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Dunbar, R.I.M. |
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Title |
The social brain hypothesis and its implications for social evolution |
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2009 |
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Annals of Human Biology |
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Annals of Human Biology |
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36 |
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5 |
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562-572 |
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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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Taylor & Francis |
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0301-4460 |
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doi: 10.1080/03014460902960289 |
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Equine Behaviour @ team @ |
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6546 |
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Stanley, C.R.; Dunbar, R.I.M. |
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Consistent social structure and optimal clique size revealed by social network analysis of feral goats, Capra hircus |
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2013 |
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Anim Behav |
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85 |
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Equine Behaviour @ team @ Stanley2013 |
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6253 |
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Shi, J.; Dunbar, R.I.M.; Buckland, D.; Miller, D. |
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Dynamics of grouping patterns and social segregation in feral goats (Capra hircus) on the Isle of Rum, NW Scotland |
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2005 |
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Mammalia |
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69 |
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Equine Behaviour @ team @ Shi2005 |
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6257 |
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Pérez-Barbería, F.J.; Shultz, S.; Dunbar, R.I. |
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Title |
Evidence for coevolution of sociality and relative brain size in three orders of mammals |
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2007 |
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Evolution |
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61 |
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Equine Behaviour @ team @ Pérez-Barbería2007 |
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6221 |
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Pérez-Barbería, F.J.; Shultz, S.; Dunbar, R.I.M.; Janis, C. |
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Title |
Evidence For Coevolution Of Sociality And Relative Brain Size In Three Orders Of Mammals |
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Journal Article |
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Year |
2007 |
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Evolution |
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61 |
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12 |
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2811-2821 |
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Keywords |
Brain size, carnivores, coevolution, primates, sociality, ungulates |
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Abstract
As the brain is responsible for managing an individual's behavioral response to its environment, we should expect that large relative brain size is an evolutionary response to cognitively challenging behaviors. The “social brain hypothesis†argues that maintaining group cohesion is cognitively demanding as individuals living in groups need to be able to resolve conflicts that impact on their ability to meet resource requirements. If sociality does impose cognitive demands, we expect changes in relative brain size and sociality to be coupled over evolutionary time. In this study, we analyze data on sociality and relative brain size for 206 species of ungulates, carnivores, and primates and provide, for the first time, evidence that changes in sociality and relative brain size are closely correlated over evolutionary time for all three mammalian orders. This suggests a process of coevolution and provides support for the social brain theory. However, differences between taxonomic orders in the stability of the transition between small-brained/nonsocial and large-brained/social imply that, although sociality is cognitively demanding, sociality and relative brain size can become decoupled in some cases. Carnivores seem to have been especially prone to this. |
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doi: 10.1111/j.1558-5646.2007.00229.x |
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Call Number |
Equine Behaviour @ team @ |
Serial |
4781 |
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Author |
Kudo, H.; Dunbar, R.I.M. |
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Title |
Neocortex size and social network size in primates |
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Journal Article |
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Year |
2001 |
Publication |
Animal Behaviour. |
Abbreviated Journal |
Anim. Behav. |
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Volume |
62 |
Issue |
4 |
Pages |
711-722 |
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Primates use social grooming to service coalitions and it has been suggested that these directly affect the fitness of their members by allowing them to reduce the intrinsic costs associated with living in large groups. We tested two hypotheses about the size of grooming cliques that derive from this suggestion: (1) that grooming clique size should correlate with relative neocortex size and (2) that the size of grooming cliques should be proportional to the size of the groups they have to support. Both predictions were confirmed, although we show that, in respect of neocortex size, there are as many as four statistically distinct grades within the primates (including humans). Analysis of the patterns of grooming among males and females suggested that large primate social groups often consist of a set of smaller female subgroups (in some cases, matrilinearly based coalitions) that are linked by individual males. This may be because males insert themselves into the interstices between weakly bonded female subgroups rather than because they actually hold these subunits together. |
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0003-3472 |
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Equine Behaviour @ team @ |
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4726 |
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Author |
Dunbar, R.I.M.; Shultz, S. |
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Title |
Evolution in the Social Brain |
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Journal Article |
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Year |
2007 |
Publication |
Science |
Abbreviated Journal |
Science |
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Volume |
317 |
Issue |
5843 |
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1344-1347 |
