Your social brain Matt 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. This resource is part of P SYCHOLOGY R EVIEW, a magazine written for A-level students by subject experts. To subscribe to the full magazine go to