1. Real-World Social Networks: Structure and Dynamics Bottom Up
Robin Dunbar
Institute of Cognitive &
Evolutionary Anthropology
University of Oxford

2. The 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?

3. Does Technology Really Widen Your Horizons?
The answer from Facebook’s own data seems to be: No
Modal number of friends is
You may list 100s of friends, but you only talk to a few  
WHY?
Cameron Marlow web-blog 3

4. To Begin at the Beginning….
Social Brain Hypothesis
Among primates, social group size is determined by neocortex volume
Predicted group size for humans is ~150
[Dunbar’s Number]
Monkeys
Apes
Dunbar (1992, 1993)

5. These all have mean sizes of 100-200
Twitter exchange contacts
Human Social Networks
Gonçalves et al. (2011)
Killworth
et al (1984))
Her 152 facebook friends
….remembered forever
These all have mean sizes of
Neolithic villages 6500 BC
military units (company) (N=10) 180
* Hutterite communities (N=51) 107
Nebraska Amish parishes (N=8) 113
business organisation <200
ideal church congregations <200
Doomsday Book villages
C18th English villages
* GoreTex Inc’s structure
Research sub-disciplines (N=13)
Twitter personalised contacts
Small world experiments (N=2) 134
Hunter-Gatherer communities
Xmas card networks
“Reverse” Small World
Experiments
100 10
Hunter-Gatherer Societies
Dunbar (1993)
Individual Tribes
SusyJ87
Hill & Dunbar (2003)
Xmas Card Networks
Dunbar (1993, 2008) 5

6. BUT….Human Networks are NOT Homogenous
Less like this
…..and more like this

7. Intimacy, Frequency and Trust
Contact frequency differs across layers
There is a relationship between frequency of contact and intimacy
Hill & Dunbar (2003) 7

8. The Fractal Periodicity of Human Group Sizes
Sizes of Hunter-Gatherer Groupings
Peak at =5.4
Slope  3
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)

9. The Friendship Shells
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
Intensity
EGO 5 15 50
150
1500
500

10. Intimacy, Frequency and Trust
Mean contact frequency/day
Mean Emotional Closeness
Network Layer
Sutcliffe et al (in press)
Contact frequency and emotional closeness differs across layers
The layers appear to be quite discrete 10

11. Network Structure Has Consequences
Happy
Intermediate
Unhappy
Fowler et al (2008) Christakis (2007)
Happiness and obesity are contagious
…with effects up to three degrees away

12. 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
9.81
CONTACT_FREQUENCY
0.34
0.02
13.88
AGREEABLENESS of TARGET
0.09
0.01
7.34
CONSCIENTIOUSNESS of TARGET
7.76
NETWORK DENSITY
2.79
Would you lend £5000?
Curry & Dunbar (in press)

13. The Circles of Acquaintanceship
Our networks are structured by more than just social closeness
Intensity
EGO
Our networks are also split roughly equally between Family (kin) and Friends – two separate sub-networks that intersect
FRIENDS 5
FAMILY 15 50
150
500

14. The Kinship Factor Our networks consist of about 50% kin [family]
80 close networks
Inner
layers
Outer layers
Slope  -1
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!
250 complete networks
-0.3 < slope< -0.9
Total Kin

15. Blood is Thicker Than Water
How much I value you relative to myself
We value kin more than we value friends
….. in any given layer of the network
Welfare Trade-off Ratio
Family
Friends
Network Layer
Curry & Dunbar (in press)

16. Stable Family, Fragile Friends
Stay
KIN
Move
Friends
Change in Network Layer
Change over Time
months
Kin Friends
Roberts & Dunbar (2011)

17. by change in activity score by change in contact frequency
How to Prevent Relationships Decaying
Change in Emotional Closeness months 0-9
This is for friends only.
Contact frequency here is based on self-report data, as I am still processing the detailed data from the phone bills.
First graph – shows how change in emotional closeness is affected by change in the number of activities that ego and alter do together. So either decrease in activities from month 1 to month 9, no change, or doing more activities at month 9 than at beginning of study. For females, doesn’t seem to make much difference – decline in emotional closeness regardless of activities done together. For males, to offset decay in emotional closeness, physically doing things together seems to work well.
This is the same graph for contact frequency – this includes both face-to-face and non face-to-face contact. So have decrease in contact frequency from month 1 to month 9, no change, or increase in frequency of communication from month 1 to month 9. For here, for females, it seems that to increase emotional closeness, communication rather than shared activities is the key, whereas for men, not such a strong effect of contact frequency.
Supports previous research in this area – men’s friendships based around shared activities, whereas women's friendships based around communication and emotional intimacy. The advantage of this study is that we can look at how things like shared activities and communication dynamically affect relationships over the course of 18 months, and have very fine-grained data on communication patterns from the mobile bills.
Roberts & Dunbar (2010)
by change in activity score
by change in contact frequency 17 17

18. What Makes Relationships Work?
Primate social bonds seem to involve two distinct components:
An emotionally intense component
[=grooming]
A cognitive component
[=brain size + cognition]

19. 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

20. The Cognitive Limits to Sociality
The Orders [or Levels] of Intentionality
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
Stiller & Dunbar (2007)
Powell et al (2010)

21. Insights from Neuroimaging
Powell et al (2010 & in press)
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
Lewis et al (in press) 21 21

22. How Grooming Works endorphins are relaxing
An experimental study with monkeys
Opiates block social drive;
Opiate-blockers enhance social drive
Sal
endorphins are relaxing
They create a psycho-pharmacological environment for building trust?

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

24. 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?

25. Laughter as Virtual Touch?
Change in Pain Threshold in Response to Laughter
Factual vs Comedy Videos
Pain threshold as an assay for endorphin activation
Laughter as a form of virtual grooming to bond more individuals?
Comedy
EdinburghFringe
Edinburgh
Fringe
Neutral
Procedure:
pain test
video/activity
pain re-test
Dunbar et al (submitted)

26. Nothing Beats Reality….?
Both perceived happiness AND laughter rates, F2F and Skype are better than all other media
Laughter influences happiness
[except in Skype]
And may be more important
than duration of interaction
in promoting satisfaction
Satisfaction Rating
Frequency of Laughter
Satisfaction Rating
Vladovik et al (submitted)
NO YES
Laughter

27. 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

28. With Thanks to…. Funding: British Academy EPSRC ESRC Leverhulme Trust
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 Academy
EPSRC
ESRC
Leverhulme Trust
EU-FP7