Now let us turn to the other side of the argument. Under domestication we see much
variability, caused, or at least excited, by changed conditions of life. variability, caused, or at least excited, by changed conditions of life. 1869 |
variability. 1859 1860 1861 1866 |
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 |
↑1 blocks not present in 1869 1872; present in 1859 1860 1861 1866 | This seems to be mainly
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.
|
This variability This variability 1869 | Variability 1859 1860 1861 1866 1872 |
is governed by many complex laws,— by
correlation, correlation, 1869 | correlation 1859 1860 1861 1866 | correlated 1872 |
....... 1869 | of growth, 1859 1860 1861 1866 | growth, 1872 |
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 definite and by the definite 1869 |
and by the direct 1859 1860 1861 1866 |
of parts, and the definite 1872 |
action of the
surrounding surrounding 1869 1872 | physical 1859 1860 1861 1866 |
conditions. conditions. 1869 1872 | conditions 1859 1860 1861 1866 |
....... 1869 1872 | of 1859 1860 1861 1866 |
....... 1869 1872 | life. 1859 1860 1861 1866 |
There is much difficulty in ascertaining how
largely largely 1869 1872 | much modification 1859 1860 1861 1866 |
our domestic productions have
been modified; been modified; 1869 1872 | undergone; 1859 1860 1861 1866 |
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
....... 1869 1872 | wholly 1859 1860 1861 1866 |
cease cease 1869 1872 | cease; 1859 1860 1861 1866 |
under domestication for a very long period; for under domestication for a very long period; for 1869 |
for 1859 1860 1861 1866 |
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
oldest oldest 1869 1872 | most anciently 1859 1860 1861 1866 |
domesticated productions. |
Man does Man does 1859 1860 1861 1866 1869 | Variability is 1872 |
not actually
produce variability; produce variability; 1859 1860 1861 1866 1869 |
caused by man; 1872 |
he only unintentionally exposes organic beings to new conditions of life, and then nature acts on the
organisation, organisation, 1859 1860 1861 1866 1869 | organisation 1872 |
and causes
variability. variability. 1859 1860 1861 1866 1869 |
it to vary. 1872 |
But man can and does select the variations given to him by nature, and thus
accumulate accumulate 1859 1860 1861 1866 1869 | accumulates 1872 |
them in any desired manner. He thus adapts animals and plants for his own benefit or pleasure. He may do this methodically, or he may do it unconsciously by preserving the individuals most useful
or pleasing to him or pleasing to him 1869 1872 |
to him at the time, 1859 1860 |
to him at the time 1861 |
to him 1866 |
without any
intention intention 1869 1872 | thought 1859 1860 1861 1866 |
of altering the breed. It is certain that he can largely influence the character of a breed by selecting, in each successive generation, individual differences so slight as to be
....... 1861 1866 1869 1872 | quite 1859 1860 |
|