《实验经济学》课程教学资源（参考文献）In Search of Homo Economicus：Behavioral Experiments in 15 Small-Scale Societies.pdf_大学文库

In Search of Homo Economicus: Behavioral Experiments in 15 Small-Scale Societies By 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 the textbook representation of Homo economicus (Alvin E. Roth et al., 1991; Ernst Fehr and Simon Gachter, 2000; Colin Camerer, 2001). One problem appears to lie in economists' ca- nonical assumption that individuals are entirely self-interested: in addition to their own material payoffs, many experimental subjects appear to care about fairness and reciprocity, are willing to change the distribution of material outcomes at personal cost, and are willing to reward those who act in a cooperative manner while punish- ing those who do not even when these actions are costly to the individual. These deviations from what we will term the canonical model have important consequences for a wide range of economic phenomena, including the optimal design of institutions and contracts, the alloca- tion of property rights, the conditions for suc- cessful collective action, the analysis of incomplete contracts, and the persistence of noncompetitive wage premia. Fundamental questions remain unanswered. Are the deviations from the canonical model evidence of universal patterns of behavior, or do the individual's economic and social environ- ments shape behavior? If the latter, which eco- nomic and social conditions are involved? Is reciprocal behavior better explained statistically by individuals' attributes such as their sex, age, or relative wealth, or by the attributes of the group to which the individuals belong? Are there cultures that approximate the canonical account of self-regarding behavior? Existing research cannot answer such ques- tions because virtually all subjects have been university students, and while there are cultural differences among student populations through- out the world, these differences are small com- pared to the range of all social and cultural environments. To address the above questions, we and our collaborators undertook a large cross-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 from 15 small-scale societies exhibiting a wide vari- ety of economic and cultural conditions. Our sample consists of three foraging societies, six that practice slash-and-burn horticulture, four nomadic herding groups, and three sedentary, small-scale agriculturalist societies. Our results are described in detail, with extensive ethno- graphic accounts of the cultures we studied and citations to the relevant literature, in Henrich et al. (2001); an extended overview paper is avail- able online.1 We can summarize our results as follows. First, the canonical model is not supported in any society studied. Second, there is consider- ably more behavioral variability across groups than had been found in previous cross-cultural research, and the canonical model fails in a wider 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 of California 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 of Technology, Pasadena, CA 91125; Fehr: Institute for Em- pilical Research in Economics, University of Ztiiich, Bltim- lisalpstrasse 10, CH-8006, Zurich, Switzerland; Gintis: University of Massachusetts, Amherst, MA 01003. The research described in this paper was funded by the MacArthur Foundation's Research Group on the Nature and Origin of Norms and Preferences, directed by Robert Boyd and Herbert Gintis. The field experiments were calTied out by Henrich, McElreath, Michael Alvard, Abigail Barr, Jean Ensminger, Francisco Gil-Vhite, Michael Gurven, Kim Hill, Frank Marlowe, John Patton, Natalie Smith, and David Tracer. 1 URL: (www.santafe.edu) 73 This content downloaded from 218.106.182.240 on Tue, 01 Mar 2016 11:52:59 UTC All use subject to JSTOR Terms and Conditions

74 AEA PAPERS AND PROCEEDINGS MAY 2001 integration explain a substantial portion of the behavioral variation across societies: the higher the degree of market integration and the higher the payoffs to cooperation, the greater the level of cooperation in experimental games. Fourth, individual-level economic and demographic variables do not explain behavior either within or across groups. Fifth, behavior in the experi- ments is generally consistent with economic patterns of everyday life in these societies. I. The Evidence Because the ultimatum game (UG) has been conducted throughout the world with student populations and has generated robust violations of the canonical model, we conducted this game in all of our 17 societies. The "proposer" in this game is provisionally assigned an amount equivalent to a day or two' s wages in the society and asked to propose an offer to a second per- son, the "respondent." The respondent may then either accept the offer, in which case the two players receive the proposed amounts, or reject it, in which case the two receive nothing. If both players conform to the canonical model and if this is common knowledge, it is easy to see that the proposer will know that the respondent will accept any positive offer and so will offer the smallest possible amount, which will be accepted. In