THE DOCTRINE OF EVOLUTION 115 



D and R 





Of the three dominant individuals one is a pure dominant, 

 but it is impossible to say at first which one that is, except 

 by further breeding. The pure dominant, when bred with 

 another pure dominant, will produce only gray rabbits, and 

 these will produce gray rabbits generation after generation. 

 Albinos ^obtained in experiments like the one described will 

 breed true generation after generation, if mated with other 

 albinos. When one of the hybrid dominants, D(R), is mated 

 with a recessive animal, half the young are hybrid dominants 

 and half are recessives. Two hybrid^ mated will produce 

 young in the proportion of three gray to one albino, as in the 

 third generation. 



Experiments to determine the dominant or recessive nature 

 of other characters, such as length of hair and smoothness of 

 coat, show that short hair in guinea-pigs dominates over long 

 hair, and a rough coat over a smooth coat. It is also true 

 that the various characters, so far as tested, are inherited 

 quite independently of one another. A smooth coat may be 

 associated with white hair or with pigmented hair in guinea- 

 pigs, and a rough coat also with white hair or with pigmented 

 hair. An experimenter, by controlling the combinations of a 

 number of characters, knowing which is dominant and which 

 recessive, may produce several distinct types of animals 

 within the same species. 



If future experiments should support Mendel's law, we 

 should then be able to understand how it is that races sud- 

 denly spring into existence in nature and become established. 



