Dun-coloured ponies are not rare in the mountainous
parts of Devonshire, Wales, and Scotland, where the aboriginal breed would
have had the best chance of being preserved. In South America in the time
of Azara, when the horse had been feral for about 250 years, 90 out of 100
horses were "bai-chatains," and the remaining ten were "zains," and not
more than one in 2000 {61} black. Zain is generally translated as dark
without any white; but as Azara speaks of mules being "zain-clair," I
suspect that zain must have meant dun-coloured. In some parts of the world
feral horses show a strong tendency to become roans.[137]

In the following chapters on the Pigeon we shall see that in pure breeds of
various colours, when a blue bird is occasionally produced, certain black
marks invariably appear on the wings and tail; so again, when variously
coloured breeds are crossed, blue birds with the same black marks are
frequently produced. We shall further see that these facts are explained
by, and afford strong evidence in favour of, the view that all the breeds
are descended from the rock-pigeon, or _Columba livia_, which is thus
coloured and marked. But the appearance of the stripes on the various
breeds of the horse, when of a dun-colour, does not afford nearly such good
evidence of their descent from a single primitive stock as in the case of
the pigeon; because no certainly wild horse is known as a standard of
comparison; because the stripes when they do appear are variable in
character; because there is far from sufficient evidence of the appearance
of the stripes from the crossing of distinct breeds; and lastly, because
all the species of the genus Equus have the spinal stripe, and several have
shoulder and leg stripes. Nevertheless the similarity in the most distinct
breeds in their general range of colour, in their dappling, and in the
occasional appearance, especially in duns, of leg-stripes and of double or
triple shoulder-stripes, taken together, indicate the probability of the
descent of all the existing races from a single, dun-coloured, more or less
striped, primitive stock, to which our horses still occasionally revert.

{62}

THE ASS.

Four species of Asses, besides three of zebras, have been described by
naturalists; but there can now be little doubt that our domesticated animal
is descended from one alone, namely, the _Asinus taeniopus_ of
Abyssinia.[138] The ass is sometimes advanced as an instance of an animal
do