188 ON THE ORIGIN OF SPECIES 



as not to be distinguished. If Mozart, instead of playing 

 the pianoforte at three years old with wonderfully little 

 practice, had played a tune with no practice at all, he 

 might truly be said to have done so instinctively. But 

 it would be the most serious error to suppose that the 

 greater number of instincts have been acquired by habit 

 in one generation, and then transmitted by inheritance 

 to succeeding generations. It can be clearly shown that 

 the most wonderful instincts with which we are ac- 

 quainted, namely, those of the hive-bee and of many 

 ants, could not possibly have been thus acquired. 



It will be universally admitted that instincts are as 

 important as corporeal structure for the welfare of each 

 species, under its present conditions of life. Under 

 changed conditions of life, it is at least possible that 

 slight modifications of instinct might be profitable to a 

 species ; and if it can be shown that instincts do vary 

 ever so little, then I can see no difficulty in natural 

 selection preserving and continually accumulating 

 variations of instinct to any extent that may be 

 profitable. It is thus, as I believe, that all the most 

 complex and wonderful instincts have originated. As 

 modifications of corporeal structure arise from, and are 

 increased by, use or habit, and are diminished or lost 

 by disuse, so I do not doubt it has been with instincts. 

 But I believe that the effects of habit are of quite 

 subordinate importance to the effects of the natural 

 selection of what may be called accidental variations of 

 instincts ; — that is of variations produced by the same 

 unknown causes which produce slight deviations of 

 bodily structure. 



No complex instinct can possibly be produced through 

 natural selection, except by the slow and gradual 

 accumulation of numerous, slight, yet profitable, 

 variations. Hence, as in the case of corporeal 

 structures, we ought to find in nature, not the actual 

 transitional gradations by which each complex instinct 

 has been acquired — for these could be found only in 

 the lineal ancestors of each species — but we ought to 

 find in the collateral lines of descent some evidence of 



