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This chapter looks at the social brain hypothesis. The term social brain has come to stand for the argument that the human brain, and indeed that of some other animals, is specialized for a collective form of life. One part of this argument is evolutionary: that the size and complexity of the brains of primates, including humans, are related to the size and complexity of their characteristic social groups. However, the social brain hypothesis is more than a general account of the role of brain size: for in this thesis, the capacities for sociality are neurally located in a specific set of brain regions shaped by evolution, notably the amygdala, orbital frontal cortex, and temporal cortex—regions that have the function of facilitating an understanding of what one might call the “mental life” of others.

Most primates are intensely social and spend a large amount of time servicing social relationships. The social brain hypothesis suggests that the evolution of the primate brain has been driven by the necessity of dealing with increased social complexity. This chapter uses social network analysis to analyse the relationship between primate group size, neocortex ratio and several social network metrics. Findings suggest that social complexity may derive from managing indirect social relationships, i.e. relationships in which a female is not directly involved, which may pose high cognitive demands on primates. The discussion notes that a large neocortex allows individuals to form intense social bonds with some group members while at the same time enabling them to manage and monitor less intense indirect relationships without frequent direct involvement with each individual of the social group.

The adoption of an explicitly cognitive approach has become prominent in archaeological research during the last decade, helping to place Palaeolithic archaeology into a driving role in the development of archaeological theory and developing inter-disciplinarity with the cognitive sciences. Two prominent approaches have emerged: the social brain hypothesis and the distributed mind. Precisely how these can be integrated into a single, unified approach for the study of the evolution and nature of the human mind remains unclear, if indeed it is desirable to do so. This chapter reflects on the emergence of these approaches within archaeology and comments upon their relative strengths and weakness.

This chapter examines contemporary hunter-gatherer societies in Africa and elsewhere in light of the social brain and the distributed mind hypotheses. One question asked is whether African hunter-gatherers offer the best model for societies at the dawn of symbolic culture, or whether societies elsewhere offer better models. The chapter argues for the former. Theoretical concepts touched on include sharing and exchange, universal kin classification, and the relation between group size and social networks. The chapter offers reinterpretations of classic anthropological notions such as Wissler's age-area hypothesis, Durkheim's collective consciousness and Lévi-Strauss's elementary structures of kinship. Finally, the chapter outlines a theory of the co-evolution of language and kinship through three phases (signifying, syntactic and symbolic) and the subsequent breakdown of the principles of the symbolic phase across much of the globe in Neolithic times.

The hypothesis that the complexity of social life selects for large brains is currently very prominent. This functional hypothesis has been tested mainly through experiments which aim to identify the cognitive processes or mechanisms that may underlie social behavior. Such research is inherently challenging because it is extremely difficult to design experiments that conclusively allow the exclusion of simple cognitive processes as an explanation for successful behavior. This chapter argues that cognitive scientists should not focus on processes alone but rather quantitatively test what animals can do with their brain: how fast, how precise, how much they can learn. Many differences between species concerning cognitive tasks in the social domain are quantitative in nature (e.g., the number of group members, past behavior that an individual has to recognize, the number of opportunities for social learning or cooperation that arise per time unit, etc.). Tests on how such quantitative differences between species translate into quantitative cognitive performances should be conducted in many species to provide a comparative approach, where predictions about relative performance can be made based on detailed knowledge of each study species’ ecology. Comparative approaches are methodologically challenging but can be tackled through large-scale cooperation.

This chapter places human cognition into an evolutionary context by describing brain and cognitive evolution in humans' closest relatives, the primates (prosimians, monkeys, and apes), and how human cognition differs from that of other animals. In particular, it examines ‘social cognition’, the kinds of cognitive processes that are believed to underlie social behaviour and social relationships. After reviewing what is known about social cognition in the brain and what insights neuroimaging has provided about how humans execute socio-cognitive tasks, the chapter discusses the contribution that has been made by the rapid advances in neuroimaging technology during the last decade or so. Finally, it explores the main assumptions of the social brain hypothesis, which attributes the large brains of primates to the cognitive demands imposed by social complexity.

This chapter examines the debate over the shape of the Palaeolithic as stages, which contain long periods of stasis interspersed with revolutions, and gradients, where incremental advances add up to a non-revolution. It argues that the debate has distracted archaeologists from addressing a more important question: what drove the timetable of innovation in technology and culture. More precisely, it explores the relationship between the social brain hypothesis, which posits that the complexity of humans' social lives selected for encephalisation, as well as the material and emotional resources that underpin social interaction. To this end, the chapter reviews relevant data organised in three temporal movements: the evolution of Homo some 1.6 to 2.6 million years ago (Ma), the appearance of large-brained hominins about 400,000 to 1.5 million years ago, and global distribution and population increase 25,000–300,000 years ago.

