This paper surveys the literature on group selection. I describe the early contributions and the group selection controversy. I also describe the main approaches to group selection in the recent literature; fixation, assortative group formation, and reproductive externalities.

We construct a parsimonious model of a financial market where the marginal investor is an endogenous noise trader. Such a trader anticipates that future shocks may force him to exit his position. In compensation he requires a higher return. We show that the original seller of the asset pays the...