232 



The Journal of Heredity 



while duplex by simplex should produce 

 123 simplex children considerably in 

 defect of the number found (137). 

 'J'he discrepancies are so ijjreat that it 

 must be concluded that some more com- 

 plicated exj)lanation must be adopted 

 than that of a sinjjle unit factor. 



In addition to the evidence above is 

 the evidence that light eyed parents may 

 have children with darker eyes than 

 their own. There are a number of such 

 cases in Davenport's data. Holmes and 

 Loomis have several cases including 

 one in which two blue-eyed parents had 

 a brown-eyed child. The writer knows 

 personally of two distinct cases. Sum- 

 ming up, we may say that the factor 

 or factors for light eyes have .•some- 

 what more tendency to be recessive 

 than dominant, but we cannot affirm 

 that a single unit factor is the principal 

 cause of differences. 



IIAIK COLOR 



Turning to hair color, we tind a simi- 

 larly unsatisfactory situation from 

 the Mentlelian standpoint. Daxenport'"' 

 classifies variations in hair color into 

 two independent groujjs. I le considers 

 the granular pigment of black and 

 brown hair as wholly distinct, jihysio- 

 logically and genetically, from the dif- 

 fuse red pigment of clear red hair. He 

 holds that these two kinds of pigment 

 can be mixed in any proportions. In the 

 presence of the granular pigment the 

 color is black regardless of whether 

 diffuse pigment is present or absent. 

 Diffuse pigment in the absence of 

 granular ])igment is responsible for red, 

 while with both pigments absent, or 

 nearly so. the color is white to flaxen. 

 The relations may be represented in the 

 following scheme in which intermediate 

 colors have been introduced. \'aria- 

 tions in amount of granular pigment 

 are represented horizontally; variations 

 in amount of diffuse pigment verticallv : 



Black Rcfl(lisIi-l)ro\vn Rtd 



Black YcUow-hrown Yellow 



Black Brown Flaxen 



Objections can be raised to this 

 scheme on theoretical grounds, based 



on our present knowledge of the rela- 

 tions of the colors in other mammals. 

 In guinea-pigs, for example, we have 

 black granules and diffuse red pigment 

 (as well as red granules), which one 

 can hardly doubt are closely similar to 

 the human i)igments."' In guinea-pigs, 

 however, it is certain that red and black 

 cannot be treated as independent phy- 

 siologically. The same factors for pie- 

 bald (class la) inhibit lx)th colors in 

 spots in the fur ; factors in the albino 

 series (class lb) dilute both colors, 

 while factors of class 2a, as the tortoise 

 shell and agouti factors, may replace 

 a black, which is unassociated with red 

 pigment, by intense red. These state- 

 ments hold good for factors in classes 

 la, lb, and 2a in all other mammals 

 which have been discussed. However, 

 it will be shown that a scheme which 

 dff'ers only in theory from that above 

 may be devised, which is in harmony 

 with the relations of black and red in 

 other mammals. 



Davenport concluded, from a study 

 of pedigrees, that the more intense con- 

 dition of either pigment is dominant 

 over the less intense. He gives abun- 

 dant evidence that the lighter colors 

 may be transmitted by dark haired per- 

 sons. As in the case of eye color, how- 

 ever, we find rather numerous cases 

 which do not fit the theory. Thus in 

 one family, in Davenport's tables, flaxen 

 by light brown produced red. In two 

 cases, two light brown parents produced 

 either auburn or red-haired children. 

 In these cases, the children seem to 

 have had more red pigment than either 

 parent. Cases in which the children 

 had more dark pigment than either 

 parent are even more abundant, espe- 

 cially when we compare grandparents 

 and parents in the table. It is not sur- 

 prising, on any theory, that young chil- 

 dren should seldom be darker than their 

 parents, as the full intensity of hair 

 color is not reached until maturity. In 

 Davenport's tables we find two light 

 brown parents producing dark or black- 

 haired children in several cases. We 

 tiiid that red bv reil m;i\- proijuce 

 black. In one remarkable case light 



"Davenport. C. 15. . and (',. C Davenport. I'JIW, .hiu-r. Xnt., 4.i:l<M-Jll. 

 "Hunt, H. R.. and S. WriKlit. 1918, JoiR. Hkr.. 9:178-181. 



