Yet, unless it be thoroughly ingrained in the mind, I am convinced that the
whole economy of Nature, with every fact on 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 and beasts of
prey; we do not always bear in mind that, though food may be now
superabundant, it is not so at all seasons of each recurring year."--(p.
62.)

"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 a few 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 to be the slowest breeder of all known animals, and I
have taken some pains to estimate its pro!)able minimum rate of natural
increase; it will be under the mark to assume that it breeds when thirty
years old, and goes on breeding till ninety years old, bringing forth three
pairs of young in this interval; if this be so, at the end of the fifth
century there would be alive fifteen million elephants, descended from the
first pair.

"But we have better evidence on this subject than mere theoretical
calculations, namely, the numerous recorded cases of the astonishingly