Prosociality is a general term referring to a variety of positive emotions, attitudes, and behaviors directed toward others, which may be manifested through acts of sharing, helping, and cooperating (Knafo-Noam et al., 2015). There is increasing recognition that neither prosociality nor its underlying motivations are unitary constructs (Batson and Powell, 2003; Singer and Steinbeis, 2009; Böckler et al., 2016). Likewise, there are multiple prosocial tendencies, which are classified differently according to two major taxonomic models of personality, the Big Five (Goldberg, 1981; Digman, 1990; John et al., 2008; DeYoung, 2015) and the HEXACO (Honesty-Humility, Emotionality, eXtraversion, Agreeableness, Conscientiousness, Openness to Experience; Lee and Ashton, 2004).

Social preferences represent a number of channels through which humans deviate from narrow self-interest and engage in prosocial behaviors. Distributive preferences capture concerns for egalitarianism and generosity, while preferences for reciprocity promote favorable or unfavorable treatment conditional on the previous acts or intentions of others. Emerging research has demonstrated considerable heterogeneity in these preferences, which may be partially underpinned by prosocial personality traits. However, most of this research has focused on the trade-off between self- and other-regarding interests in the dictator game. Detailed relations between prosocial personality traits and other forms of social preferences are less well understood, and inferences are often cobbled together from a mixture of different games and personality measures. As a result, it is difficult to disentangle trait effects from the influence of contextual factors across variable game environments (given that traits too are contextualized; DeYoung, 2015) and to interpret the findings when certain game decisions are used to approximate social preferences (e.g., the trust game, which may not capture positive reciprocity; Ben-Ner and Halldorsson, 2010; Thielmann and Hilbig, 2015).

The aims of the current research were threefold: (1) To identify a richer set of social preferences beyond egalitarianism and inequality aversion, (2) to examine the source of individual differences in these preferences using theoretical models of distinct prosocial traits, and in doing so, (3) address some of the major limitations of the existing literature (e.g., fragmented games and traits).

We developed a novel paradigm using six simple modifications of the dictator game to test multiple social preferences. This design was inspired by Charness and Rabin (2002), who incorporated reciprocity and efficiency concerns into a series of binary-choice tasks. We first manipulated the costliness of decisions by setting half the games as constant-sum (i.e., costly dictator games) and half with a fixed personal payoff but variable partner payoff (i.e., costless generosity games). Second, we manipulated the conditions for reciprocity by positioning these games after a prior decision by a partner that hurt or helped the participant, vs. a baseline condition where there was no history with a partner.

The benefit of this design is that it provided a suite of tightly controlled and manipulable conditions ideal for localizing specific prosocial constructs. For example, comparing costly vs. costless game decisions allowed us to identify different patterns of behavior after controlling for the influence of self-interest. Similarly, reciprocal tendencies can be teased apart from overall altruistic motivations. Existing studies suggest that Big Five agreeableness and HEXACO honesty-humility are associated positively with positive reciprocity and negatively with negative reciprocity, but these preferences have been largely considered in isolation. Given that these traits are already associated with greater dictator allocations, the current design will reveal whether they produce an additional effect for reciprocity, above and beyond unconditional kindness (Ben-Ner and Halldorsson, 2010; Thielmann and Hilbig, 2015).

We then examined the sources of heterogeneity within this paradigm with respect to the theoretically relevant prosocial domain of personality: agreeableness and its aspects of politeness and compassion within the Big Five model, and honesty-humility and agreeableness within the HEXACO model. In particular, we focused on the discriminant validity between similar prosocial personality constructs and identified unique trait effects to help shed light on the specific mechanisms and motivations taking place within economic games (for a recent example, see Zhao et al., 2016). We sought to address some of the limitations and expand on the existing research by bringing together two large and relatively diverse community samples. Sample sizes in both studies (Ns = 304, 256) were well above the recommended minimum provided in the wake of the replicability crisis, including total N > 150 for individual differences research (Mar et al., 2013) and total N > 180 as a general requirement for personality and social psychological research (Vazire, 2016). As the design was within-subjects, the per condition sample sizes provided 80% power to identify effect sizes of approximately rs = 0.16–0.18 (Faul et al., 2009), which is reasonably sensitive given the average effect sizes in the field (r = 0.21; Richard et al., 2003; Fraley and Marks, 2007).

