able 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 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 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 {237}
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. It may well be asked how is it
possible to reconcile this case with the theory of natural selection?

First, let it be remembered that we have innumerable instances, both in our
domestic productions and in those in a state of nature, of all sorts of
differences of structure which have become correlated to certain ages, and
to either sex. We have differences correlated not only to one sex, but to
that short period alone when the reproductive system is active, as in the
nuptial plumage of many birds, and in the hooked jaws of the male salmon.
We have even slight differences in the horns of different breeds of cattle
in relation to an artificially imperfect state of the male sex; for oxen of
certain breeds have longer horns than in other breeds, in comparison with
the horns of the bulls or cows of these same breeds. Hence I can see no
real difficulty in any character having become correlated with the sterile
condition of certain members of 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, disappe