Now let us turn to the other side of the argument. Under domestication we see much
variability. variability. 1859 1860 1861 1866 |
variability, caused, or at least excited, by changed conditions of life. 1869 |
variability, caused, or at least excited, by changed conditions of life; but often in so obscure a manner, that we are tempted to consider the variations as spontaneous. 1872 |
This seems to be
in part in part 1866 | mainly 1859 1860 1861 |
due to the reproductive system being eminently susceptible to changes in the conditions of life; so that this system, when not rendered impotent, fails to reproduce offspring exactly like the parent-form.
Variability Variability 1859 1860 1861 1866 1872 | This variability 1869 |
is governed by many complex laws,— by
correlation correlation 1859 1860 1861 1866 | correlation, 1869 | correlated 1872 |
of growth, of growth, 1859 1860 1861 1866 | growth, 1872 | of growth, 1869 |
by by 1859 1860 1861 1866 1869 |
compensation, the increased 1872 |
use and
disuse, disuse, 1859 1860 1861 1866 1869 | disuse 1872 |
and by the direct and by the direct 1859 1860 1861 1866 |
and by the definite 1869 |
of parts, and the definite 1872 |
action of the
physical physical 1859 1860 1861 1866 | surrounding 1869 1872 |
conditions conditions 1859 1860 1861 1866 | conditions. 1869 1872 |
of of 1859 1860 1861 1866 | of 1869 1872 |
life. life. 1859 1860 1861 1866 | life. 1869 1872 |
There is much difficulty in ascertaining how
much modification much modification 1859 1860 1861 1866 | largely 1869 1872 |
our domestic productions have
undergone; undergone; 1859 1860 1861 1866 | been modified; 1869 1872 |
but we may safely infer that the amount has been large, and that modifications can be inherited for long periods. As long as the conditions of life remain the same, we have reason to believe that a modification, which has already been inherited for many generations, may continue to be inherited for an almost infinite number of generations. On the other
hand, hand, 1866 1869 1872 | hand 1859 1860 1861 |
we have evidence that
variability, variability, 1859 1860 1861 1866 1869 | variability 1872 |
when it has once come into play, does not
wholly wholly 1859 1860 1861 1866 | wholly 1869 1872 |
cease; cease; 1859 1860 1861 1866 | cease 1869 1872 |
for for 1859 1860 1861 1866 |
under domestication for a very long period; for 1869 |
under domestication for a very long period; nor do we know that it ever ceases, for 1872 |
new varieties are still occasionally produced by our
most anciently most anciently 1859 1860 1861 1866 | oldest 1869 1872 |
domesticated productions. |