hich strikingly resemble each
other, and they fill nearly the same end in the economy of the
farm-yard; but although the swede so much more resembles a turnip than
its presumed parent the field cabbage, no one thinks of putting it out
of the cabbages into the turnips. Thus the greyhound and racehorse,
having been selected and trained for extreme fleetness for short
distances, present an analogical resemblance of the same kind, but less
striking as that between the little otter (Marsupial) of Guiana and the
common otter; though these two otters are really less related than <are>
the horse and dog. We are even cautioned by authors treating on
varieties, to follow the _natural_ in contradistinction of an artificial
system and not, for instance, to class two varieties of the
pine-apple{445} near each other, because their fruits accidentally
resemble each other closely (though the fruit may be called _the final
end_ of this plant in the economy of its world, the hothouse), but to
judge from the general resemblance of the entire plants. Lastly,
varieties often become extinct; sometimes from unexplained causes,
sometimes from accident, but more often from the production of more
useful varieties, and the less useful ones being destroyed or bred out.

{442} In a corresponding passage in the _Origin_, Ed. i. p. 423,
vi. p. 579, the author makes use of his knowledge of pigeons. The
pseudo-genera among dogs are discussed in _Var. under Dom._, Ed.
ii. vol. I. p. 38.

{443} _Origin_, Ed. i. pp. 419, 427, vi. pp. 575, 582.

{444} _Origin_, Ed. i. pp. 423, 427, vi. pp. 579, 583.

{445} _Origin_, Ed. i. p. 423, vi. p. 579.

I think it cannot be doubted that the main cause of all the varieties
which have descended from the aboriginal dog or dogs, or from the
aboriginal wild cabbage, not being equally like or unlike--but on the
contrary, obviously falling into groups and sub-groups--must in chief
part be attributed to different degrees of true relationship; for
instance, that the different kinds of blood-hound have descended from
one stock, whilst the harriers have descended from another stock, and
that both these have descended from a different stock from that which
has been the parent of the several kinds of greyhound. We often hear of
a florist having some choice variety and breeding from it a whole group
of sub-varieties more or less characterised by the peculiarities of the
parent. The case of