HUMAN brains can only remember up to 150 meaningful relationships, despite the huge amount of Facebook friends some people can gather.

Robin Dunbar, professor of evolutionary anthropology at Oxford University, says that this number has been the same throughout history and among different societies.



“The interesting thing is that you can have 1500 friends (online) 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,” Prof Dunbar told the Times Online.



Last year, Facebook's in-house research scientist Cameron Marlow told The Economist he found that Facebook users only actively communicate with a few of their online friends.



Prof Dunbar is known for his earlier theory of "Dunbar's number", which claims the brain's neocortex - which processes language and conscious thought - only allows humans to manage 150 friends no matter how many people they are in touch with.



His latest work tested Facebook to see if it allowed for a larger number of genuine friendships, but it seems the social network does not help the brain expand its capacity to care about more people, he says.



Prof Dunbar defines "meaningful relationships" as being with people you care about that you contact at least once a year, and ones that you can figure out how they relate to other people in your inner circle.



Prof Dunbar's study is due for publication later in 2010.