A Mystery: Why Can’t We Walk Straight? : Krulwich Wonders… : NPR

Try this: Put a blindfold on someone, take them to a park or a beach or a meadow and ask them to walk for as long as they can in a straight line. Then watch what happen.

http://www.npr.org/blogs/krulwich/2010/11/03/131050832/a-mystery-why-can-t-we-walk-straight