apparently such trifling importance, that they could hardly have been
acted 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 parent, and must
therefore believe that they have been acquired by independent acts of
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 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 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 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 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
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