there is a laying down of nervous system and
food-canal, muscular system and skeleton, and so proceeds what is
learnedly called differentiation. Out of the apparently simple there
emerges the obviously complex. As Aristotle observed more than two
thousand years ago, in the developing egg of the hen there soon appears
the beating heart! There is nothing like this in the non-living world.
But to return to the developing human embryo, there is formed from and
above the embryonic food-canal a skeletal rod, which is called the
notochord. It thrills the imagination to learn that this is the only
supporting axis that the lower orders of the backboned race possess. The
curious thing is that it does not become the backbone, which is
certainly one of the essential features of the vertebrate race. The
notochord is the supporting axis of the pioneer backboned animals,
namely the Lancelets and the Round-mouths (Cyclostomes), such as the
Lamprey. They have no backbone in the strict sense, but they have this
notochord. It can easily be dissected out in the lamprey--a long gristly
rod. It is surrounded by a sheath which becomes the backbone of most
fishes and of all higher animals. The interesting point is that although
the notochord is only a vestige in the adults of these types, it is
never absent from the embryo. It occurs even in man, a short-lived relic
of the primeval supporting axis of the body. It comes and then it goes,
leaving only minute traces in the adult. We cannot say that it is of any
use, unless it serves as a stimulus to the development of its
substitute, the backbone. It is only a piece of preliminary scaffolding,
but there is no more eloquent instance of the living hand of the past.
One other instance must suffice of what Professor Lull calls the
wonderful changes wrought in the dark of the ante-natal period, which
recapitulate in rapid abbreviation the great evolutionary steps which
were taken by man's ancestors "during the long night of the geological
past." On the sides of the neck of the human embryo there are four pairs
of slits, the "visceral clefts," openings from the beginning of the
food-canals to the surface. There is no doubt as to their significance.
They correspond to the gill-slits of fishes and tadpoles. Yet in
reptiles, birds, and mammals they have no connection with breathing,
which is their function in fishes and amphibians. Indeed, they are not
of any use at all, except that the first becomes the Eustachian tube
bringing the ear-passage into connection with the back of the mouth, and
that the second and third have to do with the development of a curious
organ called the thymus gland. Persistent, nevertheless, these
gill-slits are, recalling even in man an aquatic ancestry of many
millions of years ago.
When all these lines of evidence are considered, they are seen to
converge in the conclusion that man is derived from a simian stock of
mammals. He is solidary with the rest of creation. To quote the closing
words of Darwin's _Descent of Man_:
We must, however, acknowledge, as it seems to me, that man with all
his noble qualities, with sympathy which feels for the most debased,
with benevolence which extends not only to other men but to the
humblest living creature, with his God-like intellect, which has
penetrated into the movements and constitution of the solar
system--with all these exalted powers--man still bears in his bodily
frame the indelible stamp of his lowly origin.
We should be clear that this view does not say more than that man sprang
from a stock common to him and to the higher apes. Those who are
repelled by the idea of man's derivation from a simian type should
remember that the theory implies rather more than this, namely, that man
is the outcome of a genealogy which has implied many millions of years
of experimenting and sifting--the groaning and travailing of a whole
creation. Speaking of man's mental qualities, Sir Ray Lankester says:
"They justify the view that man forms a new departure in the gradual
unfolding of Nature's predestined plan." In any case, we have to try to
square our views with the facts, not the facts with our views, and while
one of the facts is that man stands unique and apart, the other is that
man is a scion of a progressive simian stock. Naturalists have exposed
the pit whence man has been digged and the rock whence he has been hewn,
but it is surely a heartening encouragement to know that it is an
ascent, not a descent, that we have behind us. There is wisdom in
Pascal's maxim:
It is dangerous to show man too plainly how like he is to the
animals, without, at the same time, reminding him of his greatness.
It is equally unwise to impress him with his greatness and not with
his lowliness. It is worse to leave him in ignorance of both. But it
is very profitable to recognise the two facts.
§ 3