In Search of Homo Economicus: Behavioral Experiments in 15 Small-Scale Societies Author(s): Joseph Henrich, Robert Boyd, Samuel Bowles, Colin Camerer, Ernst Fehr, Herbert Gintis, Richard McElreath Source: The American Economic Review, Vol. 91, No. 2, Papers and Proceedings of the Hundred Thirteenth Annual Meeting of the American Economic Association (May, 2001), pp. 73-78 Published by: American Economic Association Stable URL: http://www.jstor.org/stable/2677736 Accessed: 28/08/2008 19:20
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http://www.jstor.org In Search of Homo Economicus: Behavioral Experiments in 15 Small-Scale Societies
By JOSEPHHENRICH, ROBERT BOYD, SAMUELBOWLES, COLIN CAMERER,ERNST FEHR, HERBERTGINTIS, AND RICHARDMCELREATH*
Recent investigations have uncovered large, ments shape behavior? If the latter, which eco- consistent deviationsfrom the predictionsof the nomic and social conditions are involved? Is textbook representationof Homo economicus reciprocalbehavior better explained statistically (Alvin E. Roth et al., 1991; Ernst Fehr and by individuals' attributessuch as their sex, age, Simon Gachter, 2000; Colin Camerer, 2001). or relative wealth, or by the attributesof the One problem appears to lie in economists' ca- group to which the individuals belong? Are nonical assumptionthat individuals are entirely there cultures that approximate the canonical self-interested:in additionto their own material account of self-regardingbehavior? payoffs, many experimentalsubjects appear to Existing research cannot answer such ques- care about fairness and reciprocity, are willing tions because virtually all subjects have been to change the distributionof materialoutcomes university students,and while there are cultural at personal cost, and are willing to rewardthose differences among studentpopulations through- who act in a cooperative mannerwhile punish- out the world, these differences are small com- ing those who do not even when these actions pared to the range of all social and cultural are costly to the individual. These deviations environments.To address the above questions, from what we will term the canonical model we and our collaborators undertook a large have importantconsequences for a wide range cross-cultural study of behavior in ultimatum, of economic phenomena,including the optimal public good, and dictatorgames. Twelve expe- design of institutions and contracts,the alloca- rienced field researchers,working in 12 coun- tion of property rights, the conditions for suc- tries on five continents, recruitedsubjects from cessful collective action, the analysis of 15 small-scale societies exhibiting a wide vari- incomplete contracts, and the persistence of ety of economic and cultural conditions. Our noncompetitive wage premia. sample consists of three foraging societies, six Fundamentalquestions remain unanswered. that practice slash-and-burnhorticulture, four Are the deviations from the canonical model nomadic herding groups, and three sedentary, evidence of universalpatterns of behavior,or do small-scale agriculturalistsocieties. Our results the individual's economic and social environ- are described in detail, with extensive ethno- graphicaccounts of the cultures we studied and citations to the relevant literature,in Henrich et * Henrich: School of Business Administration,Univer- sity of Michigan, Ann Arbor, MI 48109; Boyd and McEl- al. (2001); an extended overview paper is avail- reath: Department of Anthropology, University of able online.1 California at Los Angeles, Los Angeles, CA 90095; We can summarize our results as follows. Bowles: Department of Economics, University of Massa- First, the canonical model is not supportedin chusetts, Amherst,MA 01003, and SantaFe Institute;Cam- any society studied. Second, there is consider- erer: Department of Economics, California Institute of Technology, Pasadena, CA 91125; Fehr: Institute for Em- ably more behavioral variability across groups pilical Research in Economics, University of Ztiiich, Bltim- than had been found in previous cross-cultural lisalpstrasse 10, CH-8006, Zurich, Switzerland; Gintis: research, and the canonical model fails in a University of Massachusetts, Amherst, MA 01003. The wider variety of ways than in previous experi- research described in this paper was funded by the MacArthurFoundation's Research Group on the Natureand ments. Third, group-level differences in eco- Origin of Norms and Preferences,directed by Robert Boyd nomic organization and the degree of market and HerbertGintis. The field experiments were calTiedout by Henrich, McElreath,Michael Alvard, Abigail Barr,Jean Ensminger,Francisco Gil-Vhite, Michael Gurven,Kim Hill, FrankMarlowe, John Patton, Natalie Smith, and David Tracer. 1 URL: (www.santafe.edu) 73 74 AEA PAPERSAND PROCEEDINGS MAY2001
