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Evolutionary Pulse Found, But Complexity as Well

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Science  28 Sep 2001:
Vol. 293, Issue 5539, pp. 2377
DOI: 10.1126/science.293.5539.2377

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According to one theory of human origins, the world took an abrupt step toward glaciation, the East African cradle of the human species dried to grasslands, and human ancestors coped with dwindling forests by evolving bigger and better brains. A new study of one of the best fossil records for testing this theory lends some support: It finds an abrupt shift in East African species that coincided with a known climate change 2.8 million years ago. But the story emerging from East Africa is not a simple one, and the link to human evolution remains tenuous at best.