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The evolution of unusually large brains in some groups of animals, notably primates, has long been a puzzle. Although early explanations tended to emphasize the brain's role in sensory or technical competence (foraging skills, innovations, and way-finding), the balance of evidence now clearly favors the suggestion that it was the computational demands of living in large, complex societies that selected for large brains. However, recent analyses suggest that it may have been the particular demands of the more intense forms of pairbonding that was the critical factor that triggered this evolutionary development. This may explain why primate sociality seems to be so different from that found in most other birds and mammals: Primate sociality is based on bonded relationships of a kind that are found only in pairbonds in other taxa. |
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Equine Behaviour @ team @ |
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4243 |
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Author |
O'Connell, S.; Dunbar, R.I.M. |
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Title |
The perception of causality in chimpanzees (Pan spp.) |
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Journal Article |
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Year |
2005 |
Publication |
Animal Cognition |
Abbreviated Journal |
Anim. Cogn. |
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8 |
Issue |
1 |
Pages |
60-66 |
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Animals; *Association Learning; Awareness; *Concept Formation; Female; *Habituation, Psychophysiologic; Male; Pan paniscus/*psychology; Pan troglodytes/*psychology; Perception |
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Chimpanzees (Pan spp.) were tested on a habituation/dishabituation paradigm that was originally developed to test for comprehension of causality in very young human infants. Three versions of the test were used: a food item being moved by a hand, a human pushing another human off a chair to obtain a food item, and a film clip of natural chimpanzee behaviour (capturing and eating a monkey). Chimpanzees exhibited similar results to those obtained with human infants, with significantly elevated levels of looking on the dishabituation trials. Since the level of response was significantly greater on natural/unnatural sequences than on unnatural/natural sequences, we conclude that the chimpanzees were not responding just to novelty but rather to events that infringed their sense of natural causation. |
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Evolutionary Psychology Research Group, School of Biological Sciences, Biosciences Building, University of Liverpool, Liverpool, L69 7ZB, UK |
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English |
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1435-9448 |
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PMID:15322943 |
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Equine Behaviour @ team @ |
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2514 |
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Shultz, S.; Dunbar, R.I.M. |
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Title |
Both social and ecological factors predict ungulate brain size |
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Journal Article |
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Year |
2006 |
Publication |
Proceedings. Biological Sciences / The Royal Society |
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Proc Biol Sci |
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273 |
Issue |
1583 |
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207-215 |
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Animals; Artiodactyla/*anatomy & histology/*physiology; Brain/*anatomy & histology/physiology; *Ecosystem; Organ Size; Perissodactyla/*anatomy & histology/*physiology; *Social Behavior |
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Among mammals, the members of some Orders have relatively large brains. Alternative explanations for this have emphasized either social or ecological selection pressures favouring greater information-processing capacities, including large group size, greater foraging efficiency, higher innovation rates, better invasion success and complex problem solving. However, the focal taxa for these analyses (primates, carnivores and birds) often show both varied ecological competence and social complexity. Here, we focus on the specific relationship between social complexity and brain size in ungulates, a group with relatively simple patterns of resource use, but extremely varied social behaviours. The statistical approach we used, phylogenetic generalized least squares, showed that relative brain size was independently associated with sociality and social complexity as well as with habitat use, while relative neocortex size is associated with social but not ecological factors. A simple index of sociality was a better predictor of both total brain and neocortex size than group size, which may indicate that the cognitive demands of sociality depend on the nature of social relationships as well as the total number of individuals in a group. |
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School of Biological Sciences, University of Liverpool, Biosciences Building, Crown Street, Liverpool L69 7ZB, UK. susanne.shultz@liv.ac.uk |
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0962-8452 |
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PMID:16555789 |
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2098 |
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Dunbar, R.I.M. |
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Title |
Male and female brain evolution is subject to contrasting selection pressures in primates |
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2007 |
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BMC Biology |
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BMC Biol |
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5 |
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21 |
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Animals; *Brain/physiology; *Evolution; Female; Humans; Male; *Selection (Genetics); *Sex Characteristics |
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The claim that differences in brain size across primate species has mainly been driven by the demands of sociality (the “social brain” hypothesis) is now widely accepted. Some of the evidence to support this comes from the fact that species that live in large social groups have larger brains, and in particular larger neocortices. Lindenfors and colleagues (BMC Biology 5:20) add significantly to our appreciation of this process by showing that there are striking differences between the two sexes in the social mechanisms and brain units involved. Female sociality (which is more affiliative) is related most closely to neocortex volume, but male sociality (which is more competitive and combative) is more closely related to subcortical units (notably those associated with emotional responses). Thus different brain units have responded to different selection pressures. |
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British Academy Centenary Research Project, School of Biological Sciences, University of Liverpool, Liverpool, UK. rimd@liv.ac.uk |
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1741-7007 |
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PMID:17493267 |
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2100 |
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