| → Habit and the use or disuse of Parts— Correlated Variation— 1872 |
| Habit— Correlation of Growth— 1859 1860 1861 1866 |
| Habit— Correlated Variation— 1869 |
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CHAPTER I. |
| VARIATION UNDER DOMESTICATION. |
| Causes of Variability— Effects of
→Habit and the use or disuse of Parts— Correlated Variation—
Inheritance— Character of Domestic Varieties— Difficulty of distinguishing between Varieties and Species— Origin of Domestic Varieties from one or more Species— Domestic Pigeons, their Differences and Origin—
of
anciently followed,
Effects— Methodical and Unconscious Selection— Unknown Origin of our Domestic Productions— Circumstances favourable to Man's power of Selection. |
|
Causes
of
Variability.
|
| WHEN we
the individuals of the same variety or sub-variety of our older cultivated plants and animals, one of the first points which strikes
is, that they generally differ
from each
do the individuals of any one species or variety in a state of nature.
we reflect on the vast diversity of the plants and animals which have been cultivated, and which have varied during all ages under the most different climates and treatment,
we are driven to conclude that this
variability is
due to our domestic productions having been raised under conditions of life not so uniform as, and somewhat different from, those to which the parent-species
been exposed under nature. There
also,
some probability in the view propounded by Andrew Knight, that this variability may be partly connected with excess of food. It seems
clear that organic beings must be exposed during several generations to
new conditions
to cause any
amount of variation; and
when the organisation has once begun to vary, it generally
for many generations. No case is on record of a variable
ceasing to
under cultivation. Our oldest cultivated plants, such as wheat, still
yield new varieties: our oldest domesticated animals are still capable of rapid improvement or modification. |
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| As far as I am able to judge, after long attending to the subject, the conditions of life appear to act in two ways, — directly on the whole organisation or on certain parts alone, and indirectly by affecting the reproductive system. With respect to the direct
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