o
believes that they have descended from no less than five primitive and
differently coloured stocks.[112] But as several species and varieties of
the horse existed[113] during the later tertiary periods, and as Ruetimeyer
found differences in the size and form of the skull in the earliest known
domesticated horses,[114] we ought not to feel sure that all our breeds
have descended from a single species. As we see that the savages of North
and South America easily reclaim the feral horses, there is no
improbability in savages in various quarters of the world having
domesticated more than one native species or natural race. No aboriginal or
truly wild horse is positively known now to exist; for it is thought by
some authors that the wild horses of the East are escaped domestic
animals.[115] If our domestic breeds have descended from several {52}
species or natural races, these apparently have all become extinct in the
wild state. With our present knowledge, the common view that all have
descended from a single species is, perhaps, the most probable.

With respect to the causes of the modifications which horses have
undergone, the conditions of life seem to produce a considerable direct
effect. Mr. D. Forbes, who has had excellent opportunities of comparing the
horses of Spain with those of South America, informs me that the horses of
Chile, which have lived under nearly the same conditions as their
progenitors in Andalusia, remain unaltered, whilst the Pampas horses and
the Puno ponies are considerably modified. There can be no doubt that
horses become greatly reduced in size and altered in appearance by living
on mountains and islands; and this apparently is due to want of nutritious
or varied food. Every one knows how small and rugged the ponies are on the
Northern islands and on the mountains of Europe. Corsica and Sardinia have
their native ponies; and there were,[116] or still are, on some islands on
the coast of Virginia, ponies like those of the Shetland Islands, which are
believed to have originated through exposure to unfavourable conditions.
The Puno ponies, which inhabit the lofty regions of the Cordillera, are, as
I hear from Mr. D. Forbes, strange little creatures, very unlike their
Spanish progenitors. Further south, in the Falkland Islands, the offspring
of the horses imported in 1764 have already so much deteriorated in
size[117] and strength that they are unfitted for catching wild cattle with
the lasso; s