integrationexplain a substantialportion of the TABLE 1-THE ULTIMATUMGAME IN SMALL-SCALE behavioralvariation across societies: the higher SOCIETIES the degree of marketintegration and the higher Low- the payoffs to cooperation,the greaterthe level offer of cooperation in experimentalgames. Fourth, Mean Rejection rejection Group Country offera Modesb ratec rated individual-level economic and demographic variables do not explain behavior either within Machiguenga Peru 0.26 0.15/0.25 0.048 0.10 (72) (1/21) (1/10) or across groups. Fifth, behavior in the experi- Hadza Tanzania 0.40 0.50 0.19 0.80 ments is generally consistent with economic (big camp) (28) (5/26) (4/5) Hadza Tanzania 0.27 0.20 0.28 0.31 patternsof everyday life in these societies. (small (38) (8/29) (5/16) camp) I. The Evidence Tsiman6 Bolivia 0.37 0.5/0.3/0.25 0.00 0.00 (65) (0/70) (0/5) Quichua Ecuador 0.27 0.25 0.15 0.50 Because the ultimatumgame (UG) has been (47) (2/13) (1/2) conducted the Torguud Mongolia 0.35 0.25 0.05 0.00 throughout world with student (30) (1/20) (0/1) populationsand has generatedrobust violations Khazax Mongolia 0.36 0.25 of the canonicalmodel, we conductedthis game Mapuche Chile 0.34 0.50/0.33 0.067 0.2 (46) (2/30) (2/10) in all of our 17 societies. The "proposer"in this Au PNG 0.43 0.3 0.27 1.00 game is provisionally assigned an amount (33) (8/30) (1/1) equivalentto a day or two' s wages in the society Gnau PNG 0.38 0.4 0.4 0.50 (32) (10/25) (3/6) and asked to propose an offer to a second per- Sangu Tanzania 0.41 0.50 0.25 1.00 son, the "respondent."The respondentmay then farmers (35) (5/20) (1/1) Sangu Tanzania 0.42 0.50 0.05 1.00 either accept the offer, in which case the two herders (40) (1/20) (1/1) players receive the proposed amounts, or reject Unresettled Zimbabwe 0.41 0.50 0.1 0.33 it, in which case the two receive nothing. If both villagers (56) (3/31) (2/5) Resettled Zimbabwe 0.45 0.50 0.07 0.57 players conform to the canonical model and if villagers (70) (12/86) (4/7) this is common knowledge, it is easy to see that Achuar Ecuador 0.42 0.50 0.00 0.00 the proposerwill know that the respondentwill (36) (0/16) (0/1) Orma Kenya 0.44 0.50 0.04 0.00 accept any positive offer and so will offer the (54) (2/56) (0/0) smallest possible amount, which will be Ach6 Paraguay 0.51 0.50/0.40 0.00 0.00 (75) (0/5 1) (0/8) accepted. Lamelarae Indonesia 0.58 0.50 0.00 0.00 In most of our field experiments subjects (63) (3/8) (4/20) played anonymously, not knowing the identity Note: PNG = Papua New Guinea. of the person or persons with whom they were a This column shows the mean offer (as a proportion) in the ultimatum paired. The stakes of most games were denom- game for each society. b This column shows the modal offer(s), with the percentage of inated in money (though in some cases tobacco subjects who make modal offers (in parentheses). c The rejection rate (as a proportion), with the actual numbers given in or other goods were used). In all cases, we parentheses. d The rejection rate for offers of 20 percent or less, with the actual tested prospectiveparticipants for their compre- numbers given in parentheses. hension of the experiment and eliminated any e Includes experimenter-generated low offers. who appearednot to grasp the game. The systematic deviations from the canonical model in our sample of simple societies can be between 40 percent and 50 percent.Finally, the inferred from Table 1, which lists all groups Ache and the Lamelarahad mean offers greater where UG's were conducted. Contraryto the than 50 percent. prediction of the standard model, even the These group differences are strikingly large groups with the smallest offers have mean of- comparedto previous cross-culturalwork com- fers greaterthan 25 percent of stake size. Illus- paringultimatum-game behavior among univer- trating our second result (the large variation in sity students (Roth et al., 1991). While mean mean offers across societies), others, including offers in industrialsocieties are typically close the Torguudand the Mapuche, offered between to 44 percent, the mean offers in our sample 30 percent and 40 percent, while still others, range from 26 percent to 58 percent. Similarly, including the Achuar and the Sangu, offered while modal offers are consistently 50 percent VOL. 91 NO. 2 ECONOMICSAND SOCIALBEHAVIOR 75
