»o THE DESCENT OF MAN 



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 per- 

 formed 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 inherited modi- 

 fication 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 consequence, each sepa- 

 rate part would perhaps tend to be less well fitted to answer 

 to particular sensations or associations in a definite and in- 

 herited — that is instinctive — manner. There seems even to 

 exist some relation between a low degree of intelligence and 

 a strong tendency to the formation of fixed, though not in- 

 herited habits; for, as a sagacious physician remarked to 

 me, persons who are slightly imbecile tend to act in every- 

 thing by routine or habit, and they are rendered much 

 happier if this is encouraged. 



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 compare their 

 actions founded on the memory of past events, on fore- 

 sight, reason, and imagination, with exactly similar actions 

 instinctively performed by the lower animals; in this latter 

 case the capacity of performing such actions has been 

 gained, step by step, through the variability of the mental 

 organs and natural selection, without any conscious intel- 

 ligence on the part of the animal during each successive 

 generation. No doubt, as Mr. Wallace has argued,* much 



» "Contributions to the Theory of Natural Selection," 1810, p. il2. 