most of our field experiments subjects played anonymously, not knowing the identity of the person or persons with whom they were paired. The stakes of most games were denom- inated in money (though in some cases tobacco or other goods were used). In all cases, we tested prospective participants for their compre- hension of the experiment and eliminated any who appeared not to grasp the game. The systematic deviations from the canonical model in our sample of simple societies can be inferred from Table 1, which lists all groups where UG's were conducted. Contrary to the prediction of the standard model, even the groups with the smallest offers have mean of- fers greater than 25 percent of stake size. Illus- trating our second result (the large variation in mean offers across societies), others, including the Torguud and the Mapuche, offered between 30 percent and 40 percent, while still others, including the Achuar and the Sangu, offered TABLE 1-THE ULTIMATUM GAME IN SMALL-SCALE SOCIETIES Low- offer Mean Rejection rejection Group Country offera Modesb ratec rated 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 (small (38) (8/29) (5/16) camp) 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 (47) (2/13) (1/2) Torguud Mongolia 0.35 0.25 0.05 0.00 (30) (1/20) (0/1) Khazax Mongolia 0.36 0.25 Mapuche 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) Ach6 Paraguay 0.51 0.50/0.40 0.00 0.00 (75) (0/5 1) (0/8) Lamelarae Indonesia 0.58 0.50 0.00 0.00 (63) (3/8) (4/20) Note: PNG = 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. between 40 percent and 50 percent. Finally, the Ache and the Lamelara had mean offers greater than 50 percent. These group differences are strikingly large compared to previous cross-cultural work com- paring ultimatum-game behavior among univer- sity students (Roth et al., 1991). While mean offers in industrial societies are typically close to 44 percent, the mean offers in our sample range from 26 percent to 58 percent. Similarly, while modal offers are consistently 50 percent This content downloaded from 218.106.182.240 on Tue, 01 Mar 2016 11:52:59 UTC All use subject to JSTOR Terms and Conditions

VOL.9I NO.2 ECONOMICS AND SOCIAL BEHAVIOR 75 in industrialized societies,our sample modes Data from public-goods games played in vary from I sev n of these societies also show the previously observed.While in industrial socie the canonical model.Public-goods games as to a common pool that expanded by nter and the e will fr ce-ride.co percent.Among the Achuar.A goods game ontribu ons with students have a 170 inod Moreover.while the Ache and Achuar made contribution between 40 p ent and 60 percent fairly equitable offers,nearly 50 percent of Tsi By contrast,for instance,the Machiguenga have 0percent,yet all ing, with not a sir ed only one gle s offer ite the of rating the fact that over 75 per ent of their offers were ent.At the other end of f the rejed with few or no contributions at full free-riding rejecte coop t and below Unlike the Hadza who thes I low offers,the Au and typical behavior in industrialized societies and Papua New Gu canonical predic dictator game pk t y to with university subiects receives s that amount.Among university stu offers are generally cons dents,the di s"in the dictator n or reje typically I a se of s uns the modal hebavior of the model predicts that people will give zer ersis not consistent with expected income trasting with both.the Orma have a mode at 50 a se ndary mo de at 20 0 percen ins?00 sh nd 50 low offers.The rejection rate for all other offers is also zero.Yet the modal offer in both o offers;the mean was 32 percent,and the groups is 50 perce and the average of mode was 25 percent. are d5 I.What Explains Group-Level Differences? hbetween the size of the offer and the frac tion of rejections to estimate income maxi The large variations across th e different mizing o for the group in question In on cultu Igroups sugg th sor ex confirming the canonical model;but Hadza fairness norms.The large variance in institu responder ently substantia sand norms in our sample ng the mits questi ior of pro osers in the UG.We rank-ordered the most cases by a substantial amount societies along two dimensions: This ontent downl

VOL. 91 NO. 2 ECONOMICS AND SOCIAL BEHAVIOR 75 in industrialized societies, our sample modes vary from 15 percent to 50 percent. As shown in the last two columns of Table 1, rejections are also much more variable than previously observed. While in industrial socie- ties offers below 20 percent are rejected with probability 0.40 to 0.60, rejections of low offers are extremely rare among some groups. In other groups, 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 after 16, 51, and 70 proposer offers, respectively. Moreover, while the Ache and Achuar made fairly equitable offers, nearly 50 percent of Tsi- mane offers were at or below 30 percent, yet all were accepted. Similarly, Machiguenga re- sponders rejected only one offer, despite the fact that over 75 percent of their offers were below 30 percent. At the other end of the rejec- tion scale, Hadza responders rejected 24 percent of all proposer offers and 43 percent of offers at 