44 The Selection Theory 



the struggle for the possession of the female, we might name many 

 kinds of means, but it would be difficult to suggest any which is not 

 actually employed in some animal group or other. I begin with the 

 mere difference in strength, through which the male of many animals 

 is so sharply distinguished from the female, as, for instance, the lion, 

 walrus, "sea-elephant," and others. Among these the males fight 

 violently for the possession of the female, who falls to the victor in 

 the combat. In this simple case no one can doubt the operation of 

 selection, and there is just as little room for doubt as to the selection- 

 value of the initial stages of the variation. Differences in bodily 

 strength are apparent even among human beings, although in their 

 case the struggle for the possession of the female is no longer decided 

 by bodily strength alone. 



Combats between male animals are often violent and obstinate, 

 and the employment of the natural weapons of the species in this 

 way has led to perfecting of these, e.g. the tusks of the boar, the 

 antlers of the stag, and the enormous, antler-like jaws of the stag- 

 beetle. Here again it is impossible to doubt that variations in 

 these organs presented themselves, and that these were considerable 

 enough to be decisive in combat, and so to lead to the improvement 

 of the weapon. 



Among many animals, however, the females at first withdraw from 

 the males ; they are coy, and have to be sought out, and sometimes 

 held by force. This tracking and grasping of the females by the 

 males has given rise to many different characters in the latter, as, 

 for instance, the larger eyes of the male bee, and especially of the 

 males of the Ephemerids (May -flies), some species of which show, in 

 addition to the usual compound eyes, large, so-called turban-eyes, so 

 that the whole head is covered with seeing surfaces. In these species 

 the females are very greatly in the minority (1 100), and it is easy 

 to understand that a keen competition for them must take place, and 

 that, when the insects of both sexes are floating freely in the air, an 

 unusually wide range of vision will carry with it a decided advantage. 

 Here again the actual adaptations are in accordance with the pre- 

 liminary postulates of the theory. We do not know the stages through 

 which the eye has passed to its present perfected state, but, since 

 the number of simple eyes (facets) has become very much greater in 

 the male than in the female, we may assume that their increase is due 

 to a gradual duplication of the determinants of the ommatidium in 

 the germ-plasm, as I have already indicated in regard to sense-organs 

 in general. In this case, again, the selection-value of the initial 

 stages hardly admits of doubt ; better vision directly secures re- 

 production. 



In many cases the organ of smell shows a similar improvement. 



