I'll start. I'm low on friends, for various reasons. Scientists poke their calculators into everything, and the number of friends we can have is one of them. Here is what one of them came up w.
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The way in which our social world is constructed is part and parcel of our biological inheritance. Together with apes and monkeys, we're members of the primate family – and within the primates there is a general relationship between the size of the brain and the size of the social group. We fit in a pattern. There are social circles beyond it and layers within – but there is a natural grouping of 150.
This is the number of people you can have a relationship with involving trust and obligation – there's some personal history, not just names and faces.
And this is is the Dunbar number! How did you come up with this concept?
I was working on the arcane question of why primates spend so much time grooming one another, and I tested another hypothesis – which says the reason why primates have big brains is because they live in complex social worlds. Because grooming is social, all these things ought to map together, so I started plotting brain size and group size and grooming time against one another. You get a nice set of relationships.
It was about 3am, and I thought, hmm, what happens if you plug humans into this? And you get this number of 150. This looked implausibly small, given that we all live in cities now, but it turned out that this was the size of a typical community in hunter-gatherer societies. And the average village size in the Domesday Book is 150 [people].
It's the same when we have much better data – in the 18th century, for example, thanks to parish registers. County by county, the average size of a village is again 150. Except in Kent, where it was 100.
http://www.guardian.co.uk/technology/2010/mar/14/my-bright-idea-robin-dunbar
If the wt was divinely directed, its congregations would all be of about this number.
S
Ps, the people of kent must be assholes;)