20 percent and below. Unlike the Hadza, who preferentially rejected low offers, the Au and Gnau of Papua New Guinea rejected both unfair and hyper-fair (greater than 50 percent) offers with 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 majority of groups the modal behavior of the propos- ers is not consistent with expected income- maximization. In the Tsimane and Ache cases, for instance, there are no rejections of offers below 20 percent, although there were several low offers. The rejection rate for all other offers is also zero. Yet the modal offer in both groups is 50 percent, and the average offers are 37 percent and 51 percent, respectively. Where possible, we used the relationship between the size of the offer and the frac- tion of rejections to estimate income-maxi- mizing offers for the group in question. In one group, the Hadza proposers approximated the income-maximizing offer quite closely, thus confirming the canonical model; but Hadza responders frequently rejected substantial positive offers, thus violating the canonical model. In all other groups, average offers exceeded the income-maximizing offer, in most cases by a substantial amount. Data from public-goods games played in seven of these societies also show much greater variation than previously found, and again they exhibit novel deviations from the predictions of the canonical model. Public-goods games ask subjects to contribute to a common pool that will be expanded by the experimenter and then redistributed to all subjects. The canonical prediction is that everyone will free-ride, con- tributing nothing. Typical distributions of public- goods game contributions with students have a U-shape, with the mode at contributing nothing, a secondary mode at full cooperation, and mean contribution between 40 percent and 60 percent. By contrast, for instance, the Machiguenga have a mode at contributing nothing, with not a sin- gle subject cooperating fully, yielding a mean contribution of 22 percent. Also, the Ache and Tsimane both exhibit inverted distributions, with few or no contributions at full free-riding or full cooperation. In three dictator games played in three of these societies, groups also deviate both from typical behavior in industrialized societies and the canonical predictions. The dictator game allows the proposer simply to assign some frac- tion of the stake to a passive second party who receives that amount. Among university stu- dents, the distribution of "offers" in the dictator game typically has a mode at zero and a sec- ondary mode at 50/50, while the canonical model predicts that people will give zero. Con- trasting with both, the Orma have a mode at 50 percent and a secondary mode at 20 percent. Hadza dictators show a mode at 10 percent. Offers of 0 percent and 50 percent are also popular. Among the Tsimane, there were no zero offers; the mean was 32 percent, and the mode was 25 percent. II. What Explains Group-Level Differences? The large variations across the different cultural groups suggest that preferences or ex- pectations are affected by group-specific condi- tions, such as social institutions or cultural fairness norms. The large variance in institu- tions and norms in our sample allowed us to address this question systematically. Because of space limits we here concentrate on the behav- ior of proposers in the UG. We rank-ordered the societies along two dimensions: This content downloaded from 218.106.182.240 on Tue, 01 Mar 2016 11:52:59 UTC All use subject to JSTOR Terms and Conditions

76 AEA PAPERS AND PROCEEDINGS MAY 2001 (i)Pavoffs t hes tant and how large is a group's pa operation in economi c production? New Guinea,accepting gifts, even unsolicited (ii)Ma ntegration (MI) commits on on marke aesgoctt gifts als in a subordin position.Consequently,excessively large especially unsolicite ones.wil frequently be simane ran e unspe independent at the family level and engag and high reiection rates of the Hadza ar to rarely in productive activities involving more reflect their reluctant process of sharing (termed than memb family.By contrast,the by ling ethnographer o edby a d eIs go e ely shar The rationale for PCas a predictor of UG offers the social consequences of not sharing,in the will be little sha ret form of inf a cooperation like the I amelara must develop d to the rin ental ways of sharing the joint surplus. Thus w might expect that a higher ve and despite this the vast majority of the in the m h variable is that the more frequently onle ex phic de criptions indicating widesp hey will meat-sharing and cooperation in community rd ring princip te the ar of pun hon kill the We sought to explain group mean UG offers camp,the hunt on the basis of these two their catch is later red and collected by s and malized regression were in the me seemed to some of the Ache subjects magnitude (about 0.3).and the two measures ointly explai catch varianc The higu the lov cooper tion show es in fers.including individual measures such as se of Mes. which report little co oneration exchange o wealth. village population size sharing beyond the family unit.By contras th ubjects quickly dubbed th group.Surpr related to offers A plausible interpretation of our subiects level voluntary contributions for public-goods behaviors is that, when f d with novel sit- such as s or road Not surpris they loc daily familiar situation is this game like?and he subiects contribute in similar experiments. acted in a way appropriate for the instance,the ong the Au and Cnau and Ths conent dow-52-59 UTC

