Fish swam the Sahara, bolstering out of Africa theory

Charles Q. Choi -

Fish may have once swum across the Sahara, a finding that could shed light on how humanity made its way out of Africa, researchers said.

The cradle of humanity lies south of the Sahara, which begs the question as to how our species made its way past it. The Sahara is the largest hot desert in the world, and would seem a major barrier for any humans striving to migrate off the continent.

Scientists have often focused on the Nile Valley as the corridor by which humans left Africa. However, considerable research efforts have failed to uncover evidence for its consistent use by people leaving the continent, and precisely how watery it has been over time is controversial.

Now it turns out the Sahara might not have been quite as impassable as once thought — not only for humanity, but for fish as well.

"Fish appeared to have swam across the Sahara during its last wet phase sometime between 10,000 and 6,000 years ago," researcher Nick Drake, a geographer at King's College London, told LiveScience. "The Sahara is not a barrier to the migrations of animals and people. Thus it is possible — likely? —that early modern humans did so, and this could explain how we got out of Africa."

Using satellite imagery and digital maps of the landscape, the researchers found the Sahara was once covered by a dense network of rivers, lakes and inland deltas. This large waterway channeled water and animals into and across the Sahara during wet, "green" times. [See digital map of ancient Sahara]

In their analysis, Drake and his colleagues found evidence that many creatures, including aquatic ones, dispersed across the Sahara recently. For example, 25 North African animal species have populations both north and south of the Sahara with small refuges within the desert, including catfish (Clarias gariepinus), tilapia (Tilapia zillii), jewel cichlid fish (Hemichromis letourneuxi) and freshwater snails such as the red-rimmed melania (Melanoides tuberculata).

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