In an ever-increasing globalized world, cooperation with foreign citizens becomes vital to deal with important challenges, such as the management of climate change negotiations or the containment of a pandemic such as COVID-19. While humans possess remarkable abilities to cooperate with unknown strangers, national parochialism – the tendency to cooperate more with members of the own nations – might represent an obstacle to the management of global public goods around the world. A new study involving more than 18,000 participants from 42 societies around the world finds that national parochialism is a pervasive phenomenon that occurs around the world and with little variation across nations.

The experiment

Romano, Sutter, Liu, Yamagishi and Balliet’s study (2021) consisted of an online experiment in which participants were asked to make decisions in a variant of the prisoners' dilemma, the standard game to study cooperation. Participants worked together in pairs and were provided with a small amount of money (10 monetary units), with their economic value standardized across nations. They could decide how much of this initial endowment to keep and how much to give to an unknown fellow player – without knowing what the other would do. In the process, the amount invested was doubled. A cooperative act would be to donate the whole amount to the other participant such that each member of the pair would end up with double the amount of money compared to the initial endowment. However, in these situations people are tempted to behave selfishly by keeping both their amount and the amount invested by their partner. Participants were asked to make 12 independent decisions with partners of the same nationality (i.e., ingroup), of different nations (i.e., outgroup), or unidentified partners (i.e., strangers).

National parochialism is widespread across nations

Results were clear: in 39 out of 42 societies participants significantly cooperated more when they were informed that their partner was from the same nation. The remaining three countries, although there was not a statistically significant difference, displayed the same pattern: people preferred to cooperate with partners from the same nation compared to partners from other nations. Moreover, Romano and colleagues found that the extent to which people favored members of their nations was also similarly robust across situations. In fact, national parochialism was independent of whether participants made their choice in private or in public, and was not associated to prominent cultural, ecological, or institutional differences across nations. Additionally, the authors find evidence that national parochialism was driven by a general positive bias toward the own nation, rather than a sense of spite toward the outgroup.

Impersonal cooperation varies around the world

Having found that national parochialism is ubiquitous and comes with little variation across societies, Romano et al. investigated the variation across nations in impersonal cooperation – the degree to which people cooperated with other people independently from their nationalities. Relatively to national parochialism, Romano et al. found a greater amount of between-nations variation in impersonal cooperation. Cross-national variation in impersonal cooperation was higher between cultural distant societies and was associated with differences in institutions (history of exposure to western church), norms (egalitarian, more tolerant), values (individualistic) and social ecological conditions (low pathogen stress, flexible and fluid social relations).


Many social, environmental, and economic challenges require cooperation across nations. As managing the tendency to favor ingroup members is fundamental in successfully solving these challenges when they transcend borders, it is key to pursue research on the conditions that expand people’s willingness to cooperate more beyond group boundaries.


Romano, A., Sutter, M., Liu, J. H., Yamagishi, T., & Balliet, D. (2021). National parochialism is ubiquitous across 42 nations around the world. Nature Communications, 12(1), 1-8.