and that there has consequently been less destruction of the old and
young, and that nearly all the young have been enabled to breed. In
such cases the geometrical ratio of increase, the result of which never
fails to be surprising, simply explains the extraordinarily rapid
increase and wide diffusion of naturalised productions in their new
homes.
In a state of nature almost every plant produces seed, and amongst
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 most rapidly stock every station
in which they could any how exist, and that the 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 forget 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 rapidly 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 of a tree, which lived on an average for a thousand years, if a
single seed were produced once in a thousand years, supposing that this
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