82 THE SHADOW OF THE WORLD’S FUTURE 
to migration, For the transfer of people with unsuit- 
able ideals into the midst of others of higher status 
would be a most unsatisfactory migration. We are 
involved thus in considering aspects of the question 
which at first sight might appear quite irrelevant. 
To consider for a moment the simple matter of the 
degree of luxury to which a people has become 
accustomed, the complication of its mode of living, 
and the consequential effects of these, it is easy to 
see how these things operate. Increase of population 
depends mainly upon the frequency of marriage, upon 
its taking place early, upon its fertility, and upon the 
age at which that fertility eventuates. A thrifty 
self-denying people reaches the economic possibility 
of marriage earlier, while luxuriousness, inordinate 
love of wealth, marriage with persons of disparate 
age,! etc., all tend to reduce both the frequency of 
marriage and its fertility when it actually occurs. 
The economic load borne by a fertile married people 
is greater than that which is borne by those of less 
fertility. Thus personal qualities are factors of very 
high importance, a fact well illustrated by history. 
The growth of the population of the United States of 
America reveals this in a very remarkable way. As 
was mentioned earlier, from 1790 to 1860 the rate of 
increase was sensibly uniform, and was no less than a 
little over 3 per cent. per annum. And since 3 per 
cent. per annum means the doubling of a population 
in 23°45 years, the attainment of such a rate involves 
the exercise of sterling physical and moral qualities. 
These in their turn have an influence on migration: 
see the table hereinbefore, Chapter V. (page 58). 
Although physical and other complexities in the 
distribution of the human race over the earth’s surface 
+ It has been shown that fecundity depends upon the ages of both 
husband and wife. See Mathematical Theory of Population, sec. 
Di-isogeny, pp. 349-69, G. H. Knibbs