- Our knowledge, and to some degree even our intelligence, is strongly social
- Our social intelligence/culture co-evolves with our bodies
His favorite examples of social intelligence are the young children vs chimps in problem solving. When both are young enough, the chimps are faster at figuring out simple problems, but even at that age the children completely outclass the chimps in learning from others. (Once language is involved, no creature comes even close to human performance.) Another is the explorers starving--or being slowly poisoned--in the midst of plenty of food they just don't know how to prepare. South American preparation of cassava is intricate; African methods are somewhat simpler--and chronic cassava poisoning is a problem in some places. The primitive toolkit of the Eskimos would take someone with plenty of time on his hands years to develop--and a castaway typically has no leisure for figuring out a good material for binding together a fish spear.
Humans predigest our food, so we don't need as large a large intestine as other creatures--and it isn't as large. We have a vast amount of cultural knowledge for our clan members to pick up, and it turns out that humans take far longer to mature than similar creatures.
He noticed that some South Pacific tribes have taboos that have subtle safety effects. Women are forbidden certain fish, which it turns out often carry parasites that can harm unborn children.
Here I wonder if he's cherry-picking the data. Dr Harley's Native African Medicine with Special Reference to its Practice in the Mano Tribe of Liberia summarized the local treatments as being roughtly 1/3 effective, 1/3 neutral, and 1/3 harmful. Is there a systematic analysis of the taboos Henrich mentions?
He tries to explain how culture can literally evolve. Hang around near high status people to pick up either status or knowledge, depending on how they got their status. Over time, status from knowledge grows knowledge and reproductive success.
He admits--insists on--the fact that this sort of knowledge/culture growth is delicate, and information can be lost (forever as far as your tribe is concerned) in a famine or plague or dead end approach). He gives a New Guinea example--a tribe forgot how to fish. And forgot lots of other things too.
Hmm. It seems so delicate, and takes so long, that one comes away with the impression that this kind of cultural/physical evolution isn't possible. There should have been more signicant culture earlier or much more rapid physical changes recently. Or a combination gift.