The Evolution of the Large, Complex Human Brain
The evolution of the human brain can be reconstructed by looking for shared features present in the brains of other mammals. Those features shared only with our closest surviving biological relatives likely were present in a more recent common ancestor, and those shared by even more distant relatives likely were retained from ever more distant common ancestors. We can also infer aspects of brain evolution from the endocasts of fossil skulls of extinct species. Using such information, we can infer that the brains of early mammals were of small relative body size, and the forebrain was dominated by olfactory cortex and little neocortex. Early primates had larger brains, but they were smaller relative to body size than those of present-day primates. While primate brains vary greatly in size and organization, a set of cortical areas characteristic of all primates, has been retained from early primate and earlier non-primate ancestors. Numbers of cortical areas appear to have increased in at least some anthropoid primates, and some cortical areas became more structurally more specialized. The fossil record indicates that brain size increased greatly in the branch of anthropoid evolution leading to modern humans, especially over the last two million years. The large human brain has more cortical areas, more structural specialization of cortical areas, and major hemispheric differences in cortical organization and function.
Readings:
Kaas, J.H. and Preuss, T.M. Human Brain Evolution. In: L.R. Squire (Ed.) Fundamental Neurosciences, 3rd edition, San Diego, Elsevier, 2008, pp. 1017-1035.
Kaas, J.H. Neocortex in early mammals and its subsequent variations. Ann. N.Y. Acad. Sci., 2011, 1255:28-36.
Due to file size limitations, the video recording of this talk is offered in two parts.