What 'Dunbar's Number' Tells Us About Our Closest Friendships

by Susie b Cross
Tim Robberts/Getty

If you ask evolutionary psychologist Robin Dunbar, friendship is quantifiable. Dunbar, author of Friends: Understanding the Power of Our Most Important Relationships (which will be released in the U.S. in January), is the originator of “Dunbar’s Number,” which at its barebones refers to the number of relationships a person is able to maintain. Dunbar suggests that the number is 150, on average.

“Dunbar’s Number” is a bit more complex than a single figure, he would explain. According to Dunbar, relationships are best understood as a series of concentric circles, something like a dartboard. Near the bullseye, you will find only the most intimate connections, probably your romantic partner. The next ring, topping out around five (a number that includes that innermost person as well) would be those who “will drop everything to support us when our world falls apart.” As the rings radiate outward (in multiples of three), the intimacy lessens as the number of those within that ring grows. The final ring, which, when combined with all the other layers equals our 150, is your “weddings and funerals group,” the people who are expected to attend once-in-a-lifetime events.

It makes perfect sense to me that our smallest two circles only accommodate a mere .033% of that 150. Nurturing and maintaining an intimate friendship takes commitment—and time. At different points in our lives we have more or less of this precious commodity and, if it’s less, our most tried and true are going to slip far from that bullseye (maybe even as far back as the measly only-for-big-barbeques crowd of 50).

We are bound to lose and gain a couple from our close group just naturally, as relationships are always in flux. Our new friend from work, who understands the genius behind Broad City (and will let you be Ilana) is probably going to ace out the friend who thinks Fresh Prince is the pinnacle of TV art; our friend who voted for Trump is going to be pushed way back, her position usurped by someone who…didn’t.

But do we have to shuffle people in and out? Can’t we just keep them all? Well, according to Dunbar, if the inner-ish circle only fits five (which is really four, if you add in that one lovey-dovey bullseye person), it only fits five. That’s it. I like to think of it like a teensy-weensy clown car. You can only sardine a finite number in, and if you try to squeeze in extras, somebody has to be ousted.

“Dunbar’s Number” suggests this: even though we can have a large number of overall relationships, we can only foster so many really meaningful relationships, no matter how many we’d like to have. It’s just not possible.

This makes a lot of sense when I think about it, though I’ve never really considered friendship in such math-y terms. What’s interesting to me, though, is what happens when you take into account that we are not the only ones who operate according to “Dunbar’s Number”; everyone has their own set of fickle rings.

Let me illustrate:

Fourth grade. I vomited on my desk. That next day, Shelly Rizzolo un-invited me to her slumber party. Mrs. Rizzolo (very suddenly and suspiciously) said Shelly could only have three girls and not four. And so, with one false barf, I was cast out of Shelly’s closest friend group.

Senior year. I got ghosted by my number one BFF. When I, half a bottle of Boone’s Farm apple wine in, confronted Kathy at a party, she told me I “wasn’t popular enough.” A gut punch that sent me to the outer ring, on par with people she barely talked to in Algebra class.

28 years old. I went to Spain for six months to master the art of homesickness and how to say “your pants are nice” in Spanish. I came home to two roommates who decided the renter I sublet to was a better fit than me. Ouch. Exiled again.

Sometimes it doesn’t matter how you, personally, configure that 150 number; your most intimate ring has to jibe with others’ most intimate rings. Mine didn’t mesh with Shelly’s, Kathy’s, or the (disloyal) roommates’. And those are just a few I have in the forefront of my brain. (Like you can only have so many close friends, you can probably only hold on to so many grudges….)

It works the other way, too. At least a handful of times, I have avoided building any sort of relationship with an overly-zealous acquaintance. My mantra has always been “I have enough friends”—and I always thought I was being a little callous. Now, thanks to Dunbar, it’s apparent I am not a big jerk. More likely I’m simply protecting my established .033%.

“Dunbar’s Number” reminds us that we have to be realistic about the ebb and flow of friendships. Our dance card might not always be full, and (to mix metaphors) our wee clown car might even have a number of open seats. More open seats than we’d like. We might even try to force a potentially-new confidante’s circle to mimic ours. In the end it’s clear, though: you can only lure clowns into your tiny mobile if they’re willing to hitch a ride. And some people would prefer to walk.