Real-World Social Networks:Structure and Dynamics Bottom Up

Robin Dunbar

Institute of Cognitive & Evolutionary Anthropology

University of Oxford

The The Global Village?Global Village?

The Internet was based on the promise of enlarging your social world beyond the limits of the local village

But does it actually work?

Does Technology ReallyDoes Technology Really Widen Your Horizons? Widen Your Horizons?

The answer from Facebook’s own data seems to be: No

Modal number of friends is 120-130

You may list 100s of friends, but you only talk to a few

Cameron Marlow web-blog

WHY?

To Begin at the Beginning….To Begin at the Beginning….

Social Brain HypothesisAmong primates, social group size is determined by neocortex volume

Predicted group size for humans is ~150

[Dunbar’s Number]

Apes

Monkeys

Dunbar (1992, 1993)

HumanHumanSocial NetworksSocial Networks

These all have mean sizes of 100-200

Neolithic villages 6500 BC 150-200

military units (company) (N=10) 180* Hutterite communities (N=51) 107Nebraska Amish parishes (N=8) 113business organisation <200ideal church congregations <200Doomsday Book villages 150C18th English villages 160* GoreTex Inc’s structure 150Research sub-disciplines (N=13) 100-200Twitter personalised contacts 100-200

Small world experiments (N=2) 134Hunter-Gatherer communities 148Xmas card networks 154

Maximum Network Size

350-374

325-349

300-324

275-299

250-274

225-249

200-224

175-199

150-174

125-149

100-124

75-99

50-74

25-49

0-24

Nu

mb

er

of

Ca

ses

10

9

8

7

6

5

4

3

2

1

0

“Reverse” Small World Experiments

1

10

100

1000

10000

0 10 20 30

Hunter-Gatherer Societies

Xmas Card Networks

Individual Tribes

Dunbar (1993)

Hill & Dunbar (2003)

Killworth

et al (1984))

Twitter exchange contacts

100

10

Gonçalves et al. (2011)

Dunbar (1993, 2008)

Her 152 facebook friends ….remembered forever

SusyJ87http://www.youtube.com/watch?v=ApOWWb7Mqdo

BUT….Human Networks are BUT….Human Networks are NOT HomogenousNOT Homogenous

Less like this

…..and more like this

Intimacy, Frequency and TrustIntimacy, Frequency and Trust

Contact frequency differs across layers

There is a relationship between frequency of contact and intimacy

Emotional Closeness

109876543210

Me

an

Tim

e S

ince

La

st C

on

tact

(M

on

ths)

8

6

4

2

0

Hill & Dunbar (2003)

The Fractal Periodicity of Human Group Sizes

Peak at=5.4

Peak at=5.2

Xmas Card Database

Social Groupings Database [N=60]

Scaling ratio = exp(2π/) = 3.2 and 3.3

Zhou, Sornette, Hill & Dunbar (2005)

Sizes of Hunter-Gatherer Groupings

Hamilton et al (2007)

Slope 3

The Friendship Shells

5

15

50

150

Intensity

EGO

5001500

Our social worlds consist of layers of relationships …with 150 as the core number

….and a scaling ratio of ~3

…but extending beyond to 500, 1500

Intimacy, Frequency and TrustIntimacy, Frequency and Trust

Contact frequency and emotional closeness differs across layers

The layers appear to be quite discrete

Sutcliffe et al (in press)

Layer50015050155

Co

nta

ct r

ate

per

day

0.4

0.3

0.2

0.1

0.0

Mean contact frequency/day

Network Layer Network Layer50015050155

Mea

n E

mo

tio

nal

Clo

sen

ess

8

6

4

2

0

Mean Emotional Closeness

Network Structure Has Consequences

Fowler et al (2008) Christakis (2007)

Happy Intermediate Unhappy

Happiness and obesity are contagious…with effects up to three degrees away

Network Density is Important

How well integrated your close network is influences your willingness to act altruistically

Estimates of Fixed Effectsa

Parameter Estimate Std. Error

df t Sig.

Intercept 2.35 0.60 321.59 3.92 0.00

AGREEABLENESS 0.07 0.05 283.66 1.47 0.14

CONSCIENTIOUSNESS -0.09 0.06 281.99 -1.54 0.12

YEARS_KNOWN 0.03 0.00 2139.46 9.81 0.00

CONTACT_FREQUENCY 0.34 0.02 2127.63 13.88 0.00

AGREEABLENESS of TARGET 0.09 0.01 2065.93 7.34 0.00

CONSCIENTIOUSNESS of TARGET 0.12 0.02 2079.31 7.76 0.00

NETWORK DENSITY 0.05 0.02 2170.82 2.79 0.01

Would you lend £5000?

Curry & Dunbar (in press)

The Circles of Acquaintanceship

5

15

50

150

Intensity

EGO

500

Our networks are structured by more than just social closeness

FAMILY

FRIENDSOur networks are also split roughly equally between Family (kin) and Friends – two separate sub-networks that intersect

Our networks consist of about 50% kin [family]

Kin are given priority over Friends

If you come from a large extended family, you have fewer friends!

