In humans' mysterious journey to become intelligent, socializing creatures like no other in the animal world, one innovation played an essential role: religion.

That's the theory that a preeminent evolutionary scientist is setting out to prove.

"You need something quite literally to stop everybody from killing everybody else out of just crossness," said Robin Dunbar. "Somehow it's clear that religions, all these doctrinal religions, create the sense that we're all one family."