Humans likely evolved to cooperate locally with members of small groups, at the expense of people in other groups. Because within-group cooperation and inter-group conflict is commonly assumed to be the default scenario, the factors that favour inter-group cooperation have been little investigated. Here, we ask whether the same mechanisms that promote within-group cooperation can also promote inter-group cooperation.
This question is of both theoretical and applied importance. From a theoretical perspective, cooperation shows remarkable scaling between levels of organization (e.g. genes to individuals to groups), but with each additional level comes increased opportunity for conflict. Thus, inter-group cooperation may be qualitatively as well as quantitatively different from within-group cooperation. From an applied perspective, many current issues arising from a breakdown of cooperation span the boundaries of multiple groups: for example, management of overexploited natural resources or setting targets for reducing carbon dioxide emissions. Can in-group favouritism be overcome to achieve cooperation on the inter-group scale needed to address these challenges?
In this study, we empirically tested factors affecting inter-group cooperation in an environmental 'collective risk dilemma'. Participants played an economic game that modelled a 'climate catastrophe' occurring when cooperation fell below a certain threshold. First, we investigated whether framing the game as a two-group dilemma versus single group dilemma influenced people’s willingness to cooperate. We found that it did not, in contrast to widely-reported group favouritism in lab games. Second, we investigated two different inter-group scenarios, where the two groups were dependent on each other’s contributions, versus able to compensate for each other’s lack of contributions. We found that cooperation was lower when groups were interdependent, in contrast to the common finding that interdependence promotes within-group cooperation.
Together, our results suggest that different mechanisms promote inter-group cooperation versus within-group cooperation, indicating a qualitative difference between these scales of cooperation.