Anthropology, Regression and Dunbar’s number

“The number 150 really refers to those people with whom you have a personalised relationship, one that is reciprocal …if you asked them to do a favour, they would be more likely to say yes than those outside the 150.”

–          Robin Dunbar in his book  “How Many Friends Does One Person Need?”

Robin Dunbar, a British Anthropologist, did interesting research in 1992. He studied 38 species of primates (monkeys, apes etc.); he calculated size of neocortex to rest of brain and size of social group for each of them. He found positive correlation between two i.e. higher the neocortex ratio, larger the size of social group.


Based on values of these two variables i.e. ratio of neocortex to rest of brain and size of social group, he developed regression equation, he then calculated ratio of neocortex to rest of brain for humans and used regression equation to find corresponding value for size of social group. The value obtained was 148, which was rounded off to 150. In other words, extrapolating from the results of primates, humans can only comfortably maintain 150 stable relationships. This number (i.e.150) was called Dunbar’s number.

dunbar graph

Next Dunbar and his team decided to gather empirical evidence to support their statistical analysis. They estimated sizes of a Neolithic farming village, Hutterite settlements, basic unit of professional armies and organisational unit. The number was around 150, which supported statistical findings.


Research study has shown that Dunbar’s number is also applicable to online social networks. So ideally you should have around 150 connections on Facebook!

What if you want to maintain stable relationship with more than 150 people? You will have to increase size of your brain.


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