Exclusive Dunbar Number
150 — "The Exclusive Dunbar Number".
"Robin Dunbar got much of the discussion of group thresholds started with his article, "Co-Evolution Of Neocortex Size, Group Size And Language In Humans." However, as I've written previously, and as I've described in this article, Dunbar's group threshold of 150 applies more to groups that are highly incentivized and relatively exclusive and whose goal is survival.
Dunbar makes this obvious by the statement that such a grouping "would require as much as 42% of the total time budget to be devoted to social grooming."
The result of the grooming requirement is that communities bounded by the Exclusive Dunbar Number are relatively few. You will find hunter/gatherer and other subsistence societies where this is a natural tribe size. You'll also find these groups sizes in terrorist and mafia organizations.
As we step up toward higher group thresholds, more and more time is required to simply keep the group going. You see this in depictions of mafia life — in the TV series The Sopranos a lot of time is spent dining, hanging out, and drinking together. That is part of that 42% social grooming time required for that intense of a survival group.
It is possible for a large company to force groups up to this size by expending lots of energy (which is to say money) to keep it healthy. Apple did this during the invention of the Macintosh, the first OS X operating system, and the iPhone, but the intensity required of such large teams is not sustainable for long periods of time.
Without that extra energy, few modern tightly-knit communities can reach this threshold, or else can't hold it for very long. Instead they fracture into groups of individual interest (even if they continue to "meet" in the same real-world or online forum), which are more than more likely to be bounded by the Non-Exclusive Dunbar number.
Given the difficulty in even arriving at the Exclusive Dunbar number, it may well be the highest limit of all for a tightly-knit community. Beyond this limit, communities are less cohesive, less trusted, and less participatory (and the topic of my third article in this series.)" (http://www.lifewithalacrity.com/2008/09/group-threshold.html)