The Size of Social Networks: Primates on Facebook
economist.com
economist.com
It's interesting how small humanity's core and even extended groups are. Modern civilization and population density is very recent in evolutionary terms, and our brain's just can't make good use of that much humanity.
But even the casual circle is interesting, I think of everybody on LinkedIn as a kind of casual circle. Business casual, where we're all advertising our business acumen to each other. Both as desirable employees, and as desirable people to work for.
Do large twitter circles advertise casual habits? To what end?
Here is a popular article about the characteristics of networks if someone is interested:
http://scitation.aip.org/journals/doc/PHTOAD-ft/vol_61/iss_1...