106 SEXUAL DIMORPHISM 



the Suidre or swine family. In the common wild boar the 

 lower canines are developed into long curved tusks, which 

 are employed in fighting with other boars, and Darwin 

 quotes Sir W. Elliot as authority for the belief that in the 

 breeding season in India the boar consorts with several 

 females, an indication of exclusive possession of the latter. 

 On the shoulder there is an area of gristly skin, which 

 receives the blow of the opponent's tusk. Here once more 

 we find the direct effect of mechanical impact. 



In the Babirusa boar of Celebes the upper canines are 

 enlarged into enormous tusks, so much curved that their 

 points cannot be presented, while the lower are shorter, less 

 curved, and very formidable. The upward curvature of such 

 tusks in the upper jaw is to be attributed in the first 

 instance to the pressure of the lower tusk, which, as it 

 elongates in evolution, necessarily turns up the point of the 

 upper canine. Afterwards the continual use of the upturned 

 tusk will cause its continued enlargement. Darwin gives a 

 description of the African wart-hog, Phacochcerus ccthiopicus, 

 and no one can help being struck with the correspondence 

 between the character and position of the skin pads beneath 

 the eyes, and the stroke which the tusk of an opponent must 

 give. The stroke of the tusk would necessarily harden the 

 skin, and the peculiarity which is now specific and hereditary 

 is evidently only an intensification of the effect which would 

 be produced in the individual. The tusks and the " wart " 

 are both present in the female as well as in the male, but on 

 a reduced scale in the former, and this is possibly due to 

 similar pugnacious habits in the female. A similar but more 

 prominent wart is present in the African river-hog, Pota- 

 mochoerus penicillatus. Darwin mentions that after a fight 

 between a river-hog and a wart-hog, these thickened parts 

 of the skin were covered with blood, and were scored and 

 abraded in an extraordinary manner. Is it possible, in 



