mistletoe is disseminated by birds, its
existence depends on them; and it may metaphorically be said to struggle
with other fruit-bearing plants, in tempting the birds to devour and
thus disseminate its seeds. In these several senses, which pass into
each other, I use for convenience sake the general term of Struggle for
Existence.

GEOMETRICAL RATIO OF INCREASE.

A struggle for existence inevitably follows from the high rate at which
all organic beings tend to increase. Every being, which during its
natural lifetime produces several eggs or seeds, must suffer destruction
during some period of its life, and during some season or occasional
year, otherwise, on the principle of geometrical increase, its numbers
would quickly become so inordinately great that no country could support
the product. Hence, as more individuals are produced than can possibly
survive, there must in every case be a struggle for existence, either
one individual with another of the same species, or with the individuals
of distinct species, or with the physical conditions of life. It is the
doctrine of Malthus applied with manifold force to the whole animal and
vegetable kingdoms; for in this case there can be no artificial increase
of food, and no prudential restraint from marriage. Although some
species may be now increasing, more or less rapidly, in numbers, all
cannot do so, for the world would not hold them.

There is no exception to the rule that every organic being naturally
increases at so high a rate, that, if not destroyed, the earth would
soon be covered by the progeny of a single pair. Even slow-breeding
man has doubled in twenty-five years, and at this rate, in less than
a thousand years, there would literally not be standing room for his
progeny. Linnaeus has calculated that if an annual plant produced only
two seeds--and there is no plant so unproductive as this--and their
seedlings next year produced two, and so on, then in twenty years there
would be a million plants. The elephant is reckoned the slowest breeder
of all known animals, and I have taken some pains to estimate its
probable minimum rate of natural increase; it will be safest to assume
that it begins breeding when thirty years old, and goes on breeding
till ninety years old, bringing forth six young in the interval, and
surviving till one hundred years old; if this be so, after a period of
from 740 to 750 years there would be nearly nineteen million elephants
alive des