Despite the global headlines emphasizing division and conflict, humans actually have a long history of forming friendships across group boundaries. But which criteria do they use for picking friends from a different group? In collaboration with three populations of horticulturalists in Bolivia, researchers of the Max Planck Institute for Evolutionary Anthropology and the University of California Santa Barbara found that we use very similar criteria when choosing friends from among in-group and out-group strangers – individual cooperative qualities are most important in both cases. Only when it comes to dividing limited resources, qualities associated with a group can affect partner preference.