212 ON THE ORIGIN OF SPECIES 



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 my 

 whole theory. I allude to the neuters or sterile females 

 in insect-communities : 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 

 structure ; for it can be shown that some insects and 

 other articulate animals in a state of nature occasion- 

 ally 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 

 very great difficulty in this being effected by natural 

 selection. But I must pass over this preliminary diffi- 

 culty. 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 prodigious difference in this respect between the 

 workers and the perfect females, would have been far 

 better exemplified by the hive-bee. If a working ant 

 or other neuter insect had been an animal in the 

 ordinary state, I should have unhesitatingly assumed 

 that all its characters had been slowly acquired through 

 natural selection ; namely, by an individual having 

 been born with some slight profitable modification of 

 structure, this being inherited by its offspring, which 

 again varied and were again 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. 



