The Evolution of Human Physical Activity - Running and the Brain 

Excellent use of public datasets for natural experiments on potential evolutionary levers. Not hard to fathom those who can gather a few more calories daily and who may be feeling more personable may have better reproductive success.

"Only humans exercise" I seem to recall that when I was a child my hamster loved to run on his wheel every night!

I'm surprised Dr. Lieberman doesn't consider play behavior, which is ubiquitous among mammals, as a form of exercise.

Dude can outrun horses. I'd listen to him.