Collaborative partnerships are often formed following a first encounter. For example, unacquainted individuals may collaborate to complete a project, develop a product, or solve a problem. Using the Social Relations Model, this study examined the extent to which first-encounter trait perceptions predicted collaborative partner preferences. Previously-unacquainted participants (N = 297, 55 groups, 55.9% female) interacted dyadically and provided round-robin ratings of extraversion, honesty-humility, competence, and partner preference. At the target level, individuals who were consistently viewed as extraverted and competent were consistently preferred more as partners. At the relationship level, individuals who were uniquely viewed as honest-humble and competent were uniquely preferred more as partners. Findings underscore the relevance of target- and relationship-specific perceptions in predicting first-encounter collaborative partner preferences.

Online video conferencing experiments have proven advantageous for collecting data on naturalistic human social interactions, enabling effective recruitment of diverse study participants and scalability without requiring specialized facilities. However, the common practice of using ad hoc solutions for such studies poses challenges. These challenges include the time-consuming adjustment of methods for specific experiments, potential privacy risks, reduced data control when relying on cloud-based tools, the necessity of special software installations by participants, and difficult management of remote participants during the live experiments. To address these limitations, we introduce openVIMO, a software framework for creating video-based online interaction experiments built on open-source technologies. It can be deployed on a server under a researcher's control without relying on additional commercial third-party services. Concretely, it enables (1) the creation of web-based experiments and surveys involving video calls between participants, as well as (2) the remote monitoring of participants' progress throughout a study, including means for communication and intervention throughout a protocol. Moreover, openVIMO facilitates (3) collecting and storing survey and interaction data (incl. audio and video). Finally, the platform has been designed to (4) allow the staging of highly customized experimental protocols and to be dynamically expanded by the research community.

Current theories pose that intergroup competition elevates intragroup cooperation and put forward hypotheses about conditions that increase the magnitude of this effect. Here, we report a preregistered meta-analysis of studies using experimental games that manipulate the presence of intergroup competition and its effect on intragroup cooperation. Our investigation reveals the overall direction and magnitude of the effect, which addresses mixed empirical findings. We identified 25 articles to meet inclusion criteria, which yielded 70 effect sizes. A multilevel random effects model revealed a medium positive effect of intergroup competition on intragroup cooperation (g = .677, N = 6,051). Studies involving intergroup competition with interdependence produced a strong effect, whereas this effect was weaker for studies without interdependence. Our findings present meta-analytic evidence that intergroup competition promotes intragroup cooperation and identify opportunities for future research.

Trait activation theory posits that personality traits are expressed when trait-relevant situational cues-affordances-are present. While prior work has primarily examined how situational affordances moderate trait-behavior associations (an affordance-gradient perspective), comparatively less attention has been given to how multiple traits are differentially activated within affordance-relevant situations (an affordance-configured perspective), especially in ecologically valid settings. We addressed this gap using a retrospective diary design with 224 respondents (Ndiary = 448), combining self- and independently rated assessments of situational affordances and behavioral expressions. Consistent with the affordance-configured perspective, traits showed stronger associations with behavior in affordance-relevant situations relative to other traits. In contrast, interaction effects for the affordance-gradient perspective were mostly absent. These findings extend trait activation theory to everyday life and underscore the value of situational affordances for understanding personality expression.

