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Friendship by the Numbers

What the numbers 5, 15, and 150 tell you about your social network.

Adobe Stock Images
Source: Adobe Stock Images

Let's start with this: Make a list of the top 15 people in your life, ranked by the frequency and intimacy of your contact with them.

I'll wait.


OK, now draw a circle around the top 1.5. (Yes, I realize it will chop someone dear to you in half. My apologies. It is just a list, though.)

These one-and-a-half people likely share a dwelling with you (or have in the past) and probably often see you at your very worst, both physically and emotionally. You don't put on a mask for them. They are likely your spouse, your mother, your child, your best friend in the world. You probably talk or text with them on a daily basis.

Next, draw a second circle that encompasses the top five people in your life — including the original 1.5. These are your intimate life partners. The people who can probably tell just by looking at you when you are stressed. The people you call first when bad news strikes. The people who can most easily make you laugh.

These are people you are likely to contact at least weekly in some form. If we were to measure how much of your social time and effort you spend on other people (yes, psychologists do such things), you would probably be spending a full 40 percent of your "social capital" on just these five people.

Trends in Cognitive Sciences
Source: Trends in Cognitive Sciences

The third circle encompasses the entire 15. These are your very good friends — you care for them deeply, you know you can rely on them if you were to suddenly need support, and you are probably in contact at least monthly. These are what some people call "the sympathy circle," the people whose hearts would rend wide open were you to suddenly die.

These 15 people comprise about 60 percent of your social capital and may be the basis of a "childcare exchange" network. In other words, if you chose to have kids, these are the people you could wrangle to babysit sometimes.

We could expand the circles even more — the next 35 friends you would definitely sidle up to in a bar uninvited and are likely on your Christmas card list, but you may not talk to them more than once or twice a year, and they probably aren't privy to your innermost fears and desires.

We'd hit a limit around 150, which based on the best anthropological evidence is the maximum size of a functional social network for human beings. That isn't to say that you can't recognize or be familiar with many more than 150 other human beings, but rather that you wouldn't be able to maintain relationships in which you contribute your physical and emotional time to the well-being of more than that number. This number, 150, is known as Dunbar's number, for anthropologist and evolutionary psychologist Robin Dunbar.

Dunbar recently published a wonderful article in the journal Trends in Cognitive Science called "The Anatomy of Friendship." He reviewed multiple types of literature — anthropological, comparative (cross-species), psychological, and neurobiological — to illustrate how friendship works (on average, of course). He also shares that we each have a social fingerprint — our own peculiarities in how frequently we prefer social contact and how exactly we divvy up our social capital among our fellow life travelers.

Disruptions and Variations

A few more fascinating tidbits from Dunbar's research:

  • When we fall in love, our new beloved zooms right up to the top five, often with catastrophic consequences for some of our deepest relationships. On average, during the infatuation period, we lose one close family member and one close friend from this inner circle, temporarily shifting it to four instead of five and greatly changing the composition of our inner circle.
  • These numbers and proportions remain remarkably stable over time, even as membership shifts. If a close friendship dissolves, we tend to slide a new person into the slot, expending strikingly similar amounts of time and emotion on the new person.
  • "Kin-keepers" are individual people who tend to shoulder the responsibility for keeping all of the family in close contact with each other — scheduling reunions or nudging people who have fallen out of touch.
  • While oxytocin tends to get all the press, Dunbar's review of the evidence suggests that endorphins released during "social grooming" (laughter, singing, dancing, and emotional storytelling) play a much greater role in bonding.
  • 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. If the conversation involves speculating about an absent person's mental state (e.g., gossiping), then the cap is three — which is also a number that Shakespeare's plays respect.
  • Finally, analyses of "reciprocated posting" on Facebook (I post a meme on your Timeline, and a few days later you tag me in a Throwback Thursday post) yields the same layering and numerical limits as all of this face-to-face research. The Internet isn't changing us that much, yet.

Facebook image: Jacob Lund/Shutterstock


The Anatomy of Friendship. Dunbar, R.I.M. Trends in Cognitive Sciences , Volume 22 , Issue 1 , 32 - 51

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