Your social brainMatt Jarvis

Your social brain

Animal societies

Primates are unique in the

importance of friendships.

Friendship helps with defence

strategies and gives groups

stability.

However friendship is a two-edged sword because our enemies have

friends that pose a threat to us. Managing this requires a big brain.

Your social brain

The social brain hypothesis

The larger the social group the more complex the social world

and the larger the brain needs to be to cope with this.

Dunbar’s number

By correlating group size and

brain size in a range of primates

Dunbar has looked at the human

brain and calculated that we are

designed to live in groups of

around 150.

Your social brain

Groups of 150 people

The size of the average person’s social network

Also the size of the typical English village in the Domesday book

This supports the idea of Dunbar’s number

Your social brain

Human social networks

Although Facebook and Twitter are very new, humans have always

had social networks.

We do not interact equally often with

everyone in our network. We typically

have around 150 friends that we see at

least once a year.

Your social brain

Where family fit in

Family have priority over friends in the innermost layers of the social

network.

Family are different because

they aid you regardless of

your current popularity in the

social network

Your social brain

Online social networks

Facebook allows us to maintain much larger social networks if we

choose. BUT in practice:

Most of us post regularly

to no more than 15

people and maintain a

total number of 150ish

contacts

Your social brain

Conclusions

• Primates, including humans, place unique importance on friends.

• Among primates brain size correlates with group size.

• Human brain size predicts a group size of 150.

• This is the typical size of English Middle Ages villages.

• We typically have around 150 people in our social network.

• This is also true of online social networks.

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