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An entire mammoth was unearthed
in Siberia, Russia, in 1900—the first
complete example ever found. A cast
of it is on display in St. Petersburg’s
Natural History Museum.See also: The first humans arrive in Australia 20–21 ■ Cave paintings at Altamira 22–27 ■
The settlement at Çatalhöyük 30–31 ■ The Law Code of Hammurabi 36–37HUMAN ORIGINS
England. Such huge amounts of sea
water froze that sea levels dropped,
exposing low-lying land such as
Beringia, the continental shelf that
connects North America and
Asia—and the route by which
humans first reached the Americas.Rising temperatures
Temperatures eventually rose
again, and today’s relatively warm
and stable climate had become
established by around 7000 bce.
The ice caps melted, and rising sea
levels separated Eurasia from the
Americas, turned Southeast Asia
into an archipelago, and made
islands out of peninsulas such as
Japan and Britain, thereby isolating
many human groups. The impact
on ecosystems was particularly
severe for the large animals known
as megafauna—mammoths, for
example. The open glacial steppe
grasslands in which megafauna
thrived were replaced by expanding
forests, and across the globe the
combination of environmental
change and human hunting drove
many species to extinction.The forests and wetlands of the
new post-glacial world offered
humans many new opportunities.
They hunted large forest animals
such as red deer and wild boar,
as well as smaller mammals like
rabbits, and they foraged for a
range of aquatic and coastal food
sources. Migratory fish like salmon,
sea mammals such as seals, and
shellfish, seasonal wildfowl, and
a range of fruits, tubers, nuts,
and seeds all became important
dietary staples.Changing lifestyles
In areas that were particularly
rich in natural resources, human
groups may not have settled in
one place, sending small bands
on forays further afield to target
specific resources. The Natufian
communities of the Eastern
Mediterranean, for example, were
able to exploit abundant stands
of wild cereals in the Near East.
Some groups began to manipulate
their environments, burning
vegetation and cutting down
trees to encourage their preferredplant and animal species to thrive.
They started to select and care for
productive plant species and sowed
the seeds of favored strains, while
managing and controlling certain
animals. This manipulation led to
these species becoming ever more
reliant on human input—and to
the development of agriculture, a
radical change in the human way
of life that has since resulted in
even more dramatic human impact
on the environment. ■Ice cores and past environments
Paleoclimatologists study the
elemental composition of the
sediments laid down over time
on ocean floors to understand
how climates have changed in
the past. Tiny sea creatures
known as foraminifera absorb
two different forms of oxygen,(^16) O and (^18) O, from sea water.
Because^16 O is the lighter of the
two, it evaporates into the air
more easily, but during warmer
periods it falls as rain and drains
back to the sea. So^16 O and^18 O
exist in sea water and appear
in the shells of foraminifera, in
roughly equal ratios. However,
in cold conditions most of the
evaporated^16 O does not return
to the ocean but freezes as ice,
so sea water contains more^18 O
than^16 O. When foraminifera die,
their shells sink to the ocean
floor, building up over time.
Paleoclimatologists drill into
the ocean floor to extract cores
of sediment and study the
changing proportions of^16 O and
(^18) O in different layers to see how
climates have changed over time.
Few humans have ever
lived in a world of such
extreme climatic and
environmental change.
Brian Fagan
Expert in human prehistory
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