Two theories of bipedalism

At the end of May, there was a news story doing the rounds about how bipedalism evolved in the trees and not, as has been traditionally thought, via knuckle-walking on the ground. Now, a new study says bipedalism evolved because it uses less energy than knuckle-walking.

What is an interested non-expert supposed to think? (Actually, for the record, as an interested non-expert, I didn’t buy the first story at all.)

Anyway, I only mention this second story, because it included a funny photo of a chimpanzee on a treadmill:

This one will have the animal rights people doing their nuts.