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Oceans set stage for human evolution

Temperature changes off the coast dried out East Africa 2 million years ago

5:10pm, February 18, 2012

VANCOUVER — Scientists may now be able to explain one of the key events that shaped human history: why East Africa got drier starting around 2 million years ago, with forests giving way to grasslands on which Homo could further evolve. Ocean temperature changes, especially the arrival of a strong warm/cool difference along the equator in the Indian Ocean, could have triggered the change.

“Those gradients are responsible for shifting rainfall towards or away from East Africa,” said Peter deMenocal, a paleoclimatologist at the Lamont-Doherty Earth Observatory in Palisades, N.Y. He presented new details about his idea on February 17 at the annual meeting of the American Association for the Advancement of Science.

Researchers infer that East Africa, where humans first evolved, started shifting toward grasslands by looking at data on the proportion of fossils of grazing animals, which peaked around 1.5 million years ago. Around

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