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.