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 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 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.
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