In looking at many small points of difference between species, which, as
far as our ignorance permits us to judge, seem quite unimportant, we must
not forget that climate, food, etc., have no doubt produced some direct
effect. It is also necessary to bear in mind that, owing to the law of
correlation, when one part varies and the variations are accumulated
through natural selection, other modifications, often of the most
unexpected nature, will ensue.
As we see that those variations which, under domestication, appear at any
particular period of life, tend to reappear in the offspring at the same
period; for instance, in the shape, size and flavour of the seeds of the
many varieties of our culinary and agricultural plants; in the caterpillar
and cocoon stages of the varieties of the silkworm; in the eggs of poultry,
and in the colour of the down of their chickens; in the horns of our sheep
and cattle when nearly adult; so in a state of nature natural selection
will be enabled to act on and modify organic beings at any age, by the
accumulation of variations profitable at that age, and by their inheritance
at a corresponding age. If it profit a plant to have its seeds more and
more widely disseminated by the wind, I can see no greater difficulty in
this being effected through natural selection, than in the cotton-planter
increasing and improving by selection the down in the pods on his
cotton-trees.
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