272 Heredity and Eui^eiiies 



their germ cells will have the determiner, and all children 

 will be nuUiplex, or blue eyed. I have gone into the inherit- 

 ance of eye color at some length because it serves as a 

 paradigm of the method of inheritance of any unit-character. 



Let us now consider some of the physical traits of man 

 that follow the same law as brown eye color, traits that are 

 clearlv positive, and due to a definite determiner in the 

 germ plasm. And first, I may refer to hair color. 



Hair color is due either to a golden-browTi pigment that 

 looks black in masses, or else to a red pigment. The 

 lighter tints difi'er from the darker by the absence of some 

 pigment granules. If neither parent has the capacity of 

 producing a large quantity of pigment granules in the hair, 

 the children cannot have that capacity, that is, two flaxen- 

 haired parents have only flaxen-haired children. But a 

 dark-haired parent may be either simplex or duplex; and 

 so two such parents may produce children \^dth light hair; 

 but not more than one out of four. In general, the hair 

 color of the children tends not to be darker than that of 

 the darker parent. Skin pigment follows a simflar rule. 

 It is really one of the surprises of modern studies that 

 skin pigment should be found to follow the ordinary law 

 of heredity; it was commonly thought to blend. In 

 crosses between Xegroes and Caucasians, such a blend was 

 stated to occur, and it was believed to be permanent, so 

 long as the hybrids were mated together. Actually, the 

 method of inheritance is like that of hair pigment, the 

 skin color of the children rarely much exceeds that of the 

 darker i)arent. There are stories of two white parents 

 ha\'ing black-skinned children, and if these are true they 

 constitute striking exceptions to the general rule. The 

 inheritance of skin color is not dependent on race; two 



