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

Abstract

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.

Fractal structure of human and primate social networks optimizes information flow

“…Alternatively, large groups may be produced, when required by some external need, by a bottom-up process of agglutination whereby sets of lower level groupings are ‘bolted’ together to create a higher level grouping (three 15-layer groups create a 50-layer, three 50-layer groups create a 150-layer, etc.). If the base unit is always of a constant size in all species (as appears to be the case [27]), this would explain why only certain group sizes are possible [10]. What remains to be explained is why the scaling relationship is approximately 3, rather than, say, approximately 2 or approximately 4.…”

“…In this sense, it can refer to anything that constitutes a tie or attraction between nodes in a network. Hence, while we phrase our analysis in terms of ‘information flow’ between nodes, this might be actual information (passed on by cultural transmission, learning or teaching) or it might be the ‘gravitational’ attraction between social partners [27] created in primates by social grooming or in humans by activities like conversation, laughter or storytelling [28]. This same generic usage has been used to underpin models of economic Webs in global finance and stock markets, the social meshes of governments and terrorist organizations, the transportation networks of planes and highways, the eco-Webs of food networks and species diversity, the physical wicker of the Internet and the bio-net of gene regulation.…”

Four errors and a fallacy: pitfalls for the unwary in comparative brain analyses

“…This does not mean that everyone grooms, or has a bonded relationship, with everyone else in the group, especially in very large groups. In bonded social groups, individuals devote almost all their grooming to a very limited number of group members (Kudo & Dunbar, 2001;Dunbar, 2003Dunbar, , 2023. In humans, for example, 60% of total social effort (whether measured as time invested, frequency of contact or emotional closeness) is devoted to just 15 people (Sutcliffe et al, 2012).…”

“…These size regularities derive from the mathematical properties of networks and the way animals choose to allocate their limited social time (Tamarit et al ., 2018; Tamarit, Sánchez & Cuesta, 2022; West et al ., 2020, 2023). All that animals need do is maintain visual (or even auditory) contact with their one or two closest grooming partners, and the more casual (weak) links between sub‐networks are sufficient to maintain group cohesion (Castles et al ., 2014; Dunbar, 2023) – unless, of course, groups get very large and/or day journeys very long, in which case groups may fission down the fracture line created by the weak links between sub‐networks (Dunbar & Shultz, 2022).…”

Fractal Structure of Human and Primate Social Networks Optimizes Information Flow

“…By the same token, although we have phrased our analysis in terms of ‘information flow’ between nodes, the results hold irrespective of what creates that flow. So, this quantity might be actual information (passed on by cultural transmission, learning or teaching) or it might be the ‘gravitational’ attraction between social partners [27] created in primates by social grooming or in humans by activities like conversation, laughter, or storytelling [28].…”