The Descent of Man

heads; and such changes are manifestly due,
not to any one pair, but to all the individuals
having been subjected to the same conditions,
aided, perhaps, by the principle of reversion.
The new sub- breeds in such cases are not descended
from any single pair, but from many
individuals which have varied in different degrees,
but in the same general manner; and we
may conclude that the races of man have been
similarly produced, the modifications being
either the direct result of exposure to different
conditions, or the indirect result of some form
of selection. But to this latter subject we shall
presently return.
ON THE EXTINCTION OF THE RACES OF
MAN.
The partial or complete extinction of many races
and sub-races of man is historically known.
Humboldt saw in South America a parrot
which was the sole living creature that could