Chimps and Humans can be traced biologically back to a common ancestor. The Cognitive Tradeoff Hypothesis theorizes about the two different paths of development - particularly cognitive development - that occurred in these two species after the split. Chimps stayed in the trees and developed some extraordinary cognitive capabilities which are shown by the research work of Japanese scientists at the Primate Research Center connected with Kyoto University - capabilities far surpassing that of normal humans - while humans, who came down into the savanna, developed social and language capabilities. The theory is that humans "traded" some aspects of cognitive development by re-purposing areas of the brain that had evolved in the context of other uses. A fascinating research project.
—Roger Coe