Why are we intelligent? A comparison of the ecological and social theories on the evolution of large brains in primates, birds, and cetaceans

Abstract

Primates, parrots, corvids, and cetaceans are amongst the most intelligent animals. However, intelligence is an energetically costly trait and researchers are yet to agree on what selection pressures have driven its convergent evolution across these phylogenetically distant taxa. Two overarching theories have traditionally been proposed for the evolution of intelligence in primates: ecological and social. Ecological theories suggest how cognitive mapping and extractive foraging techniques used by primates to find high-quality foods demanded increased cognitive capacity. Social theories, in contrast, suggest how forced cooperation between conspecifics and resulting social hierarchies encouraged an arms race of Machiavellian strategies to compete for mates and food. This paper attempts to find a theory consistent with the characteristics and behaviours of primates, parrots, corvids, and cetaceans. Cognitive mapping is only exhibited by some primate and corvid species, so is an unsuitable candidate. Extractive foraging is exhibited by species within all present taxa. Social behaviours like cooperation, alliances, and complex mating patterns were found in primates and cetaceans but much less so amongst bird species. Social learning, however, was found amongst all taxa. A mixture of extractive foraging and social learning, sometimes described as the socioecological model, is, therefore, proposed as the most likely explanation for the convergent evolution of intelligence across these taxa.