Page:Popular Science Monthly Volume 40.djvu/704

684 that he can gallop with speed. Instead of coming into the world with the general outline of an American bison (as he ought to do upon accepted physiological dicta), he is, as is well known, proportionately higher at the rump and lower at the shoulder than in after-life. The mention of the American bison reminds me that it is another capital illustration of the same fact; for a young buffalo calf must have speed from its earliest days to enable it to keep up with the herd on the open prairie; and, in consequence, we find that it is much better developed behind (the hind legs being the chief propellers in all galloping animals) than the full-grown bull or cow, and has none of the comma-like, whittled-off aspect of its adult parents. The massive fore end of the bull bison arises from his habit of using himself as a projectile wherewith to batter his rivals out of the overlordship of the herd; but the bison calf is almost as level-backed as the young of our domestic cattle—though it is a much more active, wide-awake little beast than an ordinary calf.

Why, then, are the head and upper extremities so apparently abnormally developed in the young infant? I conceive the true reason to be something like this: For untold ages the perfection of the arms was a sine qua non of the continuance of the race; and as man, or the thing which was to be man, took to living by his wits—when, that is, mind began to take precedence of brute force and direct reflex action in the forefront of the struggle for existence—it became an absolute necessity for the being that was to live by his wits to be furnished with an abundant supply of the raw material out of which wits are made—that is, brains. Now, every man, actual or in posse—having elected, be it remembered, to fight chiefly with his brains, and having renounced forever the more gross and carnal weapons, such as huge canine teeth and heavy, claw-armed limbs—would be certainly bested in the struggle, and driven out of being, if his chosen armature were not up to the mark. In other words, every incipient homo who was born with deficient mind-material lived but a short time and left no offspring. And, since the potentialities of the brain depend far more upon its primary degree of development than do, for instance, the potentialities of the muscles, only those infants which were born with crania capacious and well-furnished would attain that degree of excellence which would prevent them from being fatally plucked in Nature's great perennial competitive examination. Only those infants, then, survived and became our ancestors which had from the first a good development of head and arm, and, to insure this, Nature has provided for a suitable blood-supply during the early period of growth.

With regard to the forward bend of the thighs in young infants, which is constant in all cases, as any one who has the opportunity