in industrialized societies, our sample modes Data from public-goods games played in vary from 15 percent to 50 percent. seven of these societies also show much greater As shown in the last two columns of Table variationthan previously found, and again they 1, rejections are also much more variable than exhibit novel deviations from the predictionsof previously observed. While in industrialsocie- the canonical model. Public-goods games ask ties offers below 20 percent are rejected with subjects to contribute to a common pool that probability0.40 to 0.60, rejectionsof low offers will be expandedby the experimenterand then are extremely rareamong some groups.In other redistributed to all subjects. The canonical groups, however, we observe substantialrejec- prediction is that everyone will free-ride, con- tions rates, including frequentrejections of of- tributingnothing. Typical distributionsof public- fers above 50 percent.Among the Achuar,Ache goods game contributionswith students have a and Tsimane, we observe zero rejections after U-shape, with the mode at contributingnothing, 16, 51, and 70 proposer offers, respectively. a secondarymode at full cooperation,and mean Moreover, while the Ache and Achuar made contributionbetween 40 percentand 60 percent. fairly equitableoffers, nearly 50 percentof Tsi- By contrast,for instance,the Machiguengahave mane offers were at or below 30 percent,yet all a mode at contributingnothing, with not a sin- were accepted. Similarly, Machiguenga re- gle subject cooperating fully, yielding a mean sponders rejected only one offer, despite the contributionof 22 percent. Also, the Ache and fact that over 75 percent of their offers were Tsimane both exhibit inverted distributions, below 30 percent.At the other end of the rejec- with few or no contributionsat full free-riding tion scale, Hadzaresponders rejected 24 percent or full cooperation. of all proposeroffers and 43 percentof offers at In three dictator games played in three of 20 percent and below. Unlike the Hadza, who these societies, groups also deviate both from preferentiallyrejected low offers, the Au and typical behavior in industrializedsocieties and Gnau of PapuaNew Guinearejected both unfair the canonical predictions. The dictator game and hyper-fair (greater than 50 percent) offers allows the proposersimply to assign some frac- with nearly equal frequency. tion of the stake to a passive second party who In experiments with university subjects, receives that amount. Among university stu- offers are generally consistent with income- dents, the distributionof "offers"in the dictator maximization, given the distribution of rejec- game typically has a mode at zero and a sec- tions. In our sample, however, in the majority ondary mode at 50/50, while the canonical of groups the modal behavior of the propos- model predicts that people will give zero. Con- ers is not consistent with expected income- trastingwith both, the Orma have a mode at 50 maximization. In the Tsimane and Ache cases, percent and a secondary mode at 20 percent. for instance, there are no rejections of offers Hadza dictators show a mode at 10 percent. below 20 percent, although there were several Offers of 0 percent and 50 percent are also low offers. The rejection rate for all other popular. Among the Tsimane, there were no offers is also zero. Yet the modal offer in both zero offers; the mean was 32 percent, and the groups is 50 percent, and the average offers mode was 25 percent. are 37 percent and 51 percent, respectively. Where possible, we used the relationship II. What Explains Group-Level Differences? between the size of the offer and the frac- tion of rejections to estimate income-maxi- The large variations across the different mizing offers for the group in question. In one cultural groups suggest that preferences or ex- group, the Hadza proposers approximated the pectations are affected by group-specificcondi- income-maximizing offer quite closely, thus tions, such as social institutions or cultural confirming the canonical model; but Hadza fairness norms. The large variance in institu- responders frequently rejected substantial tions and norms in our sample allowed us to positive offers, thus violating the canonical addressthis question systematically.Because of model. In all other groups, average offers space limits we here concentrateon the behav- exceeded the income-maximizing offer, in ior of proposersin the UG. We rank-orderedthe most cases by a substantial amount. societies along two dimensions: 76 AEA PAPERSAND PROCEEDINGS MAY2001
