Dunbar’s Number

Sorry to get personal, but how large is your – oh, what’s the word – your guild? Or supergroup, clan, allegiance or other moiety of players in your massively multiplayer online game (MMOG) of choice? Does it have, perhaps, around 150 players?

And with how many of those players do you feel close, such that playing with them increases your immersion in the game? No more than a dozen, right?

Okay, maybe you’re different. But if you ask around among the other players, most of them will hang out with fewer than a dozen people online, and they hardly ever belong to a group larger than 150 people.

That’s not a limit in the game’s code or its interface. Some people suggest the limit is hard-wired in your brain.


In 1993, Dr. Robin I. M. Dunbar, an evolutionary psychologist then at the Human Evolutionary Biology Research Group of the University College London anthropology department, was studying the behavioral ecology of primates, the relationship of primates to their environment. Dunbar analyzed numerical data from primate studies conducted worldwide. He observed certain “defining behavioural characteristics,” such as “the time devoted to social interaction, the level of social skills and the degree of tactical deception practiced.”

Dunbar noticed a given species always formed groups no larger than a certain size, and a member of that group always had about the same number of grooming partners. For instance, chimpanzee tribes have a maximum size of about 50 chimps, and each chimp has no more than two or three partners. Dunbar proposed maximum group size depends on the size of the primate brain’s neocortex (the part that thinks) – the larger the neocortex, the larger the group. “Animals cannot maintain the cohesion and integrity of groups larger than a size set by the information-processing capacity of their neocortex.”

Extrapolating to human societies based on the size of the human neocortex, Dunbar theorized human beings naturally form groups no larger than about 150 (147.8, actually) and “cliques” of about a dozen. Dunbar’s paper, “Coevolution of neocortical size, group size and language in humans,” appeared in Behavioral and Brain Sciences Vol. 16, issue 4.

The figure of 150 people has become known as “Dunbar’s Number.” The Number is a conjecture so far, supported only by statistical and anecdotal evidence. Dunbar, now at the University of Liverpool School of Biological Sciences, is conducting a 10-year study that may offer firm proof in 2008.

But some have already seized on the Number as proven fact. Malcolm Gladwell, in his bestselling 2003 business management book, The Tipping Point: How Little Things Can Make a Big Difference, popularized Dunbar’s Number (or, as he called it, “the Magic Number One Hundred and Fifty”). Similar books by Duncan Watts and Mark Buchanan advance the Number as a foundational structure for organizations and marketing campaigns.

On the web, humorist David Wong used the Number to launch a funny (but not-safe-for-work) screed about the “monkeysphere” – “the group of people who each of us, using our monkeyish brain, is able to conceptualize as people. … [I]n our monkey brains the old woman next door is a human being, while the cable company is a big, cold, faceless machine. That the company is, in reality, nothing but a group of people every bit as human as the old lady, or that some kind old ladies actually work there and would lose their jobs if enough cable were stolen, rarely occurs to us.”

Today, Dunbar’s Number has gained currency among sociologists, anthropologists, managers and – increasingly – online game designers.

Recommended Videos


The principal analysis of Dunbar’s Number as it concerns online gaming comes from Christopher Allen, founder of MUD operator Skotos Tech, on his intriguing (if sporadically updated) blog, Life With Alacrity. Starting with a lengthy March 2004 treatise, Allen spent half a dozen posts analyzing the Number’s relevance to online gaming:

“I’ve seen similar limits myself in some of the small online games that Skotos produces. For instance, in Castle Marrach , which is a social-dominant game (i.e. like a MUSH), the game grew quickly until we reached approximately 150-200 active users. However, whenever it grew beyond that number, it always seemed that politics and dissatisfaction would bubble up such that people would drop out, leaving us back close to 150 or 160.”

In an August 2005 post, Allen analyzed guild sizes in Ultima Online and World of Warcraft. (MMOG social scientist Nick Yee compiled the data in June 2005 at Allen’s request and presented it on the PlayOn blog.) The WoW breakpoint lay close to 50, versus UO‘s 150, and smaller guilds were far more common in WoW than in UO. “If one-person guilds are excluded, the average guild size was 16.8, the median was 9,” Allen wrote. “My guess is that there is something about Worlds [sic] of Warcraft such that even participating in very small groups can be useful, whereas for Ultima Online the utility is gained mainly by sharing the resources earned by larger groups. Thus Worlds of Warcraft has groups that are ‘bands’ as well as ‘tribes,’ while with Ultima Online groups are more likely to be just ‘tribes.'”

