252 OBJECTIONS TO tfHE THEOEY 



wax, having succeeded best, and having transmitted their 

 newly-acquired economical instincts to new swarms, which in 

 their turn will have had the best chance of succeeding in the 

 struggle for existence. 



OBJECTIONS TO THE THEORY OF NATURAL SELECTION AS 

 APPLIED TO INSTINCTS : NEUTER AND STERILE INSECTS. 



It has been objected to the foregoing view of the origin 

 of instincts, that " the variations of structure and of instinct 

 must have been simultaneous and accurately adjusted to each 

 other, as a modification in the one without an immediate 

 corresponding change in the other would have been fatal." 

 The force of this objection rests entirely on the assumption 

 that the changes in the instincts and structure are abrupt. 

 To take as an illustration the case of the larger titmouse 

 (Parus major), alluded to in a previous chapter ; 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 nut-hatch, at the same time that 

 habit, or compulsion, or spontaneous 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 titmouse 

 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 



