The Descent of Man

to be used in fighting, for stallions bite with
their incisors, and do not open their mouths
wide like camels and guanacoes. Whenever the
adult male possesses canines, now inefficient,
whilst the female has either none or mere rudiments,
we may conclude that the early male
progenitor of the species was provided with
efficient canines, which have been partially
transferred to the females. The reduction of
these teeth in the males seems to have followed
from some change in their manner of fighting,
often (but not in the horse) caused by the development
of new weapons.
Tusks and horns are manifestly of high importance
to their possessors, for their development
consumes much organised matter. A single
tusk of the Asiatic elephant—one of the extinct
woolly species—and of the African elephant,
have been known to weigh respectively 150,
160, and 180 pounds; and even greater weights
have been given by some authors. (33. Emerson