Robin Dunbar, professor of Evolutionary Anthropology at Oxford University, falls back on a theory he developed in the 1990s, known as 'Dunbar's number,' to prove his point.
The theory claims that that the size of our neocortex - the part of the brain used for conscious thought and language - limits us to managing social circles of around 150 friends, no matter how sociable we are.
The figure was reached after Dunbar checked how many people contacted at least once a year in a variety of societies, ranging from neolithic villages to modern office environments.
Now he has applied his theory to studying social networking websites.
And, he insists that the "Facebook effect" has hardly had an impact on the size of social groupings.
"The interesting thing is that you can have 1,500 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," Timesonline quoted Dunbar as saying.
He added: "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.
"There is a big sex difference though ... girls are much better at maintaining relationships just by talking to each other. Boys need to do physical stuff together."
Dunbar's study is expected to publish later this year.