In line with previous research, we expected politeness from the Big Five model to be uniquely associated with costly prosocial allocations (i.e., dictator games) but expected compassion to play a relatively stronger role in costless prosocial allocations (i.e., generosity games), where allocations are less norm-driven and capture motivations of improving the wellbeing of others. Within the HEXACO model, we predicted that honesty-humility would have a unique role in both costly and costless prosociality, given its core characteristic of benevolence. Furthermore, we hypothesized that HEXACO agreeableness—which captures tendencies toward forgiveness and non-retaliation—would be negatively associated with negative reciprocity. Finally, in light of the evidence demonstrating the role of Big Five agreeableness and HEXACO honesty-humility in both positive reciprocal game behaviors and dictator game allocations, we were interested in examining whether any prosocial traits could explain positive reciprocity beyond their established role in unconditional kindness.

The results of Study 1 showed clear evidence of social preferences beyond inequality aversion and egalitarianism. Individuals allocated significantly more wealth to their partners when decisions were costless than when they were costly, demonstrating tendencies toward generosity. In addition, there was evidence of positive reciprocity, with individuals allocating more wealth to their partner after their partner had assisted them. However, we found no evidence of negative reciprocity, and individuals did not allocate any differently when they had been denied a higher payoff by a hurtful partner. These findings were further moderated by gender, with men allocating more than women in the generosity games and when their partner had not previously hurt them.

The results presented a mixed picture of predicted and unexpected findings regarding the role of personality, revealing a main effect for politeness (but not so much compassion) in the Big Five model. In the HEXACO model, honesty-humility predicted greater allocations in the dictator game, in keeping with a large body of previous research (Hilbig and Zettler, 2009; Hilbig et al., 2015a; Zhao and Smillie, 2015). However, contrary to its putative mechanism of benevolence, honesty-humility did not play any role in the generosity game, where decisions were costless. Here, it was HEXACO agreeableness—or the tendency to be tolerant, lenient, and forgiving—which instead predicted greater generosity.

An important consideration in Study 1 is that the decisions were hypothetical, featuring imagined partners and stakes. Previous studies have been conflicted as to whether hypothetical paradigms produce comparable results to incentivized games, especially when trait effects are involved (Ben-Ner et al., 2008; Engel, 2011; Lönnqvist et al., 2011; Ferguson and Starmer, 2013; Hilbig et al., 2015a; Zhao et al., 2016). Another potential limitation stems from correlating self-reported personality traits with self-reported hypothetical responses, where there is a risk of inflated associations arising from common method variance (Podsakoff et al., 2003). Finally, the dearth of actual assessment of behavior has been a prominent issue in personality research, leading to calls for a broader range of data beyond self-reports and hypothetical scenarios (Funder, 2001; Baumeister et al., 2007). In light of these concerns, we ran a second study using an identical—but incentivized—paradigm with the aim of replicating our previous findings and identifying robust effects.

The incentivized results of Study 2 replicated many of the main findings from the hypothetical paradigm of Study 1. Again, there was clear evidence of inequality aversion, generosity, and positive reciprocity, which were moderated by gender. When we examined the role of prosocial personality traits, honesty-humility once more interacted with game type, predicting greater allocations in dictator—but not generosity—games. In the Big Five model, we again observed a main effect of politeness—but not compassion—which was globally and uniquely associated with greater allocations across all games.

However, the results of Study 2 also introduced two non-trivial differences compared with Study 1. First, the previous interaction between agreeableness and game type in the HEXACO model disappeared in the incentivized paradigm. In fact, HEXACO agreeableness was not associated with allocations of any kind. Second, a novel and unpredicted interaction with game type emerged for compassion in the Big Five model, in which it was not related to dictator allocations, but predicted lower allocations in the generosity game, once politeness was controlled for. This combination of consistent and less consistent findings across the two studies demonstrates the importance of replication and comparisons across incentivized and hypothetical paradigms.

In line with a large body of literature, our two studies showed that humans are responsive to additional social preferences that stray from both narrow self-interest and inequality aversion. The findings from the generosity game correspond to previous research showing that many individuals are willing to assist others even when it means being relatively less well off, as long as absolute costs are minimal (Charness and Rabin, 2002; Engelmann and Strobel, 2004; Güth et al., 2012). Generosity may be crowded out by the trade-off between self- and other-interests in the dictator game, but when it is costless, “most of us try to make the world a better place” (Güth et al., 2009, p. 13). Likewise, many real-world gestures of prosociality, such as giving directions to a stranger and offering a seat on public transport, are ubiquitous precisely because they are relatively inexpensive forms of benevolence.

