TRIVIAL AND USELESS INSTINCTS. 275 



implanting of instincts by a supernatural cause. Next, we ^ 

 must be perfectly sure, in any given case, that the instinct! 

 which appears to be trivial or useless is really such. This 

 point is mentioned by Mr. Darwin, and he cites some very 

 good cases to show how the important utility, or even abso- 

 lute necessity, of an instinct may readily escape observation. 

 But even after due allowance is made on this score, some few 

 instincts certainly do remain which it seems impossible to 

 suppose of the smallest utility. How, then, are these to be 

 explained ? 



I believe they admit of being satisfactorily explained by 

 two considerations. The first of these is that our theory 

 does not suppose natural selection to be the only influence at 

 work in the formation of instincts. We have repeatedly 

 insisted that the lapsing of intelligence is another influence 

 of scarcely less importance ; and we have also seen abundant 

 evidence to show that non-adaptive habits occur in indi- 

 viduals and may be inherited in the race. Therefore, if from 

 play, affection, curiosity, or even mere caprice, the intelligence 

 of the animal should lead the animal to perform any useless 

 kind of action habitually (as, for instance, in the case of the 

 ratels tumbling head-over-heels),* and if this habit were to 

 become hereditary in the similarly constituted progeny, we 

 should have a trivial or useless instinct. The only condition, 

 so far as I can see, that would require to be satisfied would 

 be that the trivial or useless habit should not be actually 

 detrimental to the species exhibiting it, so that its growth 

 into an instinct should not be prevented by natural selec- 

 tion. 



The other consideration to which I have alluded as 

 mitigating or dispelling the difficulty in question is this. In 

 the analoo'ous case of structures, as is well known, we meet 

 with innumerable cases of useless organs ; but here, so far 

 from the fact being deemed a difficulty in the way of the 

 theory of evolution by natural selection, it is justly deemed 

 one of its strongest supports ; and the reason is that in 

 all such cases we have evidence of the useless and perhaps 

 rudimentary organs being of use in other and allied animals. 

 iS'ow I see no reason to doubt that the same may be true of 

 instincts, and therefore that what we now find to be ap- ; 

 j)arently trivial and certainly useless exhibitions of hereditary 



* See p. 189. 



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