Their study showed that people who have real friends have to use more cognitive skills.
This, however, does not apply to "online" friends on social networking sites, including Facebook and Twitter.
Scientists have discovered a link between the number of friends, and the size of their orbital prefrontal cortex - the area of the brain just above the eyes.
The findings, published in the journal "Proceedings of the Scientific Society," for the first time show that social skills depend on the size of the human brain.
"We found that people who have more friends, to cope with intellectual tasks better, and have a larger size of the forebrain, located directly above the eyes," says Professor Robin Dunbar, who led the study.
"Understanding the relationship between the size of the human brain and the number of friends he helps us to understand the mechanisms that led to an increase in the human brain, compared with the brain of primates.
"In particular, the frontal lobe of the brain, in the last half million years, humans have increased significantly & quot ;.
He added: "Of course, there is free time to socialize, location, identity and gender - all affect the friendly relations. However, we also know that at least some of these factors, in particular the floor, also affects the ability of smart ».
"Our study found a link between people's ability to understand what others think and say, and the size of the circle of communication».
In testing involved 40 people with anatomical characteristics of "his master brain" to measure the size of the prefrontal cortex, which is used for high-level thinking.
All of them were graduate students, volunteers of the same age, with potentially similar capabilities for social activities & quot ;.
Participants were asked to compile a list of people with whom they are socially - not professional - contacted within seven days.
They also conducted a test to determine how competent they were at the intellectual level. As well as the ability to understand what another person is thinking - an important aspect of adaptation to the social world.
The study, funded by the British Academy research projects and the British Academy Professorship, showed a direct link between people with lots of friends, and the large size of the prefrontal cortex.
Dr. Joanne Powell of the University of Liverpool, added: "Perhaps the most important result of our study is that we were able to show that the relationship between brain size and the size of social relationships due to intellectual knowledge.
"This tells us that the size of your brain determines your social skills, namely those that allow you to have a lot of friends & quot ;.