(i) Payoffs to cooperation (PC).-How impor- reflect the culture of gift-giving found in these tant and how large is a group's payoff from societies. Among these groups, like many in cooperationin economic production? New Guinea, accepting gifts, even unsolicited (ii) Market integration (MI).-How much do ones, commits one to reciprocateat some future people rely on market exchange in their time to be determinedby the giver. Receipt of daily lives? large gifts also establishes one in a subordinate position. Consequently,excessively large gifts, On the first dimension, payoffs to coopera- especially unsolicited ones, will frequently be tion, the Machiguenga and Tsimane rank the refused because of the anxiety about the unspe- lowest; they are almost entirely economically cific strings attached. Similarly the low offers independent at the family level and engage and high rejection rates of the Hadza appearto rarely in productive activities involving more reflect their reluctantprocess of sharing(termed than members of a family. By contrast, the "toleratedtheft" by a leading ethnographerof Lamelarawhale-hunters go to sea in large ca- the Hadza). While the Hadza extensively share noes manned by a dozen or more individuals. meat, many hunters look for opportunities to The rationalefor PC as a predictorof UG offers avoid sharing and share only because they fear is that with little cooperative production there the social consequences of not sharing, in the will be little necessity to share returns, while form of informal social sanctions, gossip, and those whose livelihood depends on large-scale ostracism. This behavior is apparently trans- cooperation like the Lamelara must develop ferred to the experimentalsetting. ways of sharing the joint surplus. Thus we Unlike the Hadza, the Ache did not reject low might expect that a higher level of PC will offers, and despite this the vast majorityof the increase sharingbehavior in the UG. The ratio- Ache (94 percent)made offers above 40 percent nale for market integration as an explanatory of the stake size. This coincides neatly with variable is that the more frequently people ex- ethnographicdescriptions indicating widespread perience markettransactions, the more they will meat-sharing and cooperation in community also experience abstractsharing principles con- projects despite the absence of a fear of punish- cerningbehaviors toward strangers of which the ment in Ache society. Ache hunters, retuming UG is an example. home, quietly leave their kill at the edge of We sought to explain group mean UG offers camp, often claiming that the hunt was fruitless; on the basis of these two dimensions of eco- their catch is later discovered and collected by nomic structure.In a regression, both PC and others and then meticulously shared among all MI were highly significant,their (positive) nor- in the camp. We think it likely that the stake in malized regression coefficients were large in the game seemed to some of the Ache subjects magnitude (about 0.3), and the two measures as analogous to their catch. jointly explained 68 percent of the variance. The Machiguenga show the lowest coopera- The impact of PC and MI remains large and tion rates in public-good games, reflecting eth- robust in an equation predicting individual of- nographic descriptions of Machiguenga life, fers, including individualmeasures such as sex, which report little cooperation, exchange, or age, relative wealth, village population size, sharing beyond the family unit. By contrast, stake size, and experimenterexperience with the Ormaexperimental subjects quickly dubbedthe group.Surprisingly, none of these individuallevel public-goods experimenta harambee game, re- measureswas significantlyrelated to offers. ferring to the widespreadinstitution of village- A plausible interpretationof our subjects' level voluntary contributionsfor public-goods behaviors is that, when faced with a novel sit- projects such as schools or roads. Not surpris- uation (the experiment), they looked for ana- ingly, they contributedgenerously (58 percent logues in their daily experience, asking "What of the stake), somewhat higher than most U.S. familiar situation is this game like?" and then subjects contributein similar