Psychologists, economists, and cultural anthropologists are unlikely companions. Psychologists study minds, with the implicit assumption that there are species-typical processes that shape our desires, motivations, and thought. Economists study the production, consumption, and transmission of wealth, using formal models which assume that aggregate patterns of behavior are the product of rational calculations of individuals maximizing personal goals and preferences. Anthropologists study societies, with the explicit aim of documenting the wide range of variation in beliefs, values, and behavior across time and space. Even when psychologists, economists, and anthropologists adopt an evolutionary perspective, the gulf looms. 

Studies of social preferences provide hints about how to bridge the gap. Behavioral economists, who devised experimental procedures that produce conflicts between self-interest and altruism, discovered that people prefer outcomes that increase their own welfare, but they also have ‘social preferences’ for outcomes that increase the welfare of others. For example, in the Dictator Game, subjects are given a sum of money that they can divide any way that they want between themselves and an absent anonymous recipient. In Western societies, people typically give 20-30% of the money away, but when a group of anthropologists and economists led by Joseph Henrich ran the same experiment in 15 small-scale societies they found wide cultural variation in the amounts that people give. This variation was not random: people tended to give more in societies that were larger and more integrated into market economies (societies in which cooperation between strangers is likely frequent), and less in societies that were smaller and had more limited involvement in markets (societies in which most cooperation is likely between relatives and familiar partners).

About ten years ago we became interested in understanding how this cultural variation in sharing emerges during childhood, and coordinated a cross-cultural study of the development of social preferences in children using a simplified version of the Dictator Game. At each field site, children were given a choice between two options: a generous option delivered one reward (a tasty food item) to the subject and one reward to another child, and a selfish option delivered two rewards to the subject and none for the other child. Like Henrich and his colleagues, we found wide variation in the behavior of children across societies. However, this variation did not emerge until children reached middle childhood (around the ages of 7-9 years), as children converged on the behavior of adults within their own societies. These results suggest that during middle childhood children become sensitive to culturally-specific information about how to behave. This “information” may be encoded in local norms, which children acquire through an evolved human psychology for learning and conforming to normative information. This implies that that we ought to have a universally-developing psychology for becoming sensitive to normative information, and that variation in prosocial behavior ought to be linked to variation in the content of a society’s social norms, and not to variation in development.

We recruited a largely new set of collaborators working in 8 societies around the world to help us test these ideas. These societies represented considerable diversity in size, subsistence strategies, and geographical location. The title of our paper, Universal norm psychology leads to society diversity in prosocial behavior and development, gives away the punch line. But how did we get to this conclusion?

The first step was to connect the behavior of adults to local social norms. There is a broad consensus that norms play an important role in shaping human behavior, but there is also little direct evidence that societal variation in normative expectations gives rise to variation in prosocial behaviors. To make this link, we needed to show that individuals’ prosocial behavior is predicted by what members of their society believe to be ‘correct’ in a particular situation (social norms).  And we must distinguish this from individuals’ own beliefs about what is ‘correct’ (personal norms).

We tackled this problem by presenting adults with a choice between generous and selfish options in the Dictator Game. Before they made their choice, they were shown a video in which a local adult explained that both options were “OK to choose”. After they made their choice, they were presented with two additional videos that introduced very different norms: the 'Generous’ video said that the generous option was “right and good to choose”, while the ‘Selfish’ video said the same thing about the selfish option. Then, they were asked which video they believed to be most correct. If social norms matter, then adults’ behavior in the Dictator Game should be at least partly influenced by the beliefs of other people within their own societies. And that is what we found. The likelihood that individuals would choose the generous option was predicted by the probability that members of their society thought the generous option was the most appropriate choice, and this was separate from the influence of individuals’ own ideas about which option was most correct. 

To evaluate whether the sensitivity to social norms is part of an evolved, universally-developing psychology we examined the development of children’s tendency to respond to novel social norms about choices in the Dictator Game. Over 800 children aged 4-17 were each shown one of the three videos, each presenting a different norm about how to make choices in the game. Then, we presented them with the same choice between the generous and selfish options. Very young children were largely unaffected by the norm presented in the videos. It’s not because they were confused about the task: these children had passed comprehension tests about the consequences of their choices and the content of the norm videos. 

As children got older, their behavior changed. By about age 6-8, children that saw the Generous norm video were more likely to choose the generous option, and children that saw the Selfish norm prime were more likely to choose the selfish option. The development of children’s responsiveness to these norms unfolded in more or less the same way across societies. 

Our findings support the view that children become ‘good’ by internalizing local social norms about appropriate prosocial behavior. But what constitutes goodness varies considerably across societies. Before children can become good they have to figure out what is expected of them in their society. Perhaps our children are only as good as they believe we expect them to be.