Travel Reference
In-Depth Information
during the Great Migration as the migrants moved into new areas. The devas-
tating ecological consequences of this behavior forced some of the migrants
to move on, perhaps only a generation or two later. Meanwhile, the people
who stayed behind were forced to learn to modify their behaviors in ways
that helped to preserve the land's productivity.
How people were changed by the Great Migration
What evolutionary impact did the Great Migration have on the populations
that took part in it? To begin with, the migrants remained surprisingly iso-
lated for many thousands of years. There are no signs in their mitochondrial
DNA that they mated with the much earlier migrants,
Homo erectus
and their
relatives, that they encountered along the route. But such matings cannot be
ruled out, as is shown by recent discoveries of a Neanderthal signal in the
nuclear DNA of modern humans.
Perhaps the biggest puzzle is why this migration seems to have been a
unique event, bringing with it only a small sample of the genetic diversity
found among modern human populations in Africa. The genetic pattern
seen along the southern rim of Asia suggests that only one band or a few
bands of people managed to pass through the barrier of the Middle East,
and it was their descendants that migrated all the way to Australia. Why did
nobody else follow for so long?
Conditions along the route of the Great Migration may simply have been
too challenging, especially in the dii cult country of the Middle East. Much
of the Middle East would have been desert, and the parts that could support
hunter-gatherer populations were already inhabited by Neanderthals. Cores
from Antarctic glaciers with ice layers from 60,000 years ago contain an
unusually large amount of red dust, signs of dust storms that extended from
pole to pole. We are seeing similar worldwide dusty conditions today, as a
result of our rapidly spreading deserts.
Nonetheless, people survived in these grim regions over long spans of
time. Iranian archeologists have recently discovered massive numbers of
stone tools near the city of Semnan in northern Iran. The tools date from
