36 EVOLUTION AND GENETICS 



of individuals have been seen to suddenly appear. 

 The new characters that they show are transmitted 



ft''' 



to their descendants. In some cases the new charac- 

 ters depart widely from those of the stock from 

 which the new individual has sprung; in other cases 

 the departure may be very slight and pass unnoticed 

 unless one is very familiar with the parent stock. In 

 fact, it is owing, in large part, to a minute examina- 

 tion of plants and animals, that many of the new 

 characters studied by geneticists have been discov- 

 ered. So small are some of the observed changes that 

 they are not greater than the fluctuating changes 

 due to the environment. The inheritance of the new 

 character, when it is as slight as this, can only be 

 determined by a careful study of successive genera- 

 tions under controlled conditions both genetic and 

 environmental. It is the realization of these require- 

 ments that has enabled genetics to make its contri- 

 bution to the theory of evolution. 



While it is true that most of these mutant changes 

 have been observed in animals under domestication, 

 or in species that have recently been brought into 

 the laboratory, there is no evidence that they owe 



ft -^ ft' 



their appearance to cultivation or to domestication. 

 On the contrary similar mutants have been found in 

 wild species. Cultivated plants and domesticated 

 animals are more familiar to us, and more carefully 



-^ ft- 



scrutinized, than are wild species. Hence in large 



