184 EVOLUTION AND GENETICS 



from mulattos of later generations might in some 

 few cases be accounted for in this way. On the other 

 hand the intermediate color of the mulatto of the 

 first generation might be due to the interaction of 

 the incompletely dominant genes of the two parents, 

 and in later generations it might not be possible to 

 distinguish by inspection alone such a condition from 

 that due to the restoration of the original normal 

 genes. It would require elaborate genetic tests to 

 settle such a question. 



Meanwhile we shall have to rest content with the 

 admission that there is no single type of human nor- 

 mal individual with which to standardize the differ- 

 ent racial tj^pes. At best, cases of human atavism 

 produced by crossing, would be expected to go no 

 further back than the race to which the modern types 

 of men converge, and from an evolutionary point of 

 view this is a very recent event. We should antici- 

 pate, therefore, that all the races of mankind have 

 an enormous number of genes in common and only 

 few that are different. The latter produce the rela- 

 tively slight structural differences that are found in 

 different races. 



The Inheritance of Physical Defects 



A few examples of the inheritance of physical 

 characters in man will suffice to show that in his in- 

 heritance man conforms to the same laws that regu- 

 late the inheritance of other animals and plants. 



