In Search of Homo Economicus: Behavioral Experimentsin 15 Small-Scale Societies

By JOSEPHHENRICH, 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 ofHomo economicus(Alvin E. Roth et al., 1991; Ernst Fehr andSimon Gachter, 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.1

We 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, Blum-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. 1 URL: ^www.santafe.edu&

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integration 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 Evidence

Because 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, offered

between 40 percent and 50 percent. Finally, theAcheand the Lamelara had mean offers greaterthan 50 percent.

These group differences are strikingly largecompared to previous cross-cultural work com-paring ultimatum-game behavior among univer-sity students (Roth et al., 1991). While meanoffers in industrial societies are typically closeto 44 percent, the mean offers in our samplerange from 26 percent to 58 percent. Similarly,while modal offers are consistently 50 percent

TABLE 1—THE ULTIMATUM GAME IN SMALL -SCALE

SOCIETIES

Group CountryMeanoffera Modesb

Rejectionratec

Low-offer

rejectionrated

Machiguenga Peru 0.26 0.15/0.25 0.048 0.10(72) (1/21) (1/10)

Hadza Tanzania 0.40 0.50 0.19 0.80(big camp) (28) (5/26) (4/5)

Hadza Tanzania 0.27 0.20 0.28 0.31(smallcamp)

(38) (8/29) (5/16)

Tsimane 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(47) (2/13) (1/2)

Torguud Mongolia 0.35 0.25 0.05 0.00(30) (1/20) (0/1)

Khazax Mongolia 0.36 0.25Mapuche Chile 0.34 0.50/0.33 0.067 0.2

(46) (2/30) (2/10)Au PNG 0.43 0.3 0.27 1.00

(33) (8/30) (1/1)Gnau PNG 0.38 0.4 0.4 0.50

(32) (10/25) (3/6)Sangu Tanzania 0.41 0.50 0.25 1.00

farmers (35) (5/20) (1/1)Sangu Tanzania 0.42 0.50 0.05 1.00

herders (40) (1/20) (1/1)Unresettled Zimbabwe 0.41 0.50 0.1 0.33

villagers (56) (3/31) (2/5)Resettled Zimbabwe 0.45 0.50 0.07 0.57

villagers (70) (12/86) (4/7)Achuar Ecuador 0.42 0.50 0.00 0.00

(36) (0/16) (0/1)Orma Kenya 0.44 0.50 0.04 0.00

(54) (2/56) (0/0)Ache Paraguay 0.51 0.50/0.40 0.00 0.00

(75) (0/51) (0/8)Lamelarae Indonesia 0.58 0.50 0.00 0.00

(63) (3/8) (4/20)

Note: PNG 5 Papua New Guinea.a This column shows the mean offer (as a proportion) in the ultimatum

game for each society.b This column shows the modal offer(s), with the percentage of

subjects who make modal offers (in parentheses).c The rejection rate (as a proportion), with the actual numbers given in

parentheses.d The rejection rate for offers of 20 percent or less, with the actual

numbers given in parentheses.e Includes experimenter-generated low offers.

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in industrialized societies, our sample modesvary from 15 percent to 50 percent.

As shown in the last two columns of Table1, rejections are also much more variable thanpreviously observed. While in industrial socie-ties offers below 20 percent are rejected withprobability 0.40 to 0.60, rejections of low offersare extremely rare among some groups. In othergroups, however, we observe substantial rejec-tions rates, including frequent rejections of of-fers above 50 percent. Among the Achuar, Ache´and Tsimane´, we observe zero rejections after16, 51, and 70 proposer offers, respectively.Moreover, while the Ache´ and Achuar madefairly equitable offers, nearly 50 percent of Tsi-maneoffers were at or below 30 percent, yet allwere accepted. Similarly, Machiguenga re-sponders rejected only one offer, despite thefact that over 75 percent of their offers werebelow 30 percent. At the other end of the rejec-tion scale, Hadza responders rejected 24 percentof all proposer offers and 43 percent of offers at20 percent and below. Unlike the Hadza, whopreferentially rejected low offers, the Au andGnau of Papua New Guinea rejected both unfairand hyper-fair (greater than 50 percent) offerswith nearly equal frequency.

In experiments with university subjects,offers are generally consistent with income-maximization, given the distribution of rejec-tions. In our sample, however, in the majorityof groups the modal behavior of the propos-ers is not consistent with expected income-maximization. In the Tsimane´ and Achecases,for instance, there are no rejections of offersbelow 20 percent, although there were severallow offers. The rejection rate for all otheroffers is also zero. Yet the modal offer in bothgroups is 50 percent, and the average offersare 37 percent and 51 percent, respectively.Where possible, we used the relationshipbetween the size of the offer and the frac-tion of rejections to estimate income-maxi-mizing offers for the group in question. In onegroup, the Hadza proposers approximated theincome-maximizing offer quite closely, thusconfirming the canonical model; but Hadzaresponders frequently rejected substantialpositive offers, thus violating the canonicalmodel. In all other groups, average offersexceeded the income-maximizing offer, inmost cases by a substantial amount.

