Read/View the following two links:

(1) Neo-Cortex:  The enlargement and species-specific elaboration of the cerebral neocortex during evolution holds the secret of humans’ mental abilities.  The neocortex, as the name implies, is the newest addition to our brain and is considered to be the crowning achievement of evolution and the biological substrate of human mental prowess.  (Taken from "Evolution of the neocortex: Perspective from developmental biology,"  by Pasko Rakic)