gible answer is, that their supply of food is
more precarious. It appears evident, therefore, that so long as a
country remains physically unchanged, the numbers of its animal
population cannot materially increase. If one species does so, some
others requiring the same kind of food must diminish in proportion. The
numbers that die annually must be immense; and as the individual
existence of each animal depends upon itself, those that die must be the
weakest--the very young, the aged, and the diseased,--while those that
prolong their existence can only be the most perfect in health and
vigour--those who are best able to obtain food regularly, and avoid
their numerous enemies. It is, as we commenced by remarking, "a struggle
for existence," in which the weakest and least perfectly organized must
always succumb.

Now it is clear that what takes place among the individuals of a species
must also occur among the several allied species of a group,--viz. that
those which are best adapted to obtain a regular supply of food, and to
defend themselves against the attacks of their enemies and the
vicissitudes of the seasons, must necessarily obtain and preserve a
superiority in population; while those species which from some defect of
power or organization are the least capable of counteracting the
vicissitudes of food, supply, &c., must diminish in numbers, and, in
extreme cases, become altogether extinct. Between these extremes the
species will present various degrees of capacity for ensuring the means
of preserving life; and it is thus we account for the abundance or
rarity of species. Our ignorance will generally prevent us from
accurately tracing the effects to their causes; but could we become
perfectly acquainted with the organization and habits of the various
species of animals, and could we measure the capacity of each for
performing the different acts necessary to its safety and existence
under all the varying circumstances by which it is surrounded, we might
be able even to calculate the proportionate abundance of individuals
which is the necessary result.

If now we have succeeded in establishing these two points--1st, _that
the animal population of a country is generally stationary, being kept
down by a periodical deficiency of food, and other checks_; and, 2nd,
_that the comparative abundance or scarcity of the individuals of the
several species is entirely due to their organization and resulting
habits, which, rend