Page:Evolution of Life (Henry Cadwalader Chapman, 1873).djvu/204

154 the farmer lived in Florida, and would turn his pigs in the woods, nature would blindly bring about the same result, since the white pigs would soon die, it being well known that pigs eat "the paint roots (Lachnanthes ), which color their bones pink, and which cause the hoofs of all but the black varieties to drop off:" hence the squatters say "we select the black members of a litter for raising, as they alone have a good chance of living." Suppose man to be heartless enough to abolish all hospitals, almshouses, etc., soon nature would eliminate, as Sparta got rid of, the sickly and deformed, the result being the survival of the fittest. We have seen that there is a most complex struggle for existence, that while like begets like, plants and animals vary in their organization; it follows, necessarily, that those organisms whose variations give them an advantage in the struggle for existence will survive, or be naturally selected, while those not so favored will die out. We see, therefore, that Natural Selection neither implies the existence of a Natural Selector nor is the Survival of the Fittest effected by chance. The facts of Inheritance are to be explained by the laws of Generation, those of Variation by Nutrition. The Struggle for Existence is caused by the number of individuals that are born being out of all proportion to the size of the earth they live in. The ever-changing conditions of Nature have the effect of eliminating the conservative kinds of life, while the plastic organisms survive and transmit their peculiarities to posterity. These variations become more marked from generation to generation, until finally, in the course of ages, there result very different forms of plant and animal life.

A good illustration of this whole subject is the history of the Siredon and Amblystoma. The Siredon lichenoides (Fig. 65) is a perennial gill-breathing Batrachian reproducing Siredons; the Amblystoma mavortium (Fig. 66) breathes by lungs and reproduces Amblystomas. These forms were