56 THE SHADOW OF THE WORLD’S FUTURE 
square mile, though England and Wales have no less 
than 671 per square mile, has been made. 
What actually does govern the rate of increase are 
factors of the following character, viz.:— 
(1) The force of the reproductive impulse which 
characterises the particular nation or com- 
munity as a whole, but modified by any 
contraceptive influences. 
{ii) Its social traditions as to the proper frequency 
of reproduction, and the constancy of such 
traditions. 
(iif) ‘The known natural resources of the territory 
inhabited, and also the success with which 
they are exploited: both of these are variable 
factors. 
(iv) The political security and the economic stability 
of the territory, and all factors which affect 
these. 
{v) The relative numbers in the community of 
each sex and age, that is, what has been 
called “its constitution according to sex 
and age.” 
(vi) The health of the inhabitants at each age and 
of each sex, and particularly of the females 
of child-bearing age. 
(vii) The characteristic ages of the males and of the 
females, at which marriage takes place, which 
1s also a variable factor. 
So long as these elements, and any other elements 
affecting the reproductive function, remain unchanged, 
the rate of increase will continue uniform. Thus the 
normal law of increase of a population is what is 
known as the compound-interest-law, the interest 
being continually added to the principal. The con- 
tinuity of a particular series of rates of mortality 
according to sex and age has not been mentioned,