888 TEXTBOOK OF ZOOLOGY 



While this mutation theory of origin of new species has prompted 

 much study and thought on evolution it seems not to have displaced 

 Darwin's general conception of the origin of new species. So far as 

 Darwin's theory is concerned, the occurrence of mutations only 

 hastens the process of evolution since they produce quick abrupt 

 variations instead of the slower smaller continuous variations. 

 Natural selection will operate with either. Biologists now consider 

 both small and large variations as mutations, and have turned back 

 to Darwin's idea of natural selection as the most likely explanation 

 of the development of new kinds of animals. 



