According to researcher Robin Dunbar, our brain defines the maximum size of human groups.
Have you ever heard of Dunbar’s number? This is the number that the psychologist, anthropologist and biologist Robin Dunbar proposed to refer to the number of people with whom we usually interact.
What are its origins and what relationship does it have with our ancestors, and with primates? And with the cerebral neocortex? In this article we will answer all these questions and, in addition, we will explain how the Dunbar number is related to religious congregations, according to data from a recent study.
What is the Dunbar number?
The Dunbar number is a number that was made known, more than 25 years ago, by British psychologist, anthropologist and biologist Robin Dunbar (full name Robin Ian MacDonald Dunbar). It consists of the number of people we usually interact with, which is approximately 150.
According to Dunbar, this number is related to the size of our cerebral neocortex and its processing capacity. Remember that the cerebral neocortex (or neocortex) is the area of the brain that allows us to reason and think logically and consciously. In other words, it collects our higher mental functions, and enables executive functions to function.
Social brain hypothesis
Dunbar’s number is part of the social brain hypothesis, also developed by Robin Dunbar, according to which there is a correlation between the size of the brain (specifically, of the neocortex) and the number of social relationships that people can establish ( although it also applies to primates, as we will see later).
It is a number that aroused a lot of curiosity in different fields and sciences, such as sociology and anthropology, but also other more “numbers” sciences, such as business administration and statistics.
Origin of this concept in the work of Robin Dunbar
What is the origin of the Dunbar number? Many years ago, primatologists (that is, professionals who study the behavior of primates), observed the following: primates have a highly social nature, which causes them to maintain (and need) social contact with other members of your group.
But not only did they observe this, they also found that the number of members of the group with which the primates maintained social contact was directly related to the volume of their cerebral neocortex. That is, they determined that there is a social group size index in each species of primates, which differs from one to another according to the volume of the neocortex of each one of them.
A few years later, in 1992, Robin Dunbar used the correlation that had been determined in non-human primates to predict how large the social group would be in humans (that is, he applied Dunbar’s number to humans).
Specifically, Dunbar determined that the Dunbar number in humans was the size of 147.8 (which is normally rounded to 150), although Dunbar specified that it was an approximate value.
Findings in human societies
The cerebral neocortex is an area of the brain that developed about 250,000 years ago. Dunbar began to investigate different nomadic societies, tribes and villages, to find the Dunbar number of each one of them.
Thus, he investigated the sizes of the social groups of all these societies, and found that Dunbar’s number could be classified into three categories: 30 to 50 people, 100 to 200 and 500 to 2,500.
As for his findings and observations, he also noted that a group of 150 people required a very high incentive to stick together.
In this sense, a conclusion reached by Dunbar is that, for a group of this size to remain united and cohesive, its members had to invest a minimum of 42% of their time in socializing with the other members of the group.
What groups reached Dunbar’s number?
Dunbar also found that only those groups or societies that were under great pressure to survive, or that had a very strong need (such as some nomadic tribes, subsistence villages, and different military groups) could reach Dunbar’s number.
Furthermore, he found that these people were almost always in physical contact (or at least close to each other). In contrast, dispersed groups (the members of which he was not physically close) had fewer ties, fewer ties.
The importance of language
Dunbar not only studied the importance of socialization and needs in explaining the Dunbar number, but also the importance and power of language. According to him, this could have emerged as a tool to facilitate socializations. This, in turn, could improve cooperation, production, survival …
Thus, language constitutes a cohesion tool in societies which, in turn, reduces the need to be in intimate contact with others, on a physical and social level.
Relationship with religious communities
A recent article (2020) by Bretherton and Dunbar, relates the Dunbar number to religion; specifically, with the literature on church growth. Thus, this study reveals that the Dunbar number could also be applied to the size and growth of religious communities.
The study goes a little further, and also analyzes other aspects surrounding the famous Dunbar number; Specifically, the researchers made the following findings or conclusions:
On the one hand, they found that larger congregations have less active participation from each of their members. On the other hand, and this has a lot to do with the Dunbar number, congregations that have only one leader usually have a number of participants that is around 150.
Also, these types of congregations (with 150 members) are stratified into even smaller functional or social groups.
But what about congregations of more than 150 members? The researchers revealed that they suffer from great internal tensions that lead them to have to reorganize internally. These same congregations (of more than 150 members), in fact, need structural subdivisions for the active participation of their members to take place.
The article, very interesting to read, what it basically does is provide a theoretical framework that unifies the observations of the literature on church growth, together with the Social Brain Hypothesis and Dunbar’s number.
Bretherton, R. and Dunbar, R. (2020). Dunbar’s Number goes to Church: The Social Brain Hypothesis as a third strand in the study of church growth. International Association for the Psychology of religion.
Dunbar, R. (1988). Primate Social Systems. Chapman Hall and Yale University Press.
Dunbar, R. (1992). Neocortex size as a constraint on group size in primates. Journal of Human Evolution 22 (6): 469-493.
Dunbar, R. (1993). Co-Evolution of Neocortex Size, Group Size and Language in Humans. Behavioral and Brain Sciences 16: 681-735.