EVOLUTION AND VARIATION 61 



Sex is not a, necessary attribute of living things, 

 but it is a very necessary attribute if progress in 

 the evolution of new forms is to occur, as they 

 have progressed through the past ages and as we 

 now see them progressing on this planet. 



We have lately learned that the power to vary 

 in plants and animals is as readily transmissible 

 as stability of character and we also now know 

 that plants and animals brought up for genera- 

 tions under different environments acquire dif- 

 ferent habits and appearances and, after a 

 time, differences in structure. Each species 

 has had different experiences in adapting itself 

 to its surroundings, and no two individuals 

 of any species, though having similar experi- 

 ences, have exactly the same. By combination 

 the experiences of both are, by heredity, trans- 

 mitted either latently or obviously to one or 

 many of their descendants. This combination 

 by crossing, happening again and again, gives 

 added ability to meet and overcome every chang- 

 ing environment; in other words, the power to 

 vary to meet varying environment, and by addi- 

 tion fixing characters which benefit the species 

 through natural selection, giving the new com- 

 binations new abilities to advance. Only thus, 

 through combination by sex, has the marvelous 

 variety of plants and animals which now have 



