In this paper, we use the classical twin design to provide estimates of genetic and environmental influences on experimentally elicited preferences for risk and giving. Using standard methods from behavior genetics, we find strong prima facie evidence that these preferences are broadly heritable and our estimates suggest that genetic differences explain approximately twenty percent of individual variation. The results thus shed light on an important source of individual variation in preferences, a source that has hitherto been largely neglected in the economics literature.

Although laboratory experiments document cooperative behavior in humans, little is known about the extent to which individual differences in cooperativeness result from genetic and environmental variation. In this article, we report the results of two independently conceived and executed studies of monozygotic and dizygotic twins, one in Sweden and one in the United States. The results from these studies suggest that humans are endowed with genetic variation that influences the decision to invest, and to reciprocate investment, in the classic trust game. Based on these findings, we urge social scientists to take seriously the idea that differences in peer and parental socialization are not the only forces that influence variation in cooperative behavior.behavioral genetics ͉ cooperation ͉ experimental economics M any mutually beneficial transactions involve an element of interpersonal trust and may fail to materialize in the absence of an expectation that trust will be reciprocated. The prevalence of trust in a society has therefore been assigned primacy in a number of domains, for instance empirical (1) and theoretical (2) studies of economic growth. In recent years, the trust game (3) has emerged as a favorite instrument to elicit an individual's interpersonal trust and willingness to reciprocate trust. More generally, the game has been widely used to study cooperative behavior. In a trust game, an individual (the investor) decides how much money out of an initial endowment to send to another subject (the trustee). The sent amount is then multiplied by some factor, usually three, and the trustee decides how much of the money received to send back to the investor. The standard game-theoretic prediction for a single anonymous interaction between two purely self-interested individuals is for the investor to send nothing, rationally anticipating that the trustee will not reciprocate. Yet, experiments consistently show that cooperation flourishes in the trust game; the average investor sends a significant share of her endowment, and most trustees reciprocate (4). A voluminous body of theoretical and experimental work examines the mechanisms through which natural selection can favor cooperation, and proposed mechanisms include kin selection (5), reciprocity (6), indirect reciprocity (7), and group selection (8). These models offer different accounts for the ultimate explanation for the existence of cooperation and also generate different predictions about genotypic variation in equilibrium (9).To investigate whether humans are endowed with genetic variation that could help account for individual differences in trust game behavior, two separate teams of researchers independently conceived and executed a very similar experiment on twins [see supporting information (SI) for experimental procedures]. These teams became aware of each other for the first time after all data had been collected. One team recruited 658 subjects from the population-based Swedish Twin Registry, and the other team recruited 706 subjects from th...

Experimental evidence suggests that many people are willing to deviate from materially maximizing strategies to punish unfair behavior. Even though little is known about the origins of such fairness preferences, it has been suggested that they have deep evolutionary roots and that they are crucial for maintaining and understanding cooperation among non-kin. Here we report the results of an ultimatum game, played for real monetary stakes, using twins recruited from the population-based Swedish Twin Registry as our subject pool. Employing standard structural equation modeling techniques, we estimate that >40% of the variation in subjects' rejection behavior is explained by additive genetic effects. Our estimates also suggest a very modest role for common environment as a source of phenotypic variation. Based on these findings, we argue that any attempt to explain observed ultimatum bargaining game behavior that ignores this genetic influence is incomplete.cooperation ͉ experimental economics I t is frequently pointed out that humans exhibit unusually high rates of cooperation among non-kin (1), and it has further been suggested that one important factor for enhancing cooperation is that humans appear willing to forego material payoffs to punish unfair behavior (2-4). Such fairness preferences have been widely studied by using experimental games, in particular the ultimatum game (5-7).In the ultimatum game, two subjects are assigned the role of either proposer or receiver, and then they bargain over a sum of money (the ''cake''). The proposer makes an offer on how to divide the cake. If the receiver accepts the proposer's offer, the players are paid accordingly, whereas if the offer is rejected, both players receive a zero payoff. In a one-shot game, rational and moneymaximizing responders should accept any positive offer because the alternative is a zero payoff. Two stylized facts about responder behavior emerge from the ultimatum game literature: first, that unfair offers are often rejected and second, that the acceptance threshold varies substantially between individuals (5, 6). The average responder behavior has been shown to be relatively stable across Western cultures (8), whereas more variation has been observed among non-Western small-scale societies (9).Although there is a voluminous literature discussing the cultural and evolutionary origins of observed fairness preferences, the relative social and genetic contributions have hitherto been left unexplored. In this work, we use the classical twin design to estimate the heritability of the propensity to reject unfair offers in the ultimatum bargaining game. In doing so, we not only provide the first decomposition of the social and genetic contributions to ultimatum game rejection behavior but also to behavior in experimental games in general. The virtue of the twin design is that by comparing monozygotic (MZ) twins, who share the same set of genes, and dizygotic (DZ) twins, whose genes are imperfectly correlated, we can estimate the proportion of variance in...

Standard-Nutzungsbedingungen:Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden.Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen.Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. Terms of use: Documents in AbstractWe use administrative data on Swedish lottery players to estimate the causal impact of wealth on players' own health and their children's health and developmental outcomes. Our estimation sample is large, virtually free of attrition, and allows us to control for the factorssuch as the number of lottery tickets -conditional on which the prizes were randomly assigned. In adults, we …nd no evidence that wealth impacts mortality or health care utilization, with the possible exception of a small reduction in the consumption of mental health drugs. Our estimates allow us to rule out e¤ects on 10-year mortality one sixth as large the cross-sectional gradient. In our intergenerational analyses, we …nd that wealth increases children's health care utilization in the years following the lottery and may also reduce obesity risk. The e¤ects on most other child outcomes, which include drug consumption, scholastic performance, and skills, can usually be bounded to a tight interval around zero. Overall, our …ndings suggest that correlations observed in a-uent, developed countries between (i) wealth and health or (ii) parental income and children's outcomes do not re ‡ect a causal e¤ect of wealth.