Facebook & Dunbar's number

By Razib Khan | October 13, 2010 2:32 am

About 20 years ago the evolutionary anthropologist Robin Dunbar proposed his eponymous number:

Dunbar’s number is a theoretical cognitive limit to the number of people with whom one can maintain stable social relationships. These are relationships in which an individual knows who each person is, and how each person relates to every other person. Proponents assert that numbers larger than this generally require more restrictive rules, laws, and enforced norms to maintain a stable, cohesive group. No precise value has been proposed for Dunbar’s number. It lies between 100 and 230, but a commonly used value is 150

Dunbar’s number was first proposed by British anthropologist Robin Dunbar, who theorized that “this limit is a direct function of relative neocortex size, and that this in turn limits group size … the limit imposed by neocortical processing capacity is simply on the number of individuals with whom a stable inter-personal relationship can be maintained.” On the periphery, the number also includes past colleagues such as high school friends with whom a person would want to reacquaint themselves if they met again

This preliminary research served as one of the major points of discussion in Robin Dunbar’s Grooming, Gossip and the Evolution of Language. At least the descriptive model of the rough value of the number seems to have embedded itself into the Zeitgeist. To capitalize on his ideas in the web 2.0 world Robin Dunbar has come out with a new book, How Many Friends Does One Person Need?: Dunbar’s Number and Other Evolutionary Quirks. I recently heard him discuss on the radio the phenomenon of people with thousands of Facebook “friends.” Of course these aren’t really friends. People use Facebook for different reasons. Many people use Facebook like a business card, or a way to communicate with their fans or followers. In other words, more like twitter. The majority probably use Facebook the way it was intended, to mimic your real life social graph, and perhaps expand it on the margins.

After a few discussions with people who use Facebook and have given some serious thought to how these social technologies can extend our abilities, three assertions were made which I found intriguing. Below I have reformulated and elaborated upon them (that is, I added my own spin):

1) The number fixates upon a modal/median number of relationships. There is a “long tail” of individuals who have many more meaningful relationships, and this is important to overall network structure.

2) Technology can potentially double Dunbar’s number. In other words, instead of having ~150 meaningful reciprocal relationships you can now have ~300. Presumably because social technology extends our capabilities and introduces efficiencies by removing some of the “dead weight” overhang.

3) Dunbar’s number applies to coherent and self-contained groups. A pre-modern tribe or a Hutterite colony. It is not appropriate for the more multivalent and fluid relationships common in the contemporary word. For example, the same individual may be members of dozens of urban “tribes” with 10-30 members (though the coherency of the tribe may be highly subjective).

What are your thoughts? I ordered them in order of my own personal assessment of the plausibility of the assertion, but inverse order of the importance if the assertion is born out. I think #3 is a revolutionary possibility, a qualitative change of kind. In contrast, #2 is more evolutionary, a quantitative change of degree. #1 is correct to some extent, though the idea of “connectors” with which serve as nexus points within a network has been mooted elsewhere.

MORE ABOUT: Facebook, Sociology

Comments (15)

  1. bioIgnoramus

    It’s presumably pure coincidence that 150 is about the size of a year-group at your average Oxbridge College.

  2. miko

    I like #3, but I am suspicious of the idea that people can increase the Dunbar number while maintaining the criteria that one knows ” how each person relates to every other person,” which is an important component for group cohesion.

    In fact, my half-assed guess is that technology and “multi-tribalism” could decrease Dunbar’s number… it is probably harder to keep track of both within and between tribe relationships. I often have to think hard if two friends from different spheres know/have met each other.

    I love the anthropologist pretending he knows something about the brain that no one knows. Proportional to neocortex size. Ha! Tell it to a meerkat. Or the Kim-puter.

  3. Sandgroper

    My personal hypothesis (henceforth to be known as Sandgroper’s First Hypothesis and kicked along for the next 25 years by a bunch of pseudo-intellectual airheads, since it seems OK with a lot of ‘scientists’ to establish long-lived hypotheses based on slim anecdotal data) is that Dunbar’s number is shrinking. We no longer live in villages, but impersonal mega-cities. I have known of people who literally wound up not knowing anyone on any real personal level and died totally alone and friendless, some by suicide, and some sleeping and pissing on the streets despite being financially wealthy. People we converse with online we don’t really know in any true sense.

    Yeah, sometimes I wish I was a meerkat. Or at least that all of my family lived or could stay in one continent, the ones I care about at least.

    I never signed up for Facebook or Twitter, and would rather walk miles to talk to someone face to face than call them on the phone. This is eccentric of me and is going to have to change real soon.

