Hey flagamuffin Sorry it took me a while to reply. I saw that you mentioned me but couldn't answer at the time. I was first exposed to Dunbar's theory as an undergrad and I utilized aspects of it to determine the origin of modern complex language. I actually think there is sufficient evidence to continue testing his social brain hypothesis. I have yet to hear a more convincing hypothesis. In the primate world, large group size is almost always selected against. Group size is usually an intricate balance between ecological resources and predator defence. Ecology selects against a group's growth because a given environment can only support so many individuals. However, primates in groups have the ability to defend themselves from predators. So most groups will grow an increase their defence until they can no longer support such a large group, and then a fission event typically occurs. This is simplified and demands species-specific attention in most cases, but the general rule is valid.
How this relates back to Dunbar's hypothesis is pretty simple. It is hard to balance a lot of social relationships (ESPECIALLY WITHOUT LANGUAGE). In fact, I think it is impossible for any primate to exist in groups larger than 200-250 without language as a bonding mechanism (which was part of my undergrad thesis's argument). Part of the reason it is so difficult is because of coordination of fair resource allocation (in relation to what I stated about the balance between resources/predation).
Cue the social brain:
Therefore, primatologists have tried to associate neocortex size in extant primates with group size. We do see a strong correlation between relative neocortex size and group size. Interestingly, we don't see the same correlation among all mammals (which makes things more complicated than Dunbar would have liked). However, for some unknown reason the correlation is strong among primates. Perhaps it is strong because primates specifically evolved to be highly social. Either way, if we apply this theory, we see another strong correlation: expansion of hominid brain size is correlated with increase in group size. That is pretty strong support for Dunbar's hypothesis in my mind. And if we accept this hypothesis we can easily see how this would make sense in the modern world. Social science studies have shown time and again that social skills are the key to financial success and for the success of maintaining strong long-term bonds. Although it would be hard to test - this could have certainly been adaptive in the Paleolithic.
If you have any further questions, or if I didn't explain something clearly, feel free to let me know.
Wow, this is exactly what I wanted to know. I guess the further question I have is ... I'm not sure Dunbar's number holds up to humans nowadays? How could it? When we were hunter/gatherer communities (or w/e the PC term is now), I guess the same concept held true -- ecological selection against large groups, like with other primates -- but now surely this is outdated .... Not sure I'm making sense. In other words the rule seems to me to have more to do with practicality (which has been obviated now by technological increases and lifestyle changes) than with an inherent limitation on ourselves. Maybe. I'd love an answer to that any time you have a moment, but seriously no hurry.
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. This is also the case because natural selection does not operate on our species in the same way as it did throughout most of our evolution anymore (e.g., because most people live long enough to reproduce). Dunbar's number makes sense when you think about your own life. I know it does when I think about my own. How many relationships do I maintain (to any degree) at any one time? It certainly isn't more than 150. It takes up a lot of mental power to maintain social relationships. They are complicated and we only have so much space in our neocortex to handle that much information. It shouldn't surprise anyone that there is some limit on the number we can functionally maintain. That being said, how many practically do we need to maintain? Social relationships also take up a lot of time and energy. At some point we have to conduct a subconscious cost/benefit analysis when evaluating who is in our life and who isn't in our life. It would be practically impossible to maintain relationships with 1,000's of individuals. Dunbar's number has evoked a ton of controversy and interest. It is certainly an engaging idea that will require more research to solve.
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. -- 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.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.
1) Well we have largely left natural selection behind. But in order to us to have "left Dunbar's number" as well we would have needed natural selection as the pressure to do it. You need a selective mechanism if that makes sense. You can't rewire the human brain to be able to remember thousands of relationships at once unless their is a survival advantage over many generations to doing so. 2) Our neocortex is larger than any other primate, and we can exist in groups and remember more social relationships than any other primate. Chimpanzees for example roam around during the day in parties of 8-10 and exist in larger groups of up to 50 individuals. And chimps live in large groups for primates. Gelada baboons are one of the only other species that exist in groups of over 100 individuals, and that may be because of their unique ecological circumstances (not a coincidence that they exist in a savanna landscape). 3) I think that is a fair argument. As I said, the Dunbar number is a hypothesis. I personally feel as though there is more evidence supporting it than against it, so overall I find it conceptually useful. But future research may disprove it. I guess as a counterpoint to your point re: Facebook, I would say that that is an unfair comparison because you are having a computer store your friends for you. If you didn't have Facebook you wouldn't remember details about all those 500 individuals. However, that is a very small example of how we are using technology to increase our intelligence. In the past decades (and in the coming decades) we will be expanding our neocortex. I am smarter than I would have been if I lived 30 years ago. Google, Wikipedia, etc. make me smarter. They allow me to have access to all human knowledge. In the case of Facebook, they allow me to push my brain the capacity of social knowledge. This might be getting too far into it, but in the future we will use nanotechnology to actually expand the neocortex's abilities. At that point I would expect Dunbar's number to explode to perhaps include the entire human population. #TheSingularity