The Evolution of Brains and Cognitive Abilities

Abstract

Humans place great significance in intellectual abilities, and because of this, biologists have been interested in the cognitive abilities of animals since Aristotle. The difficulties in defining intelligence in a way that can be applied to taxonomically distant animals have resulted in most studies using relative brain size as a directly measurable metric of intelligence. This approach has received criticism but persists in the literature as it has proved to be informative despite imperfections. Large brain size and, by inference, arguably complex cognition have evolved independently in several lineages including primates, corvids, cetaceans, cephalopods and hymenopteran insects. In these varying taxa, the evolutionary history of intelligence is still hotly debated. Proponents of the social intelligence hypothesis suggest that the cognitive challenges of group living have driven the evolution of large brains whereas other researchers have suggested ecological drivers such as seasonal challenges, dietary differences and energetic constraints. Here I review the study of the evolution of intelligence with particular focus on the widely cited social intelligence hypothesis and cognitive buffering hypothesis. I begin by summarising the study of animal intelligence and the methods employed. I will then go on to briefly review the current state of knowledge concerning cognitive evolution in some of the most heavily studied taxa. Finally, I will summarise and evaluate the social intelligence hypothesis and the cognitive buffering hypothesis. I propose that the weight of evidence suggests that social intelligence is limited to relatively few taxa, such as primates and cetaceans, and that across other taxa, a variety of other factors have driven the evolution of advanced intelligence in animals.