The evolution of brain lateralization: A game theoretical analysis of population structure

Abstract

In recent years, it has become apparent that behavioural and brain lateralization is the rule rather than the exception among vertebrates. The study of lateralization has been so far the province of neurology and neuropsychology. We show how such research can be integrated with evolutionary biology to more fully understand lateralization. In particular, we address the fact that, within a species, left- and right-type individuals are often in a definite proportion different from 1/2 (e.g., hand use in humans). We argue that traditional explanations of brain lateralization (that it may avoid costly duplication of neural circuitry and reduce interference between functions) cannot account for this fact, because increased individual efficiency is unre- lated to the frequency of left- and right-type individuals in a population. A further puzzle is that, if a majority of individuals are of the same type, individual behaviour becomes more predictable to other organisms. Here we show that alignment of the direction of behavioural asymmetries in a population can arise as an evolutionarily stable strategy (ESS), when individually asymmetrical organisms must coordinate their behaviour with that of other asymmetrical organisms. Thus, brain and behavioural lateralization, as we know it in humans and other vertebrates, may have evolved under basically "social" selection pressures.