EVOLUTIONAL ZOOLOGY 221 



THE METHOD OF EVOLUTION 



So familiar is the doctrine of natural selection, that a 

 very brief statement here will suffice. Darwin maintained that 

 those slight fluctuating hereditary differences, or variations, 

 which happen to be so related to the environment as to be 

 beneficial to the individual, will tend to be preserved, while 

 those that are harmful will be eliminated as a result of the 

 struggle for existence. In order that the variation may be 

 selected, it must be useful, and the fundamental principle un- 

 derlying natural selection is that of utility. By a slow and 

 gradual process, as Darwin conceived it, useful variations, once 

 established, are perfected by further transmissions along the 

 same lines, until adaptations as we see them, in all their intri- 

 cate complexity and adjustment, result. 



Since only beneficial variations can come within the pale 

 of natural selection, Darwin's theory is essentially an explana- 

 tion of the origin of adaptations and not of species, for, if 

 there are specific characters that are not useful, natural selec- 

 tion could have had nothing to do with their survival. It is 

 now generally recognized that many such specific characters 

 do exist, and around this point much post-Darwinian discus- 

 sion has revolved. 



Epoch-making as Darwin's work is universally recognized 

 to have Been, it has become clear to nearly all that he did not 

 say the last word on the origin of species, and the belief is 

 now rapidly gaining ground in the inadequacy of natural 

 selection as a theory of the method of evolution, that is, as a 

 mechanical explanation of species-formation. With the re- 

 markable advance of our knowledge in several fields of bio- 

 logical investigation, hitherto undreamed of reaches in the 

 study of evolutionary phenomena have been opened up, ex- 

 posing new and previously unthought of problems and neces- 

 sitating the remodeling of earlier views. 



It is against certain basic assumptions of Darwin that 

 modern scientific criticism has been directed, and for our pres- 