Related network size

140120100806040200

Un

rela

ted

net

wo

rk s

ize

120

100

80

60

40

20

0

0 10 20 30 40 50 60

Total Kin

0

20

40

60

80

To

tal N

on

-Kin

250 complete

networks

-0.3 < slope< -0.9

80 close networks

Total Kin

Slope -1Inner layers

Outer layers

The Kinship FactorThe Kinship Factor

We value kin more than we value friends

….. in any given layer of the network

Welfare Trade-off Ratio

Family

Friends

5 15 150 Network Layer

Blood Blood isis Thicker Than Water Thicker Than Water

How much I value you relative to myself

Curry & Dunbar (in press)

Stable Family, Fragile FriendsStable Family, Fragile Friends

KIN

Friends

Kin Friends 0 9 18months

Change over Time

Change in Network Layer

Stay

Move

Roberts & Dunbar (2011)

by change in activity score by change in activity score by change in contact frequency by change in contact frequency

Activity score change

Increase in activity score

No change in activity score

Decrease in activty score

Mea

n (+

/- 1

SE

) em

otio

nal c

lose

ness

cha

nge

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

FemaleMale

Ego Gender

Change in time to last contact of any type

Increased contact frequency

Same contact frequency

Reduced contact frequency

Mea

n (+

/- 1

SE

) em

otio

nal c

lose

ness

cha

nge

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

FemaleMale

Ego Gender

Roberts & Dunbar (2010)

Change in Emotional Closeness months 0-9

How to Prevent Relationships Decaying

What Makes Relationships What Makes Relationships Work?Work?

Primate social bonds seem to involve two distinct components:

An emotionally intense component

[=grooming]

A cognitive component [=brain size +

cognition]

The Limits to The Limits to Intentionality...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]

0

20

40

60

80

100

120

2 3 4 5 6 7

ToM

Physical

% Correct

Intentionality Level

The Cognitive Limits to Sociality

5th order seems to be the limit“I intend that you believe that Fred understands that we want him to be willing to [do something]…”

Intentionality correlates

with size of support clique

Level of intensionality

9th8th7th6th5th4th3rd2nd1st

Fre

quen

cy o

f fa

ilure

20

10

0

Level of intensionality

1086420

Cliq

ue s

ize

30

20

10

0

Stiller & Dunbar (2007)Powell et al (2010)

The Orders [or Levels] of Intentionality

In a stereological analysis of gross volume: best predictor of network size and intentional competence is orbitofrontal PFC volume

In a fine-grained VBM (voxel) analysis: overlap of network size and intentional competence in the orbitovental PFC

Powell et al (2010 & in press)

Insights from Insights from NeuroimagingNeuroimaging

Lewis et al (in press)

How Grooming WorksHow Grooming Works

endorphins are relaxing

They create a psycho-pharmacological environment for building trust?

         

Group Size

160140120100806040200

So

cia

l Tim

e (

%)

50

40

30

20

10

0

Predicted for Humans

0

2

4

6

8

10

12

Num

ber

of G

room

ing

Par

tner

s

Sal Naltrex Sal Morph

An experimental study with monkeys

Opiates block social drive;

Opiate-blockers enhance social drive

Sal

Grooming Time in Humans?Grooming Time in Humans?

If we bonded our groups using the standard primate mechanism

….we would have to spend 43% of the day grooming

         

Group Size

160140120100806040200

So

cia

l Tim

e (

%)

50

40

30

20

10

0

Predicted for Humans

Grooming Time in Humnas?Grooming Time in Humnas?

In fact, we spend only 20% of our time in social interaction

…..from a sample of 7 societies from Dundee to New Guinea

How do we bond our super-large communities?

         

Group Size

160140120100806040200

So

cia

l Tim

e (

%)

50

40

30

20

10

0

Predicted for Humans

Procedure: Procedure: • pain test

• video/activity

• pain re-test

EdinburghFringe

Neutral

Comedy

Laughter as Virtual Touch?

EdinburghFringe

• Pain threshold as an assay for endorphin activation

• Laughter as a form of virtual grooming to bond more individuals?

Change in Pain Threshold in Response to Laughter

Factual vs Comedy Videos

Dunbar et al (submitted)

Nothing Beats Reality….?Nothing Beats Reality….? Both perceived happiness AND laughter rates,

F2F and Skype are better than all other media

o Laughter influences happiness [except in Skype]o And may be more important than duration of interaction in promoting satisfaction

Vladovik et al (submitted)

Satisfaction Rating

Satisfaction Rating

Frequency of Laughter

NO YES Laughter

Synchony Ramps Synchony Ramps up the Endorphinsup the Endorphins

Alone Group Alone Group

Change in pain threshold before and after 45 mins

rowing work-out on ergometers in the gym:

Alone vs in a virtual boat

With Thanks to….With Thanks to….Comparative brains: Dr Susanne Shultz

Social Networks and behaviour: Dr Sam Roberts Dr Tom Pollet Dr Oliver Curry Dr Holly Arrow Dr Jens Binder Prof Alistair Sutcliffe Tatiana Vlahovic Dr Wei Zhou Dr Russell Hill Prof Didier Sornette Prof Mark van Vugt Rebecca Baron, Ellie Pearce and

Anna Frangou

Neuroimaging: Amy Birch Joanne Powell Rachel Browne Dr Penny Lewis Prof Neil Roberts Dr Marta García-Fiñana

Funding:

British AcademyEPSRCESRCLeverhulme TrustEU-FP7