- [Voiceover] Game theory
is usually talked about
in reference to decision making,
but we can also use it
to talk about evolution
and animal behavior.
But before we do that,
I want to take a moment
to talk about how game
theory is usually discussed.
So when I think about game theory
I generally think about it as it relates
to the social sciences or maybe economics.
But we can also use it to
talk about every day behavior.
So imagine that we're
watching a group of people
play a game, an actual board game
like maybe Monopoly or Settlers of Catan.
The individuals who
are playing these games
make decisions like whether or not
to put a settlement on a wheat field.
But the results of that
decision don't only affect
that individual player.
It affects everyone who
is playing the game.
So the play offs to each of the players
depends upon the decisions
made by the overall group.
And this is where game
theory comes into play.
Because it reasons about
and tries to predict
the behaviors that we would expect to see
when the individuals
are playing this game.
So while it looks at things
like individual strategy,
it also looks at how we reason
about what the other players
are going to do.
Like the trades that they're going to make
or whether or not they'll
go for longest road.
So what does any of this
have to do with evolution?
Well, evolutionary theory
tells us that individuals
who have the best fit
with their environment
will be most likely to survive
and pass on their genes.
And because of this, the
genes that are best fit
for the environment
will become more common
within that population over
successive generations.
And the important part here, at least
as it relates to game theory,
is that reproduction part,
because that part can't
happen in isolation.
It needs to involve others.
Another thing that's important to think
about here is the environment.
Because we not only need to
think about the behaviors
that will allow the organism to be a fit
within its physical environment,
but we also need to think
about how the organism
fits in with its social environment.
It might need to work with other organisms
to find food, or deal with
predators, or raise young.
So some of the fitness
of an individual organism
deals with how well
that organisms behavior
matches up with the behavior of the group.
So let's think about this
in terms of game theory,
where life is the game.
What strategies would you expect to see
from the players?
Well, like it Settlers of Catan,
you would expect them to be concerned
with the availability
of their own resources.
But you would also expect
them to be concerned
about their social behavior
since so much of their
well-being and chances of mating
rely on their interactions with others.
And this is exactly how
evolutionary game theory
fits in with general game theory.
Because the strategy of each individual
will depend, at least in part,
on the strategies exhibited
by the other players.
I do however want to
point out a big difference
between evolutionary game theory
and general game theory.
Because game theory
generally involves intention,
or cases where individuals
are actively reasoning
about the strategies or the
behaviors of other individuals.
Evolutionary game theory is different
because it is applying
this theory to situtations
where there might not be any
overall conscious intention
on the parts of the players.
Another thing that I want to point out
about evolutionary game theory
is that it can actually
help us predict the traits
we would expect to see in populations.
Evolutionary game theory
predicts the appearance
of evolutionary stable strategies,
or behaviors that tend to
persist within a population
once they are prevalent.
So let's thinks about this in terms of
a complex behavior like altruism.
So imagine that we have
two groups of monkeys.
In one group, the monkeys act selfishly.
When one sees a predator approaching,
he takes the time to hide
and does not warn the others,
which makes it more
likely that he'll escape
and that the predator will eat one of the
other monkeys instead.
And now on the surface it seems that this
is a pretty good strategy
to ensure survival.
After all, you get out of it alive.
However, imagine what
would happen if the entire
group behaved this way.
It would mean that our monkey would be
more likely to die if another monkey
also didn't sound the alarm.
And, over time, this could
decimate that monkey population
and reduce the fitness
of the overall group.
But what if they adopted another strategy?
One that involved giving an alarm call
whenever a predator was spotted.
The monkey that would make this call
is doing this at his or her own expense,
because it could draw
the predator to them.
So initially you might think
that this strategy would fail.
But what happens when
a monkey makes a call?
It means that all of the other monkeys
within that group survive.
And of course it's
possible that the monkey
who makes the call survives as well.
And so this actually winds up being
a really successful strategy.
And I want you to really think about this,
because it means the altruism actually
increases the success
of the overall group.
So even though it might
put one individual at risk,
it increases the fitness
of the community around it,
making our monkey, or maybe
the kin of original monkey,
more likely to survive and reproduce.
And that's why evolutionary game theory
would predict the appearance
of altruism within a group.
