356 OBJECTIONS TO THE THEORY [Chap. VIIL 



gradations are known to exist; cases of instincts of such 

 trifling importance, that they could hardly have been 

 ccted 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 conse- 

 quently must believe that they vfere independently ac- 

 quired 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 insuper- 

 able, and actually fatal to the whole theory. I allude 

 to the neuters or sterile females in insect-communi- 

 ties; for these neuters often differ widely in instinct and 

 in structure from both the males and fertile females, 

 and yet, from being sterile, they cannot propagate their 

 kind. 



The subject well deserves to be discussed at great 

 length, but I will here take only a single case, that of 

 working or sterile ants. How the workers have been 

 rendered sterile is a difficulty; but not much greater 

 than that of any other striking modification of struc- 

 ture; for it can be shown that some insects and other 

 articulate animals in a state of nature occasionally be- 

 come sterile; and if such insects had been social, and 

 it had been profitable to the community that a number 

 should have been annually born capable of work, but in- 

 capable of procreation, I can see no especial difficulty in 

 this having been effected through natural selection. 

 But I must pass over this preliminary difficulty. The 

 great difficulty lies in the working ants differing widely 

 from both the males and the fertile females in structure, 

 as in the shape of the thorax, and in being destitute of 

 wings and sometimes of eyes, and in instinct. As far 



