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The Social Brain and the Nature of Relationships

The Social Brain and the Nature of Relationships. Robin Dunbar Institute of Cognitive & Evolutionary Anthropology University of Oxford. What Makes Humans SO Different?. Humans differ only marginally from other great apes in anatomy, genetics and ecology and much everyday behaviour

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The Social Brain and the Nature of Relationships

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  1. The Social Brain and the Nature of Relationships Robin Dunbar Institute of Cognitive & Evolutionary Anthropology University of Oxford

  2. What Makes Humans SO Different? • Humans differ only marginally from • other great apes in anatomy, genetics and • ecology and much everyday behaviour • Only substantive differences are in the • “world of the imagination” • Religion • Story-telling …..We do, they don’t • These are a crucial part of the mechanisms needed to enforce social cohesion

  3. Phylogeny [WHEN?] Function [WHY?] Ultimate mechanisms behavioural ecology Social psychology with backbone? Ontogeny [HOW?] Mechanisms [WHAT?] Proximate mechanisms modular mind Cognition with backbone? Tinbergen’s Four Whys

  4. The Social Brain Hypothesis • An explanation for why primates have such big brains (compared to all other species) • Primates live in unusually complex societies, and this is computationally very demanding • Group size as an index of social complexity • Neocortex ratio as an index of brain size

  5. The Monogamous Brain? b. Social System Carnivores Artiodactyls Anthropoid Primates Bats Birds Anthropoid Primates are the odd one out Monogamy is cognitively costly? Shultz & Dunbar (2007)

  6. Primate Social Style is Different Prosimians are more like other mammals Anthropoids seem to have more bonded groups Primates seem to have generalised bondedness of pairbonds to other non-reproductive dyads Shultz & Dunbat (2007)

  7. Humans and the Social Brain Hypothesis • Predicted group size for humans is ~150 “Dunbar’s Number”

  8. HumanSocial Groups These all have mean sizes of 100-200 Neolithic villages 6500 BC 150-200 Modern armies (company) 180 Hutterite communities 107 ‘Nebraska’ Amish parishes 113 business organisation <200 ideal church congregations <200 Doomsday Book villages 150 C18th English villages 160 GoreTex Inc’s structure 150 Research sub-disciplines 100-200 Small world experiments 134 Hunter-Gatherer communities 148 Xmas card networks 154 “Reverse” Small World Experiments Killworth et al (1984) Hunter-Gatherer Societies Dunbar (1993) Individual Tribes Xmas Card Networks Hill & Dunbar (2003)

  9. Intimacy, Frequency and Trust Relationship between frequency of contact and intimacy Trust and obligation seem to be important Hill & Dunbar (2003)

  10. The Fractal Periodicity of Human Group Sizes Sizes of Hunter-Gatherer Groupings Peak at=5.4 Social Groupings Database [N=60] Hamilton et al (2007) Peak at=5.2 Xmas Card Database Scaling ratio = exp(2π/) = 3.2 and 3.3 Zhou, Sornette, Hill & Dunbar (2005)

  11. The Expanding Circles • Your social world consists of layers of • relationships • …with 150 as a core number • …but extending beyond to • 500, 1500, • and 5300 (according to • Plato, 350BC)….. • BUT…. • are the layers created by: • frequency of interaction • cognition [capacity for • emotional closeness] Intensity EGO 5 15 50 150

  12. Networks Have Structural Biases • Social networks tend to be gender-biased • [males have more male friends, females have more female friends] Female-only networks Belgian dataset

  13. Kinship Takes Priority! • Upper bound lies at ~150 • Priority is given to kin over non-kin [those who come from big extended families have fewer friends] • This is NOT true at the inner layers of the network (i.e. 15 layer) Belgian dataset

  14. Stable Family, Fragile Friends Stay KIN Move Friends Change in Network Layer Change over Time 0 9 18 months Kin Friends

  15. How to Prevent Relationships Decaying Change in contact frequency Change in activities done together Kin Friends

  16. Sex Difference in How Relationships are Serviced by change in activity score by change in contact frequency Change in Emotional Closeness months 0-9 Roberts & Dunbar (2010)

  17. Obesity Clusters in Networks • The Framingham Heart Study • Probability of becoming obese increases by: • 57% if a friend becomes obese, • 40% if a sibling becomes obese, • 37% if spouse becomes obese • independent of genetic relatedness and proximity to a McDonalds Christakis [2007]

  18. Happiness is Contagious, too… Happy Intermediate Unhappy Fowler et al (2008)

  19. How We Get Higher Levels of Organisation • Demands for information flow may be critical to structure • Military organisation seems to reflect same structure • Badges+ranks (hierarchy) ensure information flow thru the system • Line management essential when organisation >200 • Crucial role of language Military Organisation Australia Netherlands [2000] [1939] Section c.16 Platoon 30-60 50 Company 100-225 150-180 Battalion 550-1000 700-750 Brigade/Regiment 2500-5000 2200-2600 Division 10,000-20,000 6000-7000

  20. War of the Spanish Succession [c.1702] • European armies, though varying widely, nonetheless show much the same structure with much the same numbers

  21. Social Bonding Primate-Style Primate social bonds seem to involve two distinct components: • An emotionally intense component [=grooming] • A cognitive component [=brain size + cognition]

  22. The Role for Social Cognition Social cognition as the likely mechanism Intentionality as a reflexively hierarchical sequence of belief states …that may be very costly in information processing terms The Levels of Intentionality

  23. The Limits to Intentionality... A natural limit at 5th order intentionality: “I intend that you believe that Fred understands that we want him to be willing to [do something]…” [level 5] % Correct Intentionality Level Kinderman, Dunbar & Bentall (1998).

