Robin Dunbar, professor of Evolutionary Anthropology at Oxford University, relies back on a theory he developed in the 1990s, known as ‘Dunbar’s number,’ to strengthen his point.

The study claimed that that the size of our neocortex - the part of the brain used for conscious thought and language – bestow us with a limited capability of remembering up to 150 important relationships.

In addition, he cited that this number has remained the same, even with the influence of social networking sites like Facebook, Bebo and MySpace.

The study was able to obtain the figure after Dunbar verified the number of people contacted at least once a year in a variety of societies, ranging from neolithic villages to modern office environments.

Currently, the theory is being applied in the study of social networking websites. He is on with a study to see whether Facebook expanded human brain capacity to enable more significant relationships.

“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 The Sunday Times.

Facebook's in-house research scientist Cameron Marlow agrees to the theory. Last year, he had told The Economist that majority of users of social networking sites restrict only to genuine relationships with several virtual friends.