Working Papers

“Cooperation, Competition, and Linguistic Diversity”, with Haiyun Chen

Abstract: We propose a theory that relates linguistic diversity (i.e. the number of languages within a region) to cooperative and competitive incentives in a game theoretic framework. In our model, autonomous groups interact periodically in games that represent either cooperation, competition, or no interaction. Language matters in these interactions because language common to a pair of groups facilitates cooperation; whereas language unique to one group affords that group an advantage in competitions against other groups. The relative frequency of cooperation and conflict in a region provide incentives for each group to modify their own language, and therefore leads to changes in linguistic diversity over time. Hence, a main contribution of our paper is to model strategic incentives as a cause of linguistic divergence. Our model predicts that higher frequency of cooperative interactions relative to competitive ones reduces a region’s linguistic diversity.

The Evolutionary Origins of Beauty Preferences: Endogamy and Prehistoric Marriage 

Abstract: This paper models information about potential spouses in the pre-Holocene marriage market. I assume that agents have better information about the quality of potential spouses from their own group than they do about those from other groups. In the absence of aversion to endogamy, I show that the exogamous marriage market breaks down completely. Repeated endogamy over many generations then results in severe fitness depression. A mutation for aversion to endogamy would be very beneficial in this situation. Such a mutation would spread, eventually resulting in a lower steady-state population-wide level of fitness depression. Introducing an additional mutation, for the capacity to credibly signal quality, decreases the level of fitness depression still further. Physical examples of credible signals of quality include the capacity of both sexes to grow long head hair, and for females to grow large breasts.

“The Origins and Incidence of Early Warfare” with Greg Dow and Clyde Reed

Abstract. Warfare can be defined as lethal conflict between organized groups. Recently there has been considerable debate over the frequency of warfare in early foraging and farming societies. We develop a formal model of early warfare over land that sheds light
on this debate. There is a production technology in which food is obtained from labor and land, and also a military technology in which the probability of a successful attack is a function of group populations. Attacks are motivated by a desire for additional land. It
is difficult to construct equilibria with warfare when site qualities are known in advance and individual agents can move easily across sites. However, environmental shocks and restrictions on individual movement can lead to situations in which one group has a large
population but a small resource base, while another has a small population but a large resource base. This can generate warfare. Our theoretical results are consistent with a set of stylized facts from archaeology and anthropology.