It is a very common but
mistaken idea that this improvement is due to crossing and feeding in
the case of animals, and to improved cultivation in the case of plants.
Crossing is occasionally used in order to obtain a combination of
qualities found in two distinct breeds, and also because it is found to
increase the constitutional vigour; but every breed possessing any
exceptional quality is the result of the selection of variations
occurring year after year and accumulated in the manner just described.
Purity of breed, with repeated selection of the best varieties of that
breed, is the foundation of all improvement in our domestic animals and
cultivated plants.
_Proofs of the Generality of Variation._
Another very common error is, that variation is the exception, and
rather a rare exception, and that it occurs only in one direction at a
time--that is, that only one or two of the numerous possible modes of
variation occur at the same time. The experience of breeders and
cultivators, however, proves that variation is the rule instead of the
exception, and that it occurs, more or less, in almost every direction.
Pages:
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158