Dunbar's Number proves that you can't realistically follow more than 150 friends on Twitter

Our maximum number of friends is actually determined by the size of our brains. Dunbar's number says 150 friends is about the human limit, and that's been true throughout history. Can human evolution withstand the insanity of social networking?

In the 1990s, British anthropologist Robin Dunbar realized that the size of primate social groups increased as the size of the primate's brain got bigger. Curious to see whether this correlation could predict the maximum size of human social groups, Dunbar used data from dozens of primate species to calculate that human group size should top out at about 148, which is often rounded to 150. The absolute maximum is a bit higher than that - perhaps as much as 230 - but 150 is the commonly cited figure, and with good reason.

This is because Dunbar then examined human social groupings throughout history, and he kept coming back to that 150 number. It's the number of people who lived in ancient Neolithic farming villages, the basic unit size for the armies of both ancient Rome and modern times, and the maximum size of most nomadic tribes. Now, as Dunbar himself is quick to point out, this doesn't describe every possible social grouping. Rather, this describes groups that have a very strong incentive to remain together.


A military unit obviously does, and so too would bands of nomads and subsistence agriculture communities. The key here is that these are all groups founded on relatively intimate social relationships - you don't have the luxury of casual relationships when your very survival is tied to the cohesion of the group. Even when your life isn't on the line, multiple studies have borne out Dunbar's basic finding that you can't maintain regular contact with more than about 150 people.

But you might see a potential counterargument to this. Is the barrier really mental, as Dunbar suggests, or is it more a product of circumstance? The sheer logistics of maintaining regular contact with, say, a thousand people might make the task impossible, but that does actually mean our minds can't cope with it? That's where new research by Indiana University's Bruno Goncalves enters the picture.

He and his research team studied the social networks built by three million Twitter users over the last four years, which meant looking at a whopping 380 million tweets. Most Twitter users fall into a familiar pattern - they start using the service, then they build up a huge number of friends, and then they get overwhelmed. Once the saturation point is reached, Goncalves found people start to pull back on the amount of people with whom they remain in regular contact.

And just what was this Twitter saturation point? Why, somewhere between 100 and 200 people, of course. Even with all the tools of the digital age, people couldn't get past the Dunbar number. It's more evidence that our basic social functions - including how many people we can really be friends with - is hardwired into our brains, and it's going to take some truly epic mind hacking to get us past that point. Of course, I find the idea of even 150 friends to be quite overwhelming...but then, I am a blogger.

arXiv via Technology Review. Image via U. S. Fish and Wildlife Service - Northeast Region.