Robin Dunbar

University of Oxford | OX · Department of Experimental Psychology

A central problem all group-living animals face is how to maintain group cohesion during the course of the day in the face of forces that drive animals apart. When activity schedules become desynchronised, groups will inevitably fragment as animals drift apart. To explore the impact that individual differences in activity scheduling might have for...

Application of social brain principles to the world of work and organisations, co-authored with two leading business consultants.

The personal network of relationships is structured in circles of friendships, that go from the most intense relationships to the least intense ones. While this is a well established result, little is known about the stability of those circles and their evolution in time. To shed light on this issue, we study the temporal evolution of friendships a...

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. In non-human primates, this same fractal distribution is also observed in the distribution of species mean group sizes and in the internal network structure of their...

The social brain hypothesis was proposed 30 years ago as an explanation for the fact that primates have much larger brains than all other animals. The claim was that primates live in unusually complex societies, and hence need a large 'computer' to manage the relationships involved. The core evidence subsequently provided in support of this claim w...

Doctrinal religions that involve recognised gods, more formal theologies, moral codes, dedicated religious spaces and professional priesthoods emerged in two phases during the Neolithic. Almost all of these appeared in a narrow latitudinal band (the northern Subtropical Zone). I suggest that these developments were the result of a need to facilitat...

Introduction The human capacity to engage with fictional worlds raises important psychological questions about the mechanisms that make this possible. Of particular interest is whether people respond differently to fictional stories compared to factual ones in terms of how immersed they become and how they view the characters involved and their act...

In contrast to long-term relationships, far less is known about the temporal evolution of transient relationships, although these constitute a substantial fraction of people’s communication networks. Previous literature suggests that ratings of relationship emotional intensity decay gradually until the relationship ends. Using mobile phone data fro...

Comparative analyses are the backbone of evolutionary analysis. However, their record in producing a consensus has not always been good. This is especially true of attempts to understand the factors responsible for the evolution of large brains, which have been embroiled in an increasingly polarised debate over the past three decades. We argue that...

Seminal studies suggest that being mimicked increases experienced social closeness and prosocial behavior to a mimicking confederate (i.e., interaction partner). Here we reexamine these results by considering the role of empathy-related traits, an indirect proxy for endorphin uptake, and their combined effects as an explanation for these results. 1...

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 aris...

The period around 400 ka coincided with a dramatic increase in hominin endocranial volume. Prior to this, there is some evidence to suggest that hominin brain sizes may have been subject to a thermally-driven energetic constraint. The increase in cranial volumes around 400 ka suggests that hominins achieved at least partial release from this constr...

Participating in rituals gives rise to exceptional social bonding, but how this happens is not well understood. We assess the roles of four potential mechanisms activated during the rituals which may promote social bonding: (1) the spiritual nature of the ritual, (2) proto-transcendental experiences (i.e., the feeling of connection to something big...

In recent years it has become evident the need of understanding how failure of coordination imposes constraints on the size of stable groups that highly social mammals can live in. We examine here the forces that keep animals together as a herd and others that drive them apart. Different phenotypes (e.g. genders) have different rates of gut fill, c...

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...

The relationship between social behaviour and the microbiome is known to be reciprocal. Research in wild animal populations, particularly in primate social groups, has revealed the role that social interactions play in microbial transmission, whilst studies in laboratory animals have demonstrated that the gut microbiome can affect multiple aspects...

Evolutionary psychiatry attempts to explain and examine the development and prevalence of psychiatric disorders through the lens of evolutionary and adaptationist theories. In this edited volume, leading international evolutionary scholars present a variety of Darwinian perspectives that will encourage readers to consider 'why' as well as 'how' men...

Intense sociality has been a catalyst for human culture and civilization, and our social relationships at a personal level play a pivotal role in our health and well-being. These relationships are, however, sensitive to the time we invest in them. To understand how and why this should be, we first outline the evolutionary background in primate soci...

In anthropoid primates, social grooming is the principal mechanism (mediated by the central nervous system endorphin system) that underpins social bonding. However, the time available for social grooming is limited, and this imposes an upper limit on the size of group that can be bonded in this way. I suggest that, when hominins needed to increase...

Group-living is stressful for all mammals, and these stresses limit the size of their social groups. Humans live in very large groups by mammal standards, so how have they solved this problem? I use homicide rates as an index of within-community stress for humans living in small-scale ethnographic societies, and show that the frequency of homicide...

Evolutionary psychiatry attempts to explain and examine the development and prevalence of psychiatric disorders through the lens of evolutionary and adaptationist theories. In this edited volume, leading international evolutionary scholars present a variety of Darwinian perspectives that will encourage readers to consider 'why' as well as 'how' men...

Characterizing non-human primate social complexity and its cognitive bases has proved challenging. Using principal component analyses, we show that primate social, ecological and reproductive behaviours condense into two components: socioecological complexity (including most social and ecological variables) and reproductive cooperation (comprising...

Primates live in stable social groups in which they form differentiated relationships with group members and use a range of communication including facial expressions, vocalizations and gestures. However, how these different types of communication are used to regulate social interactions, and what cognitive skills underpin this communication, is st...

