Evolution of Large Brain and Body Size in Mammals

Mammalian brain size varies from less than 1 g to over 9 kg, but what is the significance of this variation in terms of behavioral complexity and cognition? What are the advantages of a large brain, and what are the costs? Comparing brains of ecologically and phylogenetically disperse species provides one way to derive and test hypotheses about how brains evolve. Here I discuss the assumptions made when total brain size is compared across species and highlight potential difficulties that limit such comparisons. Chief among these is evidence that total brain size masks a hidden diversity of mammalian brain structure and cellular composition.