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All Spacer Home > Key Themes > One  Key Theme 1: Patterns of
Population  This theme comes first because the number of men and
women in the world, the distribution of populations around the
globe, and the migration patterns of people from one region to
another have always had a large effect on all other types of
change. The study of population size, density, and distribution
is called demography.  One hundred thousand years ago there may
have been fewer than a million human beings on the planet,
indeed as few as 10,000. Today there are more than six billion.
Compared to other large animals, humans have multiplied at an
astounding rate in those 100 millennia. When children of today
are thirty-something in 2025, they should expect to share the
earth with about 8.5 billion people. From 10,000 years ago to
1750 CE, population world-wide increased on average by about
67,000 people a year. By th