  24. Mentalising Tasks are Harder TASKS mentalising memory • In an fMRI analysis: • Significant contrasts • [mentalising > memory] • with a parametric effect of intentionality level • in 3 core regions involved in Theory of mind: • orbito-frontal PFC • TPJ • temporal pole A Reaction Time Experiment Mentalising vs Memory Questions (balanced for words, verbs, nouns, adjectives and people, and controlling for order) accuracy: p = 0.919 RT: p < 0.05 Lewis, Birch, & Dunbar (in prep)

  25. Cognitive Limits to Sociality? • Achievable intentionality level indexed from stories • 5th order seems to be the limit • Intentionality correlates with size of support clique [clique size = no. of core intimate relationships] [Stiller & Dunbar 2007]

  26. In a stereological analysis of gross volume: best predictor of network size and intentional competence is medial orbitofrontal PFC volume In a fine-grained VBM (voxel) analysis: overlap of network size and intentional competence in the orbitovental PFC Insights from Neuroimaging Powell et al (submitted a, b) Lewis et al (submitted)

  27. Why Time is Important • Grooming as the bonding agent in primates • Grooming time is a linear function of group size • …with an upper limit at about 20% of total daytime Dunbar (1991) Lehmann, Korstjens & Dunbar (2007)

  28. Why Does Grooming Work? An experimental study with monkeys Opiates block social drive; Opiate-blockers enhance social drive • endorphins are relaxing • They create a psycho-pharmacological environment for building trust? Sal [Keverne et al 1979]

  29. Grooming Time in Humans? • If we bonded our groups using the standard primate mechanism ….we would have to spend 43% of the day grooming

  30. Grooming Time in Primates • In fact, we spend only 20% of our time in social interaction …..from a sample of 7 societies from Dundee to New Guinea • Language might help bridge that gap ….but where does the endorphin kick come from?

  31. Language to the Rescue…..? • Language allows: • exchange of information about state of network • larger broadcast group • multitasking [talk and walk] • reinforcing group membership • reputation management Natural Social Groupings ….at Dartington’s Ways With Words

  32. Three Ways to Bridge the Gap? Religion and its rituals Modern humans Archaic humans The Bonding Gap H. erectus Music and dance Australopiths Laughter a cross-cultural trait shared with chimpanzees

  33. Some Tentative Evidence…. Singing and Laughter stimulate endorphins P=0.559p<0.001 V. Barra [2003] • Procedure: • pain test • video/activity • pain re-test J. Stowe [2000] G. Partridge [2003]

  34. LaughterThe Best Medicine? A human universal In a Public Goods Game [Dictator Game] Ss were more generous to strangers (but not “friends”) after watching a comedy video van Vugt et al (submitted)

  35. An Opium for the Masses? Religious practices are often well suited to stimulate endorphins Whirling dervishes [an Islamic Sufi sect] • Endorphins: • make you relaxed • may trigger the release of oxytocins (creating sense of “euphoric love”) • enhance sense of communality • positively influence immune system Medieval flagellants Bernini’s Ecstacy of St Theresa of Avila

  36. So….why not just get your kicks on your own? Plenty of people do…. …BUT doing it together seems to ramp up the effects

  37. Synchony Ramps up the Endorphins Change in pain threshold before and after 45 mins rowing work-out on ergometers in the gym: Alone vs in a virtual boat Alone Group Alone Group

  38. Religion at the Limits of Cognition…? • Belief as a personal phenomenon “I believe that God wants us to act with righteous intent” [3] • Belief as a social phenomenon “I intend that you believe that God wants us to act with righteous intent”[4] …. BUT why should you care? • Belief as a communal phenomenon: “I intend that you understand that we believe that God wants us to act with righteous intent”[5] …does theology provide the incentive to keep turning up?

  39. The Story-Teller’s Art Othello - An Everyday Story of Deception • BUT… Shakespeare had to do SIX 6 5 Cassio Othello Iago 3 • The audience • has to do FIVE • orders of • intentionality 2 1 4 Stories (especially “origins” stories) are an integral part of community-bonding Desdemona

  40. Conclusions • An evolutionary approach is NOT an alternative to other social science approaches – it’s an integrating framework • An evolutionary approach provides a powerful tool for exploring human behaviour because it makes us ask questions • It is important to complete the “explanatory loop” – to show both mechanism and fitness consequences [IF YOU CAN] • There are [cognitive] constraints on our behaviour…. • ….these have significant implications for how we organise our societies • Laughter, music and religion may have evolved to bond large communities [BUT they are still small scale effects]

  41. With Thanks to…. Susanne Shultz Penny Lewis Sam Roberts Holly Arrow Hiroko Kudo Julia Lehmann Didier Sornette Russell Hill Alex Bentley Mark van Vugt Charlie Hardy Amy Birch Joanne Powell Rachel Browne Neil Roberts Boguslaw Pawlowski Wei Zhou For funding: British Academy EPSRC ESRC Leverhulme Trust EU-FP7

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