THE INHERITANCE OF FAMILY TRAITS 35 



Fig. 12. — Woolly hair; a Congo negro. (Lent by American Museum Natural 



History.) 



that of woolly hair is much flattened, being only half as 

 thick as it is broad. Both the flattening and the curving 

 of hair are due to a modification of the cup or ''hair follicle" 

 in which the hair develops. Thus, while straight hair devel- 

 ops in a plain, cylindrical follicle that of the flattened types 

 is curved and inclined in relation to the surface of the skin. 

 Straight hair is the simple condition; curving is due to a 

 special modification. What, now, is the method of inherit- 

 ance of this special modification? 



First, if both parents have hair that from childhood up 

 has been straight, without natural tendency toward curving, 

 then all of the children will have straight hair. There are 

 exceptional cases reported of wavy haired children from 

 straight haired parents, but the exceptions constitute less 

 than 2 per cent. 



