You've got a good conversation going here. Thanks. Primatologist Richard Wranham has proposed that two related factors contributed to the diverging bonobo/chimp behavior: — far more plentiful food in the bonobo range than in the chimp range and, — chimps compete with gorillas for some of their food sources, while bonobos are isolated from gorillas (and chimps).

This hypothesis would seem to support our argument, in that we find that food supply was generally plentiful for prehistoric populations (with occasional crises), whereas for post-ag populations, food scarcity was a constant problem (as demonstrated by skeletal evidence).

Chris Ryan (co-author of Sex at Dawn)

Pedantic correction: his name is Richard Wrangham with a 'g'. The book is "Demonic Males: Apes and the Origin of Human Violence", co-authored with Dale Peterson. I have a post on it here.

Wrangham has another book, "Catching Fire: How Cooking Made Us Human", which theorizes that the increased calories resulting from food (particularly meat) preparation allowed us to reduce our gut size and increase our brain size, along with introducing pair-bonding. He discusses it in this diavlog.