In contrast, we found mixed results for reciprocity, with consistent evidence of positive—but not negative—reciprocity across both studies. This supports the idea that negative and positive reciprocity are indeed independent processes and are not driven by the same motivations (Yamagishi et al., 2012; Ackermann et al., 2014). Our results are also reminiscent of the original findings by Charness and Rabin (2002), where there was evidence of positive reciprocity but fewer acts of negative reciprocity, even when it was free to punish a misbehaving partner. This may reflect similar sentiments as those in the generosity game, in that individuals are generally benevolent—or at least non-spiteful—when the stakes are relatively inexpensive. In addition, we found no consistent effects for personality with respect to positive or negative reciprocity, suggesting that individual differences in the propensity to reciprocate are subsumed more generally within broader prosocial tendencies.

Other factors may also contribute to the lack of negative reciprocity in our data. First, all decisions in the games were gain-framed. Even when a partner “hurt” a participant, it simply prevented them from receiving a higher amount rather than incurring a personal loss, which may have been too weak to provoke negative reciprocity. Second, the initial payoff combination (15 for the participant, 10 for the partner) declined by the partner in the hurt conditions of the dictator game was already unequal, which may have convinced participants that their partner’s decision to pass on this offer was justified and not deserving of retaliation. Third, the assessment of different social preferences within a single paradigm may trigger a desire among participants to behave consistently, thus artificially increasing consistency in behavior and nullifying any effects for negative reciprocity. However, the differential patterns of responding across generosity and positive reciprocity conditions provide evidence against any such response set. Future investigations using loss-framed manipulations, different configurations of payoffs, and measurements separated by time may be more appropriate for investigating negative reciprocity.

One interesting finding to emerge across both studies was the interaction between gender and game type, with men consistently allocating more than women in the (costless) generosity games. In the (costly) dictator game, however, women allocated more than men in incentivized games while there were no gender differences in hypothetical responses. But given that decisions in the latter are already a costless form of prosociality—relying on words rather than actions—the absence of a gender gap here may reflect overestimates of allocations among men relative to women. Hence, while women were more inequality averse, they were not necessarily more altruistic when this involved promoting the welfare of others over and above their own.

Although these results were unpredicted and unrelated to the aims of this research, they provide a clear replication of previous research on gender and social preferences. Several studies have shown that women are more prosocial in simple dictator games, while men are more prosocial when the price of giving drops and when giving or cooperating maximizes efficiency (Eckel and Grossman, 1998; Andreoni and Vesterlund, 2001; Croson and Gneezy, 2009; Kuhn and Villeval, 2015). Even in middle childhood and early adolescence, girls more often than boys select egalitarian allocations of wealth over both selfish and generous allocations (Fehr et al., 2013).

These findings correspond to a wider literature on gender differences in preferences toward social and political inequality (i.e., social dominance orientation), which are largely stable across nations and cultures (Pratto et al., 1994, 1997; Sidanius et al., 2000). Such differences in egalitarianism are believed to arise from evolutionary differences in reproductive strategies, in particular, the accumulation of economic resources and status for male, rather than female, reproductive success (Sidanius et al., 2000). Similarly, the literature on desirable mate qualities and costly signaling indicates that men may engage in greater acts of conspicuous consumption as a display of generosity and resources to increase prestige and status (Griskevicius et al., 2007). In the current paradigm, the safest and easiest way of doing this without putting one’s actual stakes at risk is through costless allocations in the generosity game.

A prominent finding was that the politeness aspect of Big Five agreeableness consistently predicted greater overall allocations in both studies. Although we observed a trend for a main effect of compassion when decisions were hypothetical, this disappeared altogether in the incentivized paradigm. These results are in keeping with previous research demonstrating that politeness—rather than compassion—drives egalitarian allocations in the dictator game, with the divergence between the two clearest in incentivized rather than hypothetical paradigms (Zhao et al., 2016).

This unique effect of politeness suggests that prosociality in these decontextualized and neutrally framed paradigms is a function of the tendency to respect others and to adhere to social norms rather than emotional concern for others’ wellbeing. While compassion plays a fundamental role in real-world forms of prosociality (Eisenberg and Miller, 1987; Bekkers, 2006) and the related construct of empathy is theorized to be the primary conduit through which humans engage in altruistic behavior (Batson, 1991), compassionate motives may not be elicited given the impersonal nature of economic games. This has important implications for the ecological validity of economic games, suggesting that social preferences and behaviors measured in these games only capture a limited form of norm-based prosociality. Indeed, in their commentary more than 20 years ago, Camerer and Thaler (1995) argued that the outcomes of such games reveal more about the economics of manners and etiquette than they do about altruism, which is empirically supported by the current findings.

