TUE NATURAL SELECTION TUEORY EXPLAINED. The theory of natural selection is based on the facts of variation. As to the causes of variation, Darwin does not say much in the Origin of Nye vies. Basing his theory on the fact that vari ations are constantly and spontaneously arising, he claimed that the favorable variations have succeeded in the struggle for existence, while those unfit or unfavorable have perished.
Ile also remarked that as long as the conditions of life remain the same, we have reason to believe that a modification which has already been in herited for many generations may continue to be inherited for an almost infinite number of gen erations. We are also told that as each land had undergone great physical changes, we might have expected to find that organic livings have varied under nature in the same way as they have un der domestication. "And if there be any varia bility under Nature, it would be an unaccount able fact if natural selection did not come into play." "If, then," be asks. "animals and plaits
do vary, let it be ever so little or so slowly. why should we doubt that the variations or individual differenees \Odell are in any way beneficial would be preserved and aceumulated through natural selection, or the survival of the fittest ? If man can by patienee select variations useful to him. why. under changing and complex condition; of lift.. should not variations useful to Nature's living products often arise, and be preserved or selected? What limit can be put to this power. acting during long ages and rigidly scrutinizing the whole constitution, structure, and habits of each creature—favoring the good and rejecting the bad? 1 can see no limits to this power, in slowly and beautifully adapting each form to the most complex relations of life."