Interdependent subsistence styles, such as rice farming, are thought to underlie the evolution of collectivistic cultures, which emphasize collective welfare over individual gains. Rice farming can produce mutual dependence within communities but also create conflicting interests, as people cooperate to provide valuable public goods. However, current theories of the origins of collectivism fail to address the interplay between mutual dependence and conflict. As a consequence of these limitations, the evolutionary dynamics of collectivism and its association with cooperation are still unclear. We advance a theoretical model to study the evolution of cultural traits that enhance people's valuations of collective welfare, one of the key features of collectivistic cultures. Our model investigates the evolutionary dynamics of cooperation and cultural evolution in ecologies with distinct interdependence structures. We find evidence that higher degrees of mutual dependence facilitate the evolution and persistence of collectivism. However, the degree of conflicting interests also plays a crucial role in driving the diffusion and maintenance of collectivistic norms. In particular, the selective advantage of collectivism is strongest when people experience some degree of conflict of interests, an effect that is magnified by heightened mutual dependence. These results clarify how variation in interdependence could underlie the ecological origins of collectivism, lending support to and expanding the scope of current theories of the cultural evolution of cooperation. More broadly, the framework presented here elucidates how fitness interdependence can be influenced by different ecological factors, and, in turn, influence the evolution of social behaviors. (PsycInfo Database Record (c) 2026 APA, all rights reserved).

Humans evolved to solve adaptive problems with kin and non-kin across fitness-relevant domains, including childcare, resource sharing, among others. Therefore, there is a great diversity in the types of interdependences humans experience across activities, relationships, and ecologies. To identify human psychological adaptations for cooperation, we argue that researchers must accurately characterize human fitness interdependence. We propose a theoretical framework for assessing variation in fitness interdependence (FI) that applies to the social interactions humans would have experienced across situations, relationships, and ecologies in the ancestral past and continue to experience today. According to this model, FI is characterized along four dimensions: 1) corresponding-versus-conflicting interests 2) mutual-dependence-versus-independence, 3) asymmetrical-versus-symmetrical dependence (i.e., power), and 4) coordination. Because humans evolved to be highly mutually dependent on others to solve myriad adaptive problems, even compared to our closest living relatives, there is immense variability in the types of interdependences humans experience in daily life. Here, we describe the kinds of variation in interdependence humans experience, paying particular attention to social life in small-scale societies. In demonstrating the diversity of conflicts and coordination problems humans manage, we contend that humans evolved psychological adaptations to infer from signals, cues, and properties of the environment the four dimensions of FI under degrees of uncertainty to reduce the costs of cooperation. We conclude by discussing the theoretical implications of FI theory and emphasize that when individuals understand that others depend on them, it gives way to a new means of leverage to influence how others behave towards them.

People frequently participate in interdependent tasks (i.e., tasks in which the outcome of one person is reliant on the other person's actions), in which people can behave in ways that benefit others (i.e., cooperate) to achieve mutually beneficial outcomes in daily life. The ability to select appropriate cooperative partners for these tasks is essential to achieve successful outcomes. Yet, little is known about individual partner preferences for interdependent tasks and whether these preferences change in response to situational affordances of the task (i.e., which traits can affect task outcomes). Here, we report four studies (N = 1021) that investigate the relationship between partner preference, person perceptions, and partner selection in interdependent tasks that afford the expression of warmth- or competence-related traits to affect outcomes. Over four studies, participants were randomly assigned to an interdependent task affording for warmth- or competence-related traits, then rated the most important traits in a partner (Study 1-4), evaluated potential partners' warmth and competence (Study 3-4), and selected partners (Study 3-4). Overall, participants strongly prefer warmth-related traits in a partner, but partner preferences also vary depending on task affordance. Specifically, people demonstrated a stronger preference for partner trustworthiness in tasks affording warmth-related traits and preferred highly competent partners in tasks affording competence-related traits. Additionally, preferences for partner traits strengthened the relationship between the perceived partner trait afforded by the situation and partner selection. We discuss these findings in relation to theories of partner selection and cooperation, as well as the implications of these results to develop tools and interventions to help people optimize their partner selections.

