5*> THE THEORIES OF EVOLUTION 



.) 



become, the more places they will be enabled to oc- 



" 2 



cupy. 



This is what is known as the "divergence of char- 

 acter" and the more marked that divergence is in 

 a species, that is, the better adapted the individuals 

 of which it consists have become to different condi- 

 tions of life, the more chances that species has of be- 

 ing victorious in the life struggle. 



Both divergence of character^^and the extinction 

 of certain species (another very common and very 

 \ important factor in the history of the organic world) 

 can.be explained satisfactorily by natural selection 

 and constitute, Darwin thinks, a very strong presump- 

 tion in its favour, although no absolute evidence can be 

 produced. 



Natural selection was never considered by Darwin 

 as it was by his disciples, the Neo-Darwinians, as the 

 only and exclusive factor of evolution. He fully rec-' 

 ognises the direct action of the environment and says 

 I expressly that we must not attribute everything to, 

 selection. He also realises the importance of char- 

 \ * acters acquired by inheritance under the influence of 

 the environment or through use or disuse of certain 

 \ organs. He believes, nevertheless, that the struc- 

 ture of an organism is more important than its en- 

 vironment and that the other factors only play an 

 important part when natural selection can fo ster or 



2 Origin of Species, Chapter IV. 



