DARWIN'S THEORY 59 



The Malthusian doctrine, that the propagation of 

 species is excessive and, if unrestrained, must result in 

 a failure of food supply, was accepted by Darwin. A 

 constant struggle for existence, he maintained, is going 

 on in the organic world; and this struggle, through the 

 operation of the principle of natural selection, inevit- 

 ably results in the destruction of countless organisms 

 that are incapable of winning out in the battle of life, 

 and in the survival of the fittest. 



Such in the rough is the Darwinian explanation of 

 natural evolution of the species — summed up in the 

 phrases, continuous sHght variations; inheritance of 

 the characters thus produced; isolation, whether geo- 

 graphic or biologic, of evolving varieties; gradual 

 accumulation of variations until independent species 

 are developed; and, as describing the whole process and 

 determining at every stage its direction and results, the 

 principle of natural selection, by which the unfit are 

 eliminated and the fittest alone are permitted to sur- 

 vive. 



supplement his hypothesis by the theories of sexual selection and 

 pangenesis, neither of which commands undisputed support among 

 biologists. He elaborated the former theory in his Descent of Man, 

 Pts. II, HI (cf. Origin of Species, Vol. I. pp. 107-110); on which 

 also see Lock, op. cit., pp. 56-59; A. R. Wallace, Darwinism, ch. x; 

 V. L. Kellogg, Darwinism To-day, ch. v; A. Weismann, Evolution 

 Theory, Lee. xi. Darwin introduced his pangenesis theory in 

 Variations of Animals and Plants, Vol. II. p. 350. Neither of 

 these theories require attention here. The latter is concisely defined 

 in the Century Dictionary, s. v. "Pangenesis." 



