Well, if his hypothesis is validated this number should still apply to modern humans. You always have to remember that for 99% of our species existence we lived in groups of 150-250 individuals. Because biological evolution operates on very long time scales our bodies and brains are really still adapted to a hunter-gatherer lifestyle.

Okay, but don't you also have to keep in mind that during the most recent 1% of our species' lifetime, we've changed so radically that, as you say below, we've left natural selection in large part behind? Isn't it possible that in the age of instant communication and a host of other things, we've left Dunbar's number behind too? I'm no expert so this is just idle speculation.

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The latter part of your post, from "when you think about your own life" on down, seems to go back to what I said above about inherent limitation vs. practical one. What you said about the neocortex -- I know nothing about the brain, particularly, but wouldn't our neocortex be larger than any other primate's? Meaning that Dunbar's number if it holds would nonetheless be greater for us than for those species he studied?

The main anti-Dunbar's number argument I'm coming up against when I think about how many relationships I can maintain is this: I don't carry all of them around with me at once. When I'm in a certain setting, different relationship "sets" -- family, coworker, friends, casual friends, etc -- are brought to the fore of my thinking, and I don't bother with the rest. This eases the burden of knowing dozens of people relatively intimately. I haven't to my knowledge come up with a personal limit yet, dunno how many people I know, though. I have 500 Facebook friends and I could give you details on all of them, however relevant that may be (probably not at all).

Again, thank you ever so much for indulging me as a complete novice to this stuff. Feel free to stop answering at any time.