The Evolution of Bayesian Updating

An evolutionary basis for Bayesian rationality is suggested, by consid- ering how natural selection would operate on an organism's `policy' for choosing an action depending on an environmental signal. It is shown that the evolutionarily optimal policy, as judged by the criterion of maximal expected reproductive output, is the policy which for each signal, chooses an action that maximizes conditional expected output given that signal. An organism using such a policy is behaving as if it were a Bayesian agent with probabilistic beliefs about the states of nature, that it updates by conditionalization, and whose choice behaviour obeys expected util- ity maximization. This suggests a possible route by which Bayes-rational creatures might have evolved