most fertile source of the variation
in domesticated animals. <In the _Origin_, Ed. i. p. 20 the author
says that "the possibility of making distinct races by crossing has
been greatly exaggerated."> If freely allowed, the characters of
pure parents will be lost, number of races thus <illegible> but
differences <?> besides the <illegible>. But if varieties differing
in very slight respects be allowed to cross, such small variation
will be destroyed, at least to our senses,--a variation [clearly]
just to be distinguished by long legs will have offspring not to be
so distinguished. Free crossing great agent in producing uniformity
in any breed. Introduce tendency to revert to parent form."

{42} The swamping effect of intercrossing is referred to in the
_Origin_, Ed. i. p. 103, vi. p. 126.

{43} A discussion on the intercrossing of hermaphrodites in
relation to Knight's views occurs in the _Origin_, Ed. i. p. 96,
vi. p. 119. The parallelism between crossing and changed conditions
is briefly given in the _Origin_, Ed. i. p. 267, vi. p. 391, and
was finally investigated in _The Effects of Cross and
Self-Fertilisation in the Vegetable Kingdom_, 1876.

Therefore if in any country or district all animals of one species be
allowed freely to cross, any small tendency in them to vary will be
constantly counteracted. Secondly reversion to parent form--analogue of
_vis medicatrix_{44}. But if man selects, then new races rapidly
formed,--of late years systematically followed,--in most ancient times
often practically followed{45}. By such selection make race-horse,
dray-horse--one cow good for tallow, another for eating &c.--one plant's
good lay <illegible> in leaves another in fruit &c. &c.: the same plant
to supply his wants at different times of year. By former means animals
become adapted, as a direct effect to a cause, to external conditions,
as size of body to amount of food. By this latter means they may also be
so adapted, but further they may be adapted to ends and pursuits, which
by no possibility can affect growth, as existence of tallow-chandler
cannot tend to make fat. In such selected races, if not removed to new
conditions, and <if> preserved from all cross, after several generations
become very true, like each other and not varying. But man{46} selects
only <?> what is useful and curious--has bad judgment, is
capricious,--grud