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Apr 11, 2009 | Comments

Only 15 years ago, Robin Dunbar suggested that human brains can only manage 150 stable relationships.

Recently, academics began focusing on “Dunbar-like” relationships that have proliferated on social networks and MMORPGs, many well above 150. And marketers are excited about this growth. If an individual previously had an upper-bound network of 150, a post-Internet world would raise the bar of word-of-mouth marketing.

How did Dunbar arrive at 150 relationships per person?

In 1993, Robin Dunbar studied the social habits of primates. After reviewing 36 primates and the average social group size, he found a strong correlation with the size of the neocortex region of the brain. Through extrapolation, he concluded that human social groups are limited to about 150 people.

In short, it is our brain that constrains the size of our social circles. This limit is only for groups that are physically dependent, paralleling his study of primate group sizes. The real eye-popper is when Dunbar studied historical examples of human group sizes.

  • Neolithic farming size: about 150
  • Hutterite settlements split at 150
  • Average army groups from the Romans until the 1500s were about 150.

Does Technology Raise Dunbar’s Number?

Today, Dunbar’s number has little relevance. We do not live as co-dependants, as required by Dunbar’s experiments. But what it does suggest is a cognitive limit on quantity of relationships. Even intuitively, it’s difficult to track many things over a certain number, be it my Google Reader feeds or tasks at work.

But with Facebook, which allows me to track relationships more efficiently, does it raise our Dunbar number?

The Economist asked this same question to Facebook. Do to our friends’ news feed, status updates, etc., does Facebook reduce the friction of socializing and increase the size of our social circle?

Facebook reported that the average number of friends per account is 120. But those friends with which you heavily interact (write on wall, comment on photos) is only 7-10. But for even those with over 500 Facebook friends, the number only increased to 17-30.

MMORPGs, such as Warcraft, do not suggest an increase either. Average guild sizes are well below 150 for World of Warcraft and Ultima Online, with an average of 17 and a median of 9. There’s a very interesting graph of satisfaction with guild sizes, which peaks at 7 and 50 members. This level of satisfaction has a lot to do with group complexity. Life with Alacrity writes that simple groups will peak at 7 and complex groups at 60, eventually fractioning well before they reach Dunbar’s number.

In short, our brains continue to limit us to below Dunbar’s number, even with Facebook and Twitter. We haven’t quite reached the holy grail of word-of-mouth marketing with online developments–we still interact with the same 5-10 people on a close basis, and breaking the 150-mark seems too challenging to even attempt.

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