Research at Oxford University has revealed that the human brain can't cope with a full-on Facebook addiction - it can only sustain a maximum of 150 friendships at a time. That's thanks to the size of our neocortex - the bit of the brain used for conscious thought and language.

The research, by Robin Dunbar, professor of Evolutionary Anthropology at Oxford, was studying whether the growth in social networking sites was having any effect on the limit - but discovered that people still tended to self-organise in groups of around 150. Beyond that, you begin to lose track of people.

"The interesting thing is that you can have 1500 friends but when you actually look at traffic on sites, you see people maintain the same inner circle of around 150 people that we observe in the real world", said Dunbar. "People obviously like the kudos of having hundreds of friends but the reality is that they're unlikely to be bigger than anyone else's".

Interestingly, though, the study also found that females were happy to maintain relationships just by talking to each other, whereas males required some form of physical activity to keep up with others. Perhaps we're not as distant from our cave-dwelling ancestors as we'd like to think.