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....