i9o8.] IN MENDELIAN INHERITANCE. 61 



emerging from the pupal condition black pigment is laid down. The 

 pigmented area is variable in amount. The more extensively pig- 

 mented condition is dominant over the less extensively pigmented 

 (a over c, d or e — see Fig. i). In this case, also, it is clear that the 

 facts are better expressed by the statement that the more developed 

 condition dominates over the less developed. 



Still another case is that of human eye color. The pigmentation 

 of the iris is variable in amount. The blue iris is without pigment. 

 A small amount of black pigment (with or without yellow) produces 

 the grays ; still more pigment yields browns and blacks. Now it 

 appears that the offspring of parents one of whom has gray eyes 

 and the other blue eyes will have gray eyes or blue eyes, but not 

 brown eyes ; and gray will show itself dominant over blue. Simi- 

 larly brown iris color is dominant over gray ; the more advanced 

 condition of pigmentation over the less advanced. We have not 

 here to do with a qualitative difference of the presence of a character 

 opposed to its absence, but of a qualitative difference only. 



The heredity of human hair color follows a similar law. In one 

 series red pigment is absent in the hair and such colors as flaxen 

 or tow, light brown, brown, dark brown and black may be distin- 

 guished. The records collected by Mrs. Davenport and myself 

 show that two flaxen-haired parents have flaxen-haired children and 

 probably only such. Two parents with light brown hair have chil- 

 apparently only such. Two parents with light brown hair have chil- 

 dren of two parents each with dark brown or black hair produce 

 children with all of the varieties of hair color. This result means 

 that any lighter color is recessive to any darker color. 



The facts recited above and many others thus support the view 

 that, where various stages, a, b, c, in the progressive development of 

 a quality are found in individuals of the same race or species, the 

 more progressive condition will often behave as a dominant toward 

 the less progressive condition. The extreme case is, of course, that 

 in which the organ or quality is absent in one parent and present in 

 the other ; but this seems to be only a special case of a more 

 general law. 



As to the universality of this law it is still early to speak with 

 confidence. We know too little of the developmental factors of an 



