Of our capacity for friendship is that natural selection has also equipped us with the capacity
to break our friendships.
So it's not as if once you make a friendship you keep that friendship for the rest of your
life.
Most of us are familiar with the idea that friendships have some lifespan.
Sometimes you're lifelong friends, but on average the typical best friend lasts for
about 10 years or so.
We've looked at this And you make friends, and sometimes you break friendships.
It doesn't need to be a bad breakage.
It doesn't need to be a catastrophic one.
But, you know, the friendship is not as intimate or as close as it was, or maybe it disappears.
Now, there's actually quite an interesting explanation for why we have this capacity,
not only to make friendships Imagine that I forced you to be friends with someone and
to work together to achieve some objective, like a kind of high school science project.
Five of you-- the teacher says, OK, the five of you are going to work together on this
project.
And one or two of those individuals within the group are lazy, and they're not doing
their part.
They're not cooperating.
They're what is known technically as defectors or free riders.
Now what are your options?
Your options are to do the work for them-- and many of us in high school hated this type
of dilemma-- or not to do the work and also defect and maybe get a bad grade.
So if you're choosing whether to cooperate or defect with someone who's defecting, and
all you can do is choose whether to cooperate or defect, what you find is that ultimately
most people wind up defecting.
So in a rigid social structure in which people are stuck with particular other individuals,
when those individuals start not doing their part, taking advantage of you, if you're stuck
with them, then you wind up not doing your job either.
And the whole group collapses and descends into a kind of, you know, anarchy, a kind
of awfulness in But if you allow people the capacity to leave the group, Don't want to
be connected with you anymore, I don't want to be your friend anymore, because you're
taking advantage of me, that capacity actually supports cooperation within a group.
If you allow people to switch friendships, it makes it easier to sustain cooperation
because now people have a second way of communicating their dissatisfaction with someone who's taking
advantage of them.
But you don't want too much of that.
You don't want too much social fluidity.
So the relationship between the ability of groups to work together or cooperation on
the y-axis and the social fluidity on the x-axis, with total rigidity being here and
total fluidity being here, gives you a parabolic curve.
Because if you have too much fluidity, you also don't make an investment in your friendships.
If every day you have new friends, why would you invest in that person?
They're here today, they'll be gone tomorrow.
And if you think about it, there are many institutions in our society which have evolved
to put We have an institution of marriage which kind of makes it so that you declare
that you are getting married to this individual.
If we make divorce impossible and so you are stuck with your spouse, if your spouse becomes
a mean person, what's your only choice?
You become mean too, or you spend your whole life being taken advantage of.
So you get both spouses being mean.
Conversely, at the other extreme, if it were trivial to divorce your spouse-- so every
day you had a new spouse, also you wouldn't be nice to your spouse.
Why bother?
They'll be gone the next day.
So you want a set of rules that make Divorce difficult but not impossible.
You want a set of rules that put you in the middle range, that optimize your impetus to
invest in your spouse.
Or think about, for example, the home mortgage deduction that we have.
We have a set of policies in our society that try to incentivize people to stay fixed in
a neighborhood.
But we don't want them to stay too fixed.
Let's consider it again.
If you have an environment in which nobody can move-- like in Stalinist Russia, for example,
where everyone is assigned an apartment and you're stuck here and you can never leave--
when your neighbors start putting graffiti or polluting the hallways or degrading the
commons, why should you go out and clean the hallway Else is dumping their garbage there?
So you start dumping your garbage because you're all stuck in this place, and anyone
starting to defect ruins the commons.
Conversely, If every day you had new neighbors, why should you go sweep the sidewalk in front
of your house or trim the hedges between your house and the neighbors house if the next
day the person will be gone?
So you want a set of policies that stabilizes neighborhoods but not too much, doesn't make
it impossible for people to move.
And then, again, you get optimal investment in local communities.
It's the same with friendships.
You want the capacity to leave your friends precisely so that they will become your better
friends.