Evolutionary game theory

- [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.