The social brain hypothesis and its implications for social evolution
Abstract
The social brain hypothesis was proposed as an explanation for the fact that primates have unusually large brains for body size compared to all other vertebrates: Primates evolved large brains to manage their unusually complex social systems. Although this proposal has been generalized to all vertebrate taxa as an explanation for brain evolution, recent analyses suggest that the social brain hypothesis takes a very different form in other mammals and birds than it does in anthropoid primates. In primates, there is a quantitative relationship between brain size and social group size (group size is a monotonic function of brain size), presumably because the cognitive demands of sociality place a constraint on the number of individuals that can be maintained in a coherent group. In other mammals and birds, the relationship is a qualitative one: Large brains are associated with categorical differences in mating system, with species that have pairbonded mating systems having the largest brains. It seems that anthropoid primates may have generalized the bonding processes that characterize monogamous pairbonds to other non-reproductive relationships ('friendships'), thereby giving rise to the quantitative relationship between group size and brain size that we find in this taxon. This raises issues about why bonded relationships are cognitively so demanding (and, indeed, raises questions about what a bonded relationship actually is), and when and why primates undertook this change in social style.
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The social brain hypothesis proposes that a large part of our cognitive ability evolved to track the quality of social relationships, which means that people often adapt their interactions with others based on how close they feel to them.
“The social brain hypothesis proposes that a large part of our cognitive ability evolved to track the quality of social relationships (Dunbar, 2009), which means that people often adapt their interactions with others based on how close they feel to them (Zhou et al., 2005;Miller, 2012).”
From Humanoid Agents: Platform for Simulating Human-like Generative Agents (2023) · cites this paper as Dunbar, 2009
According to the social brain hypothesis, the high degree of encephalization reached by the neocortex of social mammals, especially Homo sapiens, may be a direct consequence of the cognitive demands required for the stable management of complex relationships within social groups.
“the high degree of encephalization reached by the neocortex of social mammals, especially by Homo sapiens, may be a direct consequence of the cognitive demands required for the stable management of complex relationships that occur within social groups”
From Internet use and access, behavior, cyberbullying, and grooming: Results of an investigative whole city survey of adolescents (2017) · cites this paper as [37]
Dunbar has identified an approximate number of 150 friends or social relationships that the individual human subject is actually able to maintain.
“Dunbar has come to identify an approximate number of 150 friends or social relationships that the individual human subject is actually able to maintain”
From Internet use and access, behavior, cyberbullying, and grooming: Results of an investigative whole city survey of adolescents (2017) · cites this paper as [37]
The SBH is supported by a positive relationship between brain size and social group size across primate species, suggesting a constraint imposed by the brain volume on the size of social groups.
“The SBH is supported by a positive relationship between brain size and social group size across primate species, suggesting a constraint imposed by the brain volume on the size of social groups (Dunbar, 1992(Dunbar, , 2009;;Sawaguchi & Kudo, 1990).”
From Baboons (Papio anubis) living in larger social groups have bigger brains. (2021) · cites this paper as Dunbar, 2009
The social brain hypothesis suggests that regions within social-affective circuitry with greater volume have greater processing capacity.
“Furthermore, the social brain hypothesis (Dunbar, 2009) suggests that regions within social-affective circuitry with greater volume have greater processing capacity, consistent with evidence of greater amygdala volume being linked to more social sensitivity in general rather than specifically to threats.”
From Adolescent neurobiological susceptibility to social context (2016) · cites this paper as Dunbar, 2009
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References 54 · Cited by 795
Research works printed but not linked: 8
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- Authors
- Dunbar, R. I. M.
- Affiliations
- University of Oxford (GB)
- Corresponding author
- Dunbar, R.I.M.
- ORCID
- Dunbar, R.I.M.
- Venue
- Annals of Human Biology
- Publisher
- Informa UK Limited
- Published
- 2009-01
- Volume
- 36
- Issue
- 5
- Pages
- 562-572
- ISSN
- 0301-4460 (ISSN-L)
- 1464-5033
- OpenAlex
- W2092225305
- Cited by
- 795
- References
- 54
- Citations by year
- 2026: 61 · 2025: 52 · 2024: 91 · 2023: 63 · 2022: 43 · 2021: 62 · 2020: 113 · 2019: 68 · 2018: 62 · 2017: 41 · 2016: 29 · 2015: 32 · 2014: 26 · 2013: 21 · 2012: 10
- FWCI
- 13.49
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Annals of Human Biology (publishedVersion)
- PubMed (publishedVersion)
- Oxford University Research Archive (ORA) (University of Oxford) (acceptedVersion)
- Topics
- Social Sciences › Psychology › Social Psychology › Primate Behavior and Ecology
- Life Sciences › Agricultural and Biological Sciences › Ecology, Evolution, Behavior and Systematics › Animal Behavior and Reproduction
- Social Sciences › Psychology › Experimental and Cognitive Psychology › Evolutionary Psychology and Human Behavior
- Keywords
- social brain hypothesis, brain evolution, primate sociality, social group size, brain size, mating systems, pair bonding, monogamy, anthropoid primates, social evolution
- MeSH terms
- Animals, Brain, Cognition, Biological Evolution, Humans, Primates, Social Behavior
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