I am fully convinced that species are not
immutable; but that those belonging to what are called the same genera are
lineal descendants of some other and generally extinct species, in the same
manner as the acknowledged varieties of any one species are the descendants
of that species. Furthermore, I am convinced that natural selection has
been the most important, but not the exclusive, means of modification.
CHAPTER I.
VARIATION UNDER DOMESTICATION.
Causes of Variability -- Effects of Habit and the use and 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 -- Principles of Selection, anciently followed,
their Effects -- Methodical and Unconscious Selection -- Unknown Origin of
our Domestic Productions -- Circumstances favourable to Man's power of
Selection.
CAUSES OF VARIABILITY.
When we compare the individuals of the same variety or sub-variety of our
older cultivated plants and animals, one of the first points which strikes
us is, that they generally differ more from each other than do the
individuals of any one species or variety in a state of nature. And if 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 great
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 had been exposed under nature.
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