THE EVOLUTION OF INSTINCT 135 



and in the case of many instincts it is not difficult to picture 

 to one's self how natural selection may have brought them to 

 their present state of perfection. To find, as we can in many 

 cases, instincts in various grades of development in allied 

 species of animals, while it shows the general course of their 

 evolution, tells us little of their method of evolution. That 

 instincts are variable, that they are often imperfect, that their 

 general course of development has been along adaptive lines, 

 and that, as Darwin emphasized, they are always primarily 

 of value to the species possessing them and only incidentally 

 of service to others, are facts indicative of the potency 

 of natural selection in the evolution of instinctive be- 

 havior. 



Evidence for the potency of selection is furnished by the 

 study of the striking modifications of instinct which have 

 taken place in animals under domestication. While only 

 rarely has the attempt been made to modify instincts along 

 particular lines by selection, yet they have doubtless been 

 modified as the incidental result of selection on other lines. 

 A sort of unconscious selection has probably played a part 

 in modifying especially the emotional characteristics of 

 animals. Ugly and vicious dispositions in dogs, for instance, 

 would tend to be eliminated, and the qualities of affection, 

 fidelity and other traits which commend the animals to the 

 good graces of their keepers would be fostered. The 

 useful instincts of the pointer and the setter, however they 

 may have made their beginning, have certainly been devel- 

 oped to a considerable degree by continued selection. The 

 curious instincts of tumbling and pouting which, as Whitman 

 has shown, have their basis in traits of behavior found in 

 pigeons in general, have been developed by the efforts of 

 fanciers to an almost monstrous degree. The Indian sub- 

 breed of tumblers which has been bred for at least two-hundred 



