In 1992, the British anthropologist Robin Dunbar published in the Journal of Human Evolution his hypothesis of the social brain, which comes to say that the human brain grew in response to social interactions.
“Dunbar collected a series of data on primates, using both ecological variables and others that had to do with their social groups, and looked for their possible relationships with the proportion that the neocortex occupies with respect to the rest of the brain, ” explains José Cuesta, Researcher at the Interdisciplinary Group of Complex Systems at the Carlos III University of Madrid. “He observed that the highest correlation was obtained for the size of the social group, and if this was applied to humans, a typical number would appear: 150.” Dunbar’s hypothesis to explain this result is that our cognitive capacity is limited and we can only maintain a maximum number of social relationships. “It must be taken into account that 150 is a medium number, the error bar is huge, it would range between 50 and 300, but only in very peculiar cases would figures be found above or below these”, explains the researcher.
Three years ago, Cuesta’s team published with Dunbar an article in PNAS magazine that developed a model to explain a theory postulated by the anthropologist and based on his number. In it, social interactions are organized in layers or circles depending on the type of relationships that are established, from those closest to them to those who are known by sight . “There are people with whom you only say hello and goodbye, you don’t even know their name, while others are intimate. Obviously, the cognitive effort required by one and the other is very different and this is what we wanted to explain in the article. What we saw is not something particularly special, but it is the natural mathematical consequence of having limited cognitive resources and distributing them in relationships that have different costs ”, indicates the expert. According to his model, the smallest circle would be the so-called ‘support group’ and would be made up of around five family or very close people, who would be those who are turned to, for example, when they have a serious problem. “The second circle is made up of about fifteen close friends, people with whom you have an important interaction. If any of them disappear, you are affected ”, explains Cuesta, who reminds us that these figures are always approximate and represent an average value.
The third circle would have about fifty people and they are those with whom you interact often – for example co-workers – but without having a strong relationship. In the event of absence, they also do not cause a sense of loss . “Then there are other larger circles that are diluted, they are those people with whom you have a very weak interaction, that you know by sight, of meeting on the bus, crossing you on the street, etc.”
Circles that empty and fill throughout life
Analyzing the Dunbar number, one can think that throughout a lifetime it is easy to get to interact with many more than 150 people, from first classmates to work friendships and other relationships that take place in later stages. However, many of these unions are lost over time. “That is one of the hypotheses that we are developing now, and the idea is precisely that the circles have a certain size and that we are ‘filling in the gaps’ or replacing the place of the people who leave our lives, ” explains Cuesta. Perhaps you have lost contact with many of your college classmates, but those ‘gaps’ will be filled with people from work, parents of your children’s friends, new neighbors, etc.
Are there exceptions to the Dunbar number?
Although the figures used by the model are easy to understand in the context of our society, it is worth wondering if these laws are observed in other types of communities or cultures. “In our model there was an anomalous prediction,” Cuesta tells us. “ If the number of people you interact with is very limited, then the hierarchy changes so that the inner circle becomes larger and the others are reduced . This has been observed – and verified with real data – with the immigrant communities that come to Spain. They are groups that are somewhat isolated and that consequently have much more intense relationships between them, so that superficial interactions are scarcer ”.
“When we got into this, I was somewhat skeptical of the true existence of social circles. But when I analyzed the results, I was convinced that this idea that we have a limited capacity to maintain social relationships is real ”, says the scientist. “And I no longer had any doubt when, in addition, the theory predicted this existence of anomalous circles in situations in which the number of available relationships is limited and we confirmed it with data from immigrant communities.”
The researcher explains that both the Dunbar number and the hierarchies of the circles have been verified with a multitude of very different data. “The exception is in social networks, the numbers do not appear there, but that is obvious because in them the type of relationships is totally different. You can have a friend on Facebook that you don’t even know ”, reflects the researcher.
Criticisms of Dunbar’s number
Like everything else, the 150 friends theory is not without its critics. One of the most recent was published a few months ago in the journal Biology Letters . In this article, a team of researchers from Stockholm University presents an exhaustive analysis with new data in which numbers higher than Dunbar’s are obtained, of around 290, and also with high confidence intervals. “In my opinion, it is more of a methodological criticism than something that invalidates the conclusion that the ability to maintain relationships is limited, that different relationships have different cognitive costs and that this has consequences on how we organize our relationships, ” says Cuesta. . “If Dunbar had this data in 1992, he might still have obtained a figure of around 300, or even 500, but in any case there is a limit, there would always be a ‘Dunbar number’.”