CLIMATE AND HUMAN HISTORY
OF late years a determined attempt has been made to rewrite
history in economic terms. But this does not go deep enough.
Man's thought and social life ate built on his economic life; but this,
in its turn, rests on biological foundations. Climate and gelogy be-
tween them decide where the raw materials of human industry are to
be found, where manufactures can be established; and climate
decides where the main springs of human energy shall be released.
Changes of climate cause migrations, and migrations bring about not
only wars, but the fertilizing intermingling of ideas necessary for rapid
advance in civilization.
Disease and hygiene play as important a part; half the population
of the world is permanently below par on account of animal parasites
such as the hookworm and the microscopic malaria germ; and disease
may bring about the rise or fall of empires. Nor has selection ever
ceased its rigorous activity. To pass from one mode of life to another
is not a simple affair for a people; a settled agricultural life demands
a very different temperament from hunting, and the hereditary
make-up of the race must be altered if a people is to pass successfully
from one to the other. Most migrations, too, arc selective; to take
but one example, the Puritans who first colonized Massachusetts did
not bring with them a random sample of the genes responsible for the
qualities of the English people. But selection is altered and reduced.
The better care of the young and the elaboration of social life allow
all sorts of variations, which otherwise would be snuffed out, to survive
and often to play an important part in progress. Knowledge for
knowledge's sake is out of place in a primitive hunting tribe.
When the world's climatic belts are sharply marked (as they are
to-day, in contrast to epochs like the late Eocene, when climate was
much more uniform), the temperate zones, flanked poleward by the
subarctic and the arctic, are separated from the tropics by two dry
belts, along which all the world's great deserts are strung. The only
zones where vegetation is abundant and man can easily flourish arc*,
the temperate and the tropical. But the temperate has another ad-
vantage. It contains the belt of cyclonic storms—in other words, of
rapid and frequent changes of weather. And this type of climate, as
Ellsworth Huntington has shown, is the one most stimulating to
human energy and achievement.
We are still so ignorant of the earliest steps in the evolution of man