Appendix II. 321 



other sex, though of no use to this sex. But structures thus 

 indirectly gained, although at first of no advantage to a species, 

 may subsequently have been taken advantage of by its modified 

 descendants, under new conditions of life and newly acquired 

 habits 1 ." 



It appeared and still appears tome, that where so many 

 causes are expressly assigned as producing useless specific 

 characters, and that some of them (such as climatic influences 

 and independent variability) must be highly general in their 

 action, I was justified in representing it as Darwin's opinion 

 that " a large proportional number of specific characters " 

 are useless to the species presenting them, although after- 

 wards they may sometimes become of use to genera, families, 

 &c. Moreover, this passage goes on to point out that 

 specific characters which at first sight appear to be obviously 

 useful, are sometimes found by fuller knowledge to be really 

 useless a consideration which is the exact inverse of the 

 argument from ignorance as used by Mr. Wallace, and 

 serves still further to show that in Darwin's opinion utility is 

 by no means an invariable, still less a "necessary," mark of 

 specific character. The following are some of the instances 

 which he gives. 



" The sutures in the skulls of young mammals have been ad- 

 vanced as a beautiful adaptation for aiding parturition, and no 

 dcubt they may facilitate, or be indispensable for this act ; 

 but as sutures occur in the skulls of young birds and reptiles, 

 which have only to escape from a broken egg, we may infer 

 that this structure has arisen from the laws of growth, and 

 has been taken advantage of in the parturition of the higher 

 animals 2 ." 



" The naked skin on the head of a vulture is generally con- 

 sidered as a direct adaptation for wallowing in putridity; 

 and so it may be, or it may possibly be due to the direct 

 action of the putrid matter ; but we should be very cautious 



1 Origin of Species, pp. 157-8. * Ibid. 



II. Y 



