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, disappears, when it is remembered that selection may be
applied to the family, as well as to the individual, and may thus gain
the desired end. Thus, a well-flavoured vegetable is cooked, and the
individual is destroyed; but the horticulturist sows seeds of the same
stock, and confidently expects to
get nearly the same variety; breeders of cattle wish the flesh and fat
to be well marbled together; the animal has been slaughtered, but the
breeder goes with confidence to the same family. I have such faith in
the powers of selection, that I do not doubt that a breed of cattle,
always yielding oxen with extraordinarily long horns, could be slowly
formed by carefully watching which individual bulls and cows, when
matched, produced oxen with the longest horns; and yet no one ox could
ever have propagated its kind. Thus I believe it has been with social
insects: a slight modification of structure, or instinct, correlated
with the sterile condition of certain members of the community, has
been advantageous to the community: consequently the fertile males and
females of the same community flourished, and transmitted to their
fertile offspring a tendency to produce sterile members having the same
modification. And I believe that this process has been repeated, until
that prodigious amount of difference between the fertile and sterile
females of the same species has been produced, which we see in many
182