One specific instance of this doubling process is sufficient to prove
the _power of increase_ possessed by a community, and the instance of
the American Colonies, cited by Malthus, has never been denied.

A doubling of population in 25 years was thus looked upon by Malthus as
the normal increase, under the most favourable conditions; but the
checks to increase, vice, misery, and moral restraint are operative in
varying degrees of intensity in civilized communities, and these may
limit the doubling to once in 50, or once in 100 years, stop it
altogether, or even sweep a nation from the face of the earth.

The natural increase among the lower animals is limited by misery only,
in savage man by vice and misery only, and in civilized man by misery,
vice, and moral restraint.

Misery is caused by poverty, or the need of food or clothing, and is
thus proportionate to the means of subsistence. As the means of
subsistence are abundant, misery will be less, the death-rate lower,
and _caeteris paribus_ the birth-rate higher. The increase will be
directly proportional to the means of subsistence.

Vice as a check to increase, is common to civilized and savage man, and
limits population by artificial checks to conception, abortion,
infanticide, disease, and war. The third check, moral restraint, is
peculiar to civilized man, and in the writings of Malthus, consists in
restraint from marriage or simply delayed marriage.

Bonar says (Malthus and his Work, p. 53), "Moral restraint in the pages
of Malthus, simply means continence which is abstinence from marriage