The Descent of Man

stripes on the shoulders and even on the spine
frequently disappear, though we cannot explain
the cause. Very few horses, except duncoloured
kinds, have stripes on any part of
their bodies, yet we have good reason to believe
that the aboriginal horse was striped on the
legs and spine, and probably on the shoulders.
(43. The 'Variation of Animals and Plants under
Domestication,' 1868, vol. i. pp. 61-64.) Hence
the disappearance of the spots and stripes in
our adult existing deer, pigs, and tapirs, may be
due to a change in the general colour of their
coats; but whether this change was effected
through sexual or natural selection, or was due
to the direct action of the conditions of life, or
to some other unknown cause, it is impossible
to decide. An observation made by Mr. Sclater
well illustrates our ignorance of the laws which
regulate the appearance and disappearance of
stripes; the species of Asinus which inhabit the
Asiatic continent are destitute of stripes, not
having even the cross shoulder-stripe, whilst