A second major finding to appear consistently across studies was the interaction between honesty-humility and game type, where it predicted greater allocations in the dictator game but played no role in the generosity game. Honesty-Humility has been consistently linked to fair and prosocial (or at least the absence of antisocial) behaviors when there are personal profits to be made, such as delinquency (e.g., stealing money; Dunlop et al., 2012), workplace ethics and integrity (Lee et al., 2005; Cohen et al., 2014), and dishonesty (Hilbig and Zettler, 2015). Notably, across both Big Five and HEXACO models, honesty-humility is the trait most strongly and frequently associated with dictator allocations (Zhao and Smillie, 2015). Surprisingly, we found that this link to prosociality disappears when such decisions do not involve a personal cost. In the generosity game where individuals could maximize their partner’s payoffs for free, those high on honesty-humility allocated no differently from their low-scoring counterparts.

On the one hand, this implies that there are limits on the prosociality encompassed by honesty-humility, and, contrary to previous evidence (Hilbig et al., 2015b), suggests that honesty-humility is more closely tied to egalitarianism and fairness than benevolence. On the other hand, further inspection of Figure 4 shows that this interaction is more strongly driven by those at the low pole of honesty-humility. Although they are selfish when they can personally profit, they are neither competitive nor vindictive—and indeed appear concerned about efficiency—once their own stakes are secured.³ These results highlight the importance of situational context in the expression of personality traits: Given that HEXACO honesty-humility represents the tendency to cooperate with others despite the opportunity for exploitation (i.e., active cooperation), it is no longer elicited when there is no invitation to exploit in the non-constant-sum structure of the generosity game⁴.

It is noteworthy that these findings for honesty-humility were accompanied by a complementary pattern of results for HEXACO agreeableness in the hypothetical games. While HEXACO agreeableness did not predict dictator allocations, consistent with previous research (Hilbig et al., 2013), it was associated with greater allocations in the generosity game. These findings are in keeping with the core features of HEXACO agreeableness, which capture individual differences in tolerance, lenience, flexibility, and a lack of irritability or anger (Ashton and Lee, 2007; Ashton et al., 2014). All of these tendencies are antithetical to spite and envy, two major motivations for curbing a partner’s allocation in the generosity game. Nevertheless, we interpret this double dissociation with caution as it was not replicated in the incentivized paradigm, where HEXACO agreeableness was unrelated to any form of social preference.

Interestingly, however, we observed a near-identical interaction for the volatility aspect of Big Five neuroticism in the incentivized paradigm, which captures related constructs (i.e., anger and irritability; DeYoung et al., 2007, DeYoung, 2015) and is strongly negatively associated with HEXACO agreeableness (r_ss = -0.60, -0.62 in Studies 1 and 2, respectively). Bivariate correlations and exploratory analyses for volatility (see Supplementary Tables S1 and S6 in the Supplementary Material) showed a similar but inverted pattern to that previously seen for HEXACO agreeableness. Volatility has been linked to psychopathic traits (Jonason et al., 2013), and may provoke envy and resentfulness when individuals face the prospect of disadvantageous inequality in the generosity game.

The dual studies and their near-identical designs provide a useful comparison of trait effects across incentivized and hypothetical designs, which has been a topic of debate among psychologists and economists (Camerer and Hogarth, 1999; Ariely and Norton, 2007). Recent investigations of prosocial traits in the dictator game suggest that while average allocations drop between hypothetical and incentivized designs, the effects of certain traits—politeness and agreeableness from the Big Five model, and HEXACO honesty-humility—tend to be larger in incentivized paradigms (Zhao et al., 2016). Likewise, we also observed considerable discrepancies in average allocations between the two paradigms, with individuals overestimating dictator allocations when providing hypothetical responses. Such “hypothetical biases” are frequently seen in value elicitation methods, in which individuals overstate their willingness to pay for a given good (in this case, equality; Hertwig and Ortmann, 2001; List and Gallet, 2001). Yet, individuals also underestimated how benevolent or efficiency-maximizing they would be in the generosity game. It appears that in the absence of incentivization, all individuals gravitate toward the equality norm, leading to attenuated individual variation and muted trait effects. With incentivization, new trait effects emerged, including interactions for compassion and volatility. These can be understood in relation to a recent meta-analysis on the role of personality traits in cooperative game behaviors, which found moderating effects of incentivisation on Big Five agreeableness and neuroticism (Ferguson et al., 2015). With incentivization, the effect for agreeableness became stronger while the effect for neuroticism went from weakly positive to negative.