The way this is done is by artificial selection, and it is very
important to understand this process and its results. Suppose we have a
plant with a small edible seed, and we want to increase the size of that
seed. We grow as large a quantity of it as possible, and when the crop
is ripe we carefully choose a few of the very largest seeds, or we may
by means of a sieve sort out a quantity of the largest seeds. Next year
we sow only these large seeds, taking care to give them suitable soil
and manure, and the result is found to be that the _average_ size of the
seeds is larger than in the first crop, and that the largest seeds are
now somewhat larger and more numerous. Again sowing these, we obtain a
further slight increase of size, and in a very few years we obtain a
greatly improved race, which will always produce larger seeds than the
unimproved race, even if cultivated without any special care. In this
way all our fine sorts of vegetables, fruits, and flowers have been
obtained, all our choice breeds of cattle or of poultry, our wonderful
race-horses, and our endless varieties of dogs.
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