66 THE DESCENT OF ilAN. 



ferences 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 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 compatible 

 with complex instincts, and although actions, at first learned 

 voluntarily can soon through habit be performed with the quick- 

 ness and certainty of a reflex action, yet it is not improbable that 

 there is a certain amount of interference between the devel- 

 opment of free intelligence and of instinct, — which latter Implies 

 some inherited modiflcation of the brain. Little is known about 

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

 lectual 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 separate part 

 would perhaps tend to be less well fltted to answer to particular 

 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 flxed, 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 ifthis 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 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 

 intelligence 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, mak(;, 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 



" 'Contributions to the Theory of Natural Selection,' 1870, p. 212. 



