There's a theory from the latest TED talk that says our survival prior to inventing weapons (like spears) depended on running other animals to exhaustion.
The San Bushmen in the Kalahari Desert still do this today. This BBC clip on persistence hunting (narrated by David Attenborough!) is worth a watch; their endurance is absolutely incredible: http://www.youtube.com/watch?v=826HMLoiE_o
Sorry to be a snob but it's not a recent theory, I heard about something like this (men being able to sweat and run long distances, being scavengers, competing with hyenas) about 25 years ago.