The cerebral cortex has long been recognized as the seat of thinking and consciousness in humans. Various regions of the cerebral cortex differ in different organisms. One region that has been identified as changing through evolution is the isocortex. Amphibians do not possess an isocortex, and the isocortex that reptiles have consists of three layers. Even among mammals, there are differences in the size of the isocortex.
Lower mammals have proportionally less isocortex than higher mammals.
While all mammals have certain brain structures in common, more volume of higher mammalian brains is devoted to sensory processing than their lower mammalian counterparts. It has been suggested that the unique properties of the isocortex in higher mammals are responsible for much of higher consciousness. This hypothesis is consistent with the idea that increased brain size correlates with an increased processing capability, which is apparent in higher mammals. While the isocortex is well-developed in species other than humans, considerable differences have been observed between the Great Apes and humans in a region of the brain known as the prefrontal cortex . It is thought that the developed structure of the prefrontal cortex in humans is what gives people the ability to understand the mental states of themselves and others.