Primate social bonds are described as being especially complex in their nature, and primates have unusually large brains for their body size compared to other mammals. Communication in primates has attracted considerable attention because of the important role it plays in social bonding. It has been proposed that differentiated social relationships...

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 decr...

The ability to rewire ties in communication networks is vital for large-scale human cooperation and the spread of new ideas. We show that lack of researcher co-location during the COVID-19 lockdown caused the loss of more than 4,800 weak ties—ties between distant parts of the social system that enable the flow of novel information—over 18 months in...

Humans exhibit what appears to be a unique vocal property: octave equivalence whereby adult male voices are, on average, an octave lower in pitch than those of adult females and children. The evolutionary significance of this seems largely to have escaped notice. While sexual selection might explain why male voices are generally lower, it cannot ex...

Humans are social animals and the interpersonal bonds formed between them are crucial for their development and well being in a society. These relationships are usually structured into several layers (Dunbar’s layers of friendship) depending on their significance in an individual’s life with closest friends and family being the most important ones...

The social brain hypothesis was proposed 30 years ago as an explanation for the fact that primates have much larger brains than all other animals. The claim was that primates live in unusually complex societies, and hence need a large 'computer' to manage the relationships involved. The core evidence subsequently provided in support of this claim w...

Assortative mating is a phenomenon in which romantic partners typically resemble each other at a level greater than chance. There is converging evidence that social behaviours are subject to assortative mating, though less is known regarding social cognition. Social functioning requires the ability to identify and understand the mental states of ot...

We analyze the ego-alter Twitter networks of 300 Italian MPs and 18 European leaders, and of about 14,000 generic users. We find structural properties typical of social environments, meaning that Twitter activity is controlled by constraints that are similar to those shaping conventional social relationships. However, the evolution of ego-alter tie...

We use data on frequencies of bi-directional posts to define edges (or relationships) in two Facebook datasets and a Twitter dataset and use these to create ego-centric social networks. We explore the internal structure of these networks to determine whether they have the same kind of layered structure as has been found in offline face-to-face netw...

Explanations for the evolution of social monogamy in mammals typically emphasise one of two possibilities: females are overdispersed (such that males cannot defend access to more than one female at a time) or males provide a service to the female. However, the first claim has never been formally tested. I test it directly at three levels using popu...

Professional religious specialists centralised religious authority in early human societies and represented some of the earliest instances of formalised social leadership. These individuals played a central role in the emergence of organised religion and transitions to more stratified human societies. Evolutionary theories highlight a range of envi...

In contrast to stable relationships, far less is known about the temporal evolution of transient relationships, although these constitute a substantial fraction of people's communication networks. Previous literature suggests that ratings of relationship emotional intensity decay gradually until the relationship ends. Using mobile phone data from t...

Humans are social animals and the interpersonal bonds formed between them are crucial for their development and well being in a society. These relationships are usually structured into several layers (Dunbar's layers of friendship) depending on their significance in an individual's life with closest friends and family being the most important ones...

Speaking a language that obliges the future tense for linguistic Future Time Reference (FTR) has been hypothesised to cause speakers to perceive delayed outcomes as temporally distal and therefore less valuable (“temporal discounting”). Conversely, we hypothesise that the obligation to use low-certainty modal verbs, e.g. may, causes speakers to con...

Research Question: Is social media activity related to layers of intimacy in social relationships? Study design: Mixed methods, survey on social relationships with 30 participants who identified up to 20 best/close friends and their use of social media. The same 30 participants were interviewed to gather details of how they communicated with close...

Touch forms a central component of social bonding, both in primates and in humans, via the brain’s endorphin system. In primates, this involves social grooming, acting via the CT neuron system. Although humans still use soft touch for bonding relationships, they have had to find ways of triggering the endorphin system without the need for physical...

An explanation, in terms of evolutionary ecology and neuroscience, of why and how religions evolved during human evolution

The ability to rewire ties in communication networks is vital for large-scale human cooperation and the spread of new ideas. Especially important for knowledge dissemination is the ability to form new weak ties -- ties which act as bridges between distant parts of the social system and enable the flow of novel information. Here we show that lack of...

Fictional storytelling has played an important role in human cultural life since earliest times, and we are willing to invest significant quantities of time, mental effort and money in it. Nonetheless, the psychological mechanisms that make this possible, and how they relate to the mechanisms that underpin real-world social relationships, remain un...

The capacity to inhibit prepotent actions (inhibitory self-control) plays an important role in many aspects of the behaviour of birds and mammals. Although a number of studies have used it as an index of foraging skills, inhibition is also crucial for maintaining the temporal and spatial coherence of bonded social groups. Using three different sets...

The claim that nonverbal cues provide more information than the linguistic content of a conversational exchange (the Mehrabian Conjecture) has been widely cited and equally widely disputed, mainly on methodological grounds. Most studies that have tested the Conjecture have used individual words or short phrases spoken by actors imitating emotions....

