THE STRUGGLE FOE EXISTENCE 31 



plant and animal use is limited; many more individuals 

 are born than can survive; the result is a perpetual 

 struggle for survival. 



(2) The fittest individuals tend to be the ones that 

 survive; the battle is to the strong, the race is to the 

 swift. 



(3) The individuals so selected transmit many of 

 their favorable qualities to their offspring by heredity. 



(4) But although heredity produces a wonderfully 

 exact copy of the parent in the child, there is never pre- 

 cise reduplication. There is latitude for individual vari- 

 ation. If among the innumerable multitudes of indi- 

 vidual variations that may occur, one chances to appear 

 which, no matter in how slight a degree, gives the in- 

 dividual possessing it advantage in the struggle, that 

 individual is bound to be favored with longer life and 

 larger number of progeny with survival, in short. 



But the theory of natural selection proposes to ex- 

 plain only those characters which give advantage in the 

 struggle for existence. It does not explain the existence 

 of certain characters which do not give definite advan- 

 tage to their possessors and yet tend to persist from 

 generation to generation. Some of these characters, like 

 the brilliant plumage of certain birds (peacock and pea- 

 hen), would seem to be of positive disadvantage by 

 making them conspicuous to their enemies. To account 

 for these markedly contrasted sex-characters, Darwin 

 advanced the theory of Sexual Selection. He believed 

 that the individuals possessing the brilliant coloring 

 were more attractive to those of the opposite sex and so 

 had a better chance to mate than their fellows of a more 

 sober hue. By the laws of heredity the brilliant plumage 

 was transmitted, and the less attractive individuals, not 



