Page:Popular Science Monthly Volume 63.djvu/516

512 phosphorescent organs which serve as a lamp to light the pathway of these strange creatures in their strange surroundings. Such adaptations can hardly be conceived as possible, save with the very gradual shifting from lighter to darker regions through the lapse of thousands and thousands of years.

In modern times, since man's domination began, another factor has appeared, and its influence in modifying animal forms and structure has been one of the most potent and striking for such as have fallen within its scope. While man's effort has been largely to exterminate the lower forms of life, especially those inimical to his interest, he has utilized others for his service, and in the process of domestication we may see compressed into brief time such changes as under natural conditions would have occupied untold years, if, indeed, they would ever have been possible, since many of these changes unfit the forms for survival under natural conditions. So potent this factor that the immortal Darwin used its results as furnishing some of the most conclusive testimony for the theory of natural selection, believing that what could be accomplished in brief time by artificial, or human, selection could be accomplished in greater time by natural selection.

To see the power of this factor we may compare the various breeds of cattle and refer all to the primitive form from which we have absolute historic evidence that they were derived. The breeds of horses are equally striking, as the immense draft horse, the Shetland pony, the thoroughbred racer and the Arabian with hosts of special strains will attest. So, too, with dogs, cats and fowls. The pigeon which furnished Darwin with so much evidence since the native rock pigeon, the extreme breeds of fantails, carriers, etc., can be seen side by side and their relationship unquestionably fixed. Now I wish particularly to call attention to the fact that many of these domesticated forms, as a result of their domestication, have been unfitted for life in other spheres, and if dropped from the fostering care of man would almost certainly suffer rapid extermination, those surviving being the ones that had been least affected by the process of domestication. A modern hog would stand a poor show, but the southern razor-back doubtless would survive, for a considerable period at least, without man's assistance. Here then is a by-path opened in very recent time and into which certain animals have been driven by man, seldom of their own choice, if ever, the confines of which have profoundly modified many and behind them the gates have been closed never to be opened again.

Pushing away from the congenial temperatures of equatorial and temperate regions, life ventures into the inhospitable frozen zones of the polar regions, and by adaptation to such clime invades the most forbidding sphere. Earth's 'warm embrace' is here a 'cold reception,' but hosts of birds, mammals, fishes and insects have become established