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 statementAnimal 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.
Highlights
The systematic comparative study of animal societies over the last century (Espinas 1878; Deegener 1918; Allee 1927; Wheeler 1928; Scott 1956; Crook 1970; Wilson 1971, 1975; Smuts et al 1987; Lee 1994; Clutton-Brock 2016; see Rubenstein and Abbot 2017a) has revealed stunning interspecific diversity in the size, composition, and cohesion of social units, as well as in the patterning of reproductive skew, cooperation, and competition among their members
I argue that inconsistent definitions of the features of social systems contributing to social complexity, a lack of relevant operational definitions applicable to a wide range of species, variation in conceptual and methodological approaches used in the study of social insect and vertebrate societies, and lack of a general consensus on its key determinants and consequences have hampered progress towards a better understanding of social complexity
Social complexity is a key concept in the study of animal and human sociality, but different disciplines and researchers working on invertebrates and vertebrates have used different definitions, concepts, and approaches in the past to study variation in sociality
Summary
The systematic comparative study of animal societies over the last century (Espinas 1878; Deegener 1918; Allee 1927; Wheeler 1928; Scott 1956; Crook 1970; Wilson 1971, 1975; Smuts et al 1987; Lee 1994; Clutton-Brock 2016; see Rubenstein and Abbot 2017a) has revealed stunning interspecific diversity in the size, composition, and cohesion of social units, as well as in the patterning of reproductive skew, cooperation, and competition among their members. This diversity has historically been perceived as reflecting a natural gradient that has been expressed as either categorical or continuous variation in social complexity (see below and Dew et al 2016; Rubenstein et al 2016).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
