Hamilton\'s rule provides the cornerstone for our understanding of the evolution of all forms of social behavior, from altruism to spite, across all organisms, from viruses to humans. In contrast to the standard prediction from Hamilton\'s rule, recent studies have suggested that altruistic helping can be favored even if it does not benefit relatives, as long as it decreases the environmentally induced variance of their reproductive success (\"altruistic bet-hedging\"). However, previous predictions both rely on an approximation and focus on variance-reducing helping behaviors. We derived a version of Hamilton\'s rule that fully captures environmental variability. This shows that decreasing (or increasing) the variance in the absolute reproductive success of relatives does not have a consistent effect-it can either favor or disfavor the evolution of helping. We then empirically quantified the effect of helping on the variance in reproductive success across 15 species of cooperatively breeding birds. We found that a) helping did not consistently decrease the variance of reproductive success and often increased it, and b) the mean benefits of helping across environments consistently outweighed other variability components of reproductive success. Altogether, our theoretical and empirical results suggest that the effects of helping on the variability components of reproductive success have not played a consistent or strong role in favoring helping.

A large body of evidence implies the involvement of brain-derived neurotrophic factor (BDNF) in the pathogenesis of autism spectrum disorders (ASDs). A deficiency of BDNF in the hippocampus and frontal cortex of BTBR mice (a model of autism) has been noted in a number of studies. Earlier, we showed that induction of BDNF overexpression in the hippocampus of BTBR mice reduced anxiety and severity of stereotyped behavior, but did not affect social interest. Here, we induced BDNF overexpression in the frontal cortex neurons of BTBR mice using an adeno-associated viral vector, which resulted in a significant increase in the social interest in the three-chamber social test. At the same time, the stereotypy, exploratory behavior, anxiety-like behavior, and novel object recognition were not affected. Therefore, we have shown for the first time that the presence of BDNF in the frontal cortex is critical for the expression of social interest in BTBR mice, since compensation for its deficiency in this structure eliminated the autism-like deficiencies in the social behavior characteristic for these animals.

Active sensing is a behavioral strategy for exploring the environment. In this study, we show that contact vocal behaviors can be an active sensing mechanism that uses sampling to gain information about the social environment, in particular, the vocal behavior of others. With a focus on the real-time vocal interactions of marmoset monkeys, we contrast active sampling to a vocal accommodation framework in which vocalizations are adjusted simply to maximize responses. We conduct simulations of a vocal accommodation and an active sampling policy and compare them with actual vocal interaction data. Our findings support active sampling as the best model for real-time marmoset monkey vocal exchanges. In some cases, the active sampling model was even able to partially predict the distribution of vocal durations for individuals to approximate the optimal call duration. These results suggest a non-traditional function for primate vocal interactions in which they are used by animals to seek information about their social environments.

The study of social interactions lies at the core of several disciplines such as psychiatry, psychology and ethology, just to name a few. In this context, understanding the temporal patterns underlying interactive behaviors is of crucial importance. Here, we employed T-pattern detection and analysis to study social interactions in ten pairs of Wistar rats tested in an Open-Field environment. We found four different categories of interactive behaviors. One of them was of particular interest to us because it consisted of behavioral events that, taken individually, should not underlie an interaction of any kind; however, they were included in T-patterns, which is suggestive of a dyadic temporal coordination in the behavioral expression of two individuals. Within this category, we described for the first time a new subcategory of apparent interaction patterns characterized by events that one of the two rats repeats only if previously produced by the partner (i.e., behavioral mirroring). These findings are discussed in functional terms for rodents and in light of our current understanding of social interactions in humans.

Adolescence is a developmental period characterized by increasingly complex and influential peer contexts. Concurrently, developmental changes in neural circuits, particularly those related to social cognition, affective salience, and cognitive control, contribute to individuals\' social interactions and behaviors. However, while adolescents\' behaviors and overall outcomes are influenced by the entirety of their social environments, insights from developmental and social neuroscience often come from studies of individual relationships or specific social actors. By capturing information about both adolescents\' individual relations and their larger social contexts, social network analysis offers a powerful opportunity to enhance our understanding of how social factors interact with adolescent development. In this review, we highlight the relevant features of adolescent social and neural development that should be considered when integrating social network analysis and neuroimaging methods. We focus on broad themes of adolescent development, including identity formation, peer sensitivity, and the pursuit of social goals, that serve as potential mechanisms for the relations between neural processes and social network features. With these factors in mind, we review the current research and propose future applications of these methods and theories.

