Motivations to reciprocate cooperation and punish defection are calibrated by estimates of how easily others can switch partners

Evolutionary models of dyadic cooperation demonstrate that selection favors different strategies for reciprocity depending on opportunities to choose alternative partners. We propose that selection has favored mechanisms that estimate the extent to which others can switch partners and calibrate motivations to reciprocate and punish accordingly. These estimates should reflect default assumptions about relational mobility: the probability that individuals in one’s social world will have the opportunity to form relationships with new partners. This prior probability can be updated by cues present in the immediate situation one is facing. The resulting estimate of a partner’s outside options should serve as input to motivational systems regulating reciprocity: Higher estimates should down-regulate the use of sanctions to prevent defection by a current partner, and up-regulate efforts to attract better cooperative partners by curating one’s own reputation and monitoring that of others. We tested this hypothesis using a Trust Game with Punishment (TGP), which provides continuous measures of reciprocity, defection, and punishment in response to defection. We measured each participant’s perception of relational mobility in their real-world social ecology and experimentally varied a cue to partner switching. Moreover, the study was conducted in the US (n = 519) and Japan (n = 520): societies that are high versus low in relational mobility. Across conditions and societies, higher perceptions of relational mobility were associated with increased reciprocity and decreased punishment: i.e., those who thought that others have many opportunities to find new partners reciprocated more and punished less. The situational cue to partner switching was detected, but relational mobility in one’s real social world regulated motivations to reciprocate and punish, even in the experimental setting. The current research provides evidence that motivational systems are designed to estimate varying degrees of partner choice in one’s social ecology and regulate reciprocal behaviors accordingly.

Third-party punishers do not compete to be chosen as partners in an experimental game

Third-party punishment is thought to act as an honest signal of cooperative intent and such signals might escalate when competing to be chosen as a partner. Here, we investigate whether partner choice competition prompts escalating investment in third-party punishment. We also consider the case of signalling via helpful acts to provide a direct test of the relative strength of the two types of signals. Individuals invested more in third-party helping than third-party punishment and invested more in both signals when observed compared to when investments would be unseen. We found no clear effect of partner choice (over and above mere observation) on investments in either punishment or helping. Third-parties who invested more than a partner were preferentially chosen for a subsequent Trust Game although the preference to interact with the higher investor was more pronounced in the help than in the punishment condition. Third-parties who invested more were entrusted with more money and investments in third-party punishment or helping reliably signalled trustworthiness. Individuals who did not invest in third-party helping were more likely to be untrustworthy than those who did not invest in third-party punishment. This supports the conception of punishment as a more ambiguous signal of cooperative intent compared to help.

Expression unleashed: The evolutionary & cognitive foundations of human communication

Human expression is open-ended, versatile and diverse, ranging from ordinary language use to painting, from exaggerated displays of affection to micro-movements that aid coordination. Here we present and defend the claim that this expressive diversity is united by an interrelated suite of cognitive capacities, the evolved functions of which are the expression and recognition of informative intentions. We describe how evolutionary dynamics normally leash communication to narrow domains of statistical mutual benefit, and how they are unleashed in humans. The relevant cognitive capacities are cognitive adaptations to living in a partner choice social ecology; and they are, correspondingly, part of the ordinarily developing human cognitive phenotype, emerging early and reliably in ontogeny. In other words, we identify distinctive features of our species’ social ecology to explain how and why humans, and only humans, evolved the cognitive capacities that, in turn, lead to massive diversity and open-endedness in means and modes of expression. Language use is but one of these modes of expression, albeit one of manifestly high importance. We make cross-species comparisons, describe how the relevant cognitive capacities can evolve in a gradual manner, and survey how unleashed expression facilitates not only language use but novel behaviour in many other domains too, focusing on the examples of joint action, teaching, punishment and art, all of which are ubiquitous in human societies but relatively rare in other species. Much of this diversity derives from graded aspects of human expression, which can be used to satisfy informative intentions in creative and new ways. We aim to help reorient cognitive pragmatics, as a phenomenon that is not a supplement to linguistic communication and on the periphery of language science, but rather the foundation of the many of the most distinctive features of human behaviour, society and culture.

More of the Same? Comparing the Personalities of Ex-Spouse and New Partner after Divorce

The similarity of the Big Five personality traits of ex-spouses and new partners was examined post-divorce. The notion that divorcees replicate their partner choice (fixed-type hypothesis) was tested against the hypotheses that they learn to select a new partner with more marriage-stabilizing personality traits than their former spouse (learning hypothesis), or are constrained by marriage market forces to repartner with someone who has less stabilizing personality traits (marriage market hypothesis). Data was derived from a Flemish study that sampled divorcees from the national register. The sample consisted of 700 triads of divorcees, their ex-spouses, and their new partners. The analysis results rejected the fixed-type hypothesis and instead supported both the learning hypothesis and the marriage market hypothesis, with higher order repartnering supporting the latter. Women also seemed to validate both hypotheses, as their partner comparison showed decreases in both stabilizing traits (conscientiousness and agreeableness) and destabilizing traits (neuroticism and extraversion). Overall, the results seem to suggest that divorcees do not repartner with someone of the same personality as their ex-spouse, and they are in some cases constrained by marriage market forces to repartner with less stabilizing personalities, while in other cases they are able to improve their partner selection.

