324 DsSTIXCT. [Chap. VIIL 



cannot be considered as absolutely perfect ; but as details 

 on this and other such points are not indispensable, they 

 may be here passed over. 



As some degree of variation in instincts under a state 

 of nature, and the inheritance of such variations, are 

 indispensable for the action of natural selection, as 

 many instances as possible ought to be given ; but want 

 of space prevents me. I can only assert that instincts 

 certainly do vary — for instance, the migratory instinct, 

 both in extent and direction, and in its total loss. So 

 it is with the nests of birds, which vary partly in 

 dependence on the situations chosen, and on the nature 

 and temperature of the country inhabited, but often from 

 causes wholly unknown to us : Audubon has given 

 several remarkable cases of differences in the nests of 

 the same species in the northern and southern United 

 States. Why, it has been asked, if instinct be variable, 

 has it not granted to the bee " the ability to use some 

 other material when wax was deficient " ? But what 

 other natural material could bees use ? They will work, 

 as I have seen, with wax hardened with vermilion or 

 softened with lard. Andrew Knight observed that his 

 bees, instead of laboriously collecting propolis, used a 

 cement of wax and turpentine, with which he had covered 

 decorticated trees. It has lately been shown that bees, 

 instead of searching for pollen, will gladly use a very 

 different substance, namely oatmeal. Fear of any par- 

 ticular enemy is certainly an instinctive quality, as may 

 be seeu in nestling birds, though it is strengthened by 

 experience, and by the sight of fear of the same enemy 

 in other animals. The fear of man is slowly acquired, 

 as I have elsewhere shown, by the various animals 

 which inhabit desert islands; and we see an instance 



