A new study by researchers in the United Kingdom has found a link between the number of friends you have and the size of a particular region of your brain. If you have a relatively large orbital prefrontal cortex, you’re in [social] luck: you likely possess the necessary skills and processing power to maintain a larger social network (in the traditional sense) than your less prefrontally-endowed compatriots.
The social network here described doesn’t include all the people you know, nor does it refer to all your Facebook friends or Twitter. Rather, it refers to all the people you know well enough to have a true relationship with.
The study suggests that we need to employ a set of cognitive skills to maintain a number of friends. These skills are described by social scientists as “mentalizing” (or “mind-reading”): a capacity to understand what another person is thinking. An essential skill our complex social world, “mentalizing” includes the ability to hold conversations with one another.
To get their data, the researchers took anatomical MRIs of the brains of 40 volunteers — all postgraduate students of similar age and background — then compared the size of their subjects’ prefrontal cortices. Participants were then asked to make a list of everyone they had had social, as opposed to professional, contact with over the previous seven days. They then took a test to gauge their competency in mentalizing.
“We found that individuals who had more friends did better on mentalizing tasks and had more neural volume in the orbital frontal cortex, the part of the forebrain immediately above the eyes,” said University of Oxford Professor Robin Dunbar. “Understanding this link between an individual’s brain size and the number of friends they have helps us understand the mechanisms that have led to humans developing bigger brains than other primate species.”
“Perhaps the most important finding of our study,” said Dr. Joanne Powell of the University of Liverpool, “is that we have been able to show that the relationship between brain size and social network size is mediated by mentalizing skills. What this tells us is that the size of your brain determines your social skills, and it is these that allow you have many friends.”
The study is a part of the larger Lucy to Language Project, which aims to explore how the early hominid brain evolved from its essentially ape-like beginnings. The Lucy to Language Project is led by Professor Robin Dunbar of the University of Oxford in a collaboration with Dr Joanne Powell and Dr Marta Garcia-Finana at Liverpool University, Dr Penny Lewis at Manchester University and Professor Neil Roberts at Edinburgh University. It is funded by a 7-year research grant from the British Academy Centenary.