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Abstract:Researchers from across the social sciences have found consistent deviations from the predictions of the canonical model of self-interest in hundreds of experiments from around the world. This research, however, cannot determine whether the uniformity results from universal patterns of human behavior or from the limited cultural variation available among the university students used in virtually all prior experimental work. To address this, we undertook a cross-cultural study of behavior in ultimatum, public goods, and dictator games in a range of small-scale societies exhibiting a wide variety of economic and cultural conditions. We found, first, that the canonical model -based on self-interest -fails in all of the societies studied. Second, our data reveal substantially more behavioral variability across social groups than has been found in previous research. Third, group-level differences in economic organization and the structure of social interactions explain a substantial portion of the behavioral variation across societies: the higher the degree of market integration and the higher the payoffs to cooperation in everyday life, the greater the level of prosociality expressed in experimental games. Fourth, the available individual-level economic and demographic variables do not consistently explain game behavior, either within or across groups. Fifth, in many cases experimental play appears to reflect the common interactional patterns of everyday life.

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As a result of a spate of studies geared to investigating Brazilian racial categories, it is now believed by many that Brazilians reason about race in a manner quite different to that of Americans. This paper will argue that this conclusion is premature, as the studies in question have not, in fact, investigated Brazilian categories. What they have done is elicit sorting tasks on the basis of appearances, but the cognitive models of respondents have not been investigated in order to determine what are the boundaries of their concepts. Sorting based on appearances is not suf cient to infer the boundaries of concepts whenever appearance is not a de ning criterion for the concepts in question, as the case appears to be for racial and ethnic categories. Following a critique of the methods used, I review a terminological and theoretical confusion concerning the use of the terms 'emic ' and 'etic' in anthropology that appears directly responsible for the failure so far to choose methods appropriate to parsing the conceptual domain of 'race' in Brazil.

Lamba and Mace's critique (1) of our research (2-4) is based on incorrect claims about our experiments and several misunderstandings of the theory underpinning our efforts. Their findings are consistent with our previous work and lead to no unique conclusions.Lambda and Mace (1) incorrectly claimed that we "mostly" sampled from single communities within sites, and that we ignored "ecological" and "demographic" variables. In fact, much of our work focused on studying the variation among communities within sites. In phase I (2), 8 of 15 sites involved multiple communities, and in phase II (3, 4), 11 of our 16 sites sampled from multiple communities. Several sites included 5 communities*, and 1 site included 9 communities (5).During both phases, we conducted analyses like Lamba and Mace's (1) within each of our sites (2-4). Except for community size, which emerged as a focal predictor (4), we studied versions of all the key variables (age, network centrality, and siblings) of Lamba and Mace (1) in some populations. Occasionally, these were significant, but none had consistent effects across populations, games, or in retests years later. Lamba and Mace (1) also failed to find any predictors that were consistent across their experiments, despite trying dozens of variables. Moreover, their predictors are neither theoretically well-grounded nor particularly ecological. Nonetheless, Lamba and Mace (1) concluded that "ecology drives variation in cooperation."Our analyses show that the key claim of Lamba and Mace (1), that the fraction of variation they observed for monetary games (4%) among communities is comparable to the fraction we observe among our sites (12% for ultimatum game offers in phase I) is not correct, even allowing for their assumption that 12 ≈ 4. (1) is consistent with our data, but their data tell us nothing about the variation across sites (contrary to their claim).Our theoretical framework is also not made clear, because Lamba and Mace (1) claimed that our approach holds that only norms matter, and that norms cannot evolve in response to ecological variation. They further imply that if demographic or ecological variation is important, norms cannot be. Our research is based on the idea that people can acquire context-specific expectations (e.g., "one wife per man") and internalized motivations (e.g., "extramarital sex is wrong") as a consequence of cultural learning. These expectations and motivations then influence their decision making along with other factors, including evolved motivations linked to self-interest and genetic relatedness (2). Thus, as conditions vary, so too does behavior, even if people share such norms.*

We would like to thank the commentators for their generous comments, valuable insights and helpful suggestions. We begin this response by discussing the selfishness axiom and the importance of the preferences, beliefs, and constraints framework as a way of modeling some of the proximate influences on human behavior. Next, we broaden the discussion to ultimate-level (that is evolutionary) explanations, where we review and clarify gene-culture coevolutionary theory, and then tackle the possibility that evolutionary approaches that exclude culture might be sufficient to explain the data. Finally, we consider various methodological and epistemological concerns expressed by our commentators.

This is a report on a series of studies conducted in the field with methodology approximating lab experimental methods to the degree possible. The studies were designed to investigate how human actors process and think about ethnic categories. The motivating hypothesis is that humans essentialize ethnic groups because these resemble "species" in several of their salient properties. The studies tested whether ethnic membership is a matter of enculturation or descent; whether ethnic categories are essentialized, with associated behavioral expectations; and whether physical differences between the two local groups drive the essentialism or if essentializing the categories in the first place drives this perception of physical differences. It was found that membership is held to be a matter of blood, most respondents essentialize the ethnic groups, and the distribution of phenotypes may not justify the extent to which respondents intuit that the contrast ethnic groups differ physically. EXPERIMENTAL PSYCHOLOGICAL ANTHROPOLOGYThis study is principally concerned with what kind of category is an "ethnie" in people's ordinary intuitions and the methodological issues that arise when one attempts to approximate lab experimental methods in the field to investigate native systems of categories. When people think about their own ethnie, or about out-group ethnic categories, what cognitive resources (i.e., assumptions and biases) are mobilized? Specifically, the studies I discuss here investigate and test the possibility that ethnic categories are essentialized in ways similar and perhaps homologous to the way "species" categories are essentialized.The methodology I used attempted to approximate the lab experimental methods of psychologists because there are great benefits to making anthropology more experimental and/or psychology more field oriented. Although Humphrey (1996) has observed that anthropologists ignore psychological research at their peril, she remarks in the same breath that psychology cannot