Like Dunbar himself, Allen believes the limit of 150 relationships is practical mainly for groups faced with a strong reason to remain together, such as military units or tribes facing a hardscrabble struggle for survival. In such large groups, each individual member may spend quite a lot of time on “social grooming.” Absent this desperate environment, an individual will choose to maintain far fewer close relationships; this “non-survival-oriented” figure, Allen says, “hovers somewhere between 25-80, but is best around 45-50.” He also postulated several other breakpoints in group size for practical working teams (five to nine members), small businesses (25-80), and larger businesses with middle management (500+). Above or below these ranges, group efficiency and satisfaction fall sharply. (Allen’s analysis gained chilling confirmation from military theorist John Robb. In his blog about “fourth-generation warfare,” Global Guerrilas, Robb analyzed the optimal size of an Iraqi terrorist network and a Mafia crime family. Both fit the same breakpoints as an MMOG guild.)

Of course, members of certain professional classes, such as doctors, salespeople and politicians, routinely socialize with hundreds, even thousands of acquaintances. Allen suggests this can work because these professionals practice “Dunbar triage“: They spend far more time than average on their relationships, prioritize ruthlessly and meet most of their contacts in highly structured situations. Allen moves into uncharted territory with “Cheers: Belongingness and Para-Social Relationships.” He speculates that tracking a character’s created life on a TV show is a “junk relationship” that takes up a Dunbar slot. If this unsettling idea is true, it would help explain the social life of, say, a comic book fan, who can instantly recite all the melodramatic events of many hundreds of superheroes but has few friends.


For social network theorists, not to mention guild leaders, this is all interesting. But is there really a Dunbar limit hard-coded into your brain?

Despite the statistics and anecdotal evidence, it’s unlikely. Research has yet to determine the human brain’s memory capacity. Back in the ’70s, memory artist Harry Lorayne, about an hour before his nightly stage act, would go out front and mingle with his audience. He’d learn their names and interesting facts about them, and then during his show he would name each one, every member of an audience of hundreds. (If Lorayne plays World of Warcraft nowadays, he probably knows everyone on his server.) Obviously, just remembering someone’s name doesn’t mean he’s in your monkeysphere. The point is, the human brain doesn’t melt down at 150 names.

More likely, the limitation isn’t in your cortex, but in your schedule. It takes time and energy to maintain a relationship. Physical space is sometimes an issue, too; one commenter on the Life With Alacrity blog observed that workgroups broke down when they got too large for one member to shout across the room to another.

Yet new venues like MySpace are simplifying this logistical challenge, and it will get easier as time goes on. Are we at the beginning of a “Dunbar Transformation”?

We can easily envision tech fixes that could expand your “socialization limit,” in the way writing and data storage expand your “memory.” Maybe Dunbar’s cortical limit implies you can only think about 150 people at a time, at one given moment – hold their data in your personal RAM, so to speak, as opposed to your neural hard drive. If that’s true, is it important? On the futurist site Edge.org, entrepreneur and mathematician Adrian Scott envisioned a technological platform that would permit us to maintain vastly expanded social networks by using tailored Customer Relations Management (CRM):

“We end up with personal CRM systems to handle our increased interaction load, and then add … heads-up display style interfaces in glasses and, eventually, retinal and neuronal interfaces. ‘Hi Jerry! Ahh.. we met back in 1989, May 14th at 7pm, and since then we’ve exchanged 187 e-mails and 39 phone calls. I hope your cousin’s daughter Gina had a wonderful graduation yesterday.’ The whole range of interactions becomes organized. Introductions from one person to another and rating systems become automated.”

(Game designers may someday help create such a reputation system. See “Game Design in the Transfigured World” in The Escapist 21.)

It’s likely this “personal CRM” would evolve first in online games, where we routinely interact with hundreds of strangers, often worldwide. As this hypothetical infrastructure developed, your guilds would grow lots bigger, and you’d swim in a figurative ocean of friends and acquaintances.

Do you want that?

What do you expect from a relationship, anyway? That the other person attends your birthday party, knows your children’s names and would lend you money in an emergency? (Or, in online game terms, will team with you and let you take the drops?) Possibly that’s good enough, right now – but in the future, when anyone may know your name or do you a favor, will we therefore raise the threshold of “friendship”?

“With these trends, the friction costs of personal introductions go down, and consequently the value of quality measurement and gatekeeping go up dramatically,” Adrian Scott wrote in his Edge essay. “As the depth of knowledge in a relationship increases, the threshold point at which you ‘really know someone’ increases also. It’s an arms race of intimacy.”

Allen Varney designed the PARANOIA paper-and-dice roleplaying game (2004 edition) and has contributed to computer games from Sony Online, Origin, Interplay and Looking Glass.

related content
Read Article Alone in the Dark
Read Article The Introversion Aesthetic
Read Article Killjoy
Related Content
Read Article Alone in the Dark
Read Article The Introversion Aesthetic
Read Article Killjoy