50 SEXUAL DIMORPHISM 



w.unen sometinn's fight by tearing one another's hair, must 

 not be forgotten. If there is any truth in the view that the 

 special growth of the beard is due to such causes as I have 

 suggested, then it is reasonable to suppose that those causes 

 have been in action in the ancestors of the Caucasian race 

 more than in those of the other two races. It is not impos- 

 siUe, if primitive man was derived from a single ancestral 

 species, that in the earlier stages of his evolution he may have 

 developed different habits in different races, and that in one 

 race the hair of the face was stimulated in the fights of the 

 men, in others not. What is wanted is evidence concerning 

 the influence of mechanical irritation of the hair follicles on 

 the growth of the hair. The Primates generally are distin- 

 guished among all the Mammalia for the extraordinary 

 variety of special developments of hair about the head and 

 on other parts of the body, and it would be of great interest 

 to know whether these special growths were generally associ- 

 ated with special mechanical stimulations due to particular 

 habits. At present observations on the habits of the various 

 species in their natural state necessary for such an inquiry 

 appear to be wanting. 



If we suppose that the beard and moustache so well 

 developed in the white or Caucasian race are derived from 

 the original single ancestral species of man, it follows that in 

 most other races, except the Papuans, Australians, and 

 Fijians, the beards have very much diminished, or almost 

 disappeared. There seems to be very little if any evidence 

 that this can have been caused by sexual selection on the 

 part of the women. It seems necessary to attribute it to 

 spontaneous variation without selection. It is important, 

 however, to notice that there are indications of the influence 

 of climatic conditions in causing modification of the beard 

 and hair in definite directions. In the North American 

 Indians the beard is rudimentary, and in the present in- 



