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Page:Popular Science Monthly Volume 18.djvu/816

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avoidable disadvantages. Man's adaptations to the conditions of nature are necessarily limited. Thus it might be supposed that a perfect animal would be adapted to traverse the water and the air, as well as the land. But such an adaptation would require extra organs, extra weight, and extra consumption of force in their support. Man, on the contrary, has become adapted to the highest field of life, and escaped an adaptation to inferior fields which would prove a disadvantage in the struggle for existence with land-animals.

His extreme sensitiveness to exterior influences gained by his naked skin is, of course, a sensitiveness to temperature as well as to touch. He is thus limited organically to tropical regions, and to some extent to a life in the shade—to a forest residence. In fact, he seems more limited in locality and in powers of resistance than most other animals. His unclad skin renders him acutely sensitive to extremes of heat and cold. He has no cortical defense against the attack of his animal foes. His limbs have become adapted to grasping and to support, but have lost their character as offensive weapons. Finally, his adaptation to an arboreal residence has become imperfect. He can not climb like a monkey, run like a deer, swim like an otter, mine like a mole, or crouch like a cat.

Physically, then, man is one of the most poorly protected of animals, seemingly a form not likely to survive in competition with his swift-ruining, flying, and climbing neighbors, and with his carnivorous foes, armed with tearing claws and rending teeth.

Yet in other respects he has decided advantages. One of these is a feature in which very few animals rival him, a differentiation in his adaptations to nutriment, enabling him to masticate, digest, and assimilate both vegetable and animal food. This is a decided advantage. Man is at once herbivorous and carnivorous, his field of possible food thus being doubled, and his consequent variety of adaptation to nature being likewise doubled. There is no other animal adapted to this double diet to the same degree as man. By a rather unpleasant resemblance, the hog most nearly approaches him in this respect. Yet the hog is principally a vegetable feeder, and only occasionally varies his diet to animal flesh.

A second advantage is the economy of muscular force gained by the vertical attitude. The force thus saved might have been employed in the production of an extreme agility, enabling man to escape danger by speed and alertness. It has fortunately been applied in another direction, that of the production of mental acuteness. From the time that man first employed the grasping power of his hands to seize stick or stone for defense against his foes, a process was begun which is yet far from completion. It was, in its full results, the process of mental evolution. But, for our present purpose we must give it a more narrow significance.

In all probability man, physically, is not now what he was origi-