Evolutionary theory suggests that partner selection - the ability to identify and preferentially interact with individuals willing (warmth) and able (competence) to work towards mutual benefits - is a key driver of cooperative behavior. However, partner selection is complex, requiring the integration of various information, such as impression formation and task affordances. Despite its importance, there is limited research on the effect of these factors on partner selection for cooperative tasks. Thus, this paper investigates how person perceptions (warmth and competence), task affordances, and facial and acoustic nonverbal behavior inform partner selection for cooperative tasks. For this purpose, we asked participants to select partners for a task that either expressed warmth- or competence-related traits. Participants had a 3-minute (online) conversation with up to five individuals, reported their evaluations, selected partners for the task, and then engaged in the task. Results indicate that person perceptions guide partner selection, with each trait being more predictive in relevant tasks. Additionally, we found that the perceptions of warmth, but not competence, can be predicted by facial and acoustic cues during conversations. Lastly, we find that in the context of online social interactions, individuals were more cooperative towards selected participants than unselected. We discuss these implications in the context of the theory of partner selection and offer insights on how these results can be used in future efforts for designing socially intelligent artificial systems that support partner selection decisions.

Two theoretical perspectives (i.e., the risk management perspective and the resource perspective) offer competing predictions that higher class individuals-relative to lower class individuals-tend to be less versus more prosocial, respectively. Different predictions can also be drawn from each perspective about how the class-prosociality association varies across sociocultural contexts. To date, each perspective has received mixed empirical support. To test these competing perspectives, we synthesized 1,106 effect sizes from 471 independent studies on social class and prosociality (total N = 2,340,806, covering the years 1968-2024) conducted within 60 societies. Supporting the resource perspective, we found higher class individuals to be slightly more prosocial (r = .065, 95% confidence interval [.055, .075]); this association held for children, adolescents, and adults and did not significantly vary by any sociocultural variable. In testing the methodological moderators, we found no significant difference in the class-prosociality association in studies measuring objective social class (r = .066) and those measuring or manipulating subjective social class (r = .063). Nevertheless, the observed class-prosociality association was stronger when assessing prosocial behavior involving actual commitment of material or nonmaterial resources (r = .079) compared to prosocial intention (r = .039), and stronger under public (r = .065) than private (r = .016) circumstances. These findings generally support the resource perspective on class-based differences in prosociality-that the relatively higher cost of prosocial behavior, combined with heightened experience of deprivation, results in lower levels of prosociality among individuals with a lower social class background. (PsycInfo Database Record (c) 2025 APA, all rights reserved).

Direct reciprocity has been long identified as a mechanism to support the evolution of cooperation in social dilemmas. While most research on reciprocal cooperation has focused on symmetrical interactions, real world interactions often involve differences in power. Verbal theories have either claimed that power differences enhance or destabilize cooperation, indicating the need for a comprehensive theoretical model of how power asymmetries affect direct reciprocity. Here, we investigate the relationship between power and cooperation in two frequently studied social dilemmas, the prisoner's dilemma (PD) and the snowdrift game (SD). Combining evolutionary game theory and agent-based models, we demonstrate that power asymmetries are detrimental to the evolution of cooperation. Strategies that are contingent on power within an interaction provide a selective advantage in the iterated SD, but not in the iterated PD. In both games, the rate of cooperation declines as power asymmetry increases, indicating that a more egalitarian distribution of the benefits of cooperation is the prerequisite for direct reciprocity to evolve and be maintained.

Prisoner's dilemma (PD) games exist in a variety of configurations. Although the normative solution for any one-shot PD game is defection, empirical research shows that games differ in the amount of cooperation they elicit from human players. Different researchers have developed a variety of indexes, which are functions of the specific payoffs in a given PD, aiming to measure the level of anticipated cooperation elicited by that game. The purpose of the first study in this article was to collect, organize, and compare the mathematical properties of these various indexes. Our results show that many superficially different indexes are the same and that in general six fundamental PD indexes exist. We propose that the six families of indexes correspond to psychological processes and preferences involving prosociality, greed, fear, and risk. In the second study, we provide a meta-analysis of the relationship between selected indexes and cooperation in PD games (k = 280). The amount of variance in cooperation explained by each index ranged from 0.00% to 7.57%. The first family of indexes (described as indexes of the incentive for cooperation in the first study) had the most consistently strong relationships with cooperation. In general, the findings of the meta-analysis aligned with predictions based on our own review and taxonomy of six index families proposed in Study 1.

