68 The Descent of Man. Pabt I. 



to o'lr ignorance, are often said to arise spontaneously. We can, 

 I think, come to nn 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 off- 

 spring 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 compatibla 

 with complex instincts, and although actions, at first learnt 

 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 inherited 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 pai'ticular sensations or associations in a definite 

 and inherited— 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 inherited 

 habits; for as a sagacious physician remarked to me, persons 

 who are slightly imbecile tend to act in everything by routine 

 or habit ; and they are rendered much happier if this is en- 

 couraged. 



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 foresight, 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 

 intelligenoe on the part of the animal during each successive 

 generation. No doubt, as Mr. Wallace has argued,' much of the 

 intelligent work done by man is due to imitation and not to 

 reason; but there' is this great difference between his actions 

 and many of those performed by the lower animals, namely, that 

 man cannot, on his first trial, make, for instance, a stone hatchet 

 or a canoe, through his power of imitation. He has to learn his 

 work by practice ; a beaver, on the other hand, can make its 

 dam or canal, and a bird its nest, as well, or nearly as well, and 



• 'i-ontiibutions to the Theory of \atural Seiection,' 1870, p. 212, 



