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Robin DunbarBritish Academy Centenary Project
Institute of Cognitive & Evolutionary Anthropology
University of Oxford
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! Predicted group sizefor humans is ~150
[Dunbars Number]
Primates have big brains
because they live in a
complex social world
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These all have mean sizes of100-200
Neolithic villages 6500 BC 150-200
military units (company) (N=10) 180
* Hutterite communities (N=51] 107Nebraska Amish parishes (N=8) 113business organisation
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! Relationship betweenfrequency of contactand intimacy
! Trust and obligationseem to be important
Hill & Dunbar (2003)
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Peak at!=5.4
Peak at!=5.2
Xmas Card
Database
Social Groupings
Database [N=60]
Scaling ratio = exp(2!/!)
= 3.2 and 3.3Zhou, Sornette, Hill & Dunbar (2005)
Horton Order Analysis of
Hunter-Gatherer Group Sizes
Hamilton et al (2007)
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A hierarchically inclusiveseries of levels of
acquaintanceship
Levels reflectfamiliarity and
emotional closeness
The boundary at 150seems to demarcatepersonalised
relationships
5
15
50
150
Intensity
500
1500
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~50
~150
~5
~15
Friends
Kin
Roberts & Dunbar (2010)
Kin
Friends
Last Contact
Emotional Closeness
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Structural Biases in Networks
! Kin are given preference inthe network [individualsfrom large families have
fewer friends]
! Strong same-sexpreferences
Number of Relatives
Friends
Number of Females
Males
Females Networks
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KIN
Friends
Kin Friends0 9 18
months
Change over Time
Change in
Network Layer
Stay
Move
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How Bonding Works
Bonding is a dual-process
mechanism
"An emotionally intensecomponent
[= grooming]
"A cognitive component[= cognition#brain size]
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A natural limit at 5thorder
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)
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! Achievable intentionality levelindexed from stories
! 5thorder seems to be the limit
[Stiller & Dunbar 2007]
! Intentionality correlateswith clique size
! We now have two neuroimagingstudies to support this
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Significant contrasts
[mentalising > memory]
with a parametric effect ofintentionality level
" 4 core regions involved inmentalising:
dorsal medial PFC ventro-medial PFC Rt frontal pole temporal-parietal junction
Lewis, Rezaie, Browne , Roberts & Dunbar
(submitted)
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! A stereological analysis of gross volume! Best predictor is Dorsal PFC volume
Powell, Lewis, Dunbar, Garcia-Finana & Roberts (in prep)
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How to Prevent Decay
Change in contact frequency Change in activities done together
Kin
Friends
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Roberts &
Dunbar(2010)
Change in
Emotional
Closeness
months 0-9
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! A touch is worth athousand words.
We underestimate the importance of physical
contact
Laughter as touch at a distance
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! Constraint may beinternal rather thantechnical
! Three key issues:"Why do people want
to contact each other?
"Are all contactsreally equal?
"Can technology everreplace face-to-faceinteraction?
"Texting:averaging 120
texts per day
to just 2
people
"Technology:may slowrelationship
decay rate,
but be poor
for creating
new ones
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! There are cognitive constraints on sociality! Human social groupings are structured in discrete layers! Does Cognition or Time (or both) limit network size and
structure?
! Implications for the structure of organisations?! And.
will cognition limit electronic networks? can technology help us to overcome this?
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! Sam Roberts! Susanne Shultz! Oliver Curry! Anna Machin! Holly Arrow! Hiroko Kudo! Didier Sornette! Russell Hill! Penny Lewis! Neil Roberts! Joanne Powell! Amy Birch! Rachel Browne
For funding:
British Academy
EPSRC
ESRC
EU-FP7 SocialNets
EU-FP7 ICTe