Relative brain size and the distribution of innovation and social learning across the nonhuman primates

The history of comparative learning could simply be classified as disappointing. The comparative psychologist often appears to know little more than the grade school child who would rather have a pet dog than bird, or bird than fish, or fish than worm, simply because they make better friends, as they can be taught more. This state of affairs did not arise without considerable effort. (RIDDELL, 1979, P. 95) Ecology and "intelligence" are two commonly invoked explanations for species differences in the reliance on socially learned traditions, yet we know little about how social learning evolved. Here, I examine hypotheses for the evolution and evolutionary consequences of social learning and detail possible routes to address these ideas. I will test social and ecological hypotheses for primate brain evolution to illustrate possible approaches to the study of traditions. This chapter explores cognitive, ecological, and life-history variables that may accompany a propensity for social learning, specifically, the roles of brain size and social group size. I also examine the distribution of innovations and tool use across the nonhuman primates, to determine how these aspects of behavioral plasticity are associated with social learning and to explore the relationship between asocial and social learning. Such analyses can provide important clues as to whether we can sensibly talk about the "evolution of traditions", or whether an increased reliance on social learning is simply a by-product of selection for generalized learning abilities.