I was reading this great article in Discover Magazine this morning on how humans are more adapted to running than most other animals. I especially like the reason of our many many sweat glands helping to cool our bodies down, while other mammals usually pant. And the idea of the tail used by other animals to balance and humans using their huge rear ends :)

Here's a link to the article:
http://www.discover.com/issues/may-06/features/tramps-like-us/