Darwin s Artificial and Natural Selection 143 



occasionally become 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 

 incapable 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 as instinct alone 

 is concerned, the wonderful difference in this respect between 

 the workers and the perfect females, would have been better 

 exemplified by the hive-bee. If a working ant or other neuter 

 insect had been an ordinary animal, I should have unhesitat- 

 ingly assumed that all its characters had been slowly ac- 

 quired through natural selection ; namely, by individuals 

 having been born with slight profitable modifications, which 

 were inherited by the offspring ; and that these again varied 

 and again were selected, and so onwards. But with the 

 working ant we have an insect differing greatly from its 

 parents, yet absolutely sterile ; so that it could never have 

 transmitted successively acquired modifications of structure 

 or instinct to its progeny. It may well be asked, how is 

 it possible to reconcile this case with the theory of natural 

 selection ? " 



Darwin's answer is that the differences of structure are 

 correlated with certain ages and with the two sexes, but this 

 is obviously only shifting the difficulty, not meeting it. He 

 concludes, " I can see no great difficulty in any character 

 becoming correlated with the sterile condition of certain 

 members of the insect communities, the difficulty lies in 

 understanding how such correlated modifications of structure 

 could have been slowly accumulated by natural selection." 

 " This difficulty, though appearing insuperable, is lessened, or, 

 as I believe, disappears, when it is remembered that selection 



