Few of us,
however, know what a million really means: Mr. Croll gives the following
illustration: Take a narrow strip of paper, eighty-three feet four inches
in length, and stretch it along the wall of a large hall; then mark off at
one end the tenth of an inch. This tenth of an inch will represent one
hundred years, and the entire strip a million years. But let it be borne
in mind, in relation to the subject of this work, what a hundred years
implies, represented as it is by a measure utterly insignificant in a hall
of the above dimensions. Several eminent breeders, during a single
lifetime, have so largely modified some of the higher animals, which
propagate their kind much more slowly than most of the lower animals, that
they have formed what well deserves to be called a new sub-breed. Few men
have attended with due care to any one strain for more than half a century,
so that a hundred years represents the work of two breeders in succession.
It is not to be supposed that species in a state of nature ever change so
quickly as domestic animals under the guidance of methodical selection.
The comparison would be in every way fairer with the effects which follow
from unconscious selection, that is, the preservation of the most useful or
beautiful animals, with no intention of modifying the breed; but by this
process of unconscious selection, various breeds have been sensibly changed
in the course of two or three centuries.
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