ORIGIN AND DEVELOPMENT OF INSTINCTS. 17 



CHAPTER XII. 



Instinct (continued). 



Origin and Development of Instincts. 



Instincts probably owe their origin and development to one 

 or other of two principles. 



I. The first mode of origin " consists in natural selection, ^ 

 or survival of the fittest, continuously preserving actions 

 which, although never intelHgent, yet happen to have been of 

 benefit to the animals which first chanced to perform them. 

 Thus, for instance, take the instinct of incubation. It is 

 quite impossible that any animal can ever have kept its eggs 

 warm with the intelligent purpose of hatching out their con- 

 tents, so we can only suppose that the incubating instinct 

 began by warm-blooded animals showing that kind of atten- 

 tion to their eggs which we find to be frequently shown by 

 cold-blooded animals. Thus crabs and spiders carry about 

 their eggs for the purpose of protecting them; and if, as 

 animals gradually became warm-blooded, some species, for 

 this or for any other purpose, adopted a similar habit, tlie 

 imparting of heat would have become incidental to the car- 

 rying about of the eggs. Consequently, as the imparting of 

 heat promoted the process of hatching, those individuals 

 which most constantly cuddled or brooded over their eggs 

 would, other things equal, have been most successful in 

 rearing progeny; and so the incubating instinct would be 

 developed without there ever having been any intelligence in 

 the matter."* 



II. The second mode of origin is as follows : — By the > 

 efiects of habit in successive generations,, actions which Avere 

 originally intelligent become, as it were, stereotyped into per- 



* Quoted from my own article on "Instinct," in the EncijclopcBdia Bri- 

 tannica. 



M 