76 AEA PAPERS AND PROCEEDINGS MAY 2001 (i) Payoffs to cooperation (PC).-How impor- tant and how large is a group's payoff from cooperation in economic production? (ii) Market integration (MI).-How much do people rely on market exchange in their daily lives? On the first dimension, payoffs to coopera- tion, the Machiguenga and Tsimane rank the lowest; they are almost entirely economically independent at the family level and engage rarely in productive activities involving more than members of a family. By contrast, the Lamelara 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 offers is that with little cooperative production there will be little necessity to share returns, while those whose livelihood depends on large-scale cooperation like the Lamelara must develop ways of sharing the joint surplus. Thus we might expect that a higher level of PC will increase sharing behavior in the UG. The ratio- nale for market integration as an explanatory variable is that the more frequently people ex- perience market transactions, the more they will also experience abstract sharing principles con- cerning behaviors toward strangers of which the UG is an example. We sought to explain group mean UG offers on the basis of these two dimensions of eco- nomic structure. In a regression, both PC and MI were highly significant, their (positive) nor- malized regression coefficients were large in magnitude (about 0.3), and the two measures jointly explained 68 percent of the variance. The impact of PC and MI remains large and robust 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 the group. Surprisingly, none of these individual level measures 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 "What familiar situation is this game like?" and then acted in a way appropriate for the analogous situation. 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 these societies. Among these groups, like many in New Guinea, accepting gifts, even unsolicited ones, commits one to reciprocate at some future time to be determined by the giver. Receipt of large gifts also establishes one in a subordinate position. Consequently, excessively large gifts, especially unsolicited ones, will frequently be refused because of the anxiety about the unspe- cific strings attached. Similarly the low offers and high rejection rates of the Hadza appear to reflect their reluctant process of sharing (termed "tolerated theft" by a leading ethnographer of the Hadza). While the Hadza extensively share meat, many hunters look for opportunities to avoid sharing and share only because they fear the social consequences of not sharing, in the form of informal social sanctions, gossip, and ostracism. This behavior is apparently trans- ferred to the experimental setting. Unlike the Hadza, the Ache did not reject low offers, and despite this the vast majority of the Ache (94 percent) made offers above 40 percent of the stake size. This coincides neatly with ethnographic descriptions indicating widespread meat-sharing and cooperation in community projects despite the absence of a fear of punish- ment in Ache society. Ache hunters, retuming home, quietly leave their kill at the edge of camp, often claiming that the hunt was fruitless; their catch is later discovered and collected by others and then meticulously shared among all in the camp. We think it likely that the stake in the game seemed to some of the Ache subjects as 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, or sharing beyond the family unit. By contrast, Orma experimental subjects quickly dubbed the public-goods experiment a harambee game, re- ferring to the widespread institution of village- level voluntary contributions for public-goods projects such as schools or roads. Not surpris- ingly, they contributed generously (58 percent of 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 This content downloaded from 218.106.182.240 on Tue, 01 Mar 2016 11:52:59 UTC All use subject to JSTOR Terms and Conditions

VOL910.2 ECONOMICS AND SOCIAL REHAVIOR experimental subiects 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 e the substantial variability in could wel ed in a ionof the la in order to in the structures of social interaction and modes share with others,or to punish unfair actions.as e interpret these results our experimenta subjects did.A n number of due me the va recen cont ons nave at n that this explains the markedly differing behav. iors across groups.however,since the experi ulations,prosocial behavior n proliferate in a ments were run al protocols ac ach could test for experimenter effects we found IV.Conclusion none.It is possible also that sumed h 0m9 whil do not imply that econo major revisi ipants convinced us that this was not the case First,the canonical model of the self-interested inally,it could