The science of life : fully illustrated in tone and line and including many diagrams

BOOK 3

too, have their third eyelid reduced to a vestige.

Our wisdom-teeth are on the way to becoming vestigial. In most of us they only appear between the ages of twenty and twenty-five. In quite a number of people, however, they are never cut at all, but remain, useless or even the cause of disagreeable inflammation, within the gums.

Nor is any exception made by man to the animal practice of recapitulating the past of the race during individual development. We have the same family secrets in our embryonic cupboards as the rest of our mammalian relatives. The gill-clefts, the tail, and the furry coat with which our persons were once adorned have already been mentioned (Figs. 63, 64, 136). We may add that the human tail is formed complete with all the muscles for wagging it ; later, as the tail fades into insignificance, the muscles degenerate or are turned to other uses.

The early human embryo has nostrils connected with the mouth by a deep groove on either side. Sometimes, through a failure of development, this condition remains throughout life, and we call it hare-lip. It is a reminiscence of the way in which the nostrils were formed in our early fish-like ancestors, and you have only to look at a dog-fish or a skate to see that they still show this construction (Fig. 68). Similar abnormalities of development sometimes allow the prenatal hair to persist, giving us the dog-faced men and _ hair women of our fairs and shows; or the embryonic tail forgets to shrink and a baby is born with a little pink tail like a suckingpig’s; or the closure of the gill-clefts is arrested and we have adult human beings with actual slits on the side of their neck, or with white patches of skin marking the thin places where they closed just before birth.

Then there is the extraordinary capacity of the new-born human babe to support its own weight for several minutes at a time when hanging by its hands alone ; indeed, in most cases the child can hang by either hand singly. This capacity persists for a month or so after birth, but then normally fades away, and only after several years is the child again capable of such a feat. All monkey and ape mothers travel through the branches with their babies. But as they need their own arms for travelling, the baby, even from birth, must have the capacity for holding on tight by its tiny hands to its mother’s fur. There can be no doubt that the presence of this power in human infants

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THE SCIENCE OF LIFE

CHAPTER 5

is a survival, now wholly useless, of what was once a matter of life and death. It is interesting to find, as Mr. Kallen has demonstrated with his daughter, that if the baby be repeatedly stimulated by putting graspable objects into its hands, and tugging upwards when the little hands close round the object, the capacity may be reawakened even after it has died out naturally, and may then be made to persist for many months. The inborn, automatic nature of this power is shown by the fact that it was present in a child born without any forebrain (cerebrum), and persisted in full force until the defective infant died at eighteen days of age.

Another recapitulation, which only fades after birth, is the greater prehensile capacity of the human baby’s foot, and the fact that its big toe is much more widely separated from the rest than a grown man’s. Why should a baby’s foot be half-way to an ape’s if there is no real relationship between ape and man ?

Those who still doubt or reject the truth of Evolution should ponder their own case. For their own private and particular evolution even though it was all compressed into a nine months’ span, was just as spectacular as the slow evolution of life as a whole. Even that valiant apostle of Fundamentalism, Mr. William Jennings Bryan, began his existence as a single cell, passed from this stage of protozoan resemblance through the stage of a cell-colony ; hinted at ancestral polyps as he became two-layered ; revealed himself akin to Amphioxus in producing a notochord, only to destroy it later in favour of a backbone; indulged in reminiscence of the sea-life led by his fishy forbears by constructing with his amnion a little ‘* private pond ” of fluid in which he might embryonically float, and by piercing his neck with gill-clefts, only to do away with them when he subsequently recapitulated his ancestor’s greatest feat, the conquest of the land; recalled the furry, four-footed stage of his genealogy by his tail, all ready to be wagged, and his coat of flaxen down ; and, even after birth, was unable to help recalling what he later regarded as a blot on his escutcheon—his simian past—by the active, semi-prehensile big toes on his babyish feet and his soon-lost ability (probably never exercised, but undoubtedly present in the first weeks of his free existence) to support his own weight when hanging with his hands.

We are thus no exception to life’s rule. The human species has come into being like the rest, not from a sudden act of creation,