84 THE DESCENT OF MAN 



witli the trunk, favors tlie inference — on tlie assumption that 

 the hair was lost before man became erect; for the parts 

 which now retain most hair would then have been most 

 protected from the heat of the sun. The crown of the 

 head, however, offers a curious exception, for at all times 

 it must have been one of the most exposed parts, yet it is 

 thickly clothed with hair. The fact, however, that the other 

 members of the order of Primates, to which man belongs, 

 although inhabiting various hot regions, are well clothed 

 with hair, generally thickest on the upper surface, °° is op- 

 posed to the supposition that man became naked through 

 the action "of the sun. Mr. Belt believes'" that within the 

 tropics it is an advantage to man to be destitute of hair, as 

 he is thus enabled to free himself of the multitude of ticks 

 (acari) and other parasites, with which he is often infested, 

 and which sometimes cause ulceration. But whether this 

 evil is of sufficient magnitude to have led to the denudation 

 of his body through natural selection, may be doubted, since 

 none of the many quadrupeds inhabiting the tropics has, 

 as far as I know, acquired any specialized means of relief. 

 The view which seems to me the most probable is that man, 

 or rather primarily woman, became divested of hair for orna- 

 mental purposes, as we shall see under Sexual Selection; 

 and, according to this belief, it is not surprising that man 

 should differ so greatly in hairiness from all other Primates, 

 for characters, gained through sexual selection, often differ 

 to an extraordinary degree in closely related forms. 



According to a popular impression, the absence of a tail 



'* Isidore G-eoffroy St.-Hilaire remarka ("Hist. Nat. Gen^rale," torn, ii., 

 1869, pp. 215-21'?) on the head of man being covered with long hair; also on 

 the upper surfaces of monkeys and of other mammals being more thickly clothed 

 than the lower surfaces. ' This has likewise been observed by various authors. 

 Prof. P. Gervaia ("Hist. Nat. des Mammif^res," torn, i., 1854, p. 28), however, 

 states that in the Gorilla the hair is thinner on the back, where it is partly 

 rubbed off, than on the lower surface. 



*' "The Naturalist in Nicaragua," l&li, p. 209. As some confirmation 

 of Mr. Belt's view, I may quote the following pasaage from Sir W. Denison 

 ("Varieties of Yioe-Regal Life," vol. i., 1870, p. 440): "It is said to be a 

 practice with the Australians, when the vermin get troublesome, to singe 

 themselves. ' ' 



