long neck or proboscis. To reach the foliage at a considerable height
(without climbing, for which hoofed animals are singularly ill-constructed)
implies greatly increased bulk of body; and we know that some areas support
singularly few large quadrupeds, for instance South America, though it is
so luxuriant, while South Africa abounds with them to an unparalleled
degree. Why this should be so we do not know; nor why the later tertiary
periods should have been much more favourable for their existence than the
present time. Whatever the causes may have been, we can see that certain
districts and times would have been much more favourable than others for
the development of so large a quadruped as the giraffe.

In order that an animal should acquire some structure specially and largely
developed, it is almost indispensable that several other parts should be
modified and coadapted. Although every part of the body varies slightly,
it does not follow that the necessary parts should always vary in the right
direction and to the right degree. With the different species of our
domesticated animals we know that the parts vary in a different manner and
degree, and that some species are much more variable than others. Even if
the fitting variations did arise, it does not follow that natural selection
would be able to act on them and produce a structure which apparently would
be beneficial to the species. For instance, if the number of individuals
existing in a country is determined chiefly through destruction by beasts
of prey--by external or internal parasites, etc.--as seems often to be the
case, then natural selection will be able to do little, or will be greatly
retarded, in modifying any particular structure for obtaining food.
Lastly, natural selection is a slow process, and the same favourable
conditions must long endure in order that any marked effect should thus be
produced. Except by assigning such general and vague reasons, we cannot
explain why, in many quarters of the world, hoofed quadrupeds have not
acquired much elongated necks or other means for browsing on the higher