A solitary bison in Yellowstone National Park. Amelia Templeton/NPR hide caption

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Teeth from a cremated child were excavated from a site believed to be 11,500 years old. The color differences show uneven burning. The scale is in millimeters. Science/AAAS hide caption

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A new study finds that radio waves from a cell phone can affect the metabolism of brain cells, though there is no evidence that the effect is harmful. Here, a pedestrian talks on her phone on a street in San Francisco. Justin Sullivan/Getty Images hide caption

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Some 16,000 years ago, people may have been curling up next to the fire with red foxes. iStockphoto.com hide caption

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