Ross Mayfield from Social Text gave a talk recently as part of ASC's new PARC Forum series and he mentioned a bunch of “Numbers” relevant to network effects (e.g., Metcalf's Number). He mentioned Dunbar's Number, which is one of my favorites because it highlights how social awareness and reasoning improves our fitness, and may explain why the human head exploded (at least on the scale of evolutionary time). The September 7 issue of Science included a whole section of social cognition, included an article by Dunbar on his recent work in the area.
So what is Dunbar's number? Well, it's 150. That's the theoretical limit of the number of people that you can “know socially” in the sense that you know them as individuals and know something about their relations to one another (and you), and the reason why it's an interesting number is that it seems to be related to the size of that melon sitting on your shoulders.
As an undergraduate I joint-majored in anthropology and psychology, so I'm generally interested in brains, but even more so because it has been a bit of a mystery as to why ours (homo sapiens) got so big. Second only to the heart, the brain consumes a massive amount of our energy intake, and those big heads make childbirth more problematic than our primate relatives. Most people probably would tend to believe that bigger brains mean greater intellectual capacity, and that somehow that provides a a substantial increase in out ability to, say, forage, to offset the costs of big brains. But as Dunbar notes in his Science article, there is no reason for a chimp to have a brain so much bigger than squirrel when they basically solve the same foraging problems.
It turns out that neocortext ratio for various species is strongly correlated with the average size of the social group for members of that species (and for humans that number is 150 at the limit), Recent evidence suggests that it is more specifically correlated with pairbonding. But even more importantly, it appears that increasing sociality increases reproductive success. So social cognition increases fitness.
This frames all sorts of interesting questions about social technologies. James Surowieki's “The Wisdom of Crowds” argues that one can get more accurate and “wiser” judgments from large-scale aggregate behavior in things like electronic markets or voting systems. But if was just the size of the herd that mattered then cows would be wizards. The claims made by the comparative biologists studying brain size is that our ability to maintain awareness and reason about complex social relations buys us something important. So, assuming that things like Twitter and Facebook (or the Wikidashboard) and the rest give us greater social awareness and reasoning--what exactly does it buy us?