74 THE SHADOW OF THE WORLD’S FUTURE 
that even the insect-world can menace him. Observa- 
tion has shown that this menace can develop upon a 
colossal scale. It is too soon to say whether he will be 
able to meet this source of trouble or will be overcome 
thereby. That is the problem for the economic 
entomologist. Already situations of difficulty have 
occasionally developed from insect invasions. Will a 
redistribution of densities of populations in any way 
alleviate this? If it will, then the migration question 
takes a place of still greater importance. 
As already indicated, the magnitude of recent rates 
of population-increase has been brought about by 
Man’s inventive powers and by his accessions of 
knowledge. His ability to utilise the great resources 
of Nature, often previously undreamt of, has been 
enhanced in a very extraordinary way. He has learnt, 
to some extent, to avoid the incidence of her evil 
inflictions. To a remarkable extent this has been 
brought about by his migrations from one region to 
another. He has learnt of the possibilities of new 
advances and of new dangers, and in facing the 
menaces that characterised the regions to which he 
wandered he has acquired knowledge of general value 
for human increase. En passant we may remark that 
such facts as he has learnt by these experiences show 
us that the exact dates at which we shall reach given 
population-numbers cannot be predicted with any 
precision. 
One aspect of the migration question, which informs 
us of its great importance at the present time, is that 
certain consequences arise from population-expansions 
themselves. It has already been noted that some 
agricultural countries grow more than is needed for 
their own food-supplies. Such a condition immedi- 
ately admits of other countries expanding industrially, 
increasing their numbers and their political power. 
Increases of material wealth and man-power in the case