|
Article Excerpt
Recent research, using small-scale experiments based on standard game formats from economics, has shown that people often apply criteria of fairness to social interactions, accede to social pressure and engage in 'altruistic punishment' (punishment that incurs a benefit to the community as a whole, but at a cost to the punishing individual: Fehr & Fischbacher, 2004; Fehr, Fischbacher, & Gachter, 2002; Fehr & Gachter, 2000, 2002; Gintis, Bowles, Boyd, & Fehr, 2003; Orstrom, Gardner, & Walker, 1994). Humans are thus characterized by an unusual level of prosociality: individuals are, in general, willing to adhere to social norms of behaviour delineated by their community, even though they may incur personal costs by doing so.
These kinds of prosocial predispositions are however set into a complex background of more explicit biological interests and social obligations (e.g. those established by the customary modes of the society). Indeed, even in these micro-economic tests, individuals were not immune to the costs of altruism: when the costs to the punisher increased, the frequencies of altruistic punishment declined (Fehr & Gachter, 2002). More importantly, however, even though kinship provides an important strand of the social nexus within which any prosocial behaviour is necessarily embedded, it has been explicitly excluded from all of these studies (as is conventional in micro-economic experiments).
Altruistic behaviour originally proved difficult to explain in evolutionary terms: in a simple Darwinian world, any gene promoting altruism should be rapidly driven to extinction. The solution was provided by Hamilton (1964; popularized by Dawkins, 1976), who showed that evolution occurs as the result of copies of genes being propagated, and that the replication of genes into future generations can occur through either personal reproduction or the reproduction of individuals carrying the same gene(s). Formally known as Hamilton's rule of kin selection, Hamilton's core finding was that a gene for altruism can evolve in a population, providing:
rB > C
where B is the benefit to the recipient, C the cost to the altruist (both measured as the number of offspring gained or lost) and r the coefficient of relationship (i.e. the probability that they share the same gene by descent). In essence, altruism evolves when the altruist's actions allow it to contribute more copies of its genes to future generations by enabling a relative to reproduce more successfully than by reproducing itself. In effect, when all else is equal, more closely related individuals should be favoured over less closely related individuals. While the currency in Hamilton's (1964) technical definition of altruism is fitness (for which even reproductive success is only a proxy), this cannot easily be measured directly in most real-world studies; most studies of altruism in animals have therefore used as an operational definition, the expenditure of energy or resources that may increase the welfare of one individual at the expense of another (Barash, 1977; Dawkins, 1989).
Hamilton's rule has been a foundation stone of modern evolutionary biology and the study of animal behaviour for nearly half a century (e.g. Sober & Wilson, 1998), and there is widespread observational and experimental evidence of its role in moderating altruistic behaviour in non-human animals (e.g. Cheney & Seyfarth, 1990). There is also abundant evidence that humans behave more altruistically towards closer than towards more distant relatives. In societies reliant on subsistence agriculture, cooperation between farmers is twice as likely between relatives as non-relatives (Berte, 1988; Hames, 1987). In industrial societies, beneficiaries of a will tend to receive slices of the deceased's estate that are broadly proportional to their genetic relatedness, r, to the deceased (Smith, Kish, & Crawford, 1987). Similarly, kinship patterns correlate with: willingness to murder political rivals and form stable alliances (Dunbar, Clark, & Hurst, 1995; Johnson & Johnson, 1991), taking sides in disputes (Chagnon & Bugos, 1979; Hughes, 1988), emotional and material support within social networks (Barber, 1994; Berte, 1988; Betzig & Turke, 1986; Dunbar & Spoors, 1995; Hames, 1987; Hill & Hurtardo, 1996), cooperation under catastrophic circumstances (Grayson, 1993; McCullough & Barton, 1991) and combat situations (Shavit, Fischer, & Koresh, 1994), the coherence and fission of cohabitational units (Chagnon, 1981; Hurd, 1983; Koertvelyessy, 1995), membership of cooperative labour units (Morgan, 1979), exchange of information among US inshore fishermen (Palmer, 1992), safeguarding against infanticide (Hill & Hurtado, 1996) and the investment tendencies of both parents (Chagnon, 1992; Firth, 1957; Hill & Kaplan, 1988) and more distant kin (Euler & Weitzel, 1996; Gaulin, McBurney, & Brakeman-Wartel, 1997; Hawkes, O'Connell, & Blurton-Jones, 1989; Hill & Hurtado, 1996; Pashos, 2001). Finally, across most societies, women are far more likely to provide child care for their relatives than for unrelated neighbours (Bereczkei, 1998; Burton, 1990; Ivey, 2000; Judge, 1995; Pennington & Harpending, 1993; Silk, 1990; Stack, 1975).
