EXPERIMENTAL 139 



Darwin's open-minded dualism in this matter of the factors of 

 evolution appeals to me at any rate more than the jealous attitude 

 of Weismann and his eminent adherents. 



Miss Whipple is less determined than I am in claiming for 

 Selection the cause of the primitive slope of hair in mammals. 

 It is the only conceivable arrangement that could exist for the 

 advantage of the primitive forms in their simple life, and is, I submit, 

 as much a matter of adaptation to needs governed bj r Selection as 

 the possession of a dermal covering itself. 



One more point, which, I think, is a small one and a fair one 

 to raise, is worthy of a few remarks. Miss Whipple states that 

 before variations in hair-direction can be logically attributed to 

 external forces (giving the instance of the human scalp) " it should 

 be shown that a change in the direction of the external, more or 

 less wiry portion of the hair produces a change in the direction 

 of the follicle." As it happens, this change is easily seen in the 

 case of the reversed hairs of the human forearm, if the hair be 

 dark and the skin thin. The essence of the theory that dragging 

 on the skin by muscular traction causes the hair to change its 

 direction is that the relatively important portion within the hair-pit 

 is pulled here or there according to the incidence of the prevailing 

 force. But it is, to my mind, very clear that much repeated friction 

 or pressure or gravity acting on the external and longer portion 

 of the hair must, in course of time, drag the portion buried in the 

 skin with it and so change its direction. These two portions of a 

 hair cannot be arbitrarily separated. Shortly, one may say that 

 the push of a force is as evident as the pull. A similar change 

 in the direction of the buried part of a tree -trunk from a prevailing 

 wind can be traced. 



The last point is that I " omit to explain the mechanical 

 process by which divergent muscular action could affect hair- 

 direction." This is well answered in the chapter on " Can muscular 

 action in the individual change the diiection of the hair ? " for 

 there it is shown by numerous examples in the human eyebrow 

 that the muscles underneath the hairs which are embedded in the 

 true skin for a tangible depth, do play havoc with the normal 

 arrangement of hair, as the conflict proceeds, the resultant " pull ' : 

 being actually engraved, signed and sealed by physiological 

 wrinkles of the forehead and face. 



