Explaining altruistic behavior in humans
Introduction
The explanatory power of inclusive fitness theory and reciprocal altruism Hamilton, 1964, Trivers, 1971, Williams, 1966 convinced a generation of researchers that what appears to be altruism—personal sacrifice on behalf of others—is really just long-run self-interest. Dawkins, 1976, Dawkins, 1989, for instance, struck a responsive chord when, in The Selfish Gene, he confidently asserted “We are survival machines—robot vehicles blindly programmed to preserve the selfish molecules known as genes.…This gene selfishness will usually give rise to selfishness in individual behavior.” Dawkins allows for morality in social life, but it must be socially imposed on a fundamentally selfish agent. “Let us try to teach generosity and altruism,” he advises, “because we are born selfish.” Yet, even social morality, according to R. D. Alexander, the most influential ethicist working in the William–Hamilton tradition, can only superficially transcend selfishness. In The Biology of Moral Systems, Alexander (1987, p. 3) asserts, “ethics, morality, human conduct, and the human psyche are to be understood only if societies are seen as collections of individuals seeking their own self-interest.” In a similar state of explanatory euphoria, Ghiselin (1974, p. 247) claims “No hint of genuine charity ameliorates our vision of society, once sentimentalism has been laid aside. What passes for cooperation turns out to be a mixture of opportunism and exploitation…Scratch an altruist, and watch a hypocrite bleed.”
However, recent experimental research has revealed forms of human behavior involving interaction among unrelated individuals that cannot be explained in terms of self-interest. One such trait, which we call strong reciprocity Gintis, 2000b, Henrich et al., 2001, is a predisposition to cooperate with others and to punish those who violate the norms of cooperation, at personal cost, even when it is implausible to expect that these costs will be repaid either by others or at a later date.
In this article, we present empirical evidence supporting strong reciprocity as a schema for explaining important forms of altruism in humans. We then explain why, under conditions plausibly characteristic of the early stages of human evolution, a small fraction of strong reciprocators could invade a population of self-regarding types, and why strong reciprocity is an evolutionarily stable strategy. Although most of the evidence we report is based on behavioral experiments, the same behaviors are regularly observed in everyday life, for example in wage setting by firms (Bewley, 2000), tax compliance (Andreoni, Erard, & Feinstein, 1998), and cooperation in the protection of local environmental public goods Acheson, 1988, Ostrom, 1990.
In supporting the importance of strong reciprocity, we of course do not deny the importance of either kin altruism (Hamilton, 1964) or reciprocal altruism (Trivers, 1971). Both are beyond doubt potent forces in human motivation. We do believe, however, that the evolutionary success of our species and the moral sentiments that have led people to value freedom, equality, and representative government are predicated upon strong reciprocity and related motivations that go beyond inclusive fitness and reciprocal altruism.
We wish to avoid three common misunderstandings of our argument. First, many contemporary researchers reject our critique of Dawkins, Alexander, and others in the “selfish gene” school by asserting that their pronouncements should not be taken at face value. Rather, they say, references to phenotypic behavior as “selfish” should be understood as asserting that the underlying genetic structures are subject to Darwinian evolutionary forces. Yet, these authors understood that their assertions were likely to be taken at face value, rather than being dramatic circumlocutions expressing completely unexceptionable propositions. It is only plausible, then, to suggest that they meant them, that it was plausible at the time to make such statements, but that they are now seen to be incorrect.
Second, we are often interpreted as rejecting the “gene-centered” approach to modeling human behavior. In fact, our results in no way contradict the standard population biology approach to genetic and cultural change. A gene that promotes self-sacrifice on behalf of others will die out unless those helped carry the mutant gene or otherwise promote its spread. In a population without structured social interactions of agents, behaviors of the type found in our experiments and depicted in our models could not have evolved. However, multilevel selection and gene–culture coevolutionary models support cooperative behavior among nonkin (Bowles et al., in press, Feldman et al., 1985, Gintis, 2000a, Gintis, in press-a, Gintis, in press-b, Henrich & Boyd, 2001, Sober & Wilson, 1998). These models, some of which are discussed below, are not vulnerable to the classic critiques of group selection by Dawkins (1976), Maynard Smith (1976), Rogers (1990), Williams (1966), and others.
