Not to give us a collective swelled head or anything, but the Homo sapiens brain is big. Really big.

For years, researchers have puzzled over why our noggin-embiggening occurred: Big brains are, after all, costly to feed. One leading theory held that our brains increased in size to manage the cognitive demands of ever-more complex communications and other social processes. New research suggests, however, that interactions with each other played only a small role compared with the big driv