Gifts given, gifts taken: The behavioral ecology of nonmarket, intragroup exchange

Behavioral ecologists combine evolutionary models of mechanism and ecological models of circumstance to analyze the origins and forms of intragroup exchange among social foragers, a category that includes primates, hominids, and recent and modern hunter-gatherers. Evolutionary mechanisms encompass individual, sexual, reciprocal, kin, group, and cultural selection; models of circumstance include tolerated theft, scrounging, marginal value, trade, show-offs, and risk reduction. After a critical review, I develop a partial synthesis of these models. The results show that exchange behaviors have multicausal origins and they likely will be diverse due to differing combinations of mechanism and circumstance. They also help explain seemingly unique features of foraging economies, including constrained production and routine demand sharing.