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March 20, 2012

Cumulative culture and cooperation in humans and other primates

Two recent papers compare the problem-solving abilities of humans and other primates. Individual humans are smarter than individual chimps, of course. But our most-impressive intellectual feats depend on the accumulation of cultural knowledge over many generations. A blacksmith might make some of her own tools, but she didn't invent most of them, or smelt the iron from ore she mined herself. Computer programmers, in turn, depend on technology that built on the work of blacksmiths and many others.

I once read a story in which Earth was visited by aliens with vastly superior technology. Initially, humans assumed that the aliens must be much smarter than we are. It turned out that most of them were pretty stupid, easily duped by humans. It's just that their civilization was older, so they'd had time to invent spaceships and such, even with fewer geniuses than we have. How much of our technological superiority to nonhuman primates is due to superior individual problem-solving ability, and how much to cumulative culture?

"Identification of the Social and Cognitive Processes Underlying Human Cumulative Culture" was published in Science by L.G. Dean and others. They compared the ability of groups of 3-4 year-old human children, chimps with capuchin monkeys, in solving a "puzzle box", where retrieving the most-valued food reward depended on solving three successive levels of increasing difficulty. Only one chimp of 33 got to level 3, while many humans did. Why?

Humans copied others more than chimps or monkeys did. Chimps tended to copy the moves needed to get to the first level, but not beyond that, so it didn't help much to let them see a chimp that had been trained to reach level 3. All 23 clear cases of "teaching" (2/3 verbal and 1/3 via gestures) were by humans. Humans were more generous in other ways also: 47% shared food with others, while none of the chimps or monkeys did. Chimp mothers stole from their own offspring. In summary:

"The children responded to the apparatus as a social exercise, manipulating the box together, matching the actions of others, facilitating learning in others through verbal instruction and gesture, and engaging in repeated prosocial acts of spontaneous gifts of the rewards they themselves retrieved. In contrast, the chimpanzees and capuchins appeared to interact with the apparatus solely as a means to procure resources for themselves, in an entirely self-serving manner, largely independent of the performance of others, and exhibiting restricted learning that appeared primarily asocial in character."

Human adults may be different, however, with rich (or well-educated?) adults acting more like chimps. See last week's post.

The second paper also compares cooperation in humans and other primates. "Old World monkeys are more similar to humans than New World monkeys when playing a coordination game" was recently published by Sarah Brosnan and others in Proceedings of the Royal Society B. Pairs of humans, rhesus monkeys, and capuchin monkeys played the Assurance (or Stag Hunt) game, using computer joysticks to enter their moves. An individual choosing Hare gets a reward whatever the other player does. But if both choose Stag, they each get double the reward.

All of the human pairs talked, but only some talked about the game. Of those that did, all 22 pairs ended up playing mostly cooperatively -- but not 100%, even after seeing the potential benefit. Those who talked about other topics played mostly noncooperatively, forgoing the benefits of cooperation.

The two monkey species differed. For both species, if individuals could see the other's move, they learned to "cooperate" and got high rewards. (They could see each other, but did they realize they were playing with each other, rather than with the computer?) The capuchins played more randomly when they didn't know the other's move, whereas two pairs of rhesus monkeys quickly learned to trust their partner and cooperate (or, anyway, to play as if they did). Rhesus monkeys are native to Africa, rhesus monkeys to South America. So, as the authors put it:

"Old World primates outperformed New World primates,
rather than humans outperforming non-humans."
They speculate that, perhaps:
"...humans' abilities are built on a shared foundation that extends back at least as far as the split with Old World monkeys [which was longer ago than the split between apes and old-world monkeys, let alone the split between humans and other apes]."
An interesting hypothesis, but I would like to see data for more species.