Which brings us to us. We are a species too, and we have our range,
which is currently every continent bar Antarctica. Yet in the nascence
of our evolution as Homo sapiens sapiens, around 150,000 years
ago, our range was restricted to the Rift Valley in central Africa -
for 50,000 happy years. What happened to make us leave the comfy
ancestral home?

Climate change is what happened. :::[Vanity Fair: Out of Africa]

What
set these migrations in motion? Climate change—today's...

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Which brings us to us. We are a species too, and we have our range,
which is currently every continent bar Antarctica. Yet in the nascence
of our evolution as Homo sapiens sapiens, around 150,000 years
ago, our range was restricted to the Rift Valley in central Africa -
for 50,000 happy years. What happened to make us leave the comfy
ancestral home?

Climate change is what happened. :::[Vanity Fair: Out of Africa]

What
set these migrations in motion? Climate change—today's big threat—seems
to have had a long history of tormenting our species. Around 70,000
years ago it was getting very nippy in the northern part of the globe,
with ice sheets bearing down on Seattle and New York; this was the last
Ice Age. At that time, though, our species, Homo sapiens,[/i]
was still limited to Africa; we were very much homebodies. But the
encroaching Ice Age, perhaps coupled with the eruption of a
super-volcano named Toba, in Sumatra, dried out the tropics and nearly
decimated the early human population.

And
then something happened. It began slowly, with only a few hints of the
explosion to come: The first stirrings were art—tangible evidence of
advanced, abstract thought—and a significant improvement in the types
of tools humans made. Then, around 50,000 years ago, all hell broke
loose. The human population began to expand, first in Africa, then
leaving the homeland to spread into Eurasia. Within a couple of
thousand years we had reached Australia, walking along the coast of
South Asia. A slightly later wave of expansion into the Middle East,
around 45,000 years ago, was aided by a brief damp period in the
Sahara. Within 15,000 years of the exodus from Africa our species had
entered Europe, defeating the Neanderthals in the process...