Interesting article about humans, evolution, and running.
Bascially the article goes through the evidence that humans are designed to be long distance runners, based on two major pieces of evidence:
1) We've got all these structures that have nothing to do with walking, like big tendons, big knees, and, uh, big booo-tay.
2) We don't have body hair and we do have sweat glands, which makes us efficient at dissipating heat.
The idea is that early humans made a living by - get this - out-running other animals. Not with raw speed but with stamina. Animals that can't sweat overheat much more easily than we do, so at some point they have to stop or they keel over and die. Since we do a better job of cooling (under the right conditions), it became an advantage. Heck yes, humans rule!
Interesting hypothosis, maybe true. I guess I'll say it's a good thing I'm not feeding a family based on my running skills though. Now, if homo erectus had bikes, I'd be more likely to sign on to this theory.