Human Evolution: Why Did Our Ancestors First Walk Upright?

There's a reason our ancestors began walking on two legs instead of scampering around on all fours millions of years ago. Like us, they couldn't get by without lugging some of their stuff around. New evidence collected during two expeditions to Guinea in West Africa supports that theory, which has been one of several leading explanations for why humans became bipedal somewhere between three and six million years ago. Researchers from the United States, England, Japan and Portugal spent weeks...Full Story
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