244 MENTAL EVOLUTION IN ANIMALS. 



among animals in a state of domestication. The kind of 

 evidence on which I rely to show this is two-fold — 1st the 

 occurrence among wild animals of local varieties of instinct, 

 and 2nd the similar occurrence of specific varieties. 



Local Varieties of Instinct. 



Under the first of these two divisions I shall seek to show 

 that the mutability of instinct finds a most marked and sug- 

 gestive expression in certain cases where wild animals of the 

 same species living in different parts of the world (and there- 

 fore exposed to different environments), present differences in 

 their instinctive endowments of a marked and constant kind. 

 One class of such cases has already been given with reference 

 to the acquisition of an instinctive fear of man by those 

 animals in a state of nature which inhabit localities frequented 

 by man : but as the subject appears to me an important one 

 — seeing that a definite local variety is on its way to becom- 

 ing a new instinct — I shall now give all the best instances 

 which I have been able to collect. 



Beginning with insects, Kirby and Spence state on the 

 authority of Sturm that the dung-beetle, which rolls up 

 pellets or little balls of dung, saves itself the trouble of 

 making the pellets when it happens to live on sheep- 

 pastures; for it then "avails itself of the pellet-shaped balls 

 ready made to its hands which the excrement of the sheep 

 supplies." Here we have intelligent adaptation to peculiar 

 conditions, and so the case might have been quoted as one of 

 the plasticity of instinct ; but as sheep-pastures are definite 

 local areas, I have quoted it as a case of the local variation of 

 instinct. All cases of such local variation must have some 

 determining cause, and doubtless most frequently this cause 

 is intelligent adaptation to peculiar local conditions. There- 

 fore I have chosen this case to lead off with just because it 

 might equally well be quoted in this or in the previous 



chapter. 



Again it is stated by Lonbiere, in his history of Siam, 

 " that in one part of that kingdom, which lies open to great 

 inundations, all the ants made their settlements upon trees ; 

 no ants' nests are to be seen anywhere else." And Forel 

 states a closely similar fact with reference to a species of 

 European ant, Zasius aceruorum, which en the plains is never 



