The Great Mental Models, Volume 2: Physics, Chemistry and Biology

by Shane Parrish

Dunbar identified the following scale of closeness for humans in groups. Note that each group includes the individuals from the smaller groups, and each number is about the maximum that could be maintained at that level. 5 people: This is our inner core of closeness, the people who we support and who support us on a daily basis, such as partners, family, best friends. 15 people: This is our close friend group. These people are integrated into our lives to the extent that we have an excellent understanding of their behavior, even if we may not see them all the time. 50 people: This includes our basic friends and acquaintances. We hang out occasionally, probably more often in groups, and know a bit about what is happening in their lives. 150 people: This is the size where you feel you are a part of a community. “This is the number of people you can have a relationship with involving trust and obligation—there’s some personal history, not just names and faces.”2 500 people: This category includes friends of friends, people you know something about but don’t know as well and don’t make a sustained effort to know. 1500 people: This is the upper limit and includes all the faces you can put names to. Dunbar’s number is useful in terms of reminding us about working with our biology. Our brains can only process so much of the information required to maintain social groups. The larger the group, the more brain power required. Eventually we are going to run out. In addition, and we d...