Monday, August 20, 2007

Brain size is proportional to the number of friends you can have

Perhaps this is old news to most bayblabbers but I just found out about this recently.
Apparently, group size is a function of relative neocortical volume in nonhuman primates. Meaning larger brained primates hang out in larger numbers. This correlation was first described in 1990. It is thought that a larger brain size allows an individual to keep track of its social network to which it must use to the best of its ability in order to be as reproductively successful as possible. Social interactions among primates are maintained by social grooming. And the time devoted to social grooming is linearly related to group size among the Old World monkeys and apes.
So then based on my human brain size, how much time should I be grooming my friends and indeed how many friends can I have??
Awesome questions, answered by Dunbar, R.I.M. In a paper published in 1993, Dunbar explains how language enables us to more efficiently groom our friends, because based on our brain size, we should be grooming about 150 people. Especially with modern humans grooming obsession this would be extremely time consuming without just being able to chat. Dunbar suggests in fact that 60% of human conversations are about personal experiences and gossip, thus fulfilling its role as a social networking tool.
One hundred and fifty friends then is also known as Dunbar's number. I ran into a very interesting article that discusses the concept of Dunbar's number and how it applies to modern society. Apparently just through trial and error the military has been aware of Dunbar's number before it was proposed. And some companies, like Gore-Tex, use this number for company structuring.
An absolute KILLER blog entry at does an awesome job of discussing Dunbar's number and attempts to challenge it using data from online networks and massive multiplayer online games and their guild sizes. Check the ganked graph I ganked from that website.
On a podcast I remember stating that I thought that language evolution was all about the meme ie. being able to learn survival abstractly from others in the group and being able to pass on behaviors that can evolve faster than biology. I guess I was wrong and it's all about being able to gossip so that you can have a bigger group with which to beat down the smaller groups.


Bayman said...

Very cool. Along the lines of Dunbar's magic number 150, that reminds me of a random fact I recently came across - apparently there's an idea in schools of business management that each person can only effectively supervise up to 12 people - although the same source that quoted this figure seemed to think that this arbitrary figure was inspired by the Bible, as Jesus son of God had 12 apostles and one betrayed him so he must have been overtaxed. Ha.

Hmmmmm 12^2=about 150 hmmmmmmmm....(joke)

Would one predict that those who are addicted to facebook have bigger brains than those who don't? If so, evolution is clearly starting to backfire...virtual friends wouldn't be too much use in a street brawl.

Kamel said...

Ha ha. I'm glad you brought up facebook. Maybe the prediction is that facebook users have smaller brains because they need this extra tool to keep track of their social network. I know Myspace users seem to be below average intelligence. I don't know how well the Dunbar number holds for MMORPGs and other online groups since we all know they don't groom.

Or maybe the 'friend collectors' on those sites (you know, the ones with 700 friends, that they couldn't possibly know more than in passing) are subconsciously compensating.

Kamel said...

More seriously, though - Malcolm Gladwell's book The Tipping Point has a nice discussion about the Dunbar number and other sociological phenomena.

Anonymous Coward said...

I don't know about the size of the brain, but one could question your grooming skills Kamel. oh snap!

Aftersox said...

According to this paper the degree distribution of friends on facebook shows a very sharp decline at 250 friends.

Maybe online communication increases this number even higher?

Bayman said...

a facebook paper. cool. i wonder if someone's doing a PhD project on facebook?