38 THE DESCENT OF MAN. Part I. 



being performed during many generations, become con- 

 verted into instincts and are inherited. They 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 man- 

 ner, through the natural selection of variations of simpler 

 instinctive actions. Such variations appear to arise from 

 the same unknown causes acting on the cerebral organ- 

 isation, which induce slight variations or individual dif- 

 ferences in other parts of the body ; and these variations, 

 owing to our ignorance, are often said to arise sponta- 

 neously. We can, I think, come to no other conclusion 

 with respect to the origin of the more complex instincts, 

 when we reflect on the marvellous instincts of sterile 

 worker-ants and bees, which leave no offspring to inherit 

 the effects of experience and of modified habits. 



Although a high degree of intelligence is certainly 

 compatible with the existence of complex instincts, as 

 we see in the insects just named and in the beaver, it is 

 not improbable that they may to a certain extent inter- 

 fere with each other's development. 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 the 

 most intricate channels of intercommunication ; and as 

 a consequence each separate part would perhaps tend to 

 become less well fitted to answer in a definite and uni- 

 form, that is instinctive, manner to particular sensations 

 or associations. 



I have thought this digression worth giving, because 

 we may easily underrate the mental powers of the 

 higher animals, and especially of man, when we com- 

 pare their actions founded on the memory of past 

 events, on foresight, reason, and imagination, with 