As intelligent technology and applications have become an integral part of nearly all aspects of people's daily lives, many intelligent systems have been designed to help people navigate the complex space of social interactions. One prominent strategy for such intelligent support is providing meaningful Ad Hoc Interventions (ADI), e.g., through timely notifications. An alternative is Technology-Supported Reflection (TSR), e.g., by offering information about activities in one's past for personal insights. In contrast to straight-up interventions, the aim of the latter strategy is not to directly augment human skills but instead support learning and personal growth over time. However, while TSR has seen widespread interest in applications in some areas, such as physical fitness and mental health, its use for improving human social interactions has not yet been systematically explored. Concretely, it is currently unclear 1) what forms of self-reflection systems intend to support, 2) how their different technological components (e.g., data collection, information integration) are involved in providing support, and 3) what common limitations and design challenges they face. In this article, we present the results of a systematic literature review focusing on these questions to provide a structured foundation for targeted research. Concretely, we identified and analysed a collection of 23 relevant papers, each describing a system deploying TSR to support humans with elements of social interactions. We constructed a framework with a set of features to comprehensively describe and analyze the systems that support self-reflection, including their application domains, how they fit into the existing design framework, how they facilitate learning through reflection, how adaptive they are to individual users, and how they were evaluated. Finally, we propose a direction for designing systems that support individual's social interactions through self-reflection in an adaptive manner.

How people evaluate, select, and engage with others in cooperative settings significantly impacts their well-being, happiness, and success. However, navigating these processes is complex. Equipping systems with the ability to recognize, interpret, and even engage during such socio-cognitive processes can increase their potential to support humans in these socio-cognitive processes and be more successful in adjusting to the social environment they are embedded in (e.g., understanding human preferences and attitudes), leading to better quality interactions and decision-making for future partners. Yet, the developments of such systems depend on available datasets. However, based on our knowledge, no dataset exists that can be used to model partner selection for joint tasks. To support research focused on creating such intelligent systems, we introduce the PARSEL dataset - a comprehensive corpus of dyadic interactions designed for computational modeling of PARtner SELection processes and collaborative behavior. In total, 297 participants took part in the datasets. The dataset contains measurements of partner selection decisions over three different stages, as well as factors that may influence partner selection in the context of (online) social interactions. It includes audiovisual recordings that offer fine-grained behavioral cues used during these interactions, self-reported traits, and reported perceptions of person-, situation-, and team-specific phenomena. By providing this resource, we aim to foster advancements in computational methods that can effectively model and augment socio-cognitive processes, contributing to socially aware intelligent systems and enhanced human-system interactions.

Ingroup favoritism can represent a challenge for establishing cooperation beyond group boundaries. In a behavioral experiment conducted across 17 societies (N = 3,236), we tested pre-registered hypotheses forwarded by social identity and material security frameworks to account for ingroup favoritism in trust toward national ingroups. We related individual-level measures of national identification and perception of institutions to trust, trustworthiness, and behavioral expectations of partner's trustworthiness toward a national ingroup, outgroup, or unidentified stranger in a trust game. Our findings support a social identity framework, as national identification was positively associated with greater ingroup favoritism. However, in contrast to predictions from a material security framework, perceptions of national institutions as trustworthy and benevolent were positively associated with greater ingroup favoritism. These findings suggest some potential challenges that support for national institutions might pose to the establishment of trust beyond group borders.

