Neurothermodynamics as a contributing factor shaping the mammalian brain

As a thermogenic organ, heat generation and loss within and from the mammalian brain may play a role in determining its shape. We investigated brain shape by comparing endocranial volume (EcV, a proxy of heat generating tissue) and endocranial surface area (EcSA, a proxy of convective heat loss) in 472 species using phylogenetically appropriate methods. A distinct ancestral mammalian condition in the relationship between EcV and EcSA was found. Rodentia exhibit a more tubular brain shape, while Cercopithecoidea, Hominoidea, and Neoceti show a more spherical brain. Increased brain sphericity will reduce heat loss, providing energetic savings important in the context of natural selection.