150—Dunbar's Number

The number 150 emerged from studies of social group sizes in various societies, as well as in non-human primates, and from the ratio of neocortical volume to the total brain size. ¹Dunbar, R. I. M. (1992). Neocortex size as a constraint on group size in primates. Journal of Human Evolution, 22(6), 469 – 493.

For instance, military units have often been organized around this size, and some businesses have used it as a guide for structuring their organizations.

Here we go:

Dunbar’s Number: 150 Relationships

Robin Dunbar - Social Group Sizes - The PR Blog - Doctor Spin — Robin Ian MacDonald Dunbar is a British anthropologist, evolutionary psychologist, and specialist in primate behaviour.

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150 — Dunbar’s Number

Robin Dunbar, a British anthropologist and evolutionary psychologist, proposed what’s known as “Dunbar’s Number” — a theory suggesting that humans can only comfortably maintain about 150 stable relationships. ²Dunbar, R. I. M. (1998). The social brain hypothesis. Evolutionary Anthropology: Issues, News, and Reviews, 6(5), 178 – 190.

This includes family, friends, colleagues, and others with whom a person can keep meaningful contact. Beyond this number, the quality of relationships can diminish due to the limitations in our mental bandwidth. ³Silfwer, J. (2012, April 14). Social Group Sizes (The Social Brain Hypothesis). Doctor Spin | the PR Blog. https://doctorspin.net/group-sizes/

“Dunbar’s number is a suggested cognitive limit to the number of people with whom one can maintain stable social relationships. […] No precise value has been proposed for Dunbar’s number. It has been proposed to lie between 100 and 230, with a commonly used value of 150. Dunbar’s number states the number of people one knows and keeps social contact with, and it does not include the number of people known personally with a ceased social relationship, nor people just generally known with a lack of persistent social relationship, a number which might be much higher and likely depends on long-term memory size.”
Source: Wikipedia ⁴Dunbar’s number. (2023, May 29). In Wikipedia. https://en.wikipedia.org/wiki/Dunbar%27s_number

According to Dunbar, this limit is a direct function of relative neocortex size, which constrains our ability to keep track of complex social relationships. ⁵It’s worth noting that the concept of Dunbar’s Number has been debated and scrutinised within the scientific community.

Learn more: 150 — Dunbar’s Number

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Group Size Examples

The concept of Dunbar’s number, around 150, has been observed in various social and organizational contexts.

Here are some examples:

Hutterites. The Hutterites are a communal branch of Anabaptists who, like the Amish and Mennonites, trace their roots to the Radical Reformation of the 16^th century. They intentionally split their colonies once they grew beyond 150 members to ensure everyone within the community knew each other.
Military units. Traditionally, the “Company,” a standard unit in military organization, tends to hover around the Dunbar number. For instance, the basic fighting unit in the Roman Army, the Century, was made up of 80 men, close to Dunbar’s number.
Businesses. Some modern businesses, such as the Gore-Tex company (known for its innovative work culture), limit the size of their offices to 150 employees. This maintains a more intimate, direct, and efficient communication structure among all office members.
Neolithic farming villages. Archaeological evidence suggests that many Neolithic farming villages had a population of 120 to 150 individuals.
Hunter-gatherer societies: Anthropological research indicates that traditional hunter-gatherer societies typically had a core group size of about 100 – 150 individuals.

These are only approximate values; the actual “Dunbar’s Number” can vary from person to person or from context to context. But they suggest a general human propensity to form and maintain stable social relationships up to about this number.

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How many social connections you you comfortably sustain? According to the social brain hypothesis, limits exist. ⁶Zhou WX, Sornette D, Hill RA, Dunbar RI. Discrete hierarchical organization of social group sizes. Proc Biol Sci. 2005 Feb 22;272(1561):439 – 44.

“The ‘social brain hypothesis’ for the evolution of large brains in primates has led to evidence for the coevolution of neocortical size and social group sizes, suggesting that there is a cognitive constraint on group size that depends, in some way, on the volume of neural material available for processing and synthesizing information on social relationships.”
Source: Proceedings of the Royal Society B: Biological Sciences ⁷Zhou, X., Sornette, D., Hill, R. A., & M. Dunbar, R. I. (2005). Discrete hierarchical organization of social group sizes. Proceedings of the Royal Society B: Biological Sciences, 272(1561), … Continue reading

Scientific evidence suggests that people tend to organise themselves not in an even distribution of group sizes but in discrete hierarchical social groups of more particular sizes:

Alas, there seems to be a discrete statistical order in the complex chaos of human relationships:

Support clique (3 – 5 people)
Sympathy group (12 – 20 people)
Band (30 – 50 people)
Clan (150 people)
Megaband (500 people)
Tribe (1,000 – 2,000 people)

“Such discrete scale invariance could be related to that identified in signatures of herding behaviour in financial markets and might reflect a hierarchical processing of social nearness by human brains.“
Source: Proceedings of the Royal Society B: Biological Sciences ⁸Zhou, X., Sornette, D., Hill, R. A., & M. Dunbar, R. I. (2005). Discrete hierarchical organization of social group sizes. Proceedings of the Royal Society B: Biological Sciences, 272(1561), … Continue reading

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ANNOTATIONS[+]

ANNOTATIONS
1	Dunbar, R. I. M. (1992). Neocortex size as a constraint on group size in primates. Journal of Human Evolution, 22(6), 469 – 493.
2	Dunbar, R. I. M. (1998). The social brain hypothesis. Evolutionary Anthropology: Issues, News, and Reviews, 6(5), 178 – 190.
3	Silfwer, J. (2012, April 14). Social Group Sizes (The Social Brain Hypothesis). Doctor Spin \| the PR Blog. https://doctorspin.net/group-sizes/
4	Dunbar’s number. (2023, May 29). In Wikipedia. https://en.wikipedia.org/wiki/Dunbar%27s_number
5	It’s worth noting that the concept of Dunbar’s Number has been debated and scrutinised within the scientific community.
6	Zhou WX, Sornette D, Hill RA, Dunbar RI. Discrete hierarchical organization of social group sizes. Proc Biol Sci. 2005 Feb 22;272(1561):439 – 44.
7, 8	Zhou, X., Sornette, D., Hill, R. A., & M. Dunbar, R. I. (2005). Discrete hierarchical organization of social group sizes. Proceedings of the Royal Society B: Biological Sciences, 272(1561), 439 – 444. https://doi.org/10.1098/rspb.2004.2970

150 — Dunbar’s Number

The science of brains and relationships.

Table of contents

Dunbar’s Number: 150 Relationships

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150 — Dunbar’s Number

Group Size Examples

Typical Social Group Sizes

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Typical Social Group Sizes

PR Resource: More Psychology

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ANNOTATIONS[+]

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