Data from public-goods games played inseven of these societies also show much greatervariation than previously found, and again theyexhibit novel deviations from the predictions ofthe canonical model. Public-goods games asksubjects to contribute to a common pool thatwill be expanded by the experimenter and thenredistributed to all subjects. The canonicalprediction is that everyone will free-ride, con-tributing nothing. Typical distributions of public-goods game contributions with students have aU-shape, with the mode at contributing nothing,a secondary mode at full cooperation, and meancontribution between 40 percent and 60 percent.By contrast, for instance, the Machiguenga havea mode at contributing nothing, with not a sin-gle subject cooperating fully, yielding a meancontribution of 22 percent. Also, the Ache´ andTsimane both exhibit inverted distributions,with few or no contributions at full free-ridingor full cooperation.

In three dictator games played in three ofthese societies, groups also deviate both fromtypical behavior in industrialized societies andthe canonical predictions. The dictator gameallows the proposer simply to assign some frac-tion of the stake to a passive second party whoreceives that amount. Among university stu-dents, the distribution of “offers” in the dictatorgame typically has a mode at zero and a sec-ondary mode at 50/50, while the canonicalmodel predicts that people will give zero. Con-trasting with both, the Orma have a mode at 50percent and a secondary mode at 20 percent.Hadza dictators show a mode at 10 percent.Offers of 0 percent and 50 percent are alsopopular. Among the Tsimane´, there were nozero offers; the mean was 32 percent, and themode was 25 percent.

II. What Explains Group-Level Differences?

The large variations across the differentcultural groups suggest that preferences or ex-pectations are affected by group-specific condi-tions, such as social institutions or culturalfairness norms. The large variance in institu-tions and norms in our sample allowed us toaddress this question systematically. Because ofspace limits we here concentrate on the behav-ior of proposers in the UG. We rank-ordered thesocieties along two dimensions:

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(i) Payoffs to cooperation (PC).—How impor-tant and how large is a group’s payoff fromcooperation in economic production?

(ii) Market integration (MI).—How much dopeople rely on market exchange in theirdaily lives?

On the first dimension, payoffs to coopera-tion, the Machiguenga and Tsimane´ rank thelowest; they are almost entirely economicallyindependent at the family level and engagerarely in productive activities involving morethan members of a family. By contrast, theLamelara whale-hunters go to sea in large ca-noes manned by a dozen or more individuals.The rationale for PC as a predictor of UG offersis that with little cooperative production therewill be little necessity to share returns, whilethose whose livelihood depends on large-scalecooperation like the Lamelara must developways of sharing the joint surplus. Thus wemight expect that a higher level of PC willincrease sharing behavior in the UG. The ratio-nale for market integration as an explanatoryvariable is that the more frequently people ex-perience market transactions, the more they willalso experience abstract sharing principles con-cerning behaviors toward strangers of which theUG is an example.

We sought to explain group mean UG offerson the basis of these two dimensions of eco-nomic structure. In a regression, both PC andMI were highly significant, their (positive) nor-malized regression coefficients were large inmagnitude (about 0.3), and the two measuresjointly explained 68 percent of the variance.The impact of PC and MI remains large androbust in an equation predicting individual of-fers, including individual measures such as sex,age, relative wealth, village population size,stake size, and experimenter experience with thegroup. Surprisingly, none of these individual levelmeasures was significantly related to offers.

A plausible interpretation of our subjects’behaviors is that, when faced with a novel sit-uation (the experiment), they looked for ana-logues in their daily experience, asking “Whatfamiliar situation is this game like?” and thenacted in a way appropriate for the analogoussituation. For instance, the hyper-fair UG offers(greater than 50 percent) and the frequent rejec-tions of these offers among the Au and Gnau

reflect the culture of gift-giving found in thesesocieties. Among these groups, like many inNew Guinea, accepting gifts, even unsolicitedones, commits one to reciprocate at some futuretime to be determined by the giver. Receipt oflarge gifts also establishes one in a subordinateposition. Consequently, excessively large gifts,especially unsolicited ones, will frequently berefused because of the anxiety about the unspe-cific strings attached. Similarly the low offersand high rejection rates of the Hadza appear toreflect their reluctant process of sharing (termed“tolerated theft” by a leading ethnographer ofthe Hadza). While the Hadza extensively sharemeat, many hunters look for opportunities toavoid sharing and share only because they fearthe social consequences of not sharing, in theform of informal social sanctions, gossip, andostracism. This behavior is apparently trans-ferred to the experimental setting.

