The Skillful and the Stingy: Partner Choice Decisions and Fairness Intuitions Suggest Human Adaptation for a Biological Market of Cooperators

Flexible ability-willingness trade-offs in cooperative partner choice: Evidence from a drift-diffusion model and ERP data

Partner choice plays a crucial role in human social behavior, with previous research highlighting the importance of both partner ability and willingness to cooperate in decision-making processes. However, the dynamic interplay between these factors across different contexts and how they are influenced by individual characteristics remain poorly understood. This study investigated how task demands and individual traits modulate the tradeoff between partner ability and willingness to make social decisions. We employed a novel experimental paradigm combining three tasks (prisoner's dilemma, time estimation, and a combined task) with computational modeling and EEG recording. Fifty-three participants completed partner-selection trials across these tasks, while their behavioral and neural responses were recorded. Drift diffusion model (DDM) analysis revealed that decision weights for partner ability and willingness were systematically modulated by task demands, with willingness prioritized in cooperative contexts, but ability prioritized in skill-based tasks. Using these model-estimated weights, we found that participants with high self-perceived ability had higher ability weights, whereas those with high self-perceived willingness had lower ability weights in their decision making. EEG analysis, utilizing trial-level weights computed by the DDM, showed that the processing of willingness and ability information began approximately 300 ms post-stimulus, with distinct spatiotemporal patterns across tasks. In the combined task, EEG data indicated earlier and more extensive processing of willingness than of ability information. These findings reveal that individuals flexibly adjust their weighting of partner willingness and ability based on task demands, challenging the notion of a fixed "willingness priority" and demonstrating the dynamic nature of social decision-making across contexts.

Partner perceptions during brief online interactions shape partner selection and cooperation

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.

Willingness valued more than ability in partner choice: Insights into behavioral and ERP data

In human cooperation, people prefer to choose partners with high willingness and ability-while both are valued by partners, individuals often prioritize willingness. Two event-related potential (ERP) experiments were conducted to discern the neural processes underpinning this preference. In the first experiment, participants made a choice between two potential partners and received feedback on the selected partner's willingness to cooperate. This was followed by feedback on the partner's task performance (ability) or a gambling outcome. In contrast, the second experiment first provided feedback on ability, then presented feedback on willingness or a gambling outcome. This study revealed that a potential partner's willingness trait significantly influences individuals' emotional evaluations and monetary allocations than the ability trait. Electrophysiological data indicated that low-willingness feedback elicited a diminished feedback-related negative (FRN) and an amplified P3 compared to high-willingness feedback. In contrast, no such difference was discernible between high- and low-ability feedback. Moreover, the P3 difference from high versus low willingness was considerably more pronounced than that from gambling outcomes, whereas the difference wave between high and low ability paralleled gambling outcomes. These findings bolster the novel finding that partner willingness may provide more substantial social rewards than ability. Furthermore, this study provides the first ERP evidence of willingness and ability trait perceptions in partner choice decisions.

Rational inferences about social valuation

The decisions made by other people can contain information about the value they assign to our welfare-for example how much they are willing to sacrifice to make us better off. An emerging body of research suggests that we extract and use this information, responding more favorably to those who sacrifice more even if they provide us with less. The magnitude of their trade-offs governs our social responses to them-including partner choice, giving, and anger. This implies that people have well-designed cognitive mechanisms for estimating the weight someone else assigns to their welfare, even when the amounts at stake vary and the information is noisy or sparse. We tested this hypothesis in two studies (N=200; US samples) by asking participants to observe a partner make two trade-offs, and then predict the partner's decisions in other trials. Their predictions were compared to those of a model that uses statistically optimal procedures, operationalized as a Bayesian ideal observer. As predicted, (i) the estimates people made from sparse evidence matched those of the ideal observer, and (ii) lower welfare trade-offs elicited more anger from participants, even when their total payoffs were held constant. These results support the view that people efficiently update their representations of how much others value them. They also provide the most direct test to date of a key assumption of the recalibrational theory of anger: that anger is triggered by cues of low valuation, not by the infliction of costs.

