Humans routinely evaluate the romantic relationships of others, a capacity that carries adaptive value for social learning, mate assessment, and coalition management. The present study examined how two cooperative norms, fairness and altruism, shape third party judgements of perceived relationship longevity, and whether these judgements vary according to relationship context and observer sex. Using an observer based experimental design, undergraduate participants viewed a short video of a couple engaged in a resource allocation task, framed as being in either a short term or long-term relationship. One partner behaved either fairly by dividing resources equally or altruistically by giving a greater share to the partner. Participants then rated how likely they believed the relationship was to last. Results revealed a significant three-way interaction between cooperative behavior, relationship length, and participant sex. Fair behavior was associated with greater perceived longevity in short term relationships, whereas altruistic behavior was associated with greater perceived longevity in long term relationships, particularly among female observers. These findings indicate that cooperative behaviors are interpreted in context sensitive ways, and that the capacity to infer relationship stability from cooperative cues may serve evolutionarily relevant functions for observers.
According to the bounded generalized reciprocity theory (BGR), people are endowed with psychological devices that facilitate within-group cooperation under a situation of conflicting interests. When interacting with ingroup members, they approach the situation as one of aligned interests and expect their partner to follow suit. So far, the role of expected cooperation in ingroup favoritism remains elusive. Against this backdrop, we probed whether expected cooperation is necessary for ingroup favoritism to occur. To this end, we employed a stag hunt game (SH), which instantiates a situation of aligned interests, and tested a BGR-derived prediction that ingroup favoritism in this game would be associated with ingroup-specific elevation of expected cooperation. We found support for this view. Unexpectedly, people also cooperated less in SH with outgroup members than with unclassified strangers. This pattern has seldom been observed empirically and cannot be accounted for by existing theory.
Previous research has suggested that infant faces capture adult attention, and this effect has been interpreted as reflecting the biological salience of infant faces as positively valenced stimuli, to which humans may have evolved to respond preferentially. However, subsequent studies have not consistently replicated this phenomenon. The present study investigated attentional capture by infant faces in a sample of university students, while controlling for relevant covariates, including parental readiness and the perceived attractiveness of infant faces. The results confirmed the attention-capturing effect of infant faces; however, no significant effects of pre-parental readiness or infant facial attractiveness were observed.
Human cooperation depends on selecting reliable partners under conditions of uncertainty and limited information. I propose that personality traits function as an informational architecture that compresses high-dimensional behavioral observations into low-dimensional representations optimized for prediction and social communication. From this perspective, the Big Five can be understood not merely as a psychometric taxonomy, but as a representational format that facilitates efficient partner choice in cooperative contexts. Compressed trait representations reduce cognitive load, enhance transmission through gossip, and promote reputational consensus. Within this framework, Agreeableness plays a central role in cooperation-dominant settings. I argue that Agreeableness may signal cooperativeness through two complementary mechanisms: by structuring intrinsic cost asymmetries between altruistic and exploitative behavior, and by increasing susceptibility to social learning and norm internalization. This account integrates personality psychology with evolutionary models of partner choice and indirect reciprocity.
Languages evolve through diffusion processes similarly to biological evolution, forming linguistic clusters based on geographic proximity. A few mathematical modeling studies have tested the classical theory on the formation of a peripheral distribution of dialects, which originally assumed two conditions: (i) new words are innovated exclusively at a cultural center and (ii) these words spread outward due to the prestige of the cultural center. However, it is known that these special conditions are often not met. We examined whether and how the presence or absence of each condition influences the outcome using an extended Bayesian Iterated Learning Model. Our mathematical analyses revealed that peripheral distributions can emerge not only when both conditions are present but also when one of the two is absent. Furthermore, the satisfaction of one or both conditions in a population can be predicted by investigating the word age distribution there.
