_Conditions favourable to the production of Variations._
In order that plants and animals may be improved and modified to any
considerable extent, it is of course essential that suitable variations
should occur with tolerable frequency. There seem to be three conditions
which are especially favourable to the production of variations: (1)
That the particular species or variety should be kept in very large
numbers; (2) that it should be spread over a wide area and thus
subjected to a considerable diversity of physical conditions; and (3)
that it should be occasionally crossed with some distinct but closely
allied race. The first of these conditions is perhaps the most
important, the chance of variations of any particular kind being
increased in proportion to the quantity of the original stock and of its
annual offspring. It has been remarked that only those breeders who keep
large flocks can effect much improvement; and it is for the same reason
that pigeons and fowls, which can be so easily and rapidly increased,
and which have been kept in such large numbers by so great a number of
persons, have produced such strange and numerous varieties.
Pages:
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183