Rational information search in welfare-tradeoff cognition

One of the most important dimensions along which we evaluate others is their propensity to value our welfare: we like people who are disposed to incur costs for our benefit and who refrain from imposing costs on us to benefit themselves. The evolutionary importance of social valuation in our species suggests that humans have cognitive mechanisms that are able to efficiently extract information about how much another person values them. Here I test the hypothesis that people are spontaneously interested in the kinds of events that have the most potential to reveal such information. In two studies, I presented participants (Ns = 216; 300) with pairs of dilemmas that another individual faced in an economic game; for each pair, I asked them to choose the dilemma for which they would most like to see the decision that the individual had made. On average, people spontaneously selected the choices that had the potential to reveal the most information about the individual's valuation of the participant, as quantified by a Bayesian ideal search model. This finding suggests that human cooperation is supported by sophisticated cognitive mechanisms for information-gathering.

Hadza hunter-gatherers with greater exposure to other cultures share more with generous campmates

Humans are motivated to compete for access to valuable social partners, which is a function of their willingness to share and ability to generate resources. However, relative preferences for each trait should be responsive to socioecological conditions. Here, we test the flexibility of partner choice psychology among Hadza hunter-gatherers of Tanzania. Ninety-two Hadza ranked their campmates on generosity and foraging ability and then shared resources with those campmates. We found Hadza with greater exposure to other cultures shared more with campmates ranked higher on generosity, whereas Hadza with lower exposure showed a smaller preference for sharing with generous campmates. This moderating effect was specific to generosity-regardless of exposure, Hadza showed only a small preference for sharing with better foragers. We argue this difference in preferences is due to high exposure Hadza having more experience cooperating with others in the absence of strong norms of sharing, and thus are exposed to greater variance in willingness to cooperate among potential partners increasing the benefits of choosing partners based on generosity. As such, participants place a greater emphasis on choosing more generous partners, highlighting the flexibility of partner preferences.

Why Warmth Matters More Than Competence: A New Evolutionary Approach

Multiple lines of evidence suggest that there are two major dimensions of social perception, often called warmth and competence, and that warmth is prioritized over competence in multiple types of social decision-making. Existing explanations for this prioritization argue that warmth is more consequential for an observer's welfare than is competence. We present a new explanation for the prioritization of warmth based on humans' evolutionary history of cooperative partner choice. We argue that the prioritization of warmth evolved because ancestral humans faced greater variance in the warmth of potential cooperative partners than in their competence but greater variance in competence over time within cooperative relationships. These each made warmth more predictive than competence of the future benefits of a relationship, but because of differences in the distributions of these traits, not because of differences in their intrinsic consequentiality. A broad, synthetic review of the anthropological literature suggests that these conditions were characteristic of the ecologies in which human social cognition evolved, and agent-based models demonstrate the plausibility of these selection pressures. We conclude with future directions for the study of preferences and the further integration of social and evolutionary psychology.

Runaway Social Selection in Human Evolution

Darwin posited that social competition among conspecifics could be a powerful selective pressure. Alexander proposed a model of human evolution involving a runaway process of social competition based on Darwin’s insight. Here we briefly review Alexander’s logic, and then expand upon his model by elucidating six core arenas of social selection that involve runaway, positive-feedback processes, and that were likely involved in the evolution of the remarkable combination of adaptations in humans. We discuss how these ideas fit with the hypothesis that a key life history innovation that opened the door to runaway social selection, and cumulative culture, during hominin evolution was increased cooperation among individuals in small fission-fusion groups.

Hadza Hunter-Gatherers Disagree on Perceptions of Moral Character

To the extent that moral character is grounded in stable and observable truths, there should exist agreement between people in their judgments of others’ character. In Western populations, this agreement is found. We examine whether this is universal in Hadza hunter-gatherers of Tanzania. Ninety-four judges ranked their campmates on global character and relevant character traits for a total of 802 observations. Judges disagreed on rankings of global character, generosity, and honesty but agreed more on hard work and hunting ability. Individual rankings on specific traits predicted character evaluations. There was agreement between judges on the extent to which generosity and hard work related to character. These findings suggest that Hadza have shared beliefs about what traits constitute character but disagree on which of their campmates exhibit these traits. We discuss these findings in light of other research suggesting that stable moral dispositions may not be universal.