be that t participants though ey were in ae on.cvceho ly ctly ally do not find this interpretation compeing how excess of the expected income-maximizing of ever,since there is extensive evidenc from ced econon s t rejectic 11 hoeecnpo ond,preferenc game,when interviewed by the experimenter exogenous as the canonical model would have typically do not say that it, shaped by he s ma that 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 on eractions and et a mor We suspect that a proximate reason for these e ection be havior and the structure of everyday economic behaviors is that situations cue emotional re sponses wh haviors we hav the canonical model sponders from advanced socicties when facing a low offer,experience an emo REFERENCES ohurt the proposer for just as ect a re Bowles Sar reected hyper-fair offers in the when s y gives them an uns day life What an the ultimate determinants of our on.NJ:Princeton University Press.2001 emotions and situation-specific cues?Here (forthcoming). This downk 2170am20161529UTC

VOL. 91 NO. 2 ECONOMICS AND SOCIAL BEHAVIOR 77 experimental subjects closely corresponds to templates for these behaviors in the subjects' daily lives, and that the substantial variability in experimental behaviors across groups is an ex- pression of the large between-group differences in the structures of social interaction and modes of livelihood. How do we interpret these results? Some of the variability among groups may be due to variations in implementation. We doubt that this explains the markedly differing behav- iors across groups, however, since the experi- ments were run from identical protocols across groups and were thus as similar in procedures and stake size as we could achieve. Where we could test for experimenter effects we found none. 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 thought they were in a repeated interaction, even though the games we used were clearly one-shot. We do not find this interpretation compelling, how- ever, since there is extensive evidence from experiments in advanced economies that sub- jects understand the game very well, and those who reject a positive offer in the ultimatum game, when interviewed by the experimenter, typically do not say that they made an error, but rather affirm having goals besides maximizing a monetary payoff. Why are many subjects willing to share resources and undertake costly reciprocal ac- tions in anonymous one-shot interactions? Bowles et al. (2001) will provide a more extensive response than can be offered here. We suspect that a proximate reason for these behaviors is that situations cue emotional re- sponses which induce the behaviors we have measured. For example, many ultimatum- game responders from advanced societies, when facing a low offer, experience an emo- tional impulse to hurt the proposer for being unfair, just as the subject might in a real-life bargaining situation. Similarly, the New Guinea responders who rejected hyper-fair offers in the UG may have experienced the same anxiety that emerges when somebody gives them an unsolic- ited gift in everyday life. What are the ultimate determinants of our emotions and situation-specific cues? Here long-run evolutionary processes governing the distribution of genes and cultural practices could well have resulted in a substantial fraction of each population being predisposed in certain situations to forgo material payoffs in order to share with others, or to punish unfair actions, as our experimental subjects did. A number of recent contributions have shown that, under conditions that appear to approximate the social and physical environments of early human pop- ulations, prosocial behavior can proliferate in a population in which it is initially rare (Bowles et al., 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-interested material payoff-maximizing actor is systemati- cally violated. In all societies studied, UG offers are strictly positive and often substantially in excess of the expected income-maximizing of- fer, as are contributions in the public-goods game, while rejections of positive offers in some societies occur at a considerable rate. Sec- ond, preferences over economic choices are not exogenous as the canonical model would have it, but rather are shaped by the economic and social interactions of everyday life. This result implies that judgments in welfare economics that assume exogenous preferences are ques- tionable, as are predictions of the effects of changing economic policies and institutions that fail to take account of behavioral change. Fi- nally, the connection between experimental be- havior and the structure of everyday economic life should provide an important clue in revising the canonical model of individual choice behavior. REFERENCES Bowles, Samuel; Boyd, Richard; Fehr, Ernst and Gintis, Herbert, eds. The foundations of social reciprocity. Unpublished manuscript, Uni- versity of Massachusetts, 2001. Camerer, Colin F. Behavioral economics. Prince- ton, NJ: Princeton University Press, 2001 (forthcoming). This content downloaded from 218.106.182.240 on Tue, 01 Mar 2016 11:52:59 UTC All use subject to JSTOR Terms and Conditions