While these findings are interesting, all these studies suffer one common drawback: the evidence is entirely observational. In no case is it possible to exclude categorically all confounding variables (interaction time, reciprocity, etc.), so as to make an unequivocal test of the claim that human altruistic behaviour is modulated by the genetic relatedness, when other factors are held constant. An exception to this was an experiment reported by Caporeal, Dawes, Orbell, and van de Kagt (1989), who found that individuals were more likely to donate their fee for participating to a local charity when doing the experiment in groups than alone. Although interpreted as evidence for a natural tendency to behave altruistically, thus posing a challenge to Hamilton's rule, the experiment suffered from design flaws (principally, failure to impose a cost) sufficient to compromise the significance of its findings. A similar criticism applies to the experimental studies of prosociality by Fehr and colleagues (Fehr & Fischbacher, 2004; Fehr et al., 2002; Fehr & Gachter, 2002; Gintis et al., 2003): none meet the crucial criterion necessary for a formal test of Hamilton's rule (that the altruist pays a personal cost). Although it might be suggested that participants incur a cost by forgoing their fees, this provides only for a very weak form of altruism because the experiment is cost-neutral to the altruist (who leaves in the same state as he/she arrived, apart from a trivial loss of time). More importantly, because each of these experiments focuses on altruism among unrelated individuals, none provide an experimental test of Hamilton's rule in humans.
In contrast, self-reported frequencies of giving and receiving assistance (financial, emotional, etc.) from female residents in the US suggested that in times of need closer kin were a weightier source of assistance than more distant kin and non-kin (Essock-Vitale & McGuire, 1985). This survey, however, relied on self-reports of helping behaviour that may have been affected by social desirability and leaves many potentially confounding variables uncontrolled.
A number of studies have attempted to test the significance of kinship and Hamilton's rule using classic social psychology vignette or questionnaire designs (Burnstein, Crandall, & Kitayama, 1994; Kruger, 2003; Park & Schaller, 2005; Webster, 2004). In a series of hypothetical scenarios in which participants reported the likelihood of helping an individual as a function of genetic relatedness (with costs ranging from trivial courtesies to life-and-death heroic deeds), college students were more inclined to help relatives than non-relatives, and particularly so in life-and-death situations (Burnstein et al., 1994; Korchmaros & Kenny, 2001; Kruger, 2003). While providing prima facie evidence in support of Hamilton's rule, these experimental paradigms are open to question on grounds of both internal and ecological validity. One study (Park & Schaller, 2005), for example, failed to impose any kind of cost (actual or hypothetical); others failed to eliminate non-genetic benefits (e.g. social desirability) as confounding variables. As anthropologists and social psychologists have repeatedly discovered, humans commonly say one thing, but do something entirely different (e.g. Bliezner & Adams, 1992; Freeman, 1999; Wolf, 2001). Hence, none of these studies provides secure evidence on which to base a claim about the role of kin selection in actual human altruistic behaviour.
In this paper, we report a series of three experiments designed to test the hypothesis that, when all else is equal, an individual's willingness to bear a genuine cost (physical pain) to the benefit of another is a function of the recipient's biological relatedness. Clearly, it would be improper to influence the reproductive success of either our participants or their relations to any significant degree. However, we believe that compelling evidence for altruism of this form can only be demonstrated under controlled conditions in which the costs to the participant and benefits to their recipients are in both cases real and measurable (as is conventional in studies of altruism in animals). While these may not be sufficient to affect reproductive success, the fact that the costs and benefits are not merely hypothetical can be used to test the prediction that altruistic behaviour is mediated by Hamilton's rule. We do not seek to contrast preferences for kin with other explanations for altruism, such as prosociality or reciprocity, whether direct (e.g. Trivers, 1971) or indirect (e.g. Alexander, 1987). Our aim is to assess the strength of the kinship effect so as to provide a firm background against which the role of other modulating influences can be assessed. As such, this is the first attempt to assess experimentally the impact of kinship on altruistic behaviour, rather than on declared inclinations.
In addition, we consider two further issues. First, kinship has significant culture-specific overtones (Keesing, 1975), which makes it important to assess the extent to which kin-biased altruism might be a culture-specific phenomenon. For instance, there is wide cross-cultural variation in kinship classification systems: social relatedness, as defined...
|
