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Previous studies have suggested that the prosocial effects which arise following synchrony during music and dance may serve as a mechanism for people to bond socially. However, other research has proposed that synchrony could be a mechanism for signalling coalition to demonstrate fitness, which is expressed by a group's ability to effectively cooperate. In the present studies, we compared these theories by showing participants realistic virtual avatars engaged in different forms of group dance and then examining their perceived social closeness and formidability of the dance groups. We conducted two studies to assess the perceptual influence of movement type (unison vs. coordinated) and movement quality (temporally aligned vs. temporally misaligned). We predicted that the difference in the ratings of closeness and formidability would only emerge when the groups align movements, and this was supported. We also hypothesised that unison movement would better signal formidability while coordinated movement would better signal a group's social closeness. However, unison movement yielded higher ratings than coordinated movement for both formidability and social closeness, suggesting that a group should move in complete synchrony to maximally indicate their fitness and social bonds.

Social animals often form long-lasting relationships with fellow group members, usually with close kin. In primates, strong social bonds have been associated with increased longevity, offspring survival and reproductive success. However, little is known about the fitness effects of social bonds between non-kin, especially outside of mammals. In this study, we use long-term field research on a cooperatively breeding bird, the greater ani (Crotophaga major), to ask whether adult females benefit by remaining in long-term associations with unrelated, co-breeding females. We find that females that have previously nested together synchronize their reproduction more rapidly than those nesting with unfamiliar partners, which leads to lower competition and higher fledging success. Importantly, although previous experience with a co-breeding female influenced reproductive synchrony, the degree of reproductive synchrony did not influence whether co-breeding females remained together in subsequent years, ruling out the alternate hypothesis that highly synchronized females are simply more likely to remain together. These results indicate that switching groups is costly to females, and that social familiarity improves reproductive coordination. Stable social relationships therefore have significant fitness consequences for cooperatively nesting female birds, suggesting that direct benefits alone may favour the evolution of associations between non-relatives and contribute to long-term group stability.

The transfer of food between adults is uncommon in primates. Although golden lion tamarins (Leontopithecus rosalia) are unique among primates in the extent to which they transfer food, reports of food transfers between adults have so far been restricted to captive or reintroduced individuals. Here, I report the first recorded events of adult–adult food transfers in golden lion tamarins between individuals belonging to different groups in the wild. Given that individuals emigrate from their natal group to find reproductive opportunities, I suggest that intergroup food transfers could be a way for individuals to estimate the quality or availability of potential mates or social partners. I propose an additional function of food transfers in wild golden lion tamarins: that they create and strengthen social bonds with individuals outside of the family group.

In this study, we tested two mother-calf pairs of bottlenose dolphins in a helping task. Specifically, we provided dolphins with an enrichment tool based on the rope-pulling task paradigm to obtain a resource. The calves were unable to solve the task and get the resource on their own, and then we evaluated whether their mothers helped them. Moreover, we also evaluated whether the social bond strength among mother and calf, measured with the simple ratio index, may play an important role in determining altruistic behaviors. Our findings show that mothers performed altruistic behaviors toward their calves only when they had a strong social bond with them. Indeed, only a mother had a strong social bond with her calf, and only she acted altruistically. Moreover, as her calf grew, their social bond weakened and the mother stopped performing altruistic behaviors. As a result, our data seem to suggest the strength of social bonds has an important role in determining altruism.

Previous studies have shown that fierce competition could promote male coalitions. There are two ways for males to choose their allies in the conflict. The first is that supporters choose high-ranking individuals, and the second is that supporters choose affiliated individuals. It is necessary to clarify the factors for forming a coalition and the process of cooperation in primates with complex relationships and strict hierarchies. Thus, we conducted a study on a group of free-ranging Tibetan macaques (Macaca thibetana) in Anhui, China, and recorded the whole process of male macaques forming coalitions once agonistic support occurred. The results showed that a higher intensity of the social bond between males was associated with more frequent coalitions. Dominance rank also significantly influenced male coalitions, showing that high-ranking individuals allied more frequently. Moreover, males with longer residence times formed more stable coalitions. We suggest that male Tibetan macaques form a stable social relationship, where social bond and social rank both promote the formation of a coalition. This study provided some insights into the mechanism by which social cooperation develops in multi-male and multi-female groups.

