The Social Brain and the Nature of Relationships

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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 dont
• These are a crucial part of the mechanisms
• needed to enforce social cohesion

3
Tinbergens Four Whys

• Phylogeny WHEN?
• Function WHY?
• Ultimate mechanisms
• behavioural ecology
• Social psychology
• with backbone?

• Ontogeny HOW?
• Mechanisms WHAT?
• Proximate mechanisms
• modular mind
• Cognition with
• backbone?

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?
Anthropoid Primates
Carnivores
Artiodactyls
Bats
Birds
Anthropoid Primates are the odd one out
Monogamy is cognitively costly?
Shultz Dunbar (2007)
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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)
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Humans and the Social Brain Hypothesis

• Predicted group size for humans is 150
• Dunbars Number

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HumanSocial Groups
Reverse Small World Experiments Killworth et
al (1984)

• 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 lt200
• ideal church congregations lt200
• Doomsday Book villages 150
• C18th English villages 160
• GoreTex Incs structure 150
• Research sub-disciplines 100-200
• Small world experiments 134
• Hunter-Gatherer communities 148
• Xmas card networks 154

Hunter-Gatherer Societies Dunbar (1993)
Individual Tribes
Xmas Card Networks Hill Dunbar (2003)
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Intimacy, Frequency and Trust

• Relationship between frequency of contact and
  intimacy
• Trust and obligation seem to be important

Hill Dunbar (2003)
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The Fractal Periodicity of Human Group Sizes
Sizes of Hunter-Gatherer Groupings
Peak at ?5.4
Social Groupings Database N60
Hamilton et al (2007)
Peak at ?5.2
Xmas Card Database
Scaling ratio exp(2p/?)
3.2 and 3.3
Zhou, Sornette, Hill Dunbar (2005)
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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
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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
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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
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Stable Family, Fragile Friends
Stay
KIN
Move
Friends
Change in Network Layer
Change over Time
Kin
Friends
0 9
18 months
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How to Prevent Relationships Decaying

• Change in contact frequency

• Change in activities done together

Kin
Friends
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Sex Difference in How Relationships are Serviced
Change in Emotional Closeness months 0-9
Roberts Dunbar (2010)

• by change in contact frequency

• by change in activity score

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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
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Happiness is Contagious, too
Happy Intermediate Unhappy
Fowler et al (2008)
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How We Get Higher Levels of Organisation

• Demands for information flow may be critical to
  structure
• Military organisation seems to reflect same
  structure
• Badgesranks (hierarchy) ensure information flow
  thru the system
• Line management essential when organisation gt200
• 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
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War of the Spanish Succession c.1702

• European armies, though varying widely,
  nonetheless show much the same structure with
  much the same numbers

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Social Bonding Primate-Style

• Primate social bonds seem to involve two
  distinct components
• An emotionally intense component
• grooming
• A cognitive component
• brain size cognition

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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
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The Limits to Intentionality...
Correct

• 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

Intentionality Level
Kinderman, Dunbar Bentall (1998).
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Mentalising Tasks are Harder
TASKS mentalising memory

• In an fMRI analysis
• Significant contrasts
• mentalising gt 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 lt 0.05
Lewis, Birch, Dunbar (in prep)
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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
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Insights from Neuroimaging
Powell et al (submitted a, b)

• 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

Lewis et al (submitted)
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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)
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Why Does Grooming Work?
                 
An experimental study with monkeys Opiates block
social drive Opiate-blockers enhance social drive
Sal
Keverne et al 1979

• endorphins are relaxing
• They create a psycho-pharmacological environment
  for building trust?

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Grooming Time in Humans?
                 

• If we bonded our groups using the standard
  primate mechanism
• .we would have to spend ?43 of the day grooming

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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?

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Language to the Rescue..?
Natural Social Groupings

• Language allows
• exchange of information about state of network
• larger broadcast group
• multitasking talk and walk
• reinforcing group membership
• reputation management

.at Dartingtons Ways With Words
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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
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Some Tentative Evidence.
Singing and Laughter stimulate endorphins
P0.559 plt0.001
V. Barra 2003

• Procedure
• pain test
• video/activity
• pain re-test

J. Stowe 2000 G. Partridge 2003
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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)
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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
Berninis Ecstacy of St Theresa of Avila
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So.why not just get your kicks on your own?
Plenty of people do. BUT doing it together
seems to ramp up the effects
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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
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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?

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The Story-Tellers Art
Othello - An Everyday Story of Deception

• BUT Shakespeare had to do SIX

6
5 Cassio
Iago
Othello
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
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Conclusions

• An evolutionary approach is NOT an alternative to
  other social science approaches its 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

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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 Leverhulm
e Trust EU-FP7