This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The objecrtive of this study is to establish how brown capuchin monkeys (Cebus apella) react to their group mates in terms of the knowledge they have and the procosial vs. competitive tendencies. We asked the monkeys to indicate, on the basis of portraits projected on a computer screen, which belongs to their group. We asked them to share food with others based on what they know about their hunger state to see if they take the needs of others into account. Current projects are increasingly on reciprocity and the "snowdrift" game (i.e. a game theory situation in which both individuals benefit or both lose dependent on their cooperative tendencies). Our findings show a sophisticated level of face recognition (including the so-called inversion effect) and cooperative tendencies, with the most widely cited papers being those on inequity aversion, i.e. the way monkeys respond to obtaining a lesser reward than their partner for the same task. Thirty capuchin monkeys are available, kept in indoor/outdoor enclosures, trained for temporary separation for experiments. The laboratory at the Yerkes Primate Center serves as an educational tool for many undergraduate and graduate students, who obtain valuable training in combination with their classes.