HEREDITY OF HAIR-FORM IN MAN 



GERTRUDE C. DAVENPORT AND CHARLES B. DAVENPORT 



The hair of man shows various morphological types. 

 Between straight hair, on the one hand, and woolly hair, 

 on the other, there are all degrees of closeness of spiral. 

 For convenience three intermediate grades may be recog- 

 nized ; wavy, having a very slight or open spiral involv- 

 ing the entire hair from root to tip; curly, having a closer 

 spiral involving the distal half of the hair ; and frizzy or 

 kinky, a close tight spiral of small diameter. Now, 

 although the conditions thus named are not discontinuous, 

 they stand for types that are fairly well appreciated and 

 distinguished popularly, so that in a random lot of people 

 practically all would place a given sort of hair in the same 

 category. 



These different types of hair form are associated with 

 certain differences of the hair on cross section as well 

 as in its method of growth. Thus straight hair is 

 nearly circular on cross section, while in woolly hair the 

 cross section is elliptical and the long axis is to the short 

 as 100 : 40 or 100 : 50. In wavy hair the proportions are 

 as 100: 60 or 70. The straight hair of the Japanese has 

 the proportions of 100: 85. 



Since the hair of most mammals is straight and nearly 

 circular on cross section, we may regard this as the basal 

 condition and the flattened hair as a specialized form 

 marking an advance in the differentiation of axes. In 

 addition to this difference in cross section hairs differ 

 in the form of the hair follicle, which is in woolly hair not 

 only flattened, but curved in an arc through a quarter of a 

 circle. "Emerging from an incurvated mould, it can only 



Station 



Experimental Evolution, Carnegie Ins 

 Vashington, Cold Spring Harbor, N. Y. 



IxsTITUTIOX 



341 