Third, we are often told that the behavior we describe can in fact be explained by standard individual selection, kin selection, and reciprocal altruism models applied to the ancestral natural and social environment to which our species was subject during the period of its evolutionary emergence, where anonymous, one-shot interactions were supposedly extremely rare. Strong reciprocity in contemporary environments, according to this view, is a maladaption. We think this alternative is unlikely, and address the issues in Section 8.
Section snippets
Experimental evidence: Strong reciprocity in the labor market
In Fehr, Gächter, and Kirchsteiger (1997), the experimenters divided a group of 141 subjects (college students who had agreed to participate in order to earn money) into a set of “employers” and a larger set of “employees.” The rules of the game are as follows. If an employer hires an employee who provides effort e and receives a wage w, they employer's payoff π is 100 times the effort e, minus the wage w that he must pay the employee (π=100w−e), where the wage is between 0 and 100 (0≤w≤100)
Experimental evidence: The ultimatum game
In the ultimatum game, under conditions of anonymity, two players are shown a sum of money, say $10. One of the players, called the “proposer,” is instructed to offer any number of dollars, from $1 to $10, to the second player, who is called the “responder.” The proposer can make only one offer. The responder, again under conditions of anonymity, can either accept or reject this offer. If the responder accepts the offer, the money is shared accordingly. If the responder rejects the offer, both
Experimental evidence: The public goods game
The public goods game has been analyzed in a series of papers by the social psychologist Yamagishi, 1986, Yamagishi, 1988a, by the political scientist Ostrom, Walker, and Gardner (1992), and by economists Fehr and Gächter Fehr & Gächter, 2000, Fehr & Gächter, 2002, Gächter & Fehr, 1999. These researchers uniformly found the groups exhibit a much higher rate of cooperation than can be expected assuming the standard economic model of the self-interested actor, and this is especially the case when
Experimental evidence: Intentions or outcomes?
One key fact missing from the above presentation is a specification of the relationship between contributing and punishing. The strong reciprocity interpretation suggests that high contributors will be high punishers, and punishees will be below-average contributors. This prediction is borne out in Fehr and Gächter (2002), wherein 75% of the punishment acts were executed by above-average contributors, and the most important variable in predicting how much one player punished another was the
The evolutionary stability of strong reciprocity
Gintis (2000b) developed an analytical model showing that under plausible conditions strong reciprocity can emerge from reciprocal altruism through group selection. The article models cooperation as a repeated n-person public goods game (see Section 4) in which, under normal conditions, if agents are sufficiently forward-looking, cooperation can be sustained by the threat of ostracism Fudenberg & Maskin, 1986, Gintis, 2000a. However, when the group is threatened with extinction or dispersal,
The coevolution of institutions and behaviors
If group selection is part of the explanation of the evolutionary success of cooperative individual behaviors, then it is likely that group-level characteristics—such as relatively small group size, limited migration, or frequent intergroup conflicts—that enhance group selection pressures coevolved with cooperative behaviors. Thus, group-level characteristics and individual behaviors may have synergistic effects. This being the case, cooperation is based in part on the distinctive capacities of
Alternative explanations of strong reciprocity
We have argued that a variety of experimental data support our strong reciprocity model, and that strong reciprocity is adaptive in the sense of emerging from a gene–culture coevolutionary process that appears plausible in light of current and paleoanthropological evidence. The first of these claims is disputed by Price, Cosmides, and Tooby (2002), who present an alternative explanation of the data. The second claim is disputed by many who claim that altruistic cooperation and punishment in
Conclusion
Much more experimental and theoretical work must be done to understand the major outlines of human prosocial behavior. We suspect, on the basis of the many studies completed over the past several years, that the new knowledge obtained will give us a picture of prosociality (and its obverse, antisociality) that is fundamentally incompatible with the economist's model of the self-interested actor and the biologists' model of the self-regarding reciprocal altruist.
Contemporary behavioral theory is
Acknowledgements
We would like to thank Martin Daly, Steve Frank, and Margo Wilson for helpful comments, and the Santa Fe Institute and John D. and Catherine T. MacArthur Foundation for financial support.
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