  Extensive cooperation among biologically unrelated individuals is uniquely
human and much current research attempts to explain this fact. We draw upon
social, cultural, and psychological aspects of human uniqueness to present an
integrated theory of human cooperation that explains aspects of human
cooperation that are problematic for other theories (e.g., defector invasion
avoidance, preferential assortment to exclude free riders, and the second order
free rider problem). We propose that the evolution of human cooperative
behavior required (1) a capacity for self-sustained, self-referential thought
manifested as an integrated worldview, including a sense of identity and point
of view, and (2) the cultural formation of kinship-based social organizational
systems within which social identities can be established and transmitted
through enculturation. Human cooperative behavior arose, we argue, through the
acquisition of a culturally grounded social identity that included the
expectation of cooperation among kin. This identity is linked to basic survival
instincts by emotions that are mentally experienced as culture laden feelings.
As a consequence, individuals are motivated to cooperate with those perceived
culturally as kin, while deviations from expected social behavior are
experienced as threatening to one's social identity, leading to punishment of
those seen as violating cultural expectations regarding socially proper
behavior.
