dunbar oxford

8/13/2019 Dunbar Oxford

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Robin DunbarBritish Academy Centenary Project

Institute of Cognitive & Evolutionary Anthropology

University of Oxford

[email protected]


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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


7/20

~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

dunbar oxford

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