experiments. acted in a way appropriatefor the analogous III. Discussion situation.For instance, the hyper-fairUG offers (greaterthan 50 percent) and the frequentrejec- Our data indicate that the degree of cooper- tions of these offers among the Au and Gnau ation, sharing, and punishment exhibited by VOL. 91 NO. 2 ECONOMICSAND SOCIALBEHAVIOR 77 experimental subjects closely corresponds to long-run evolutionary processes governing the templates for these behaviors in the subjects' distribution of genes and cultural practices daily lives, and that the substantialvariability in could well have resultedin a substantialfraction experimentalbehaviors across groups is an ex- of each populationbeing predisposedin certain pression of the large between-groupdifferences situations to forgo material payoffs in order to in the structuresof social interactionand modes share with others, or to punish unfair actions, as of livelihood.How do we interpretthese results? our experimental subjects did. A number of Some of the variabilityamong groupsmay be recent contributions have shown that, under due to variations in implementation.We doubt conditions that appearto approximatethe social that this explains the markedlydiffering behav- and physical environmentsof early humanpop- iors across groups, however, since the experi- ulations, prosocial behavior can proliferatein a ments were run from identical protocols across populationin which it is initially rare(Bowles et groups and were thus as similar in procedures al., 2001). and stake size as we could achieve. Where we could test for experimenter effects we found IV. Conclusion none. It is possible also that our subjects pre- sumed that their actions would somehow be- While our results do not imply that econo- come public. In a good many of our cases, mists should abandonthe rational-actorframe- however, subsequentconversations with partic- work, they do suggest two major revisions. ipants convinced us that this was not the case. First, the canonical model of the self-interested Finally, it could be that participants thought material payoff-maximizing actor is systemati- they were in a repeatedinteraction, even though cally violated. In all societies studied,UG offers the games we used were clearly one-shot. We are strictly positive and often substantially in do not find this interpretationcompelling, how- excess of the expected income-maximizing of- ever, since there is extensive evidence from fer, as are contributions in the public-goods experiments in advanced economies that sub- game, while rejections of positive offers in jects understandthe game very well, and those some societies occur at a considerablerate. Sec- who reject a positive offer in the ultimatum ond, preferencesover economic choices are not game, when interviewed by the experimenter, exogenous as the canonical model would have typically do not say that they made an error,but it, but rather are shaped by the economic and ratheraffirm having goals besides maximizing a social interactionsof everyday life. This result monetarypayoff. implies that judgments in welfare economics Why are many subjects willing to share that assume exogenous preferences are ques- resources and undertake costly reciprocal ac- tionable, as are predictions of the effects of tions in anonymous one-shot interactions? changingeconomic policies and institutionsthat Bowles et al. (2001) will provide a more fail to take account of behavioral change. Fi- extensive response than can be offered here. nally, the connection between experimentalbe- We suspect that a proximate reason for these havior and the structureof everyday economic behaviors is that situations cue emotional re- life should provide an importantclue in revising sponses which induce the behaviors we have the canonical model of individual choice measured. For example, many ultimatum- behavior. game responders from advanced societies, when facing a low offer, experience an emo- REFERENCES tional impulse to hurt the proposer for being unfair, just as the subject might in a real-life bargainingsituation. Similarly, the New Guinea Bowles, Samuel; Boyd, Richard; Fehr, Ernst and responders who rejected hyper-fairoffers in the Gintis, Herbert, eds. Thefoundations of social UG may have experiencedthe same anxiety that reciprocity. Unpublished manuscript, Uni- emerges when somebodygives them an unsolic- versity of Massachusetts,2001. ited gift in everydaylife. 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