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- Dunbar's number - Wikipedia
‘Dunbar's number’ deconstructed

"‘Dunbar's number’ is the notion that there exists a cognitive limit on human groups of about 150 individuals. [1,2] This because ‘[t]o maintain group cohesion, individuals must be able to meet their own requirements, as well as coordinate their behaviour with other individuals in the group. They must also be able to defuse the direct and indirect conflicts that are generated by foraging in the same space’. [3] According to the hypothesis, since the neocortex is commonly believed to play a crucial role in handling social relationships [4], its size should set an upper limit on the number of stable social relationships that primate brains can keep track of and maintain."​
"The number 150 was established by extrapolating a regression line describing the relationship between group size and relative neocortex size in primates, to humans. [1,2,5,6]"​
"The expected human group size of 150 has been substantiated by observations of human communities with group sizes ranging between 100 and 200, including hunter–gatherer communities, military units, businesses, 18th-century and Neolithic villages, information from the Domesday Book [2] and Christmas card networks [6]."​
"‘Dunbar's number’ is often cited ["over 2500 citations on Google Scholar"], has had great impact in popular culture (e.g. it featured prominently in Malcolm Gladwell's book Tipping point [21]) and has had consequences such as the Swedish Tax Authority restructuring their offices to stay within the 150-person limit [22], with the implicit but hopefully unintended assumption that their employees have neither family nor friends outside work."​
"Most research on primate social evolution has not concerned cognitive limitations but instead generally focused on the so-called ‘socio-ecological model of primate social evolution’ where primate group size mainly is determined by socio-ecological factors having to do with foraging and predation, infanticide and sexual selection—not on brain or neocortex size. According to this model of social evolution, females go where it is safe and where there are resources, while males go where the females are [35–38]."​
"Further, it is easily observed that human brains function differently from those of other primates [38–42], as is evidenced by the existence of cumulative cultural evolution resulting in marvels such as Stockholm, symphonies and science [43–45]. This was concisely summarized by de Ruiter et al. [22] in their examination of Dunbar's number: ‘Dunbar's assumption that the evolution of human brain physiology corresponds with a limit in our capacity to maintain relationships ignores the cultural mechanisms, practices, and social structures that humans develop to counter potential deficiencies’."​
"Also, researchers have disputed the empirical observation of mean human group sizes approximately averaging around 150 persons, presenting empirical observations of group sizes indicating a wide variety of other numbers [46–53]. Thus, ecological research on primate sociality, the uniqueness of human thinking and empirical observations all indicate that there is no hard cognitive limit on human sociality."​
"Attempting to make a decisive deconstruction of the empirical basis of Dunbar's number, we here perform Bayesian and generalized least-squares (GLS) phylogenetic comparative analyses on larger datasets of the relationship between group size and both relative brain and relative neocortex sizes, and then extrapolate from these relationships to arrive at an updated estimate of the cognitive limit on human group size, including confidence intervals."​
"Our results (table 1) reveal that estimates of expected human group sizes vary depending on method and variable choice (Bayesian approximations between 69.2 and 108.6 and GLE approximations between 16.4 and 42.0). Note that these estimates (as was true for Dunbar's original estimated group size) are averages, not estimates of upper bounds. If an upper constraint from this type of statistical reasoning was to be determined, a better approach would be to specify the upper boundary of the 95% confidence interval. As is shown in table 1, however, 95% confidence intervals yield enormous variation in their estimates, 3.8–520.0 and 2.1–336.3, respectively, and thus indicate upper limits far exceeding 150 in almost all cases."​
"A cognitive limit on human group size cannot be derived in this manner." "Our reanalysis provides the last piece of evidence needed to disregard Dunbar's number."​
 

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