CHAP. X Instinct 163 



of the species under experiment. So far as we know, no 

 adequate experiments have been carried out. 



It is stated that the nests of British birds let loose in 

 Australia differ very greatly from the nests that they would 

 build at home. Now this may be due to the absence of 

 training and the possibilities of imitating the specific nest, 

 or it may be due to the absence of the materials with which 

 to build the characteristic nest. 



When we consider the careful provision that the Sphex 

 wasp makes for its young, young which she will never see ; 

 or the selection by a butterfly of the leaf upon which she 

 lays her eggs, the only sort of leaf, it may be, that will serve 

 the grubs, when hatched, for food, food of a kind which the 

 butterfly herself does not eat, we have before us examples 

 of instincts most wonderful in their perfection and most 

 obscure in their origin. The ideas involved are too com- 

 plex for us to believe that the actions can be the result of 

 intelligence. So far as we can see at present, such 

 instincts can only be accounted for by the Natural Selection 

 of fortunate varieties of habit. The care of young and the 

 habit of incubation are instincts upon which a certain 

 amount of thought has been bestowed. For ourselves, we 

 incline to the idea which may seem mystical to some, that 

 such habits are bom of an inevitable affection for what is so 

 nearly related to the very body of the parents. To escape 

 an explanation of such habits in terms of affection, certain 

 naturalists have suggested the demonstrably absurd notion 

 that birds sit upon their eggs in order to cool a fevered 

 breast. If such were her object, the very worst place that 

 a bird could select as her seat would be^a woolly hairy 

 nest containing eggs which, in virtue of internal chemical 

 changes, generate heat of themselves. 



4. The Origin of Instinct. — The theory of the evolu- 

 tion of instinct has been worked at by Darwin, and since his 

 day by various other authors, notably Mr. Romanes, Mr. 

 A. R. Wallace, and Professor Eimer ; while Professor 

 Weismann's doctrines have necessitated the revision of 

 certain plausible hypotheses. 



Darwin, of course, supposed that Natural Selection 



