VARIATION OF INSTINCT IN DEFINITE LINES. 229 



"when exactly four hours old they ran, jumped, chirped, 

 scratched the ground, and cuddled together as if under the 

 hen ; all actions beautifully instinctive." After giving this 

 as an instance of what I have called pure instinct, he pro- 

 ceeds by way of comparison to say, " It might have been 

 thought that the manner in which fowls drink, by filling 

 their beaks, lifting up their heads, and allowing the water to 

 run down by its gravity, would have been specially taught 

 by instinct ; but this is not so, for I was most positively 

 assured that the chickens of a brood reared by themselves 

 generally required their beaks to be pressed into a trough, 

 but if there were older chickens present, who had learnt to 

 drink, the younger ones imitated their movements, and thus 

 acquired the art." 



Upon the whole, then, with reference to the modes 

 whereby intelligence operates in modifying instinct, we may 

 say that in all cases when it does so, there must first be 

 intelligent perception of the desirability of the modification 

 on the part of certain individuals, who modify their actions 

 accordingly. In some cases the principle of imitation pro- 

 bably assists in changing the instinct by inducing other indi- 

 viduals of the same species, and living in the same area, to 

 follow the example of their more intelligent companions; or 

 the principle of imitation may come in at an earlier stage, 

 the habits of one species suggesting to the members of another 

 species the modification of an instinct. Lastly, intelligence 

 may operate by the intentional tuition of young by their 

 parents. 



But perhaps the best evidence of the extreme modification 

 which instinct may be made to undergo by the effects of 

 individual experience, or of changed conditions of life, is that 

 which is afforded by the enormous mass of facts to which we 

 are naturally led on by some of the cases just given ; 1 mean 

 the facts connected with the domestication of animals. For 

 the effects of domestication in modifying instincts are quite 

 as strongly shown as are its effects in modifying structures, 

 as was long ago observed by Dr. Iv Darwin. So important 

 and extensive ;i class of facts, however, require to DC con- 

 sidered by themselves. 1 shall therefore now proceed to do 

 tins without any further special reference to the effects of 

 iinitatii n or of education operating upon instinct during the 

 lifetime of the individual. 



