branches of trees. It can thus obtain food beyond the reach of the other
Ungulata or hoofed animals inhabiting the same country; and this must be a
great advantage to it during dearths. The Niata cattle in South America
show us how small a difference in structure may make, during such periods,
a great difference in preserving an animal's life. These cattle can browse
as well as others on grass, but from the projection of the lower jaw they
cannot, during the often recurrent droughts, browse on the twigs of trees,
reeds, etc., to which food the common cattle and horses are then driven; so
that at these times the Niatas perish, if not fed by their owners. Before
coming to Mr. Mivart's objections, it may be well to explain once again how
natural selection will act in all ordinary cases. Man has modified some of
his animals, without necessarily having attended to special points of
structure, by simply preserving and breeding from the fleetest individuals,
as with the race-horse and greyhound, or as with the game-cock, by breeding
from the victorious birds. So under nature with the nascent giraffe, the
individuals which were the highest browsers and were able during dearths to
reach even an inch or two above the others, will often have been preserved;
for they will have roamed over the whole country in search of food. That
the individuals of the same species often differ slightly in the relative
lengths of all their parts may be seen in many works of natural history, in
which careful measurements are given. These slight proportional
differences, due to the laws of growth and variation, are not of the
slightest use or importance to most species. But it will have been
otherwise with the nascent giraffe, considering its probable habits of
life; for those individuals which had some one part or several parts of
their bodies rather more elongated than usual, would generally have
survived. These will have intercrossed and left offspring, either
inheriting the same bodily peculiarities, or with a tendency to vary again
in the same manner; while the individuals less favoured in the same
respects will have been the most liable to perish.