Costly punishment of cheaters who contribute little or nothing to a cooperating group has been extensively studied, as an effective means to enforce cooperation. The prevailing view is that individuals use punishment to retaliate against transgressions of moral standards such as fairness or equity. However, there is much debate regarding the psychological underpinnings of costly punishment. Some authors suggest that costly punishment must be a product of humans' capacity for reasoning, self-control and long-term planning, whereas others argue that it is the result of an impulsive, present-oriented emotional drive. Here, we explore the inter-temporal preferences of punishers in a multilateral cooperation game and show that both interpretations might be right, as we can identify two different types of punishment: punishment of free-riders by cooperators, which is predicted by patience (future orientation); and free-riders' punishment of other free-riders, which is predicted by impatience (present orientation). Therefore, the picture is more complex as punishment by free-riders probably comes not from a reaction against a moral transgression, but instead from a competitive, spiteful drive. Thus, punishment grounded on morals may be related to lasting or delayed psychological incentives, whereas punishment triggered by competitive desires may be linked to short-run aspirations. These results indicate that the individual's time horizon is relevant for the type of social behaviour she opts for. Integrating such differences in inter-temporal preferences and the social behaviour of agents might help to achieve a better understanding of how human cooperation and punishment behaviour has evolved.

Prenatal exposure to sex hormones exerts organizational effects on the brain which have observable behavioural correlates in adult life. There are reasons to expect that social behaviours—fundamental for the evolutionary success of humans—might be related to biological factors such as prenatal sex hormone exposure. Nevertheless, the existing literature is inconclusive as to whether and how prenatal exposure to testosterone and oestrogen, proxied by the second-to-fourth digit ratio (2D : 4D), may predict non-selfish behaviour. Here, we investigate this question using economic experiments with real monetary stakes and analyse five different dimensions of social behaviour in a comparatively large sample of Caucasian participants (n = 560). For both males and females, our results show no robust association between right- or left-hand 2D : 4D and generosity, bargaining or trust-related behaviours. Moreover, no differences in behaviour were found according to sex. We conclude that there is no direct correlation between 2D : 4D and these social behaviours.

Humans often ‘altruistically’ punish non-cooperators in one-shot interactions among genetically unrelated individuals. This poses an evolutionary puzzle because altruistic punishment enforces cooperation norms that benefit the whole group but is costly for the punisher. One key explanation is that punishment follows a social-benefits logic: it is eminently normative and group-functional (drawing on cultural group selection theories). In contrast, mismatch-based deterrence theory argues that punishment serves the individual-level function of deterring mistreatment of oneself and one's allies, hinging upon the evolved human coalitional psychology. We conducted multilateral-cooperation experiments with a sample of Spanish Romani people (GitanosorCalé) and the non-Gitanomajority. TheGitanosrepresent a unique case study because they rely heavily on close kin-based networks and display a strong ethnic identity. We find thatGitanonon-cooperators were not punished by co-ethnics in only-Gitano(ethnically) homogeneous groups but were harshly punished by otherGitanosand by non-Gitanosin ethnically mixed groups. Our findings suggest the existence of culture-specific motives for punishment:Gitanos, especially males, appear to use punishment to protect their ethnic identity, whereas non-Gitanosuse punishment to protect a norm of universal cooperation. Only theories that consider normative, group-functional forces underlying punishment behaviour can explain our data.

It is documented that fetal exposure to sexual hormones has long lasting effects on human behavior. The second-to-fourth digit ratio (DR) is a putative marker for prenatal exposure to testosterone (compared to estrogens) while in uterus, with higher relative exposure to testosterone resulting in a lower DR. Although the existing literature documents the correlation of DR with various decisions, and testosterone has been related to competitive behaviors, little research has studied the effect of DR on competition in conflict situations where skills do not matter. We investigate this question in the laboratory. Based on a previously obtained large sample of student subjects, we selectively invite subjects to the laboratory if their right-hand DR is in the top (High type) or bottom (Low type) tercile for their gender. Unbeknownst to the subjects, we perform a controlled match of High and Low types as opponents in a 2-person Tullock contest. We find that Low type (higher exposure to testosterone) males expend significantly higher conflict effort than High type males, that is, they are more aggressive, which reduces their opponents’ earnings. Among females, however, everyone is more aggressive against the High type (who respond less aggressively). These results can partially be explained through high joy of winning and/or spitefulness for Low type males, and high spitefulness for Low type females. This investigation sheds light on the importance of biological aspects in the ex-ante determinants of conflict, and on contest design.

This study explores the effect of several personal religion-related variables on social behaviour, using three paradigmatic economic games: the dictator (DG), ultimatum (UG), and trust (TG) games. A large carefully designed sample of a Spanish urban adult population (N=766) is employed. From participants' decisions in these games we obtain measures of altruism, bargaining behaviour and sense of fairness/equality, trust, and positive reciprocity. Three dimensions of religiosity are examined: (i) religious denomination; (ii) the intensity of religiosity, measured by active participation at church services; and (iii) converting out into a different denomination than the one raised in.The major results are: (i) individuals with "no religion" made decisions closer to rational selfish behaviour in the DG and the UG compared to those who affiliate with a "standard" religious denomination; (ii) among Catholics, intensity of religiosity is the key variable that affects social behaviour insofar as religiously-active individuals are generally more pro-social than non-active ones; and (iii) the religion raised in seems to have no effect on pro-sociality, beyond the effect of the current measures of religiosity. Importantly, behaviour in the TG is not predicted by any of the religion-related variables we analyse. Given the accelerating share of "no religion" individuals (in Europe and elsewhere) and the large influx of immigrants – who tend to be more religiously active compared to the native populations – our findings have significant implications for the future pro-sociality patterns in Europe.

Groups make decisions on both the production and the distribution of resources. These decisions typically involve a tension between increasing the total level of group resources (i.e. social efficiency) and distributing these resources among group members (i.e. individuals’ relative shares). This is the case because the redistribution process may destroy part of the resources, thus resulting in socially inefficient allocations. Here we apply a dual-process approach to understand the cognitive underpinnings of this fundamental tension. We conducted a set of experiments to examine the extent to which different allocation decisions respond to intuition or deliberation. In a newly developed approach, we assess intuition and deliberation at both the trait level (using the Cognitive Reflection Test, henceforth CRT) and the state level (through the experimental manipulation of response times). To test for robustness, experiments were conducted in two countries: the US and India. Despite absolute level differences across countries, in both locations we show that: (i) time pressure and low CRT scores are associated with individuals’ concerns for their relative shares; (ii) time delay and high CRT scores are associated with individuals’ concerns for social efficiency. These findings demonstrate that deliberation favours social efficiency by overriding individuals’ intuitive tendency to focus on relative shares.