This Fleeting World

Beginnings: The Era of Foragers 15
changes, the accumulation of new knowledge and skills, and minor adjustments
in lifeways.
As humans spread over more and more of the Earth, human numbers
surely increased. Estimates of populations during the era of foragers are
based largely on guesswork, though genetic evidence suggests that human
numbers shrank to just a few thousands about 70,000 years ago. One of
the more influential recent estimates by demographer Massimo Livi-Bacci
suggests that thirty thousand years ago there were a few hundred thousand
humans, but by ten thousand years ago there may have been as many as 6
million. If we assume that approximately 500,000 humans existed thirty
thousand years ago, this implies a growth rate between thirty thousand
and ten thousand years ago of less than 0.01 percent per annum, which
implies that human populations were doubling approximately every eight
thousand to nine thousand years. This rate of growth can be compared
with an average doubling time of about fourteen hundred years during the
agrarian era and eighty-five years during the modern era.
Technological Change
Rates of growth during the era of foragers are striking in two contradictory
ways. Insofar as population growth is an indirect sign of technological innovation,
it provides evidence for innovation throughout the era and some
signs that innovation was accelerating. However, by comparison with later
Thought Experiment
What does the “doubling time” of a population really mean? Consider
the population growth rate of 0.01 percent per year—which is
the assumption made for the populations of thirty thousand years
ago. To understand what doubling time at this growth rate would
mean, imagine this scenario: There is a village of eleven people, just
enough for a soccer team. But they would like to play another team,
and they don’t know of any other humans. At this rate of reproduction
how long would they have to wait before there are twenty-two
people around? Answer: nine thousand years. (More if they think
there are going to have to be substitutes!)