Robin Dunbar

So it's a very, very strong relationship.

So we don't actually need to ask you how many friends you've got, Robin.

We just need to look at your brain and tell you.

Dunbar's number, yes, yes.

That's the limit on the number of meaningful relationships you can have, friends and family, and that's about 150 in humans.

That actually consists of a series of layers of friendship, of greater and greater intimacy as they come in towards you.

You've got a small group of very close intimate friendships and then bigger and bigger circles of less intimate friendships.

So the average is 150.

But how you are between 100 and 250 correlates with the size of particularly this part of your brain, but also bits around here.

That's the frontal cortex.

Yeah, it's prefrontal cortex, but also the temporal lobe.

And then inside that, there's this massive wiring connection as the default mode neural network.

And they called it the default mode neural network because they had no idea what it did.

But when you put people in the scanner, brain scanner, and told them to relax and not do anything, then this network became very, very active.

And being as though a neuroscientist, an apologist, a neuroscientist in the audience, and didn't actually know what was going on inside people's heads, they thought it must be the brain daydreaming.

And it's turned out, basically...

When do you put in that sort of situation?

What do you do?

You think about friends, family, relationships, the social network.

So the thing is going crazy because it's thinking about the network.