All organic beings are exposed to severe competition. Nothing is easier
than to admit in words the truth of the universal struggle for life, or
more difficult--at least, I have found it so--than constantly to bear
this conclusion in mind. Yet, unless it be thoroughly engrained in the
mind, the whole economy of Nature, with every fact of distribution,
rarity, abundance, extinction, and variation, will be dimly seen or
quite misunderstood. We behold the face of Nature bright with gladness;
we often see superabundance of food. We do not see, or we forget, that
the birds which are idly singing round us mostly live on insects or
seeds, and are thus constantly destroying life; or we forget how largely
these songsters, or their eggs, or their nestlings, are destroyed by
birds or beasts of prey. We do not always bear in mind that, though food
may be superabundant, it is not so at all seasons of each recurring
year.

A struggle for existence, the term being used in a large, general, and
metaphorical sense, 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