In Search of Homo Economicus: Behavioral Experimentsin 15 Small-Scale SocietiesBy JOSEPH HENRICH,ROBERT BOYD,SAMUEL BOWLES,COLIN CAMERER,ERNST FEHR,HERBERT GINTIS, AND RICHARD MCELREATH*Recent investigations have uncovered large,consistent deviations from the predictions of thetextbook representation of Homo economicus(Alvin E. Roth et al., 1991; Ernst Fehr andSimon Ga¨chter, 2000; Colin Camerer, 2001).One problem appears to lie in economists’ ca-nonical assumption that individuals are entirelyself-interested: in addition to their own materialpayoffs, many experimental subjects appear tocare about fairness and reciprocity, are willingto change the distribution of material outcomesat personal cost, and are willing to reward thosewho act in a cooperative manner while punish-ing those who do not even when these actionsare costly to the individual. These deviationsfrom what we will term the canonical modelhave important consequences for a wide rangeof economic phenomena, including the optimaldesign of institutions and contracts, the alloca-tion of property rights, the conditions for suc-cessful collective action, the analysis ofincomplete contracts, and the persistence ofnoncompetitive wage premia.Fundamental questions remain unanswered.Are the deviations from the canonical modelevidence of universal patterns of behavior, or dothe individual’s economic and social environ-ments shape behavior? If the latter, which eco-nomic and social conditions are involved? Isreciprocal behavior better explained statisticallyby individuals’ attributes such as their sex, age,or relative wealth, or by the attributes of thegroup to which the individuals belong? Arethere cultures that approximate the canonicalaccount of self-regarding behavior?Existing research cannot answer such ques-tions because virtually all subjects have beenuniversity students, and while there are culturaldifferences among student populations through-out the world, these differences are small com-pared to the range of all social and culturalenvironments. To address the above questions,we and our collaborators undertook a largecross-cultural study of behavior in ultimatum,public good, and dictator games. Twelve expe-rienced field researchers, working in 12 coun-tries on five continents, recruited subjects from15 small-scale societies exhibiting a wide vari-ety of economic and cultural conditions. Oursample consists of three foraging societies, sixthat practice slash-and-burn horticulture, fournomadic herding groups, and three sedentary,small-scale agriculturalist societies. Our resultsare described in detail, with extensive ethno-graphic accounts of the cultures we studied andcitations to the relevant literature, in Henrich etal. (2001); an extended overview paper is avail-able online.1We can summarize our results as follows.First, the canonical model is not supported inany society studied. Second, there is consider-ably more behavioral variability across groupsthan had been found in previous cross-culturalresearch, and the canonical model fails in awider variety of ways than in previous experi-ments. Third, group-level differences in eco-nomic organization and the degree of market* Henrich: School of Business Administration, Univer-sity of Michigan, Ann Arbor, MI 48109; Boyd and McEl-reath: Department of Anthropology, University ofCalifornia at Los Angeles, Los Angeles, CA 90095;Bowles: Department of Economics, University of Massa-chusetts, Amherst, MA 01003, and Santa Fe Institute; Cam-erer: Department of Economics, California Institute ofTechnology, Pasadena, CA 91125; Fehr: Institute for Em-pirical Research in Economics, University of Zu¨rich, Blu¨m-lisalpstrasse 10, CH-8006, Zurich, Switzerland; Gintis:University of Massachusetts, Amherst, MA 01003. Theresearch described in this paper was funded by theMacArthur Foundation’s Research Group on the Nature andOrigin of Norms and Preferences, directed by Robert Boydand Herbert Gintis. The field experiments were carried outby Henrich, McElreath, Michael Alvard, Abigail Barr, JeanEnsminger, Francisco Gil-White, Michael Gurven, Kim Hill,Frank Marlowe, John Patton, Natalie Smith, and David Tracer.1URL: 具www.santafe.edu典73integration explain a substantial portion of thebehavioral variation across societies: the higherthe degree of market integration and the higherthe payoffs to cooperation, the greater the levelof cooperation in experimental games. Fourth,individual-level economic and demographicvariables do not explain behavior either withinor across groups. Fifth, behavior in the experi-ments is generally consistent with economicpatterns of everyday life in these societies.I. The EvidenceBecause the ultimatum game (UG) has beenconducted throughout the world with studentpopulations and has generated robust violationsof the canonical model, we conducted this gamein all of our 17 societies. The “proposer” in thisgame is provisionally assigned an amountequivalent to a day or two’s wages in the societyand asked to propose an offer to a second per-son, the “respondent.” The respondent may theneither accept the offer, in which case the twoplayers receive the proposed amounts, or rejectit, in which case the two receive nothing. If bothplayers conform to the canonical model and ifthis is common knowledge, it is easy to see thatthe proposer will know that the respondent willaccept any positive offer and so will offer thesmallest possible amount, which will beaccepted.In most of our field experiments subjectsplayed anonymously, not knowing the identityof the person or persons with whom they werepaired. The stakes of most games were denom-inated in money (though in some cases tobaccoor other goods were used). In all cases, wetested prospective participants for their compre-hension of the experiment and eliminated anywho appeared not to grasp the game.The systematic deviations from the canonicalmodel in our sample of simple societies can beinferred from Table 1, which lists all groupswhere UG’s were conducted. Contrary to theprediction of the standard model, even thegroups with the smallest offers have mean of-fers greater than 25 percent of stake size. Illus-trating our second result (the large variation inmean offers across societies), others, includingthe Torguud and the Mapuche, offered between30 percent and 40 percent, while still others,including the Achuar and the Sangu, offeredbetween 40 percent and 50 percent. Finally, theAche´ and the Lamelara had mean