ttle more extensively, because there is added to it the influence of
food, both in regard to its abundance and its quality. Thus the
Elephants of one forest are larger than those of another; their tusks
also grow somewhat longer in places where their food may happen to be
more favorable for the production of the substance of ivory. The same
may take place in regard to the horns of Stags and Rein-deer. Besides,
the species of herbivorous animals, in their wild state, seem more
restrained from migrating and dispersing than the carnivorous species,
being influenced both by climate, and by the kind of nourishment which
they need.

We never see, in a wild state, intermediate productions between the Hare
and the Rabbit, between the Stag and the Doe, or between the Martin and
the Weasel. Human artifice contrives to produce all these intermixtures
of which the various species are susceptible, but which they would never
produce if left to themselves.

The degrees of these variations are proportional to the intensity of the
causes that produce them, namely, the slavery or subjection under which
these animals are to man. They do not proceed far in half-domesticated
species.

In the domesticated herbivorous quadrupeds, which man transports into
all kinds of climates, and subjects to various kinds of management, both
in regard to labour and nourishment, he procures certainly more
considerable variations, but still they are all merely superficial:
greater or less size; longer or shorter horns, or even the want of these
entirely; a hump of fat, larger or smaller, on the shoulder; these form
the chief differences among particular races of the _Bos Taurus_, or
domestic Black Cattle; and these differences continue long in such
breeds as have been transported to great distances from the countries in
which they were originally produced, when proper care is taken to
prevent crossing.

Nature appears also to have guarded against the alterations of species
which might proceed from mixture of breeds, by influencing the various
species of animals with mutual aversion. Hence all the cunning and all
the force that man is able to exert is necessary to accomplish such
unions, even between species that have the nearest resemblance. And when
the mule-breeds that are thus produced by these forced conjunctions
happen to be fruitful, which is seldom the case, this fecundity never
continues beyond a few generations, and would not probably proceed so