good, to fit them for infinitely {413}
diversified conditions of life, to avoid enemies of all kinds, and to
struggle against a host of competitors. Hence, under such complex
conditions, it would often happen that modifications of the most varied
kinds, in important as well as in unimportant parts, would be advantageous
or even necessary; and they would slowly but surely be acquired through the
survival of the fittest. Various indirect modifications would likewise
arise through the law of correlated variation.

Domestic breeds often have an abnormal or semi-monstrous character, as the
Italian greyhound, bulldog, Blenheim spaniel, and bloodhound amongst
dogs,--some breeds of cattle and pigs, several breeds of the fowl, and the
chief breeds of the pigeon. The differences between such abnormal breeds
occur in parts which in closely-allied natural species differ but slightly
or not at all. This may be accounted for by man's often selecting,
especially at first, conspicuous and semi-monstrous deviations of
structure. We should, however, be cautious in deciding what deviations
ought to be called monstrous: there can hardly be a doubt that, if the
brush of horse-like hair on the breast of the turkey-cock had first
appeared on the domesticated bird, it would have been considered a
monstrosity; the great plume of feathers on the head of the Polish cock has
been thus designated, though plumes are common with many kinds of birds; we
might call the wattle or corrugated skin round the base of the beak of the
English carrier-pigeon a monstrosity, but we do not thus speak of the
globular fleshy excrescence at the base of the beak of the male _Carpophaga
oceanica_.

Some authors have drawn a wide distinction between artificial and natural
breeds; although in extreme cases the distinction is plain, in many other
cases an arbitrary line has to be drawn. The difference depends chiefly on
the kind of selection which has been applied. Artificial breeds are those
which have been intentionally improved by man; they frequently have an
unnatural appearance, and are especially liable to loss of excellence
through reversion and continued variability. The so-called natural breeds,
on the other hand, are those which are now found in semi-civilised
countries, and which formerly inhabited separate districts in nearly all
the European kingdoms. They have been rarely acted on by man's {414}
intentional selection; more frequently, it is probable, by unc