Rutimeyer found differences in the size and form of the skull in the
earliest known domesticated horses (2/16. 'Kenntniss der fossilen Pferde'
1863 s. 131.), we ought not to feel sure that all our breeds are descended
from a single species. The savages of North and South America easily
reclaim the feral horses, so that there is no improbability in savages in
various quarters of the world having domesticated more than one native
species or natural race. M. Sanson (2/17. 'Comptes rendus' 1866 page 485
and 'Journal de l'Anat. et de la Phys.' Mai 1868.) thinks that he has
proved that two distinct species have been domesticated, one in the East,
and one in North Africa; and that these differed in the number of their
lumbar vertebra and in various other parts; but M. Sanson seems to believe
that osteological characters are subject to very little variation, which is
certainly a mistake. At present no aboriginal or truly wild horse is
positively known to exist; for it is commonly believed that the wild horses
of the East are escaped domestic animals. (2/18. Mr. W.C.L. Martin, 'The
Horse' 1845 page 34, in arguing against the belief that the wild Eastern
horses are merely feral, has remarked on the improbability of man in
ancient times having extirpated a species in a region where it can now
exist in numbers.) If therefore our domestic breeds are descended from
several species or natural races, all have become extinct in the wild
state.

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 horses are considerably modified. There can be no doubt that
horses become greatly reduced in size and altered in appearance by living