A Large-brained Social Animal

Publisher Summary A useful starting point in the study of large-brained animals is to scale back from an interest in specific neural structures, and instead look at a much coarser metric, i.e., brain size. “Large-brained” is a relative concept and depends on the group used for the comparison. Great apes, dolphins, and corvids are all large-brained when compared to their close relatives. These groups have diverse neuroanatomical characteristics, yet their similarly complex behavior indicates that they have convergently evolved a remarkable adaptation: high general intelligence. However, for dusky dolphins and other large-brained and cognitively complex species, more studies are needed to generate a consensus about the evolution of “braininess,” especially with respect to the social brain hypothesis (SBH). Complementing efforts to document animal relationships in nature are controlled experiments that illuminate the mechanistic connections between feeling, thinking, and behaving. The mechanisms linking large, complex brains and particular types of social relationships should be explored further in relation to the SBH. Finally, the issue of how to disentangle cause and effect in systems with feedbacks should be addressed further. The path analysis used by Dunbar and Shultz and ancestral character state reconstruction of sociality and brain size both seem to be promising approaches. Additionally, discerning the timescale of relevant ecological and evolutionary processes is critical for establishing the importance of feedback between the two processes.