L8 Evolution - Economics 112 Lecture Notes Lecture 8...

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© David Scoones 2010 Page 1 Economics 112 Lecture Notes Lecture 8. Evolution and learning We examine a model of evolution with random mutation and natural selection. To do this, we introduce the “biological” interpretation of strategies as “behaviours” rather than choices. We explore this interpretation in the now familiar hawk-dove game. The evolutionary model can also be used to interpret learning, where rather than thinking of rational individuals choosing the best strategy, we think of strategies “surviving” based on some criterion of success. Key terms: population game; evolutionary stable strategy; replicator dynamic; bounded rationality 1. New interpretations The simplest evolutionary model is based on “random mutation” and “natural selection”. We can reinterpret our rational agent model of selection of the “best” strategy into term compatible with this model. 1. Reinterpret strategies as “hard-wired behaviour”, not the object of choice. Perhaps think of these as “instincts.” 2. Reinterpret play as occurring between strategies embodied in “phenotypes” i.e. varieties of organism. Assume that populations are large enough so that the participants in each interaction are determined randomly depending on the population sizes of the strategies. 3. Reinterpret payoffs as “reproductive fitness”: relatively more successful strategies gain share in the population. Reinterpretation 2 means that, from the perspective of a representative member of one species, playing the “game” can be thought of facing an opponent who is playing a mixed strategy. Reinterpretation 3 is the replicator dynamic . 2. The Selfish Herd Social Dilemmas occur in the animal world. Hamilton develops the idea of a “selfish herd”. Collectively, animals do not benefit from clustering in herds, behaviour that makes them more conspicuous to predators. However, individually, it makes sense for animals to hide behind other members of their species who are non-threatening and provide cover from predators. Overall, this lowers average fitness.
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© David Scoones 2010 Page 2 3. The hawk-dove game We’ve seen this game a couple of times now. The game is played between two strategies, an aggressive “hawk” and a passive “dove”. Interactions are assumed to be random, in that the probability that a given “bird” meets a hawk is determined by the share of hawks in the total
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L8 Evolution - Economics 112 Lecture Notes Lecture 8...

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