This chapter explores the role of time budgets, fission-fusion sociality, kinship, and division of labour in the evolution of hominins. More specifically, it considers whether human anatomical and behavioural traits, such as bipedalism and life history traits, appeared simultaneously or, if not, in what order they appeared and how they relate to each other. Drawing on the social brain hypothesis, the chapter examines the timing of social change across the hominins, with particular reference to the close relationship between community size and brain size across the primates and modern humans. It also discusses four main phases of hominin evolution: the transition into Australopithecus; the appearance of the genus Homo sometime around 2 million years ago; the appearance of archaic humans, Homo heidelbergensis and allies, sometime around 500,000 years ago; and the appearance of anatomically modern humans around 200,000 years ago.

This chapter aims to bring the evolution of behavioral complexity and language together through the theoretical perspective of the identity model, which provides a clear link between the behavioral outputs of past hominins and a measure of their cognitive potential. The identity model proposes that in order for material culture to be imbued with symbolic social meaning, not only is a theory of mind (or second-order intentionality) essential, but it must be superseded by a third-order of intentionality at a minimum. The author uses a case study in the British Acheulean in order to assess the cognitive potential of Pleistocene hominins as predicted by the social brain hypothesis. As a result, the author proposes that the evidence for third-order intentionality within the archaeological record at a broad species-level of behavior may actually reside with those hominins that engage with prepared-core technology and composite tool manufacture rather than within the Acheulean.

This chapter demonstrates the value of an evolutionary framework by explaining why humans differ from other apes and monkeys, despite their similar evolutionary history. Drawing on various sub-disciplines of psychology, as well as other disciplines like anthropology, it argues that the real difference between humans and great apes lies in the ability to live in the virtual world of the mind — the world of culture. After providing an overview of the evolution of the social brain, the chapter considers two aspects of human behaviour that are, in many respects, archetypal of human culture: story-telling and religion. It then analyses the arguments of the social brain hypothesis, especially with respect to the role of cognition in the intense relationships found in pair-bonds (in most birds and mammals) and friendships (among anthropoid primates). Finally, it looks at the role of intentionality in a virtual mental world.

For human hypersociality to evolve required that natural selection operate both at the levels of the individual and the group as described by multilevel selection theory. According to the social brain hypothesis, increased social cognition was the driving force in human social-cognitive evolution. Infants evolved “psychological weapons” designed to obtain attention and caregiving from adults. According to Tomasello’s shared intentionality theory, infants view others as intentional agents, as reflected in shared attention beginning around 9 months, and later, between 3 and 5 years of age, in collective intentionality, in which children establish a group-minded “we” with other people. The development and evolution of hypersociality is reflected in: treating others as intentional agents, perspective taking, empathy, normativity, social learning, prosociality (helping, sharing, sense of fairness), and collaboration. Each of these and other social-cognitive abilities were necessary for the evolution of a hypersocial species and evolved as a result of changes in great ape ontogeny.

Understanding the cognitive abilities of ancestral hominins remains challenging, despite the many advances of recent years, including new fossil discoveries and paleogenetic data. However, the primary route to accessing the behavioral and cognitive worlds of our hominin ancestors still remains firmly rooted in the archaeological record, particularly stone tools, the direct products of hominin actions grounded in the physical, social, and cognitive worlds occupied by the knappers. A theory of mind (ToM) has long been considered a key component of the human condition, linked to both language and the development of abstract thought. There must therefore be a point (or perhaps multiple points) in our evolutionary history when hominins gained a ToM. This ability should, in turn, be reflected in the archaeological record. To date, however, only limited attempts have been made to correlate the two. This chapter thus explores the relationship between the various stone tool traditions and ToM.

The question of whether nonhuman animals read minds—that is, whether they are able to attribute mental states, such as intentions, beliefs, and perceptual experiences, to others by observing their behaviors within environmental contexts—has been the subject of considerable debate for more than three decades now. On one side are those who claim that some animals are mindreaders and on the other side are those who reject such a theory. This chapter explains some of the reasons why the question of mindreading in nonhuman primates is important to cognitive science and philosophy. Animal mindreading is relevant, for example to the “Machiavellian intelligence hypothesis” or “social brain hypothesis,” an influential hypothesis about the evolution of nonhuman animal intelligence. The chapter also summarizes the history of the debate over this issue, its current state of stalemate, and what must be done to advance it.

This chapter describes a new theoretical construct known as the Identity Model to access visual display and hominin cognition within the Palaeolithic. The Identity Model posits how the increasing cognitive abilities of hominins, articulated as orders of intentionality, may be expressed within the archaeological record through systems of social communication such as visual display and the construction of individual and group identity. The model is related to the social brain hypothesis, a biological predictive model that applies orders of intentionality and theory of mind (ToM) to the development of hominin social communication and the evolution of language in Homo sapiens by explaining brain encephalisation. Before expanding on the Identity Model, this chapter provides some background on ToM and orders of intentionality. It then examines the link between identity and self-awareness before concluding by relating the Identity Model to the archaeological record.