290 HEREDITY AND ENVIRONMENT 



the way from 46 per cent, to 6 per cent, of 

 black, the latter so far as skin color is con- 

 cerned being virtually white. On the other 

 hand where both parents have about the same 

 degree of pigmentation the children are more 

 nearly uniform in color ; thus seven children of 

 two mulattoes, the father having 36 per cent, 

 and the mother 30 per cent, of black, ranged 

 only from 27 per cent, to 39 per cent, of black.* 

 Such variations in color in the F 2 and in 

 subsequent generations are exactly what one 

 would expect in a Mendelian character in 

 which more than one factor is involved, as for 

 example in the case of the color of the sweet 

 peas shown in Fig. 55. Davenport, who has 

 made an extensive study of this case, con- 

 cludes that "there are two double factors 

 (AA, BB) for black pigmentation in the full 

 blooded negro of the west coast of Africa, and 

 these are separably inheritable." These fac- 

 tors are lacking in white persons (this being 

 indicated by the formula aa, bb). Since the 

 germ cells carry only single factors and not 



* In another family shown in Fig. 64 the father has 18 per 

 cent black pigment, the mother 3S per cent and the children 

 range from 17 per cent to 54 per cent. 



