The Tipping Point
[The power of context (part two)]
Perhaps the most interesting natural limit, however, is what
might be called our social channel capacity. The case for a social
capacity has been made, most persuassively, by the British anthropologist
Robin Dunbar. Dunbar begins with a simple observation. Primates
- monkeys, chimps, baboonsm humans - have the biggest brains of
all mamals. More important, a specific part of the brain of humans
and other primates - the region known as the neocortex, which
deals with complex thought and reasoning - is huge by mamal standards.
For years, scientists have argued back and forth about why this
is the case. One theory is that our brains evolved because our
primate ancestors began to engage in more sophisticated food gathering;
instead of just eating grasses and leaves they began eating fruit,
which takes more thining power. You travel much farther to fidn
fruit thanleaves, so you need to be able to create mental maps.
You have to wory about ripeness. You have to peel parts away inorder
to eat the flesh of the fruit, and so on. The problem with that
theory is that that if you try to match up brain size with eating
patterns among primates, it doesn't work. There are primate leaf-eaters
with big brains and fruit-eaters with smaller brains, just as
there are primates with small cortexes who travel great distances
for their food and primates with big brains who stay at home to
eat, so the food argument is a dead end. So what does correlate
with brain size? The answer, Dunbar argues, is group size. If
you look at any species of primate - at every variety of monkey
and ape - the larger their neocortex is, the larger the average
size of the groups they live with.
Dunbar's argument is that brains evolve, they get bigger, in order to handle the complexities of larger social groups. If you belong to a group of five people, Dunbar points out, you have to keep track of ten seperate relationships; your relationships withthe four others in your circle and the six other two way relationships between the others. That's what it means to know everyone inthe circle. You have to understand the personal dynamics of the group, juggle different personalities, keep people happy, manage the demands on your own time and attention, and so on. If you belong to a group of twenty people, however, there are now 190 two-way relationships to keep track of: 19 involving yourself and 171 involving the rest of the group. That's a fivefold increase in the size of the group, but a twentyfold increase in the amount of information processing needed to "know" the other members of the group,. Even a relatively small increase in the size of the group, in other words, creates a significant additional social and intellectual burden.
Humans socialize in the largest groups of all primates because we are the only animals wiht brains large enough to handle the complexities of that social arrangement. Dunbar has actually developed an equation, which works for most primates, in which he plugs in what he calls the neocortex ratio of a particular species - the size of the neocortex relative to the size of the brain - and the equation spits out the expected maximum group size of the animal. If you plug in the neocortex ratio for Homo sapiens, you get a group estimate of 147.8 - or roughly 150. "The figure of 150 seems to represent the maximum number of individuals whith whom we can have a genuinely social relationship that goes with knowing who they are and how they relate to us. Putting it another way, it's the number of people you would not feel embarrassed about joining uninvited for a drink if you happened to bump into them ina bar."