Hence, I can see no great difficulty in any character
becoming 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. Breeders of cattle wish the flesh and fat to be well marbled
together. An animal thus characterized has been slaughtered, but the
breeder has gone with confidence to the same stock and has succeeded. Such
faith may be placed in the power of selection that a breed of cattle,
always yielding oxen with extraordinarily long horns, could, it is
probable, be formed by carefully watching which individual bulls and cows,
when matched, produced oxen with the longest horns; and yet no one ox would
ever have propagated its kind. Here is a better and real illustration:
According to M. Verlot, some varieties of the double annual stock, from
having been long and carefully selected to the right degree, always produce
a large proportion of seedlings bearing double and quite sterile flowers,
but they likewise yield some single and fertile plants. These latter, by
which alone the variety can be propagated, may be compared with the fertile
male and female ants, and the double sterile plants with the neuters of the
same community.
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