Many of these photographs represent individuals in distant colonies, which ensured that the subjects in the study did not work with portraits of individuals they had known previously. They had to work purely on the basis of visual similarities. The subjects were first presented with a sample photograph of an adult female, representing the stimulus to be matched. The subjects made a correct response by moving the joystick-controlled cursor to select the related individual. Members of a family recognizing and helping one another in an altruistic fashion helps improve the survival of the family's genetic line.
Family members share food, defend one another, and refrain from having sex with one another.
Relationships and alliances are then made between different families which make up the social fabric of a primate community. Parr and de Waal's data suggest that chimpanzees are as good at recognizing faces, seeing similarities and differences between them, as we are. That chimpanzees can do so may help their survival in ways that are not yet fully understood, but that may have played a role in our own evolution as well. In ever more extended family networks, where one doesn't always grow up with close kin, these skills may have served the same purpose of building kin-based alliances and avoiding incest. The study was funded by the National Center for Research Resources of the National Institutes of Health.