suddenly started using such techniques more intensively. Second, the
geographical distribution of easily domesticated species may help explain the
geography of early farming. As Jared Diamond has pointed out, the Fertile
Crescent, where the Natu¿ ans lived, had many species like wheat, which can
be domesticated with only minor changes, while other regions had species
less amenable to domestication.
Third, as foragers migrated around the world, population pressure may have
built up as less land was available for new migrations. Larger populations
might have forced humans to use the knowledge they already had to extract
more energy from a given area, to “intensify” production by introducing
at least some agricultural techniques. But this argument is tricky because
modern foragers often limit population growth (for example, by prolonging
breast-feeding, which limits fertility, or by
more violent means such as killing twins or
allowing the old to die). So overpopulation
should not have been a problem. Fourth, the
Natu¿ ans may help us solve this last riddle,
for their population began to grow fast once
they settled down. This was probably because
sedentary communities, which do not have
to carry the old or the very young, have less
need to limit population size. But why should
foragers have settled down?
The ¿ fth factor, climatic change, may help
solve this puzzle. The last ice age reached its
coldest stage about 20,000 years ago, and then
climates began to get warmer. By 11,500 years
ago, after a 1,500-year cold spell, they had reached temperatures similar to
those of today. During the “interglacial” of the last 10,000 to 11,000 years,
climates were generally warmer, wetter, and more stable than those of the ice
ages. How might these changes have encouraged early forms of agriculture?
Peter Richerson and Robert Boyd have argued that agriculture was simply
impossible during the last ice age because climates were too unstable.
If they are right, it is the stability of interglacial climates that explains
the appearance of sustainable agriculture. Warmer and wetter climates
But for foragers
sedentism can be a
trap, because it may
encourage population
growth, making it
necessary within just
a few generations
to start intensifying
food production.