Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

vitamin D needed to make healthy bones. As our ancestors spread around
the globe, these opposing pressures colored the skin of people in different
regions. The dominant need for UV protection favored dark skin in the
tropics; the need for vitamin D favored lighter skin in the northern
latitudes.
Technological innovation played a key role in the spread and adaptation
of people to new environments. Roughly 30,000 years ago, immediately
before the last glaciation, the development of thin, sharp stone tools ushered
in a major technological revolution. Then, about 23,000 years ago,
just before the last glacial maximum, the art of hunting changed radically
as the bow and arrow began to replace spears. Development of eyed needles
allowed the production of hoods, gloves, and mittens from wooly animal
hides. Finally equipped to endure the long winter of another glacial
era, central Asian hunters began following large game across the grassy
steppe west into Europe, or east into Siberia and on to North America.
Unglaciated areas also experienced dramatic shifts in vegetation as the
planet cooled and warmed during glacial and interglacial times. Long before
the last glacial advance, people around the world burned forest patches
to maintain forage for game or to favor edible plants. Shaping their world
to suit their needs, our hunting and gathering ancestors were not passive
inhabitants of the landscape. Despite their active manipulation, small human
populations and mobile lifestyles left little discernable impact on natural
ecosystems.
Transitions from a glacial to interglacial world occurred many times during
the last two million years. Through all but the most recent glaciation,
people moved along with their environment rather than staying put and
adapting to a new ecosystem. Then, after living on the move for more than
a million years, they started to settle down and become farmers. What was
so different when the glaciers melted this last time that caused people to
adopt a new lifestyle?
Several explanations have been offered to account for this radical
change. Some argue that the shift from a cool, wet glacial climate to less
hospitable conditions put an environmental squeeze on early people in the
Middle East. In this view, hunters began growing plants in order to survive
when the climate warmed and herds of wild game dwindled. Others argue
that agriculture evolved in response to an inevitable process of cultural evolution
without any specific environmental forcing. Whatever the reasons,
agriculture developed independently in Mesopotamia, northern China,
and Mesoamerica.
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