Social bond analysis is of major importance for the evaluation of social relationships in group housed horses. However, in equine behaviour literature, studies on social bond analysis are inconsistent. Mutual grooming (horses standing side by side and gently nipping, nuzzling, or rubbing each other), affiliative approaches (horses approaching each other and staying within one body length), and measurements of spatial proximity (horses standing with body contact or within two horse-lengths) are commonly used. In the present study, we assessed which of the three parameters is most suitable for social bond analysis in horses, and whether social bonds are affected by individual and group factors. We observed social behaviour and spatial proximity in 145 feral horses, five groups of Przewalski’s horses (N = 36), and six groups of feral horses (N = 109) for 15 h per group, on three days within one week. We found grooming, friendly approaches, and spatial proximity to be robust parameters, as their correlation was affected only by the animals’ sex (GLMM: N = 145, SE = 0.001, t = −2.7, p = 0.008) and the group size (GLMM: N = 145, SE < 0.001, t = 4.255, p < 0.001), but not by the horse breed, the aggression ratio, the social rank, the group, the group composition, and the individuals themselves. Our results show a trend for a correspondence between all three parameters (GLMM: N = 145, SE = 0.004, t = 1.95, p = 0.053), a strong correspondence between mutual grooming and friendly approaches (GLMM: N = 145, SE = 0.021, t = 3.922, p < 0.001), and a weak correspondence between mutual grooming and spatial proximity (GLMM: N = 145, SE = 0.04, t = 1.15, p = 0.25). We therefore suggest either using a combination of the proactive behaviour counts mutual grooming and friendly approaches, or using measurements of close spatial proximity, for the analysis of social bonds in horses within a limited time frame.

PurposeEnhancing consumer engagement in e-commerce live streaming is critical for e-commerce operators to build relationships and create consumer loyalty. Using the stimulus–organism–response model and theories from relationship marketing, the authors develop and test an integrative conceptual framework that combines various relational bonds, affective commitment, and consumer engagement.Design/methodology/approachUsing 327 valid responses from consumers of Taobao Live, the authors employed the software Mplus7.0 to evaluate the measurement model and the structural model.FindingsThe results empirically demonstrate that social and structural bonds positively affect consumer engagement directly and indirectly via affective commitment, while financial bonds have only an indirect effect via affective commitment on consumer engagement.Practical implicationsThe findings provide useful insights for e-commerce operators, who should invest in establishing relational bonds and stimulating affective commitment to improve consumer engagement.Originality/valueThis study adds to e-commerce research by being one of the first empirical studies on e-commerce live streaming, extends the marketing literature by integrating different relational bonds as antecedents of consumer engagement from the relational perspective, and enriches the affective commitment literature by distinguishing commitment to the online marketplace from commitment to the broadcaster.

Why do humans make music? Theories of the evolution of musicality have focused mainly on the value of music for specific adaptive contexts such as mate selection, parental care, coalition signaling, and group cohesion. Synthesizing and extending previous proposals, we argue that social bonding is an overarching function that unifies all of these theories, and that musicality enabled social bonding at larger scales than grooming and other bonding mechanisms available in ancestral primate societies. We combine cross-disciplinary evidence from archeology, anthropology, biology, musicology, psychology, and neuroscience into a unified framework that accounts for the biological and cultural evolution of music. We argue that the evolution of musicality involves gene–culture coevolution, through which proto-musical behaviors that initially arose and spread as cultural inventions had feedback effects on biological evolution because of their impact on social bonding. We emphasize the deep links between production, perception, prediction, and social reward arising from repetition, synchronization, and harmonization of rhythms and pitches, and summarize empirical evidence for these links at the levels of brain networks, physiological mechanisms, and behaviors across cultures and across species. Finally, we address potential criticisms and make testable predictions for future research, including neurobiological bases of musicality and relationships between human music, language, animal song, and other domains. The music and social bonding hypothesis provides the most comprehensive theory to date of the biological and cultural evolution of music.

Conversation is the platform where minds meet: the venue where information is shared, ideas cocreated, cultural norms shaped, and social bonds forged. Its frequency and ease belie its complexity. Every conversation weaves a unique shared narrative from the contributions of independent minds, requiring partners to flexibly move into and out of alignment as needed for conversation to both cohere and evolve. How two minds achieve this coordination is poorly understood. Here we test whether eye contact, a common feature of conversation, predicts this coordination by measuring dyadic pupillary synchrony (a corollary of shared attention) during natural conversation. We find that eye contact is positively correlated with synchrony as well as ratings of engagement by conversation partners. However, rather than elicit synchrony, eye contact commences as synchrony peaks and predicts its immediate and subsequent decline until eye contact breaks. This relationship suggests that eye contact signals when shared attention is high. Furthermore, we speculate that eye contact may play a corrective role in disrupting shared attention (reducing synchrony) as needed to facilitate independent contributions to conversation.

This study examines the potential for small-scale acts of giving that are not directly reciprocated, or generalized generosities, to build social bonds and promote contributions to the group. Social exchange theorists define such acts as generalized exchange. The potential for generalized exchange to build strong social bonds relative to other forms of exchange is the subject of theoretical debate. In this article, I build on two prominent theories of social exchange—affect theory and the theory of reciprocity—to propose that a strong norm of generalized reciprocity may bridge the connective benefits of generalized exchange with the connective benefits of productive exchange, which is a collaborative form of social exchange that involves sharing pooled resources. I argue that a strong norm of generalized reciprocity will activate mechanisms theorized to build strong social bonds in generalized and productive exchange systems, and will promote additional behavioral investments into the group. I test my argument with a controlled laboratory experiment, finding strong support for the proposed causal model. The results of this study have implications for research on generosity, collective action, collaboration, sense of community, and social capital.