Chimpanzees organize their social relationships like humans

Culbreth

et al. 2023

Preprint

Primate and human social groups exhibit a fractal structure that has a very limited range of preferred layer sizes, with groups of 5, 15, 50 and (in humans) 150 and 500 predominating. This same fractal distribution is also observed in the distribution of species mean group sizes in primates. Here we demonstrate that this preferential numbering arises because of the critical nature of dynamic self-organization within complex social networks. We calculate the size dependence of the scaling properties of complex social network models and argue that this aggregate behaviour exhibits a form of collective intelligence. Direct calculation establishes that the complexity of social networks as measured by their scaling behaviour is non-monotonic, peaking globally around 150 with a secondary peak at 500 and tertiary peaks centred on 15 and 50, thereby providing a theory-based rationale for the fractal layering of primate and human social groups.

Section: Introductionmentioning

confidence: 67%

“…It is of particular significance that these constraints on grouping size apply not just to humans [1] but also to the sizes and substructuring of anthropoid primate social groups as well as those of other mammals with complex multi-level social systems (e.g. elephants, orcas) [10][11][12][13]41,42].…”

Section: Discussionmentioning

confidence: 99%

Fractal Structure of Human and Primate Social Networks Optimizes Information Flow

West

Culbreth

et al. 2023

Preprint

“…Finally, social and spatial scales in the same proximity activated similar brain regions. This distinction between a small inner core and a larger outer core is also characteristic of the most social primates (cercopithecine monkeys and apes) [38]–[40], and seems to involve essentially the same brain regions as in humans [41], [42]. The fact that the inner and outer layers in social networks appear to be processed in different ways in separate parts of the brain offers a possible explanation for how large social groups are built up during the course of primate evolution.…”

Section: Discussionmentioning

confidence: 97%

Processing of Different Social Scales in the Human Brain

Roseman

Arzy

2022

Preprint

For an individual to lead a healthy and fulfilling social life, it is essential to have relationships with multiple people who are at different levels of emotional closeness. Based on ethological, sociological and psychological evidence, social networks have been divided into five scales of emotional closeness, gradually increasing in size and decreasing in emotional proximity. Is this division also reflected in different brain processes? During functional MRI, participants compared their emotional closeness to different members of their social network. We examined the brain area that was differentially activated for levels of emotional closeness, and found that its vast majority (78%) showed preference for people who are closest to participants, including the temporoparietal junction, middle temporal gyrus, precuneus and dorsomedial prefrontal cortex. A different system, which includes the medial temporal lobe, retrosplenial cortex and ventromedial prefrontal cortex showed preference for all other social scales. Moreover, we found a significant correlation between brain responses to emotionally close people and smaller spaces (room, building) as well as between emotionally distant people and larger spaces (neighborhood, city). Finally, brain activity at the default mode network (DMN) was associated with social scale preference, such that its subnetwork DMN A, related to social processing, showed preference to closer social scales, while DMN C, related to spatiotemporal processing, showed preference to farther social scales. Our results show that the cognitive processing of a few intimately close people differs from the rest of the social network, emphasizing their crucial role in social life.SignificanceWe divide the people in our lives according to levels of emotional closeness, called social scales, ranging from the few people who are the closest to us, in which we invest most of our social efforts and time (support clique), to the farthest level of ∼150 acquaintances. Here, we used neuroimaging to investigate the brain processing of different social scales. We found that the area of cortex dedicated to the support clique is much larger than that of all other scales and encompasses different brain regions. Interestingly, this division is similar to the one between processing of small and larger spaces, and processed by different subregions of the default mode network. Our study emphasizes the importance of close relationships in our social lives as found in the brain.

“…The first of these solutions is structural (hypothesis H1). Primate grooming networks naturally partition into two layers: grooming cliques (in network terminology, their degree, defined by the number of grooming partners an individual has) and grooming chains (n-cliques, defined as the set of individuals linked together by a chain of such ties, even if they do not individually groom each other) [46][47][48] (Fig. 1).…”

mentioning

confidence: 99%

Structural and Cognitive Solutions to Prevent Group Fragmentation in Group-Living Species

2022

Preprint

Group-living is one of the six major evolutionary transitions. However, group-living creates stresses that naturally cause group fragmentation, and hence loss of the benefits that group living provides. How species that live in large groups counteract these forces is not well understood. I analyse comparative data on grooming networks from a large sample of primate species and show that two different social grades can be differentiated in terms of network size and structure. I show that living in large, stable groups involves a combination of increase in bonding behaviours (made possible by a dietary adjustment) and the evolution of neuronally expensive cognitive skills of the kind known to underpin social relationships in humans. The first allows the stresses created by these relationships to be defused; the second allows large numbers of weak relationships to be managed, creating a form of multilevel sociality based on strong versus weak ties similar to that found in human social networks.