Dunbar's number

The number of people with whom we can maintain a stable relationship is about 150, according to British anthropologist Robin Dunbar. He says: 

We devote around 40 percent of our available social time to our 5 most intimate friends and relations…and the remaining 60 percent in progressively decreasing amounts goes to the other 145.  

Friendship is the single most important factor influencing our health, well-being, and happiness. Creating and maintaining friendships is, however, extremely costly, in terms of both the time that has to be invested and the cognitive mechanisms that underpin them. Part of friendship is the act of mentalizing, or mentally envisioning the landscape of another's mind. Cognitively, this process is extraordinarily taxing, and as such, intimate conversations seem to be capped at about four people before they break down and form smaller conversational groups.  

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