ORIGIN OF THE LIVING MACHINE: ADAPTATION 363 



from earlier ones by descent has been the method by which the 

 present world was produced. Further, the laws formulated by 

 Darwin, DeVries, and Mendel, together with Weismann's theory 

 of heredity, all fit together to explain the method of this evolu- 

 tion. New variations have appeared suddenly, at least in many 

 cases, as germ variations (mutations) , and then have been trans- 

 mitted to the offspring as unit characters by Mendel's law, some 

 of the offspring receiving the new characters, while others do not; 

 but if inherited they are inherited as unit characters. Next, 

 the law of natural selection comes in and selects those indi- 

 viduals which have received useful mutations. Selection then 

 "fixes them" in the race by eliminating individuals with char- 

 acters less useful than those possessed by the survivors. As a 

 result of all these factors working together the race advances. 



