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The Dunbar Number as a Limit to Group Sizes
How Many Friends Does One Person Need?: Dunbar’s Number and Other Evolutionary Quirks
amazon.com
there was an upper limit at four on the number of people actually engaged with each other in a conversation and an upper limit at around three on the number of people who laughed together during a conversation.
Robin Dunbar • Friends: Understanding the Power of our Most Important Relationships
There is, they suggested, a limit on the number of people we can feel sympathy for, and this seems to set a limit on other groupings where close psychological interaction is required.