Evidence Challenges the "Out of Africa" Timeline of Human Evolution

One dominant idea among evolutionary biologists is that Homo sapiens left Africa about 60 or 70 thousand years ago, spreading across the world from there. It's called the "out of Africa" theory. But now, more evidence is challenging it.

Illustration by John Sibbick

Over on New Scientist, Catherine Brahic offers a cogent summary of the new evidence. Some comes from Asia, where scientists have discovered teeth that may be Homo sapiens dating from before 70 thousand years ago, and possibly from as long ago as 125 thousand. There are also fragments of early human skulls from Israel, which may date to as early as 150 thousand years ago.

What's emerging from this fragmentary evidence — which is still far from widely accepted — is a more complicated picture of when early humans left Africa, and where they went. Writes Brahic:

A closer look at the genetics also suggests there was an earlier migration. Recently, Katerina Harvati of the University of Tubingen in Germany and her colleagues tested the classic "out of Africa at 60,000 years ago" story against the earlier-exodus idea. They plugged the genomes of indigenous populations from south-east Asia into a migration model. They found that the genetic data was best explained by an early exodus that left Africa around 130,000 years ago, taking a coastal route along the Arabian peninsula, India and into Australia, followed by a later wave along the classic route (PNAS, doi.org/tz6).

What this suggests is that people may have been walking, or perhaps taking boats, up the coast out of Africa and into the Middle East and India. In some ways, this mirrors new discoveries about how people arrived in the Americas as well. It was once believed that people walked from Asia across a land bridge to North America, and now many scientists think that people may have arrived by traveling slowly along the coast in boats.

The picture we have of human development is growing more complicated, but it also fits with what we know of human migration today. It proceeds in fits and starts, taking many paths.

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