The Joint Log-Lift Task: A Social Foraging Paradigm

Behavioural cooperation is under intense research. Yet, popular experimental paradigms often employ artificial tasks, require training, or do not permit partner choice, possibly limiting their biological relevance. We developed the joint log-lift task, a social foraging paradigm in which animals have to jointly lift a log to each obtain a food reward. The task relies on an obligate strategy, meaning that the only way to benefit is to work jointly. We hypothesised that (1) animals learn to spontaneously solve the task, and that (2) kin and (3) more sociable individuals would engage more often together in the task and achieve greater success than non-kin and less sociable individuals, respectively. We presented the task to 8 groups of juvenile domestic pigs (Sus scrofa domesticus) in their home pen for 30 min daily. Over the course of 9 days, the pigs showed evidence of learning by progressively switching from individual to joint behaviours, leading to 68% (62 out of 91 pigs) spontaneously solving the task. Success was influenced by sociability, but not kinship. There were large differences in success among dyads, hinting at the possible role of social dynamics and inter-individual differences in the ability and/or motivation to solve the task. The joint log-lift task allows researchers to investigate spontaneous cooperative tendencies of individuals, dyads and groups in the home environment through ad libitum engagement with the apparatus. This ecologically relevant paradigm opens the way to investigate social foraging experimentally at large scale, by giving animals free choice about when and with whom to work jointly.

Gossip and competitive altruism support cooperation in a Public Good game

When there is an opportunity to gain a positive reputation, individuals are more willing to sacrifice their immediate self-interest. Partner choice creates opportunities for competitive altruism, i.e. individuals compete to be regarded as more generous and to be chosen for future partnerships. Tests of the competitive altruism hypothesis have focused so far on reputation based on direct observation, whereas the role of gossip has not been theoretically and empirically addressed. Partner choice can create an incentive to cooperate and to send truthful messages, but it can also work in the opposite direction. In order to understand the consequences of partner choice on cooperation and gossip, we designed an experimental study in which participants played a sequence of Public Goods games and gossip rounds. In our two treatments, we observed that cooperation increased when there was an opportunity to be selected, but also that cooperators sent more honest messages than defectors, and that this strategy was prevalent in the treatment in which inter-group competition was implemented. We also found evidence that participants detached themselves from the information more often when lying. Taken together, our study fills a theoretical and empirical gap by showing that partner choice increases both cooperation and honesty of gossip. This article is part of the theme issue ‘The language of cooperation: reputation and honest signalling’.

Parochial cooperation and the emergence of signalling norms

Why do people adorn themselves with elaborate body piercings or tattoos, wear obstructing garbs, engage in life-threatening competitions and other wasteful and harmful but socially stipulated practices? Norms of cooperation and coordination, which promote the efficient attainment of collective benefits, can be explained by theories of collective action. However, social norms prescribing wasteful and harmful behaviours have eluded such explanations. We argue that signalling theory constitutes the basis for the understanding of the emergence of such norms, which we call signalling norms. Signalling norms emerge as a result of the uncertainty about who is a friend and who is a foe. The need to overcome this uncertainty arises when different groups compete for scarce resources and individuals must be able to identify, trust and cooperate with their fellow group members. After reviewing the mechanisms that explain the emergence of cooperation and coordination norms, we introduce the notion of signalling norms as markers of group distinction. We argue that adherence to signalling norms constitutes a commitment promoting parochial cooperation rather than a quality-revealing signal facilitating partner choice. We formalize our argument in a game-theoretic model that allows us to specify the boundary conditions for the emergence of signalling norms. Our paper concludes with a discussion of potential applications of our model and a comparison of signalling norms with related concepts. This article is part of the theme issue ‘The language of cooperation: reputation and honest signalling’.

Direct punishment and indirect reputation-based tactics to intervene against offences

Punishment and reputation-based mechanisms play a major role in supporting the evolution of human cooperation. Theoretical accounts and field observations suggest that humans use multiple tactics to intervene against offences—including confrontation, gossip and ostracism—which have unique benefits and costs. Here, we draw a distinction between direct punishment tactics (i.e. physical and verbal confrontation) and indirect reputation-based tactics (i.e. gossip and ostracism). Based on this distinction, we sketch the common and unique social functions that different tactics are tailored to serve and describe information-processing mechanisms that potentially underlie decisions concerning how to intervene against offences. We propose that decision rules guiding direct and indirect tactics should weigh information about the benefits of changing others' behaviour versus the costs of potential retaliation. Based on a synthesis of existing evidence, we highlight the role of situational, relational and emotional factors in motivating distinct punishment tactics. We suggest that delineating between direct and indirect tactics can inform debates about the prevalence and functions of punishment and the reputational consequences of third-party intervention against offences. We emphasize the need to study how people use reputation-based tactics for partner recalibration and partner choice, within interdependent relationships and social networks, and in daily life situations. This article is part of the theme issue ‘The language of cooperation: reputation and honest signalling’.