Proposed by British anthropologist Robin Dunbar, this number would indicate “the number of individuals with whom any one person can maintain stable relationships”. Just like the much-maligned Mehrabian study, this finding was extrapolated to all manner of situations– some declared that this indicated the highest number of people you could have in your address book; others declared it was the ideal operating unit size– many companies, including W.L. Gore, organize their workers accordingly. As one of my favourite colleagues laments, “the numbers were tortured until they confessed.”

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But what is this “golden number” actually based on? According to Wikipedia’s excellent synthesis, Dunbar noted that, due to their highly social nature, primates need to maintain personal contact with the other members of their social group, which is usually done through grooming. The number of group members a primate can track appears to be limited by the volume of their neocortex. This would indicate a species-specific social group size, depending on the species’ mean neocortex volume.

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In a 1992 article, Dunbar used the correlation observed for non-human primates to predict a social group size for humans of about 150, a result he considered exploratory. He then compared this prediction with various human group sizes recorded throughout history.

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Dunbar’s surveys of village and tribe sizes seemed to confirm value, from the estimated size of Neolithic farming villages to the splitting point of Hutterite settlements or the basic unit size of professional armies from Roman antiquity to modern times since the 16th century.

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Dunbar further suggests that language may have arisen as a “cheap” means of social grooming, allowing early humans to efficiently maintain social cohesion. Without language, Dunbar speculates, humans would have to expend nearly half their time on social grooming, which would have made productive, cooperative effort nearly impossible. Language may have allowed societies to remain cohesive, while reducing the need for physical and social intimacy.