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Human brain limit of ‘150 friends’ does not check out, new study requirements

It is called Dunbar’s number: an influential and often repeated theory that suggests that the average person can only maintain about 150 stable social relationships with other people.

Proposed by British anthropologist and evolutionary psychologist Robin Dunbar in the early 1990s, Dunbar’s number, extrapolated from research into primate brain sizes and their social groups, has since become a ubiquitous part of the discourse on human social networks.

But how legitimate is the science behind Dunbar’s number anyway? According to a new analysis by researchers from Stockholm University in Sweden, Dunbar’s famous figure adds nothing.

“The theoretical foundation for Dunbar̵

7;s numbers is appalling,” says zoologist and cultural development researcher Patrik Lindenfors.

“Other primate brains do not handle information exactly as human brains do, and primate sociality is primarily explained by factors other than the brain, such as what they eat and who their predators are.”

Dunbar’s number was originally based on the idea that the volume of the neocortex in primate brains acts as a constraint on the size of the social groups they circulate among.

“It is suggested that the number of neurocortical neurons limits the information processing capacity of organisms, and that this then limits the number of conditions that an individual can monitor simultaneously,” Dunbar explained in his 1992 basic study.

“When a group’s size exceeds this limit, it becomes unstable and begins to fragment. This then places an upper limit on the size of groups that a given species can maintain as cohesive social entities over time.”

Dunbar began extrapolating the theory to human networks in 1993, and for decades, author and co-author abundantly related research findings have examined the behavioral and cognitive mechanisms underlying sociality in both humans and other primates.

But as for the original question of whether neocortex size acts as a valid constraint on group size beyond non-human primates, Lindenfors and his team are not so sure.

While a number of studies have offered support for Dunbar’s ideas, the new study refutes the claim that neocortex size in primates is equally relevant to human socialization parameters.

“It is not possible to make an estimate for humans with any precision using available methods and data,” says evolutionary biologist Andreas Wartel.

In their study, the researchers used modern statistical methods, including Bayesian and generalized least squares (GLS) analyzes, to take a new look at the relationship between group size and brain / neocortex sizes in primate brains with the benefit of updated data sets on primate brains.

The results suggested that stable human group sizes may ultimately be much less than 150 individuals – with an analysis suggesting that up to 42 individuals could be the mean limit, with another estimate ranging from a group of 70 to 107.

In the end, however, enormous amounts of inaccuracy in the statistics suggest that any method like this – attempting to calculate an average number of stable relationships for any human based on brain volume considerations – is unreliable at best.

“Specifying any number is useless,” the researchers write in their study. “A cognitive limit of human group size cannot be deduced in this way.”

Despite the general attention that Dunbar’s numbers enjoy, researchers say that the majority of primate research in social evolution focuses on socioecological factors, including feed and predators, infants and sexual selection – not so much calculations depending on brain or neocortex volume. .

The researchers further argue that Dunbar’s numbers ignore other significant differences in brain physiology between human and non-human primate brains – including that humans develop cultural mechanisms and social structures that may counteract socially limiting cognitive factors that might otherwise apply to non-human primates.

“Ecological research on primate sociality, the unique human thinking, and empirical observations all indicate that there is no hard cognitive boundary for human sociality,” the team explains.

“It is our hope, though it is useless, that this study puts an end to the use of ‘Dunbar’s number’ in science and in popular media.”

The results are reported in Biology letter.

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