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