HOW POPULATION INCREASES 57
because it is virtually included in factor (v) above: it
of course affects the rate of increase.
An examination of these factors discloses at once
that they are liable to be influenced in many ways.
For example, in regard to (i), the effectiveness of the
reproductive impulse is greatly influenced by social
traditions and religious beliefs, etc. It is also limited
by the standard-of-living assumed to be necessary,
and by the common refusal to subordinate all the more
immediate promptings involving expenditure, to the
more remote issues of the development of families.
In so far as the future is sacrified to the present, the
possibility of population is liable to be hindered.
Matters of this kind are, of course, all reflected in
the social outlook of a people. For example, many
French people in the near past regarded large families
with disfavour, and the economic situation, on a
limited view at least, and perhaps actually, appeared
to justify the attitude. People who defer marriage,
however, until every life-vicissitude appears to be amply
provided for, create a tradition which tends greatly
to limit the rapidity of increase in population.
Favourable economic conditions tend, of course, to
lessen the forces opposing marriage. A study of the
correlation of the marriage, the birth, and the increase
rates, with the production per head, for example, in
Australia, from 1860 to 1923, affords unmistakable
evidence of the economic reactions on the rate of
increase.!
The history of the United States of America supplies
perhaps one of the best possible examples of the effect
of social changes on the rate of population-increase.
From 179o to 1860 there was nearly a constant rate
of increase of about 3 per cent. per annum; see the
table previously given. It has been pointed out by
1 See the Australian Commonwealth Year-Books, and also Mezron,
Vol. V, No. 3, 1st Dec. 1925, article by G. H. Knibbs.