The human brain: Evolution and distinctive features
he human brain enlarged enormously in evolution, especially after our genus, Homo, diverged from the australopithecines. With the development of noninvasive neuroimaging and molecular biological techniques we can for the first time compare the internal organization of human brains to those of other primates, including our closest relatives, the chimpanzees. These studies reveal that most of the enlargement of the human brain was due to the expansion of the association cortex, the critical substrate for higher-order cognition. Association cortex enlargement was accompanied by extensive modification of the connections linking cortical areas into functional networks, as shown in investigations of the language and tool-manipulation systems. Surprisingly, there is no clear evidence to support the popular view that the human brain contains a large number of new cortical areas. Perhaps even more surprising is the evidence that humans possess extensive specializations at finer levels of brain organization, including cell morphology, biochemistry, and physiology.
