228 Objections to the Theory Chap. vm. 



this bird often holds the seeds of the yew between its feet on a 

 branch, and hammers with its beak till it gets at the kernel. Now 

 what special difficulty would there be in natural selection preserving 

 all the slight individual variations in the shape of the beak, which 

 were better and better adapted to break open the seeds, until a 

 beak was formed, as well constructed for this purpose as that of 

 the nuthatch, at the same time that habit, or compulsion, or spon- 

 taneous variations of taste, led the bird to become more and more 

 of a seed-eater ? In this case the beak is supposed to be slowly 

 modified by natural selection, subsequently to, but in accordance 

 with, slowly changing habits or taste ; but let the feet of the tit- 

 mouse vary and grow larger from correlation with the beak, or 

 from any other unknown cause, and it is not improbable that such 

 larger feet would lead the bird to climb more and more until it 

 acquired the remarkable climbing instinct and power of the nut- 

 hatch. In this case a gradual change of structure is supposed to 

 lead to changed instinctive habits. To take one more case : few 

 instincts are more remarkable than that which leads the swift of 

 the Eastern Islands to make its nest wholly of inspissated saliva. 

 Some birds build their nests of mud, believed to be moistened with 

 saliva ; and one of the swifts of North America makes its nest (as 

 I have seen) of sticks agglutinated with saliva, and even with flakes 

 of this substance. Is it then very improbable that the natural 

 selection of individual swifts, which secreted more and more saliva, 

 should at last produce a species with instincts leading it to neglect 

 other materials, and to make its nest exclusively of inspissated 

 saliva? And so in other cases. It must, however, be admitted 

 that in many instances we cannot conjecture whether it was instinct 

 or structure which first varied. 



No doubt many instincts of very difficult explanation could he 

 opposed to the theory of natural selection — cases, in which we can- 

 not see how an instinct could have originated ; cases, in which no 

 intermediate gradations are known to exist; cases of instinct of 

 such trifling importance, that they could hardly have been acted on 

 by natural selection ; cases of instincts almost identically the same 

 in animals so remote in the scale of nature, that we cannot account 

 for their similarity by inheritance from a common progenitor, and 

 consequently must believe that they were independently acquired 

 through natural selection. I will not here enter on these several 

 cases, but will confine myself to one special difficulty, which at first 

 appeared to me insuperable, and actually fatal to the whole theory. 

 I allude to the neuters or sterile females in insect-communities: 

 for these neuters often differ widely in instinct and in structure 



