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PDF - Wallace Online

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vin THE DEVELOPMENT OF HUMAN RACES 171secure its prey, to escape from its enemies, to resist theinclemencies of the seasons, and to rear a numerous andhealthy offspring. But a change now takes place. A seriesof cold winters, for instance, come on, making food scarce,and bringing an immigration of some other animals to competewith the former inhabitants of the district. The newimmigrant is swift of foot, and surpasses its rivals in thepursuit of game the winter; nights are colder, and require athicker fur as a protection, and more nourishing food to keepup the heat of the system. Our supposed perfect animal isno longer in harmony with its universe it is in ;danger ofdying of cold or of starvation. But the animal varies in itsoffspring. Some of these are swifter than others they stillmanage to catch food enough some are hardier;and morethickly furred they manage in the cold nights to keep warmenough the; slow, the weak, and the thinly clad soon dieoff.Again and again, in each succeeding generation, thesame thing takes place. By this natural process, which is soinevitable that it cannot be conceived not to act, those bestadapted to live, live those least ; adapted, die. It is sometimessaid that we have no direct evidence of the action ofthis selecting power in nature. But it seems to me we havebetter evidence than even direct observation would be,because it is more universal, viz., the evidence of necessity.It must be so ; for, as all wild animals increase in a geometricalratio, while their actual numbers remain on theaverage stationary, it follows that as many die annually asare born. If, therefore, we deny natural selection, it canonly be by asserting that, in such a case as I have supposed,the strong, the healthy, the swift, the well clad, the wellorganised animals in every respect, have no advantage overdo not on the average live longer than the weak, theunhealthy, the slow, the ill-clad, and the imperfectly organisedindividuals ;and this no sane man has yet been found hardyenough to assert. But this is not all ;for the offspring onthe average resemble their parents, and the selected portionof each succeeding generationwill therefore be stronger,swifter, and more thickly furred than the last ;and if thisprocess goes on for thousands of generations, our animal willhave again become thoroughly in harmony with the new con-

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