Dunbar's Number

Dunbar's number was proposed by anthropologist Robin Dunbar. By using the average human brain size and extrapolating from the results of primates, he proposed humans can comfortably maintain only 150 stable relationship. [ Source: https://twitter.com/Rainmaker1973/status/1614537744734191617 ]

This number was extrapolated from correlation in neo-cortex size in other animals and their group size. And thus this is not rigorously scientific. Direct study of human groups was not done http://pworldrworld.com/fred/?p=275.