76 THE DESCENT OF MAN. 



actions, and can hardly be distinguished from them, as in 

 the case of young animals sucking, yet the more complex 

 instincts seem to have originated independently of intelli- 

 gence. I am, however, very far from wishing to deny that 

 instinctive actions may lose their fixed and untaught char- 

 acter and be replaced by others performed by the aid of the 

 free will. On the other hand, some intelligent actions, 

 after being performed during several generations, become 

 converted into instincts and are inherited, as when birds 

 on oceanic islands learn to avoid man. These actions may 

 then be said to be degraded in character, for they are no 

 longer performed through reason or from experience. But 

 the greater number of the more complex instincts appear 

 to have been gained in a wholly different manner, through 

 the natural selection of variations of simpler instinctive 

 actions. Such variations appear to arise from the same 

 unknown causes acting on the cerebral organization, which 

 induce slight variations or individul differences in other 

 parts of the body ; and these variations, owing to our 

 ignorance, are often said to arise spontaneously. We can, 

 I think, come to no other conclusion with respect to the 

 origin of the more complex instincts, when we reflect on 

 the marvelous instincts of sterile worker-ants and bees, 

 which leave no offspring to inherit the effects of experience 

 and of modified habits. 



Although, as we learn from the above-mentioned insects 

 and the beaver, a high degree of intelligence is certainly 

 compatible with complex instincts, and although actions, 

 at first learned voluntarily, can soon through habit be 

 performed with the quickness and certainty of a reflex 

 action, yet it is not improbable that there is a certain 

 amount of interference between the development of free 

 intelligence and of instinct, which latter implies some in- 

 herited modification of the brain. Little is known about 

 the functions of the brain, but we can perceive that as the 

 intellectual powers become highly developed the various 

 parts of the brain must be connected by very intricate 

 channels of the freest intercommunication; and as a conse- 

 quence each separate part would perhaps tend to be less 

 well fitted to answer to particular sensations or associations 

 in a definite and inherited that is instinctive manner. 

 Tliere seems even to exist some relation between a low de- 

 gree of intelligence and a strong tendency to the formation 



