Genes 2 Brains 2 Mind 2 Me

How many “facebook friends” do you have?   Well, of course, this depends on many things – perhaps just a matter of how much time you spend “on” facebook.  We all know of a few super facebookers with +300 friends and super-duper profligate facebook whales with +1000 friends, but it turns out that across facebook, the average number of friends per person is about 150.  Hmmm, I have been at this level for several months now, even while acknowledging  a pathetic tendency to procrastinate away the afternoon clicking around on facebook.  Like many people, I’ve hit a comfortable level at about 150 “friends” with folks that I know via childhood, school, work, family etc.  Few, if any, token friends.  Why 150? Might there be a reason for this?  A mathematical reason? A biological reason? An evolutionary reason?  All of the above?  None of the above?

According to Robin Dunbar,  professor at the Human Evolutionary Biology Research Group at University College London, “the size of a species’ neocortex is set by the range of group size required by the habitat(s) in which it typically lives, [but also] sets a limit on the number of relationships that it can maintain through time, and hence limits the maximum size of its group.”  Loosely translated, there may be a relationship between a larger neocortex that may provide more brain power to manage larger streams of “he said, she said, she did what? Oh No he DiDiNT!” information, among primates that live in differing group sizes.

A test of this “social brain hypothesis” would be to use the “relationship [of cortex size vs. group size] in reverse to predict group sizes for living species”. In his research article, “Co-evolution of Neocortex Size, Group Size and Language in Humans“, Dunbar asks the question, “what group size would we predict for anatomically modern humans, given our current neocortex size?”.  With a neocortex volume of 1006.5 cc and a total brain volume of 1251.8 cc, Dunbar places this information into an existing relationship between neocortex ratio and mean group size for a sample of 36 primate genera and extrapolates a value of 147 (with a wide confidence window of 100-231).  Neat man, very neat indeed!

Keeping in mind that this correlation between brain size and social group size does NOT PROVE causation, and that the magic number of 150 is likely just a coincidence (or is it? – just ask the Military, Gore-Tex, or Krippendorf’s tribe), it remains an interesting question to study further.  Better yet, perhaps this will motivate me to sign off of facebook and do something more productive!