Brain Evolution
Brain evolution is concerned about the gradual development of brain size and structure. According to Purves et al (2011), during the span of human evolution which is roughly 3.5 million years, the size of the brain has increased from a volume of 450 cubic centimeters in Australopithecines, to about 1350 cubic centimeters in modern Homo sapiens and 1500 cubic centimeters in Homo neanderthalensis. This increase in brain size is attributed to the positive allometric growth of the cortex. This growth of the human brain has been attributed to genitive mechanisms. In the mammalian cortex, neurons are produced at two stages and modes of cell division. First, the progenitor cells are formed in a narrow zone around the telencephalic ventricle. Through symmetric cell division, there is exponential growth of the ventricular zone.
Often, the study of the evolution of the brain of a human being is done by comparing it with living nonhuman primates. Human tend to have big brains in comparison to their body size. According to Purves et al (2011), the average adult brain of a human being measures about 1350 cubic centimeters and contains roughly 20 billion neocortical neurons. As such, human brains are the biggest of any primate, and weigh roughly 3 times more than a chimpanzee’s brain. Therefore, brain evolution is based on the variability of the brain size, and depends on two parameters which include the body size and ecological factors. Purves et al (2011) observe that body size and ecological factors have varying effects on the structure of the brain. While traditional views on brain evolution suggest that a larger brain size means better capacity of processing, current perspectives on brain evolution suggest that ecological factors lead to an increase in the number of cells in certain regions of the brain. This leads to neural reorganization, which in turn increases the specificity of connections, thus increasing brain capacity.
References
Purves, D., Augustine, G.J., Fitzpatrick, D., Hall, W.C., Lamantia, A.S. & White, L.E. (2011) Neuroscience. Massachusetts: Sinauer Associates, Inc.
