Cognitive and Social Advantages of a Lateralized Brain

Of the many examples of lateralization in vertebrates some are expressed at the individual level only (i.e., not aligned in the population) and others at both the individual level and population level. This chapter addresses the advantages and disadvantages of both manifestations of lateralization. First, it discusses results of experiments conducted with chicks and marmosets showing that having a lateralized brain enhances an animal's ability to perform more than one task simultaneously. By allocating the processing required for one task (searching for food) to the left hemisphere and that required for the other task (detecting a predator) to the right hemisphere, animals increase their capacity to attend to both tasks at the same time. Since this advantage of having a lateralized brain applies only to the individual and does not require lateralization at the population level, another explanation is needed for the latter. Indeed, population level lateralization would seem to have the disadvantage of, for example, predators exploiting their prey's bias to respond to their presence more readily on the left side. Hence, this apparent disadvantage might have to be counteracted by other distinct advantages of population lateralization. Here the hypothesis that advantages occur in social interactions between lateralized individuals is considered. Some concluding remarks are made about lateralization in primates, and its potential association with social behavior, and the development of lateralization in the chick as a model demonstrating the multiple interactive influences of lateralization.