Cooperation underlies the ability of groups to realize collective benefits (e.g., creation of public goods). Yet, cooperation can be difficult to achieve when people face situations with conflicting interests between what is best for individuals versus the collective (i.e., social dilemmas). To address this challenge, groups can implement rules about structural changes in a situation. But what institutional rules can best facilitate cooperation? Theoretically, rules can be made to affect structural features of a social dilemma, such as the possible actions, outcomes, and people involved. We derived 13 preregistered hypotheses from existing work and collected 6 decades of empirical research to test how nine structural features influence cooperation within prisoner's dilemmas and public goods dilemmas. We do this by meta-analyzing mean levels of cooperation across studies (Study 1, k = 2,340, N = 229,528), and also examining how manipulations of these structural features in social dilemmas affect cooperation within studies (Study 2, k = 909). Results indicated that lower conflict of interests was associated with higher cooperation and that (a) the implementation of sanctions (i.e., reward and punishment of behaviors) and (b) allowing for communication most strongly enhanced cooperation. However, we found inconsistent support for the hypotheses that group size and matching design affect cooperation. Other structural features (e.g., symmetry of dilemmas, sequential decision making, payment) were not associated with cooperation. Overall, these findings inform institutions that can (or not) facilitate cooperation.

The idea that strong situations restrict variance in behaviors has been treated as a maxim in psychology. Prior work has, however, offered inconclusive support for this proposition. We aimed to overcome the limitations of prior research to conclusively test the restricted variance hypothesis derived from the situational strength framework. Specifically, we conducted a preregistered meta-analysis (k = 301, N = 25,670) in the context of cooperative behavior observed within the standard social dilemma paradigm. We found that strong, compared with weak, situations (theorized and validated via perception ratings) indeed restricted variance in behaviors. Moreover, ratings on perceived situational strength of specific experimental conditions (k = 138, nstudies = 41) further supported the hypothesis that higher levels of perceived situational strength were associated with less variance in behavior. Our findings have important theoretical implications for understanding the situational forces shaping social behavior and for advancing research on person-situation interactions.

Social situations may vary in the severity of conflict between self-interest and collective welfare, and thereby pose collective action problems that might require different institutional solutions. The present study examines the effect of conflict of interests on beliefs, norms, cooperation, and choice of sanctioning institutions in social dilemmas across two experiments (total N =1304). In each experiment, participants interacted in a public goods game (PGG), and a modified PGG with institutional choice using a 2 (conflict of interests: low vs. high) x 3 (institutional choice: peer punishment/no sanction vs. centralized punishment/no sanction vs. gossip plus ostracism/no sanction) between-participants design. More severe conflict of interests reduces individuals' own cooperation, first-order beliefs about others' cooperation, second-order normative expectations and personal norms of cooperation. This pattern is pronounced over time in repeated interactions. We did not find that conflict of interests influenced the choice to establish a sanctioning institution. Taken together, the challenges arising from stronger conflicting interests can cause the collapse of cooperation, hinder the emergence of trust and norms of cooperation, but do not provide the impetus to support a sanctioning institution to promote cooperation. Implications for solving public goods dilemmas that contain a severe conflict of interests are discussed.

Past research hypothesized that men and women differ in their tendency to cooperate with strangers in situations that involve a conflict of interests. However, recent empirical research has provided converging evidence that men and women cooperate to a similar extent, and that differences in cooperation can emerge in response to specific situational and societal contexts. Here we analyse six decades of empirical research on human cooperation using social dilemmas (1961–2017,k= 126) conducted across 20 industrialized societies, testing pre-registered hypotheses derived from evolutionary theory and social role theory. Overall, our findings revealed little-to-no evidence for an association between gender and cooperation using different meta-analytic approaches. We did not find within-study differences in cooperation between men and women (d= 0.011, 95% CI [−0.038, 0.060]). However, cooperation was slightly higher across studies with predominantly female samples (k= 972). In addition, contrary to our predictions, gender differences in cooperation did not emerge in response to the degree of conflicting interests in the situation, and societal levels of gender equality and economic development. We discuss the implications of these findings for our understanding of gender differences in cooperation.This article is part of the theme issue ‘Cooperation among women: evolutionary and cross-cultural perspectives’.