Was ability to run early man's Achilles heel?

The earliest humans almost certainly walked upright on two legs but may have struggled to run at even half the speed of modern man, new research suggests.

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<p><a href="http://www.physorg.com/news108717499.html">Was ability to run early man's Achilles heel?</a></p> <p>The earliest humans almost certainly walked upright on two legs but may have struggled to run at even half the speed of modern man, new research suggests.</p>