324 INSTINCT. [Chap. VIII. 



structure of other species. So again certain instincts 

 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 de- 

 pendence 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 cov- 

 ered decorticated trees. It has lately been shown that 

 bees, instead of searching for pollen, will gladly use a 

 very different substance, namely oatmeal. Pear of any 

 particular enemy is certainly an instinctive quality, as 

 may be seen 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 



