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a few 1859 1860 1861 1866 1869
less than a 1872

under the mark 1859 1860 1861 1866
safest 1869 1872

three pair of 1859 1860 1861 1866 1869
six 1872

if 1859 1860 1861 1866 1869
and surviving till one hundred years old; if 1872

at the end of the fifth century 1859 1860 1861 1866 1869
after a period of from 740 to 750 years 1872

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,
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
standing room
for his progeny. Linnæus has calculated that if an annual plant produced only two
seeds—and
seeds—
and
and
there is no plant
nearly so
so
unproductive as
this—and
this—
and
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
to be
the slowest breeder of all known animals, and I have taken some pains to estimate its probable minimum rate of natural
increase;
increase:
it will be under the mark to assume that it
begins breeding
breeds
when thirty years old, and goes on breeding till ninety years old, bringing forth three pair of young in
the
this
interval,
interval;
if this be so, at the end of the fifth century there would be
nearly nineteen
alive fifteen
million
elephants
elephants,
alive, descended
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 rapid increase of various animals in a state of nature, when circumstances have been favourable to them during two or three following seasons. Still more striking is the evidence from our domestic animals of many kinds which have run wild in several parts of the
world;
world:
if the statements of the rate of increase of slow-breeding cattle and horses in
South America,
South-America,
and latterly in Australia, had not been well authenticated, they would have been
quite
quite
incredible. So it is with
plants;
plants:
cases could be given of introduced plants which have become common throughout whole islands in a period of less than ten years. Several