A framework for studying social complexity

Abstract

Social complexity has been one of the recent emerging topics in the study of animal and human societies, but the concept remains both poorly defined and understood. In this paper, I critically review definitions and studies of social complexity in invertebrate and vertebrate societies, arguing that the concept is being used inconsistently in studies of vertebrate sociality. Group size and cohesion define one cornerstone of social complexity, but the nature and patterning of social interactions contribute more to interspecific variation in social complexity in species with individual recognition and repeated interactions. Humans provide the only example where many other unique criteria are used, and they are the only species for which intraspecific variation in social complexity has been studied in detail. While there is agreement that complex patterns emerge at the group level as a result of simple interactions and as a result of cognitive abilities, there is consensus neither on their relative importance nor on the role of specific cognitive abilities in different lineages. Moreover, aspects of reproduction and parental care have also been invoked to characterize levels of social complexity, so that no single comprehensive measure is readily available. Because even fundamental components of social complexity are difficult to compare across studies and species because of inconsistent definitions and operationalization of key social traits, I define and characterize social organization, social structure, mating system, and care system as distinct components of a social system. Based on this framework, I outline how different aspects of the evolution of social complexity are being studied and suggest questions for future research. Significance statement Animal and human societies differ in social complexity, i.e., the number and association patterns of group members as well as the nature and patterning of their social relationships, but the dimensions of social complexity, the processes that generate it, the selective forces that engender different levels of social complexity, and the evolutionary consequences of this variation remain to be comprehensively understood. Here, I offer a conceptual framework for the systematic and comparative studies of social complexity by defining its main components as well as their proximate and ultimate relationships.

A framework for conceptualizing dimensions of social organization in mammals

“…Although primary unit predominantly splits species into three distinct clusters, in line with previous studies (Kappeler, 2018), we found some evidence that the partitioning may require revisiting. Based on our findings, the primary unit appears to be a key dimension for categorizing societies, underlying most of the variation across species.…”

“…The way the variables are clustered shows connections between them. When looking at the contributions of the different variables to the principal components, the first three components accounted for 67.74% of the variance ( Figure A1 This partition into three clusters reflects Kappeler's description of forms of social organization for animals (Kappeler, 2018): live solitarily, coordinate with a partner (as a pair), or with a group. A large number of species in the first cluster with individuals as the primary unit suggest that there is a fourth option to this theory: a social lifestyle without coordinating all activities as a fixed group.…”

“…The intersection between these dimensions is highlighted by the suggestion of a potential fourth option for social organization (next to living solitarily, coordinating with a partner (as a pair), or with a group (Kappeler, 2018)) based on primary unit: social life without coordinating all activities as a fixed group. The intersection between these dimensions is highlighted by the suggestion of a potential fourth option for social organization (next to living solitarily, coordinating with a partner (as a pair), or with a group (Kappeler, 2018)) based on primary unit: social life without coordinating all activities as a fixed group.…”

“…Here, the authors split up sociality into three aspects: social organization, social structure, and mating systems. Here, we use the definition of social organization as pertaining to group size and composition (Jarman, 1974;Kappeler, 2018) (see Figure 1). It is not unusual that studies use the term synonymously with "social structure" which describes the patterns arising from associations and interactions between individuals (Whitehead, 2008).…”

Rethinking animal social complexity measures with the help of complex systems concepts

“…Thus, although group size is a descriptive measure, it has a causal motivation. The availability of group size data across a wide range of species enabled early comparative analyses [10,9], but mainly focused on vertebrate social complexity rather than other groups like social insects [5]. The biological relevance of interspecific comparisons, and in particular the use of group size as a measure of complexity, has been strongly debated [12][13][14].…”