252 INBREEDING AND OUTBREEDING 



are, we believe, fundamental. They give a clue as to what 

 has happened in the racial mixtures of the past, and 

 enable one to visualize more clearly the probable result of 

 the intense race amalgamation to be expected in the 

 twentieth century. 



The world faces two types of racial combination : one 

 in which the races are so far apart as to make hybridiza- 

 tion a real breaking-dowTi of the inherent characteristics 

 of each ; the other, where fewer differences present only 

 the possibility of a somewhat greater variability as a 

 desirable basis for selection. Roughly, the former is the 

 color-line problem; the latter is that of the White Melt- 

 ing Pot, faced particularly by Europe, North America 

 and Australia. 



The genetics of these two kinds of racial intermixture 

 is as follows: Consider first a cross between two ex- 

 tremes, typical members of the white and of the black race. 

 In the first generation the individuals show a notable 

 amount of heterosis, indicating differences in a large 

 number of hereditary factors. They are intermediate in 

 hair form, skin color, head shape, and various other 

 physical attributes, in mental capacity, and in psychical 

 characters in general ; although they show extraordinary 

 physical vigor. In later generations segregation and re- 

 combination in many of these characters can be traced 

 with little difficulty ; but if one describes the descendants 

 of the cross as a population, or even the total character- 

 istics of a single individual, fluctuation around the aver- 

 age of the two original races is still the rule. There may 

 be an approach to the head form of one race combined 

 with the skin color of the other, an approximation of the 

 hair of the one coupled with the other's stature; never- 



