I’ve been reading early reviews of Richard Wrangham’s  (biological anthropologist, Harvard) new book Catching Fire; I thought I would see whether anyone’s read it yet.
The hypothesis he puts forward, as I understand it, is fairly provocative:  a, or the, major breakthrough in human evolution was the moment when people understood they could use fire to cook food. This radically increased bioavailability of nutrients (many apes have to chew all day just to get enough calories), allowing, among other things, our brains to significantly expand.
There’s also an interesting tie-in to the establishment of “patriarchy” as gender roles polarize around cooking and hunting, with cooks stationary and vulnerable to attack (smoke visible for miles) and so dependent on the protection of others.