Brains advance by increasing the number of representations of sensory surfaces.
Mammals with small brains and little neocortex have only a few sensory and motor areas, which occupy most of the neocortex. Mammals with large brains and expanded neocortices have both the basic sensory and motor representations inherited from a common ancestor and a number of additional, basically unimodal sensory areas. In this view of the monkey brain, part of the temporal lobe has been removed to show structures underneath. The yellow area represents other parts of the cortex that are also associated with vision. Area V3 is not visible, since it is hidden by a fold in the cortex.