and
of the basal rhombic plates. The motive power of the process of natural
selection having been economy of wax; that individual swarm which wasted
least honey in the secretion of wax, having succeeded best, and having
transmitted by inheritance its newly acquired economical instinct to new
swarms, which in their turn will have had the best chance of succeeding
in the struggle for existence.

No doubt many instincts of very difficult explanation could be opposed
to the theory of natural selection,--cases, in which we cannot see
how an instinct could possibly have originated; cases, in which no
intermediate gradations are known to exist; cases of instinct of
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