In a state of nature almost every full-grown plant annually produces seed,
and among animals there are very few which do not annually pair. Hence we
may confidently assert that all plants and animals are tending to increase
at a geometrical ratio--that all would rapidly stock every station in which
they could any how exist, and that this geometrical tendency to increase
must be checked by destruction at some period of life. Our familiarity
with the larger domestic animals tends, I think, to mislead us; we see no
great destruction falling on them, and we do not keep in mind that
thousands are annually slaughtered for food, and that in a state of nature
an equal number would have somehow to be disposed of.

The only difference between organisms which annually produce eggs or seeds
by the thousand, and those which produce extremely few, is, that the slow
breeders would require a few more years to people, under favourable
conditions, a whole district, let it be ever so large. The condor lays a
couple of eggs and the ostrich a score, and yet in the same country the
condor may be the more numerous of the two. The Fulmar petrel lays but one
egg, yet it is believed to be the most numerous bird in the world. One fly
deposits hundreds of eggs, and another, like the hippobosca, a single one.
But this difference does not determine how many individuals of the two
species can be supported in a district. A large number of eggs is of some
importance to those species which depend on a fluctuating amount of food,
for it allows them rapidly to increase in number. But the real importance
of a large number of eggs or seeds is to make up for much destruction at
some period of life; and this period in the great majority of cases is an
early one. If an animal can in any way protect its own eggs or young, a
small number may be produced, and yet the average stock be fully kept up;
but if many eggs or young are destroyed, many must be produced or the
species will become extinct. It would suffice to keep up the full number