e
hive-bee, can be explained by natural selection having taken advantage of
numerous, successive, slight modifications of simpler instincts; natural
selection having by slow degrees, more and more perfectly, led the bees to
sweep equal spheres at a given distance from each other in a double layer,
and to build up and excavate the wax along the planes of intersection. The
bees, of course, no more knowing that they swept their spheres at one
particular distance from each other, than they know what are the several
angles of the hexagonal prisms 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 {236} 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
profit