A widespread and popular belief posits that humans possess a cognitive capacity that is limited to keeping track of and maintaining stable relationships with approximately 150 people. This influential number, ‘Dunbar's number’, originates from an extrapolation of a regression line describing the relationship between relative neocortex size and group size in primates. Here, we test if there is statistical support for this idea. Our analyses on complementary datasets using different methods yield wildly different numbers. Bayesian and generalized least-squares phylogenetic methods generate approximations of average group sizes between 69–109 and 16–42, respectively. However, enormous 95% confidence intervals (4–520 and 2–336, respectively) imply that specifying any one number is futile. A cognitive limit on human group size cannot be derived in this manner.Ruiter et al. make the point that
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...Human information process management, we argue, cannot be understood as a simple product of brain physiology. Cross-cultural comparison of not only group size but also relationship-reckoning systems like kinship terminologies suggests that although neocortices are undoubtedly crucial to human behavior, they cannot be given such primacy in explaining complex group composition, formation, or management.An article by Jenny Gross quotes Dunbar's responses to the above.
The new analysis, he said, “is bonkers, absolutely bonkers,” adding that the Stockholm University researchers conducted a flawed statistical analysis and misunderstood both the nuances of his analyses and of human connections. “I marvel at their apparent failure to understand relationships.”
Dr. Dunbar defines meaningful relationships as those people you know well enough to greet without feeling awkward if you ran into them in an airport lounge. That number typically ranges from 100 to 250, with the average around 150...Around 6000 B.C., the size of Neolithic villages from the Middle East was 120 to 150 people, judging by the number of dwellings. In 1086, the average size of most English villages recorded in the Domesday Book was 160 people. In modern armies, fighting units contain an average of 130 to 150 people, he said...Dr. Dunbar contended that his theory is still viable, even in today’s hyper-connected world, since the quality of connections on social networks is often low. “These are not personalized relationships,” he said...“It’s fairly blatantly obvious to most people when they sit down and think about it that that’s how their social network is organized,” he said. Dunbar’s number, he said, is not going anywhere.