SEXUAL SELECTION 009 



for the possession of the females, and exhibit distinctive masculine 

 characters adapted to such combats. But I do not propose to enter 

 upon a discussion of such cases, since my aim is rather to elucidate 

 the relation between sexual selection and species-selection than to 

 discuss all the phenomena of the former in detail. But the combats 

 of males illustrate with particular clearness the relation of sexual 

 selection and species-selection, since many of the weapons or pr< >tective 

 arrangements which may have arisen through sexual selection imply 

 at the same time an improvement to the species in relation to the 

 struggle for existence. Thus greater strength or sharper and larger 

 teeth in the males mean a gain to the species, and it is indifferent to 

 the species whether the weaker males succumb to a strange enemy 

 (species-selection) or to their stronger rivals (sexual selection), pro- 

 vided only that the better equipped survive and leave descendants 

 similarly endowed. 



I have intentionally begun the consideration of sexual selection 

 with the cases most difficult to interpret on this theory, with those 

 which have called forth the greatest divergence of opinion — the 

 decorative colours and forms, the song of birds and of insects ; the 

 alluring odours— in short, all the courtship-adaptations of the males; 

 these are the most difficult to deal with, because it is not easy to 

 demonstrate directly that the females do choose. But if we revise 

 them briefly in reverse order, I believe that all doubt as to the reality 

 of choice on the part of the females will disappear. Thus the last-men- 

 tioned sexual characters of greater strength and greater perfection of 

 weapons and defence in the males have been evolved by sexual selection 

 in close co-operation with species-selection. We should have to deny 

 species-selection altogether if we were to dispute this form of sexual 

 selection, which is closely connected with pure species-selection, such, 

 for instance, as is revealed in the production of dwarf males, where 

 there does not seem to be any aid from sexual selection at all. 



Then came the cases in which the tracking and grasping organs 

 of the males were strengthened or were increased in number, and here 

 too species-selection may have had its share, for instance, in evolving 

 the sickle-claws of the Daphnids, which were inevitably advanced 

 and perfected through sexual selection, which must in this case have 

 operated independently of any choice on the part of the female. In 

 other cases the result may be referred to pure sexual selection, as in 

 the grasping antennse of the male Moiaa, or in the highly developed 

 olfactory antennas of the male Leptodora. That new organs, too, can 

 arise in this way is shown by the 'turban eyes' — to which little 

 attention has hitherto been paid — of some Ephemerids of the genera 