Mammal social groups vary considerably in size from single individuals to very large herds. In some taxa, these groups are extremely stable, with at least some individuals being members of the same group throughout their lives; in other taxa, groups are unstable, with membership changing by the day. We argue that this variability in grouping patter...

Humans deploy a number of specific behaviours for forming social bonds, one of which is laughter. However, two questions have not yet been investigated with respect to laughter: (1) Does laughter increase the sense of bonding to those with whom we laugh? and (2) Does laughter facilitate prosocial generosity? Using changes in pain threshold as a pro...

Assortative mating (AM) is a phenomenon in which romantic partners typically resemble each other at a level greater than chance. There is converging evidence that social behaviours are subject to AM, though less is known regarding social cognition. Social functioning requires the ability to identify and understand the mental states of others, i.e.,...

Human behaviour follows a 24-h rhythm and is known to be governed by the individual chronotypes. Due to the widespread use of technology in our daily lives, it is possible to record the activities of individuals through their different digital traces. In the present study we utilise a large mobile phone communication dataset containing time stamps...

The C-tactile (CLTM) peripheral nervous system is involved in social bonding in primates and humans through its capacity to trigger the brain’s endorphin system. Since the mammalian cochlea has an unusually high density of similar neurons (type-II spiral ganglion neurons, SGNs), we hypothesise that their function may have been exploited for social...

In species that live in stable groups, successful management of time budget (i.e., the proportion of time involved in different behaviours) and social relationships has been proposed to be a key variable affecting individual fitness. Such management is limited by time constraints, which are group size and season dependancy. However, the link betwee...

We aimed to test the hypothesis that quantitative traits associated with autism spectrum conditions are subject to assortative mating. Study 1 examined self-reported autistic traits (Autism Spectrum Quotient [AQ]), systemizing (Systemizing Quotient-Revised [SQ-R]) and empathizing (Empathy Quotient [EQ]), as well as behavioral measures related to so...

Compared to most other mammals and birds, anthropoid primates have unusually complex societies characterised by bonded social groups. Among primates, this effect is encapsulated in the social brain hypothesis: the robust correlation between various indices of social complexity (social group size, grooming clique size, tactical behaviour, coalition...

Introduction: Previous studies have shown that engaging in formal social participation may protect against declining mental health, but social network size (the number of close social ties a person has) may moderate the relationship. We assessed the potential moderating role of social network size using longitudinal data. Methods: Nationally repr...

Human behaviour follows a 24-hour rhythm and is known to be governed by the individual chronotypes. Due to the widespread use of technology in our daily lives, it is possible to record the activities of individuals through their different digital traces. In the present study we utilise a large mobile phone communication dataset containing time stam...

An overview of 25 years research into the nature of friendship in humans.

Religious rituals are associated with health benefits, potentially produced via social bonding. It is unknown whether secular rituals similarly increase social bonding. We conducted a field study with individuals who celebrate secular rituals at Sunday Assemblies and compared them with participants attending Christian rituals. We assessed levels of...

Explanations for the evolution of monogamy in mammals typically emphasise one of two possibilities: monogamy evolves when females are overdispersed (such that males cannot defend more than one female at a time) or when males provide a service to the female. However, the first claim has never been directly tested. I test it directly at three levels...

Humans survive and thrive through social exchange. Yet, social dependency also comes at a cost. Perceived social isolation, or loneliness, affects physical and mental health, cognitive performance, overall life expectancy, and increases vulnerability to Alzheimer's disease-related dementias. Despite severe consequences on behavior and health, the n...

Network science and data analytics are used to quantify static and dynamic structures in George R.R. Martin's epic novels, A Song of Ice and Fire, works noted for their scale and complexity. By tracking the network of character interactions as the story unfolds, it is found that structural properties remain approximately stable and comparable to re...

Significance We use mathematical and statistical methods to probe how a sprawling, dynamic, complex narrative of massive scale achieved broad accessibility and acclaim without surrendering to the need for reductionist simplifications. Subtle narrational tricks such as how natural social networks are mirrored and how significant events are scheduled...

Why do some animals live in groups? The ancestral mammals were small (we can tell that from their fossils) and almost certainly solitary (as suggested by reconstructing their likely behavior from the social arrangements of living species using statistical analyses that take species evolutionary...

Evolution is one of the most important processes in life. It not only explains the detailed history of life on earth, but its scope also extends into many aspects of our own contemporary behavior-who we are and how we got to be here, our psychology, our cultures-and greatly impacts modern advancements in medicine and conservation biology. Perhaps i...

Marketers, filmmakers, and cinema-goers assume that genre has a large effect on how the audience responds to and engages with a film. However, trait measures such as transportability suggest that, in some cases, individual differences may shape audience engagement more than genre does. To investigate this disparity, we compared viewers’ enjoyment,...

Religious rituals are universal human practices that play a seminal role in community bonding. In two experiments, we tested the role of mu-opioids as the active factor fostering social bonding. We used a mu-opioid blocker (naltrexone) in two double-blind studies of rituals from different religious traditions. We found the same effect across both s...