Dunbar's number and VNN/VNNF/TAA

[lawrence dennis]

Ordinarily I would post something like this in the 'Science and Technology' subforum, but that would (unfortunately) limit the audience for this interesting discovery.


Prof. Robin Dunbar

Communities of practice and Dunbar's number

Posted at 17:01 in .
Dunbar is an anthropologist at the University College of London who hypothesized that there is a cognitive limit to the number of individuals with whom any one person can maintain stable relationships, and predicted that 150 is the "mean group size" for humans.

Ross Mayfield wrote a very interesting post last year starting from there on Ecosystem of Networks and came out with this nice summarized graph, which I have been struggling a little with to be honest since I saw it for the first time (are axes consistent from one raph to the other?..) but still it is intriguing.

Christopher Allen just elaborated further on this in a remarkable post on The Dunbar Number as a Limit to Group Sizes

Essentially, as we increase group sizes beyond 80, to 150, 200, or even 350-500, we typically do so by breaking larger groups down into smaller ones, and continually reducing community sizes down to the point where they can be understood and managed by people -- and so efficiency reasserts itself.

In my experience and vision of communities of practice, I tend to find similar numbers floating around. Typically vibrant communities of practice have around 100 - 150 members. As social structures, they are "onion-shaped", with layers of membership behaviors.

At the center, the "core group" of the community of practice is typically composed of 5 to 7 people. These are the guys who are willing to spend some time together, typically 15%-20% of their time (not much more, because they are busy on their projects anyway), reflecting on past experience and planning ahead for the community's learning activities in a peer mode. Then you have a second layer of 20-30 active contributors, typically those who follow the community ritual: they come regularly at meetings, they often contribute, and they also complain when something goes wrong in the planned schedule. These are the ones, whose attention is grabbed by other topics but have made some time for the community activities in their calendar, typically 2% to 5% of their time. And finally you have the "lurkers", who actually don't follow the community ritual, but participate just enough to be aware of what is going on. They also contribute a minima to maintain a feeling of social belonging, typically a few hours twice a year.

You might add, to try and connect even more to Ray Mayfield's graph, that a community of practice is often surrounded by a larger community of interest: people who are somewhat interested in what the community of practice does, and who will read its publications, and even give feedback in a point to point mode following something like the power law distribution.

And from wikipedia we learn:

...Primatologists have noted that, due to their highly social nature, non-human primates have to maintain personal contact with the other members of their social group, usually through grooming. Such social groups function as protective cliques within the physical groups in which the primates live. The number of social group members a primate can track appears to be limited by the volume of the neocortex region of their brain. This suggests that there is a species-specific index of the social group size, computable from the species' mean neocortex volume.

and In a 1993 article, Dunbar used the correlation observed for non-human primates to predict a social group size for humans. Using a regression equation on data for 36 primate genera, Dunbar predicted a human "mean group size" of 147.8 (casually represented as 150), a result he considered exploratory due to the large error measure (a 95% confidence interval of 100 to 230). Dunbar then compared this prediction with observable group sizes for humans. Beginning with the assumption that the current mean size of the human neocortex had developed about 250,000 years BCE, i.e. during the Pleistocene, Dunbar searched the anthropologicalethnographical literature for census-like group size information for various hunter/gatherer societies, the closest existing approximations to how anthropology reconstructs the Pleistocene societies. Dunbar noted that the groups fell into three categories — small, medium and large, equivalent to bands, cultural lineage groups and tribes — with respective size ranges of 30-50, 100-200 and 500-2500 members each.

Dunbar's surveys of village and tribe sizes also appeared to approximate this predicted value, including 150 as the estimated size of a neolithic farming village; 150 as the splitting point of Hutterite settlements; 200 as the upper bound on the number of academics in a discipline's sub-specialization; 150 as the basic unit size of professional armies in Roman antiquity and in modern times since the 16th century; and notions of appropriate company size.

villages, Dunbar has theorized that 150 would be the mean group size only for communities with a very high incentive to remain together. For a group of this size to remain cohesive, Dunbar speculated that as much as 42% of the group's time would have to be devoted to social grooming. Correspondingly, only groups under intense survival pressure, such as subsistencenomadic tribes, and historical military groupings have, on average, achieved the 150-member mark. Moreover, Dunbar noted that such groups are almost always physically close: "... we might expect the upper limit on group size to depend on the degree of social dispersal. In dispersed societies, individuals will meet less often and will thus be less familiar with each, so group sizes should be smaller in consequence." Thus, the 150-member group would only occur because of absolute necessity, i.e. due to intense environmental and economic pressures....

Recently, the number has been used in the study of Internet communities, especially MMORPGs such as Ultima Online.

So, doesn't this seem to fit VNN/VNNF? We've got about 5 to 15 'core members' (depending on how you define 'core') whose work radiates outward: Alex Linder, Chain, Stan, Rounder, Rob Roy MacGregor, Antiochus Epiphanes, the other moderators, the big TAA distributors.

And logged on to VNNF at any one time we see between 70 to 200 'members and guests' and among the most frequent posters we see a different set of 50 to 250 (depending on your definition of 'frequent').

[lawrence dennis]

This thread has dropped like a stone in the 'General Discussion' subforum. I think regular VNNF members are more likely to spot this if it is moved to the 'Science and Technology' subforum (where it would remain on the first page for awhile). Thanks. L.D.

[Fenrir]

Fascinating. Looks like good science too - the man makes a theoretical prediction based on regression and then compares it to empirical evidence.

As an aside, I think it's worth noting that this is how real social science ought to be done, rather than Jared Diamondesque lies and assumptions about anything the equality-mongers don't like. Based on these findings, one could probably speculate about racial differences in group sizes (since negroes have measurably smaller neocortexes), but with such a wide error bar as reported by Dunbar the differences probably wouldn't be significant. I'd predict any difference wouldn't be statistically measureable.