    Now if you will excuse me, I have to go back to watching the progressing rescue of 33 Chilean miners who have become very dear friends of mine (no they haven’t), plus of course the 4 rescue crew who have been lowered down the hole. What I want to know is how the last guy out is going to fasten the door on the Fenix 2 capsule so that they can winch him to the surface, given that the catches are on the outside of the door. Unless they have a duplicate set inside – I hope that’s the case, but I don’t know how smart Chilean engineers are – that contraption looks worryingly Heath-Robinson to me, and this is a field I know about.

    The last thing you want at the site of an emergency rescue operation, apart from a ravening press mob, is a slimy grandstanding politician, and here we have two. I’ve been at sites where there were dozens of the bastards, posing grinning in front of locations where corpses of victims had very recently been extracted. (In fairness, in those cases, the press were pretty good, they kept their distance and didn’t get in the way.) If you ever need anything to destroy your faith in human nature, that will do it. But that’s getting pretty far from the point. Sorry Zeeb, my brain seems to wander. Can’t imagine why.

  4. Ari

    #2 doesn’t sound right to me.

    Wasn’t the whole idea about Dunbar’s Number that this number is limited because of our cortical size? That we can only manage ~150 because that’s how many relationships our brain can juggle, not how many we have time to write letters to.

  5. Chris T

    This throws a crimp in claims that hunter/gatherer tribes are egalitarian because they have no obvious signs of status. Of course not, the tribes are small enough for one person to track their and everyone relative elses’ status in the tribe. Outward displays would be completely superfluous.

  6. Notably, in tribal groups all people tend to be categorized as kin. Any stranger can be assigned a kinship status regardless of an actual genealogical relationship between him and the speaker. This kin status assignment is accomplished by triangulating between speaker, addressee and a third person whose relationship to speaker and addressee is known. So, the complexity of actual genealogical ties between strangers gets simplified through the use of specific terms of “kinship.” Alan Barnard, who worked among Khoisan, calls is “universal kinship categorization.” So, a tribal social network is much more nuanced and structured than, say, Facebook in which everybody is a “friend.”

  7. Anthony

    the number of people with whom one can maintain stable social relationships. These are relationships in which an individual knows who each person is, and how each person relates to every other person

    Is it necessary for a “stable social relationship” that I know how each person I have such a relationship with relates to each other person with whom I have such a relationship?

    I have friends whose interactions with some other friends is unknown to me. The same has been true at various jobs I’ve had.

  8. If the main limiting factor with respect to maintaining ‘meaningful social relations’ is that it takes time to interact socially on a level that makes the social relation ‘meaningful’, ie. if the binding constraint isn’t the ‘cognitive limitations’/’the wiring’ but the time constraint, 2) makes a lot of sense because it takes a lot less time to interact with people online. A lot of other stuff also makes a lot more sense to me, ie. how the subjectively estimated/self-evaluated Dunbar number varies greatly across people with different preferences (extroverts writing about this subject always report having a much higher Dunbar number than me, an extreme introvert) and different time profiles.

    But as Sandgroper also notes, this ‘science’ is, well… I’d like to know how one could in theory disprove the theory that this number, the ‘cognitive limitation’, is even relevant; rather than time constraints, economic constraints, preferences, ect.. It seems that if people have more social relationsships than the theory predicts is possible, the weasel words take care of that problem, because those marginal social relationsships aren’t ‘genuine’ or whatever.

  9. I think that the meaningfulness of relationships is a continuous variable, not a binary option. If one was to plot by frequency of interaction against my facebook friends, I don’t think it would be a step function, but I don’t know what the shape of the curve would be.

  10. twl

    I’ve noticed how large Facebook groups, message forums, boards within forums, blog comments, settle down quickly to be dominated by “regular posters”. So even the largest groups are a functioning Dunbar’s number in size even when they may have thousands, or in some cases, over 1 million members.

    I think each individual is capable of maintaining membership of up to 15 groups in which they know closely 10 individuals. The total – Dunbar’s number – doesn’t change. If I count up all the groups – including forums, real life and family – I can call myself ‘closely associated with’ it doesn’t exceed 15. The total size of the groups with which I am a member may number 1,000s but that’s not a reflection of my social activity as I’m only close friends with a subset of each group.

    The carpet is only so big, you may think you have broken Dunbar’s number but on analysis of your behaviour and attention you actually give to different groups that cannot be the case, when you move the carpet there’s a gap at the other end of the room.

    I think the observation that technology enables individuals to become members of multiple separate groups in which they know a dozen people rather than a single group in which they know 150 is a really profound one which must have interesting social consequences.

  11. I have seen no research that says #2 has any validity. You do say “potential”, but in the absence of any data I see no evidence to support this claim. I’d love to be able to say otherwise (being your basic techno-utopian), but I’m still waiting to be convinced.


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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com


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