Comparative studies reliant on single personality surveys to rate wild primates are scarce yet remain critical for developing a holistic comparative understanding of personality. Differences in survey design, item exclusion, and factor selection impede cross-study comparisons. To address these challenges, we used consistently collected data to assess personality trait structures in wild rhesus (Macaca mulatta), bonnet (M. radiata), and long-tailed (M. fascicularis) macaques that varied in their degree of phylogenetic closeness, species-typical social styles, and anthropogenic exposure in urban or urban-rural environments. We administered 51-item personality surveys to familiar raters, and, after reliability and structure screenings, isolated 4-5 factor solutions among the species. Four consistent factors emerged: Confident, Sociable, Active, and Irritable/Equable. This latter factor had differential expression across species. Item composition of the Irritable/Equable factor was consistent with their anticipated differences in social styles, but confounded by cross-site anthropogenic variation. We also administered a 43-item survey confined to human-primate situations which paralleled our findings of social style variation, while also exhibiting variation that aligned with population differences in human density. Our findings indicate that macaque personality trait structures may be emergent outcomes of evolutionary and/or socioecological processes, but further research is needed to parse these processes\' relative contributions.

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Much evidence on heightened inflammation and social behavior focuses on social withdrawal. Building on recent theory (Muscatell and Inagaki, 2021), we focused instead on the socially affiliative experience of sex. We investigated the interplay between immunology and motivation on sexual well-being among 158 individuals in romantic relationships. Inflammation, indexed by C-reactive protein (CRP), and sexual well-being were measured multiple times over a month. Relational approach motivation (i.e., motivation toward rewards in relationships) was measured at study entry. Results revealed significant associations between CRP and sexual satisfaction and partnered orgasms frequency for those most motivated to approach rewards with their partner. Interaction effects were replicated with relationship-focused psychological correlates of sexual well-being (e.g., touch, shared laughter, social support), but not with individual-focused outcomes (e.g., adapting to change, goal progress). This is one of the first human studies to demonstrate the body and mind coordinating to promote satisfying sexual experiences within romantic relationships.

Temperamental characteristics and emerging cognitive control are meaningful predictors of children\'s development of adaptive and maladaptive social behaviors during the preschool period. However, knowledge of the interplay of these pathways, when examined concurrently to highlight their individual contributions, is limited. Using a cross-sectional sample of 3-year-old children, we examined parent-reported discrete traits of negative (anger, fear, sadness, and shyness) and positive (low- and high-intensity pleasure) temperamental reactivity as predictors of children\'s prosociality and physical aggression. Further, we tested whether the effects of discrete temperament were moderated by cognitive control, as indexed by the N2 event-related potential, during a go/no-go task. Analyses focus on a subsample of children with an observable N2 (n = 66). When controlling for other relative temperament traits, several significant main effects emerged. Moreover, at low cognitive control (smaller N2), fear was negatively associated with aggression, whereas at high cognitive control, sadness was positively associated with aggression. Heightened anger was linked to reduced prosocial behavior when cognitive control was low but linked to greater prosocial behavior when cognitive control was high. The results highlight that discrete temperament traits predict individual differences in child outcomes but that associations depend on concurrent levels of cognitive control.

Biases favoring the wealthy are ubiquitous, and they support and bolster vast resource inequalities across individuals and groups; yet, when these biases are acquired remains unknown. In Experiments 1 through 5 (Total N = 232), using multiple methods, we found that 14- to 18-month-old infants track individuals\' wealth (Experiments 1-5), prefer and selectively help rich (vs. poor) individuals (Experiments 2 and 3), and negatively evaluate poor individuals (Experiments 4 and 5). In two subsequent experiments with 11- to 13-month-old infants (Total N = 65), however, we find no evidence of preferences for rich (vs. poor) individuals (Experiment 6) or differential evaluations of rich and poor people (Experiment 7). Together, these results demonstrate that in the second year of life, wealth emerges as a central and robust dimension of evaluation that guides social decision making. (PsycInfo Database Record (c) 2024 APA, all rights reserved).