Nepotism, cronyism, and other forms of corruption aren't failures of cooperation - they *are* cooperation, but on a lower scale. Our new model extends P&B (2004) but puts people in 2 groups - a local group (L) & a global group (G), w/ the choice to contribute to either or none. 4/

In a landmark Nature paper, Panchanathan & Boyd (2004) developed an elegant model showing how reputation can sustain large-scale cooperation: we prefer to help those who've contributed to the public good. If I know you're a patriot or support climate action, I'm more likely to help you elsewhere 2/

🚨 PNAS paper: "Indirect reciprocity undermines indirect reciprocity destabilizing large-scale cooperation" w/ Eric Schnell How do we achieve global cooperation on climate or conflict reduction? The problem isn't selfishness as much as it is cooperation itself - at a smaller scale. 1/

Important caveats: data and phylogenetically controlled models alone don't tell you the causal mechanism. That's why formal theory is useful - you can model assumptions and logic for possible mechanisms. A lot of the paper explains the role of theory in helping us interpret non-causal analyses. 10/

Sociality is the main difference b/w the ABH and SBH. SBH predicts more social species should have larger brains. Sociality was not reliably associated w/ larger brains - in fact perhaps the opposite. 9/

Depth also indicates shallower-living species tended to have larger brains. This fits the idea that shallower habitats are generally more calorie-rich, biodiverse, & more cognitively demanding than open-water habitats. Again, consistent w/ the ABH. 8/

Results: consistent w/ ABH, ecology predicted brain size. Sociality didn't. The strongest predictor was habitat: cephalopods living on or near the shallow seafloors had larger brains than open water species. The relationship was enormous, ~2/3 as large as the body-brain size relationship. 7/

Prior to the CBH, the dominant theory for the evolution of large brains was the social brain hypothesis - brains evolved to cope w/ the demands of group living. Cephalopods are smart - use tools, solve problems, deceive - but they're short-lived, die after reproducing, & even cannibalistic. 3/

🚨 New paper in iScience: "Ecological not social factors explain brain size in cephalopods" In 2017, we published the Cultural Brain Hypothesis, a model of human brain evolution. It made an unexpected prediction: non-social animals could evolve big brains too, if their ecology was rich enough. 1/

How do you align AI in a world of plural, conflicting, and evolving human values? A starting point is human society itself. @sydneylevine.bsky.social and I are hiring a postdoc at NYU to combine insights from cultural evolution, computational moral cognition, and AI safety. Please share widely!1/

Any recommendations for a good evolution oriented intro psych textbook? Gray & Bjorkland's Psychology isn’t being renewed.

The first foreign translation book cover is... Korea! Blends elements of the US and UK covers. What do you think?

The Silk Roads is the best of Big History by the way - an exploration of how people, knowledge, and ideas have flowed back and forth across Eurasia reshaping its civilizations. It meant a lot that Peter read A Theory of Everyone, let alone was willing to blurb it.

I love when readers send me their feedback! I'm sure most authors do... Here's a message I received this morning (sharing anonymously with permission) about the section on inequality and inheritance taxes (Chapter 9). atheoryofeveryone.com