Original ArticleApparent health encourages reciprocity
Introduction
Reciprocity, a universal feature of human social organization (Brown, 1991), is a mutually beneficial arrangement in which individuals repay the investments of others. At the functional level, its evolution requires reliable compensation, with interest, for prior investments (Alexander, 1987, Nowak and Sigmund, 2005, Trivers, 1971; see also Roberts, 2005). Nevertheless, investments can be misdirected toward unsuitable exchange partners who subsequently fail to translate the investment into a profitable return. Thus, patterns of exchange are expected to reflect a psychology of discriminative allocation: individuals should prefer to invest in partners who are likely to make a return (Leimar, 1997, Tooby and Cosmides, 1996).
Social partners may fail to reciprocate an exchange for a number of reasons. Short time horizons will curtail the forecasted length of an exchange relationship, thus reducing the potential benefits of cooperation (Axelrod and Hamilton, 1981, Trivers, 1971), so long-lived partners will find greater incentives to partake of reciprocal exchange. Moreover, individuals with lengthier expected life spans will tend to be in better condition, and will thus accrue more resources of quality. In short, cues of health—which will be associated with longevity and condition—may make useful predictors of the value of a potential partner, because an unhealthy individual has a higher probability, moment to moment, of incapacity and death and so is less justified as a candidate for current investment against future returns.
The problem of prudent investment raises the specter of trust. Reciprocal exchanges are often complicated by incomplete information about a partner's intentions and an incentive structure that fails to compel the partner to make a return (Yamagishi & Yamagishi, 1994). We suggest that, in these circumstances, exchanges require a degree of trust, or faith, in the beneficence of one's partner. How trust is garnered, however, remains something of a puzzle.
We investigated effects of apparent health on reciprocal exchange in a series of one-shot, anonymous “Trust” games (TG; Berg et al., 1995, DeBruine, 2002, McCabe et al., 2003). In the incarnation used here, the first player (P1) chooses between two options: either to (i) terminate the game, in which case P1 and the second player (P2) are each allocated £3 (the not trusting option), or (ii) allow P2 to make the allocation decision (the trusting option) from one of two larger pools of money (Fig. 1). Hence, P1 makes a de facto investment in P2 by choosing the trusting option. In the event that P1 entrusts P2 with the allocation decision, P2's choices are either that P1 and P2 both receive £4 (the fair option) or that P1 receives £2 and P2 receives £5 (the selfish option). Thus, P1 benefits by investing in P2 only if P2 reciprocates P1's trust by paying a personal cost in order to make a fair return. Prior work shows that decisions in the TG indeed reflect a psychology of trust and reciprocity (McCabe et al., 2003, Pillutla et al., 2003), even in designs where the size of the “pot” varies between P2's options, as is the case in the current study (where the pot is £8 for the pair should P2 choose the fair option, but £7 for the pair should P2 choose the selfish option).
Exchange decisions, including P1 trust, are often associated with the attractiveness of social partners (Andreoni and Petrie, 2008, Solnick and Schweitzer, 1999, Takahashi et al., 2006, Wilson and Eckel, 2006), a finding in line with studies of character attributions (Eagly et al., 1991, Langlois et al., 2000) and labor markets (Biddle and Hamermesh, 1998, Hamermesh and Biddle, 1994). Wilson and Eckel (2006), for instance, find a “beauty premium” in the TG: more attractive P2s are entrusted with more money than their less attractive counterparts. Similar results have been reported in a group cooperation task (a Public Goods game; Andreoni & Petrie, 2008) and a bargaining task (an Ultimatum game; Solnick & Schweitzer, 1999), whereby more attractive players earned more money than other players. Much of this work, however, has relied on natural variation in attractiveness rather than experimental manipulation, potentially conflating the general property of “attractiveness” with a particular component thereof. Thus, a test of the effects of one or more components of attractiveness on exchange behavior is essential to understanding whether it is attractiveness or something confounded with it that is a cause of variation in patterns of reciprocal exchange.
In the TG, participants viewed images of ostensible partners’ faces that had been digitally altered to vary in apparent health, an important component of physical attractiveness (Jones et al., 2001, Jones et al., 2005, Jones et al., 2005, Jones et al., 2005, Rhodes et al., 2007). Apparent health could be predicted to affect reciprocal exchange decisions via its effects on attractiveness (Andreoni and Petrie, 2008, Solnick and Schweitzer, 1999, Takahashi et al., 2006, Wilson and Eckel, 2006), even when attractiveness is not actually associated with a partner's value (Mobius & Rosenblat, 2006). What remains unclear, however, is whether it will have its effects on the initial investment decision or on its reciprocation. As attractive individuals may take advantage of their appearance as recipients of an investment, they may not be especially trustworthy partners. Rather, individuals may instead reward the investments of attractive partners with enhanced reciprocation. Smith, DeBruine et al. (2009), for instance, find that attractive P1s are more trusting than less attractive P1s of ostensible P2s in the TG, but only when they are informed that the P2s can see an image of the P1's face. Thus, it seems as if attractive P1s selectively exploit their appearance when engaging in reciprocal exchange. A finding that P2s reciprocate the trust of apparently healthy P1s more fairly than that of apparently unhealthy P1s would complement Smith, DeBruine et al.'s (2009) result.
Section snippets
Stimuli
Stimulus images of ostensible exchange partners were manufactured with a digital transformation procedure, using custom image manipulation software (Tiddeman, Burt, & Perrett, 2001). Twelve male and twelve female face identities were transformed to create a total of 24 healthy and 24 unhealthy stimulus faces, divided into three different face sets of eight unique face identities (two of each face type: healthy male, unhealthy male, healthy female, unhealthy female). The original face images
Attraction to health
In both sessions, participants found healthy faces significantly more attractive than unhealthy ones (all ts>8.99, ps<.001, Cohen's ds>1.33). Male and female participants did not differ in their attractiveness preferences for health in male or in female faces (all ts<1.29, ps>.205, ds<0.44). Health preferences were significantly correlated within sessions (Session 1: r=.53, p<.001; Session 2: r=.77, p<.001) and between sessions (female faces: r=.46, p=.001; male faces: r=.44, p=.002). We thus
Discussion
In the current study, apparent health promoted the reciprocation of an investment. Controlling for individual differences in strength of attraction to health abolished this effect, suggesting that the influence of apparent health on exchange decisions is driven largely by its impact on attractiveness. Specifically, it seems that an increase in attractiveness (via the manipulation of apparent health) leads to an increase in the willingness to reciprocate fairly, at an immediate cost to the
Acknowledgments
We thank Claire Conway, Finlay Smith and Lisa Welling for help with data collection, and Martin Daly, Margo Wilson, Martin Lalumière, David Logue, Sandeep Mishra, and two anonymous reviewers for many helpful comments. Funding was provided by the Social Sciences and Humanities Research Council of Canada, the Natural Sciences and Engineering Research Council of Canada, and the University of Aberdeen.
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