Search

Patterns of reproductive uncertainty can have an important influence on population dynamics. There is a crucial distinction between what we describe here asaggregate uncertainty(in which reproductive output in each generation is correlated among the individuals in a population) andidiosyncratic risk(in which reproductive output is independent across individuals). All else being equal, populations experiencing idiosyncratic risk enjoy a higher asymptotic growth rate than do those experiencing aggregate uncertainty. Therefore individuals in populations of the former type will have a competitive advantage over individuals in populations of the latter type. Applying this distinction to models of randomly fluctuating environments, we point out that genetic variation among offspring can serve to reduce aggregate uncertainty, transforming it into a more idiosyncratic form of risk. We show that this transformation underlies the dynamics observed in several previous models of the role of outcrossing in the evolution of sex.

This paper considers a class of naive adaptive learning rules in a social setting. They generalize biological selection and have become relevant in economic theory as a consequence of their use in evolutionary game models. The environment considered here is nonstrategic but includes gambles which are more or less completely observed in each period. In the long run, individuals are more averse to a gamble which is less observable, other things being equal, and may violate first-order stochastic dominance. Thus these rules need not be consistent with rational behavior in the usual sense.Journal of Economic LiteratureClassification Numbers: D83, C72.

This paper considers the implications of explicit slight uncertainty about the strategic sequence of moves, that is, about the informational structure, for a two-person nonzero-sum game. It is shown that the set of associated informationally robust equilibria must be nonempty and must be a subset of the set of Nash equilibria. Although the present approach is conceptually reminiscent of that underlying perfectness, the two concepts are shown to be logically unrelated. There may exist no equilibrium which is both perfect and informationally robust. Journal of Economic Literature Classification Number: C72.Copyright 1994, 1999 Academic Press

Suppose God were a convex combination of Laplace and Jeremy Bentham. As did Laplace, God sees a world determined by differential equations and initial conditions,

Individual attitudes to risk are examined in an evolutionary model. Males obtain more offspring as a consequence of greater wealth both directly and because this attracts more mates. The second effect induces gambling driven by relative wealth and can create Pareto inefficiency. Fair bets involving small losses and large gains are taken if any fair bets at all are taken. Altogether, the model accords with observations concerning bets taken and declined by typical individuals despite settings of widely varying per capita wealth.Journal of Economic LiteratureClassification Numbers: C72, D81.