ANTHROPOLOGY TODAY VOL 33 NO 1, FEBRUARY 2017 11 J.L. Molina, M.J. Lubbers, H. Valenzuela-García & S. Gómez-Mestres The authors are part of the research group GRAFO, Department of Social and Cultural Anthropology, UAB, Barcelona. José Luis Molina is an economic anthropologist interested in the emergence of transnational social structures, particularly in relation to Southeast Europe. Correspondence may be sent to joseluis.molina@uab.cat. Why do humans cooperate so extensively? This intriguing question has been advanced from a variety of disciplines including biology, economics, archaeology and evolu- tionary and social anthropology, and each one has contrib- uted different pieces to the puzzle. In this article we wish to highlight the specific contribution that social anthropology has made to this field of research. In order to do so, we will first review the basic mechanisms explaining cooperation as identified in the literature – typically they are under- stood as a response to competition. We then observe that social anthropology investigates cooperation and competi- tion from a slightly different angle than is common in the wider literature, and subsequently, we describe the contri- bution of social anthropology to the field. In our conclu- sion, we summarize our review and give some suggestions for further research. In an attempt to understand why humans cooperate on such a broad scale, the literature has identified three pri- mary mechanisms for the evolution of cooperation: kin selection, reciprocity and group selection. The first mechanism, kin selection, stems from evo- lutionary biology and interprets the Darwinian theory of natural selection from the point of view of the gene. This approach assumes that it is not the individual who acts selfishly in its attempt to survive, but the gene (Dawkins 1976). In line with this assumption, the hypothesis of ‘inclusive fitness’ (Hamilton 1964) stipulates that natural selection can favour altruistic behaviours when the donor and the recipient are genetically related, and when the degree of relatedness exceeds the cost-to-benefit ratio of altruism (where the costs for the cooperator are always assumed to be lower than the benefits for the recipient). Related research on kin selection has proposed – among others – the so-called ‘grandmother hypothesis’ (Hawkes et al. 1998) that explains the long postmenopausal life-spans that distinguish humans from all other primates as an adaptive way to enhance daughters’ fertility through food sharing and additional care provided by their mothers after menopause. This hypothesis has faced strong criti- cism (Kennedy 2003) – among others, that adults older than 40 years old were very rare in prehistoric times. The second mechanism, reciprocity, considers the individual to be the unit of fitness in the theory of nat- ural selection. Rather than understanding cooperation as an act of altruism, it focuses on mutualistic cooperation as an individual strategy for more effective competition. Several versions of reciprocity have been proposed and tested from a perspective that takes into account individual costs and benefits. The first is direct reciprocity (i.e. A helps B and B, subsequently, returns the favour). Evolutionary game theory has modelled direct reciprocity with the Prisoner’s Dilemma and the Iterated Prisoner’s Dilemma 1 (Axelrod & Hamilton 1981). Results suggested that in a single encounter between two individuals, it may be more benefi- cial for each individual to defect than to cooperate, but if two individuals are to meet repeatedly, cooperation may be more beneficial to each of them. According to this line of argument, individuals accept higher relative costs of coop- eration only with higher probabilities of a new encounter. Indirect reciprocity, on the other hand, situates pair-wise interactions in a larger group context and explains why people may also help others asymmetrically (Nowak & Sigmund 2005). It specifies that the favour to be returned may be generalized to include other individuals. More spe- cifically, if A helps B, the favour may later be returned by C helping A or B helping C. Indirect reciprocity is a cognitively more demanding mechanism, since it requires individuals to not only remember their own interactions, but also monitor the interactions in the larger group. It also relies on language for the transmission of information about those interac- tions. Indirect reciprocity is thought to lead to the evolu- tion of morality and social norms. 1. The Prisoner’s Dilemma is a series of games that show how two individuals acting ‘rationally’ may not cooperate, even if it would appear to be in their own interests to do so. Apicella, C. et al. 2012. Social networks and cooperation in hunter- gatherers. Nature 481(7382): 497-501. Axelrod, R. & W.D. Hamilton 1981. The evolution of cooperation. Science 211(4489): 1390-1396. Barth, F. 1967. Economic spheres in Darfur. In R. Firth (ed.) Themes in economic anthropology. London: Tavistock Publications. Bellah, R.N. 2011. Religion in human evolution. Cambridge, MA: Harvard University Press. Bohannan, P. & G. Dalton 1965. Markets in Africa: Eight subsistence economies in transition. New York: Doubleday Anchor. Cooperation and competition in social anthropology Fig. 1. Gift exchange in a wedding ceremony in Kedah, Malaysia, 2002. J.L. MOLINA