exercise it in any peculiar manner, at least not during every
generation. He seldom allows the most vigorous males to struggle for
themselves and propagate, but picks out such as he possesses, or such as
he prefers, and not necessarily those best adapted to the existing
conditions. Every agriculturalist and breeder knows how difficult it is
to prevent an occasional cross with another breed. He often grudges to
destroy an individual which departs considerably from the required type.
He often begins his selection by a form or sport considerably departing
from the parent form. Very differently does the natural law of selection
act; the varieties selected differ only slightly from the parent
forms{241}; the conditions are constant for long periods and change
slowly; rarely can there be a cross; the selection is rigid and
unfailing, and continued through many generations; a selection can
_never be made_ without the form be _better_ adapted to the conditions
than the parent form; the selecting power goes on without caprice, and
steadily for thousands of years adapting the form to these conditions.
The selecting power is not deceived by external appearances, it tries
the being during its whole life; and if less well <?> adapted than its
_congeners_, without fail it is destroyed; every part of its structure
is thus scrutinised and proved good towards the place in nature which it
occupies.

{238} In the _Origin_ the author would here have used the word
_variety_.

{239} The whole of p. 94 and 15 lines of p. 95 are, in the MS.,
marked through in pencil with vertical lines, beginning at "Races
produced, &c." and ending with "to these conditions."

{240} See _Origin_, Ed. i. p. 83, vi. p. 102.

{241} In the present Essay there is some evidence that the author
attributed more to _sports_ than was afterwards the case: but the
above passage points the other way. It must always be remembered
that many of the minute differences, now considered small
mutations, are the small variations on which Darwin conceived
selection to act.

We have every reason to believe that in proportion to the number of
generations that a domestic race is kept free from crosses, and to the
care employed in continued steady selection with one end in view, and to
the care in not placing the variety in conditions unsuited to it; in
such proportion does the new race become "true" or subject to littl