54. THE THEORIES OF EVOLUTION 



tail serve with its special shape, except driving away 

 flies, a rather insignificant use. We must realise, 

 however, how little we know about the multiple fac- 

 tors which shape the life of individuals. It may be 

 that the uselessness of tails is only apparent and that 

 in warm countries, insects, especially mosquitoes, 

 play in the life of the large mammals a part which 

 we little suspect, although we know something about 

 it as far as African cattle are concerned. 



It may also be that the giraffe has inherited its tail 

 from its aquatic ancestors which used it in swimming, 

 and that this tail has been gradually modified and 

 adapted to its new uses. Whatever the case may be, 

 the principle of usefulness seems to be firmly estab- 

 lished and there are not, nor could there be, any 

 organs harmful to the species. We may also be mis- 

 taken when we attribute to natural selection the pres- 

 ence of an organ which may have been created by the 

 action of the environment or by a tendency to revert 

 to a long-extinct form, or by correlation, or by sexual 

 selection, etc., etc. 



Our lack of information is also responsible for one 

 objection raised against the theory of natural selec- 

 tion. What of the organs which cannot render any 

 service until they are fully developed? For instance, 

 the giraffe can, owing to its long neck, browse on the 

 foliage of trees. But if, at the time when the an- 



