172 THE GROWTH OF GROUPS 



whole will also change, because the new circumstances 

 will favour certain aberrant members of the group, 

 which will survive and give rise through their descendants 

 to a new species suited to the new circumstances. Varia- 

 tion being in all directions, the aberrant individuals are 

 always present among the species in readiness to replace 

 those that are no longer suited to their circumstances, 

 except, of course, in the special case when the new 

 circumstances are so stringent as to cause the extinction 

 of the whole. 



According to this view, change occurs primarily in 

 the environment, secondarily in the species. It takes 

 for granted the environmental change and explains the 

 evolution of living things from it. It is our custom to 

 take some things for granted and to explain others from 

 them ; indeed, this is the only way of making explanation. 

 The essence of the theory is found in the words " variation 

 is in all directions," and for many its charm lies in the 

 fact that for them it explains adaptation. 



There is much dispute over this question, but it 

 seems to me that the dispute arises out of certain essential 

 differences in the minds of the opponents, and no amount 

 of evidence can alter those differences. It is usual to 

 assert that Natural Selection must be upheld as an 

 explanation of adaptation since it is only the explanation, 

 hitherto suggested, that can be understood. To many 

 persons this seems to be a strong argument for upholding 

 the theory, while to others it does not appear to be an 

 argument at all. The two points of view are distinct, 

 some persons require explanations, others do not. From 

 the point of view of the latter, adaptation appears to be 

 a property of living matter in general, just as gravitation 



