he principle of selection,
implying separation. Even in the rare instances of sports, with the
hereditary tendency very strongly implanted, crossing must be prevented
with other breeds, or if not prevented the best characterized of the
half-bred offspring must be carefully selected. Where the external
conditions are constantly tending to give some character, a race
possessing this character will be formed with far greater ease by
selecting and breeding together the individuals most affected. In the
case of the endless slight variations produced by the indirect effects
of domestication on the action of the reproductive system, selection is
indispensable to form races; and when carefully applied, wonderfully
numerous and diverse races can be formed. Selection, though so simple in
theory, is and has been important to a degree which can hardly be
overrated. It requires extreme skill, the results of long practice, in
detecting the slightest difference in the forms of animals, and it
implies some distinct object in view; with these requisites and
patience, the breeder has simply to watch for every the smallest
approach to the desired end, to select such individuals and pair them
with the most suitable forms, and so continue with succeeding
generations. In most cases careful selection and the prevention of
accidental crosses will be necessary for several generations, for in new
breeds there is a strong tendency to vary and especially to revert to
ancestral forms: but in every succeeding generation less care will be
requisite for the breed will become truer; until ultimately only an
occasional individual will require to be separated or destroyed.
Horticulturalists in raising seeds regularly practise this, and call it
"roguing," or destroying the "rogues" or false varieties. There is
another and less efficient means of selection amongst animals: namely
repeatedly procuring males with some desirable qualities, and allowing
them and their offspring to breed freely together; and this in the
course of time will affect the whole lot. These principles of selection
have been _methodically_ followed for scarcely a century; but their
high importance is shown by the practical results, and is admitted
in the writings of the most celebrated agriculturalists and
horticulturalists;--I need only name Anderson, Marshall, Bakewell, Coke,
Western, Sebright and Knight.

{198} Selection is here used in the sense of isolation, rather than