Unlike the Hadza, the Ache´ did not reject lowoffers, and despite this the vast majority of theAche(94 percent) made offers above 40 percentof the stake size. This coincides neatly withethnographic descriptions indicating widespreadmeat-sharing and cooperation in communityprojects despite the absence of a fear of punish-ment in Achesociety. Ache´ hunters, returninghome, quietly leave their kill at the edge ofcamp, often claiming that the hunt was fruitless;their catch is later discovered and collected byothers and then meticulously shared among allin the camp. We think it likely that the stake inthe game seemed to some of the Ache´ subjectsas analogous to their catch.

The Machiguenga show the lowest coopera-tion rates in public-good games, reflecting eth-nographic descriptions of Machiguenga life,which report little cooperation, exchange, orsharing beyond the family unit. By contrast,Orma experimental subjects quickly dubbed thepublic-goods experiment aharambeegame, re-ferring to the widespread institution of village-level voluntary contributions for public-goodsprojects such as schools or roads. Not surpris-ingly, they contributed generously (58 percentof the stake), somewhat higher than most U.S.subjects contribute in similar experiments.

III. Discussion

Our data indicate that the degree of cooper-ation, sharing, and punishment exhibited by

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experimental subjects closely corresponds totemplates for these behaviors in the subjects’daily lives, and that the substantial variability inexperimental behaviors across groups is an ex-pression of the large between-group differencesin the structures of social interaction and modesof livelihood. How do we interpret these results?

Some of the variability among groups may bedue to variations in implementation. We doubtthat this explains the markedly differing behav-iors across groups, however, since the experi-ments were run from identical protocols acrossgroups and were thus as similar in proceduresand stake size as we could achieve. Where wecould test for experimenter effects we foundnone. It is possible also that our subjects pre-sumed that their actions would somehow be-come public. In a good many of our cases,however, subsequent conversations with partic-ipants convinced us that this was not the case.Finally, it could be that participants thoughtthey were in a repeated interaction, even thoughthe games we used were clearly one-shot. Wedo not find this interpretation compelling, how-ever, since there is extensive evidence fromexperiments in advanced economies that sub-jects understand the game very well, and thosewho reject a positive offer in the ultimatumgame, when interviewed by the experimenter,typically do not say that they made an error, butrather affirm having goals besides maximizing amonetary payoff.

Why are many subjects willing to shareresources and undertake costly reciprocal ac-tions in anonymous one-shot interactions?Bowles et al. (2001) will provide a moreextensive response than can be offered here.We suspect that a proximate reason for thesebehaviors is that situations cue emotional re-sponses which induce the behaviors we havemeasured. For example, many ultimatum-game responders from advanced societies,when facing a low offer, experience an emo-tional impulse to hurt the proposer for beingunfair, just as the subject might in a real-lifebargaining situation. Similarly, the New Guinearesponders who rejectedhyper-fair offers in theUG may have experienced the same anxiety thatemerges when somebody gives them an unsolic-ited gift in everyday life.

What are the ultimate determinants of ouremotions and situation-specific cues? Here

long-run evolutionary processes governing thedistribution of genes and cultural practicescould well have resulted in a substantial fractionof each population being predisposed in certainsituations to forgo material payoffs in order toshare with others, or to punish unfair actions, asour experimental subjects did. A number ofrecent contributions have shown that, underconditions that appear to approximate the socialand physical environments of early human pop-ulations, prosocial behavior can proliferate in apopulation in which it is initially rare (Bowles etal., 2001).

IV. Conclusion

While our results do not imply that econo-mists should abandon the rational-actor frame-work, they do suggest two major revisions.First, the canonical model of the self-interestedmaterial payoff-maximizing actor is systemati-cally violated. In all societies studied, UG offersare strictly positive and often substantially inexcess of the expected income-maximizing of-fer, as are contributions in the public-goodsgame, while rejections of positive offers insome societies occur at a considerable rate. Sec-ond, preferences over economic choices are notexogenous as the canonical model would haveit, but rather are shaped by the economic andsocial interactions of everyday life. This resultimplies that judgments in welfare economicsthat assume exogenous preferences are ques-tionable, as are predictions of the effects ofchanging economic policies and institutions thatfail to take account of behavioral change. Fi-nally, the connection between experimental be-havior and the structure of everyday economiclife should provide an important clue in revisingthe canonical model of individual choicebehavior.

REFERENCES

Bowles, Samuel; Boyd, Richard; Fehr, Ernst andGintis, Herbert, eds.The foundations of socialreciprocity. Unpublished manuscript, Uni-versity of Massachusetts, 2001.

Camerer, Colin F. Behavioral economics. Prince-ton, NJ: Princeton University Press, 2001(forthcoming).

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Henrich, Joseph; Boyd, Robert; Bowles, Samuel;Camerer, Colin; Fehr, Ernst; Gintis, Herbertand McElreath, Richard. “Cooperation, Reci-procity and Punishment in Fifteen Small-

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