Here is a number you may have run into without knowing where it came from: 150. It gets quoted in management books, on team-size pages, in articles about why your group chat feels too big. It traces back to Robin Dunbar, a British anthropologist and evolutionary psychologist, who proposed in the 1990s that humans can hold roughly that many stable relationships at once. He got there by an odd route, extrapolating from the correlation between neocortex size and group size in non-human primates, then doing the sum for us.

The headline number is the least interesting part. What actually lands, for me, is what sits inside it.

Quick note before we go further: I’m not a psychologist or a neuroscientist, and this piece is reading and reflection, not advice. Dunbar’s number is a contested theory, not a settled law, and the wellbeing findings here come from observational research about groups of people, which is not the same as a rule about you. Treat the layers as a useful lens, not a diagnosis.

The number everyone quotes, and what it actually means

150 is not a roster of close friends. It’s the outer edge, the most people you can keep a genuine, two-way relationship with at all. Dunbar’s framing is that “the key to the 150 and the layers within is that they’re reciprocated.” Both people know each other. Both keep the thread alive. A follower count is not a friend, and 1,500 names you’d recognise is probably not 150 people who’d recognise you back.

He also stresses that 150 is an average with a lot of slack around it. As Dunbar himself puts it, the number is “always about 150, although there is some individual variation” — driven by personality, sex, and circumstance. It’s a soft ceiling, not a hard cap.

The layers inside 150 are where it gets personal

Inside that 150 sit nested rings, each roughly three times larger than the one inside it: about 5, then 15, then 50, then 150. The really good friends number about five, with wider rings of roughly 15, then 50, then 150 meaningful contacts. The five are the shoulders to cry on. The fifteen are the ones you’d confide in. The fifty are the good friends you’d happily have round.

The lopsided bit is how much of you goes to the centre. Dubar reportedly note that around 60% of your social attention, your time and your emotional capital, goes to the innermost fifteen. That inner core, Dunbar argues, makes “a big difference to your sense of wellbeing” and your engagement with life in general.

The rebuttal: is Dunbar’s number even real?

It would be tidy to stop there, but the brain part of the theory has taken real fire. In 2021, a team at Stockholm University re-ran the primate data using modern statistical methods and updated brain data, and concluded that a cognitive limit on human group sizes cannot be derived this way.  Co-author Andreas Wartel said that “it is not possible to make an estimate for humans with any precision using available methods and data.”

His colleague Patrik Lindenfors put it more directly: “the theoretical foundation of Dunbar’s number is shaky.” A third co-author, Johan Lind, suggested that “our brain can be trained in having more social contacts.” That last point is an interpretive analogy rather than a demonstrated result, so hold it loosely. The methodological objection stands, though: deriving a precise cap on friendship from neocortex size is harder to justify than the clean number 150 makes it sound.

What the framework is actually useful for

Here’s where I’ve landed. The exact figure could be 150 or far lower or a wide smear in between, and the brain-size derivation may not survive the statisticians. None of that touches the part that’s useful, which is the shape rather than the number. Concentric rings, with most of your warmth going to a small centre, and that centre mattering more for how you feel than anything in the outer layers.

You can’t see your fifty thinning to five in real time. It happens at the speed of people quietly drifting, missed coffees, the friend who moved and the call you kept meaning to make. The framework’s gift is that it names the inner ring as the thing worth protecting, the ring that does the emotional work. 

If any of this is sitting closer to home than it is interesting, talking to a qualified counsellor or therapist is worth far more than any number on a page.

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There is a particular kind of flatness that comes from moving through the same loop of places, day after day. Home, the same desk, the same walk to the same shop, back home. Nothing is wrong, exactly. But the days start to feel laminated together, hard to tell apart in memory. You get to the weekend and struggle to recall what the middle of the week actually held, because it looked like everything around it.

There’s a finding from a few years ago that I keep turning over, because it lines up so closely with that low-grade flatness, and with its opposite.

I’m not a psychologist, and the study I’m about to describe is one observational study of a particular group of people, not a settled rule about how everyone’s mood works. It’s a clue, not a prescription. Keep that in mind as you read.

In 2020, a team published a paper in Nature Neuroscience that did something I find quietly clever. Rather than ask people to remember how varied their lives felt, they tracked it. They followed 122 people in New York City and Miami using the GPS in their phones, over three to four months, and every other day they sent a text asking people to rate how they felt, using words like happy, excited, strong, relaxed, and attentive.

What they found is the pattern above. On days people moved among more varied places, they tended to report more positive feeling. And the relationship ran both ways. As co-author Catherine Hartley put it, “if I feel better today, I’m likely to move around” and have more novel experiences the next day, and the reverse held as well. Feeling good nudged people out into the world, and getting out into the world nudged the feeling back up.

It’s worth being clear about what “varied places” actually means here. Reading this, it’s easy to picture travel, big novelty, the kind of trip you save up for. But that isn’t what the GPS was measuring. It was measuring the ordinary spread of a day. 

I notice this sort of pattern most clearly looking back on my first year living in Vietnam. Everything was new that year. The city, the noise, the food, the language, the version of myself I was becoming in the middle of it. That year felt enormous in retrospect, longer than most years since. I don’t want to flatten it into a happy postcard, because there was real loneliness in it too, visa stress, a lot of evenings alone. But the texture of that time was rich in a way that the laminated weeks are not, and the difference was variety. I was visiting new places and new experiences almost constantly, whether I wanted to or not.

That’s the dramatic end of the scale. The mundane end is the one I actually live now, and I arrived at it by accident. My weekday splits between home in the morning and two different coffee shops in the afternoon, with a walk between each block. I built that pattern to clear my head between tasks, not to manage my mood. The location variety is a byproduct. But it does rhyme with the study in a way I only noticed after reading it. My ordinary day already has a small amount of roaming baked into it, and the days I skip it, staying put from morning to night, are reliably the duller ones.

The study’s author Aaron Heller’s own reading of all this is broad. “New and varied experiences are broadly beneficial for the brain,” he told Inverse. That’s one researcher stating his interpretation confidently, and it’s worth holding it as his view rather than proven fact. But he also said something gentler that I think lands better. “Even if you may not tend towards exploring,” he noted, “there are probably benefits” to doing so anyway. The hedges are his, and they’re the right ones to keep.

The part that stays with me is the direction it can run. If feeling flat and staying put feed each other, the loop can run in the wrong direction just as easily as the right one. The worse a stretch feels, the less you go anywhere. The less you go anywhere, the more the days laminate, and the flatter the stretch feels. Nothing dramatic happens. The world just quietly shrinks to the size of the rooms you’re already in, and the shrinking is so gradual you don’t clock it as a cause.

Talking to a qualified counsellor or therapist is worth a great deal more than any study summary.

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