SEXUAL SELECTION 169 



environment. A bare superiority to existing conditions is the 

 utmost that can be expected from its operation. But Sexual 

 Selection is not thus limited, or, to put it more correctly, the 

 males by their pugnacious rivalry make an artificial environment 

 for each other, and this may be merely a more exacting form of 

 that to which the species in general is subject. When this is so, 

 there will result, not something in itself useless, such as orna- 

 mental plumage, but an improvement in some organ on which 

 the species depends for existence. 



Let us see how this applies to the old problem of the giraffe's The 

 neck. If we try to account for it by Natural Selection working ^ c a k 

 unaided, then we have to assume a series of droughts. Each of 

 the series, we must believe, was more severe or more prolonged 

 than that which preceded it. Either, then, at each recurrence, 

 the leaves of taller and taller trees (taller because more deep- 

 rooted, and, therefore, better able to stand the drought) were 

 the only food available, or else, each visitation lasting longer than 

 the last, the shoots were eaten off to progressively higher levels. 

 It is very difficult to believe that this ever happened ; but if 

 Natural Selection brought about this elongation of the giraffe's 

 neck, we must postulate for each increase in length a corre- 

 sponding increase in the altitude at, and not below, which food 

 was obtainable. 



But Sexual Selection may help to get us out of what would 

 otherwise be a tight corner, if we can show that there are fights 

 between the males, and that length of neck and fore-leg some- 

 how gives an advantage to the combatants. Now the male 

 giraffe in his own habitat is by no means the mild statuesque 

 animal that we are familiar with in the Zoological Gardens. 

 On the contrary he uses his short horns with great effect. As 

 to his height, it does not seem likely that an extra foot or half 

 foot would be of any service in an actual encounter. But 

 indirectly it may be of the greatest assistance. On the occasion 

 of a drought, the shorter members of the herd might manage 

 to survive, being able to obtain just pasturage enough to live 

 on, but the taller would be decidedly better fed. Height 

 would, therefore, be the concomitant of vigour, and the tall 



