Among all of the mammals, humans have an exceptionally big brain relative to their body size. The ASPM gene is proven to be an important genetic component in the evolutionary expansion of the human brain. Evidence has shown that the ASPM gene appears to have undergone positive selection a long time ago. It is really difficult to estimate when the ASPM gene could have undergone positive selection, but it has been estimated around the time the human brain had started to expand, which was between .2 million years ago and .4 million years ago. Recent studies have shown that the ASPM gene is not undergoing positive selection right now (Zhang).
An alternative explanation for positive selection on ASPM relates to its role in the proliferation of germ cells. It has been proposed by many scientists that the ASPM gene could be under sexual selection acting on sperm development or function. However, there is no association between ASPM and relative testis size across anthropoids. There is little evidence that shows that this type of selection is possible though. It is possible that the association between the evolutionary rate of loci with brain evolution, or the evolution of ...
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... Ganeshwaran H. Mochida, John I. Risinger, Paul Goldsmith, Michelle Gunsior, Greg Solomon, William Gersch, Jung-Hyun Kim, J. Carl Barrett, Christopher A. Walsh, Jerzy Jurka, Hiroshi Masumoto, and Vladimir Larionov. "The Microcephaly ASPM Gene Is Expressed in Proliferating Tissues and Encodes for a Mitotic Spindle Protein." 14.15 (2005): 2155-165. 22 June 2005. Web. 10 Feb. 2014.
Montgomery, Stephen H., and Nicholas I. Mundy. "EVOLUTION OF ASPM IS ASSOCIATED WITH BOTH INCREASES AND DECREASES IN BRAIN SIZE IN PRIMATES." 66.3 (2011): 927-32. 2012. Web. 18 Feb. 2014.
Wang, Yin-qiu, and Bing Su. "Molecular Evolution of Microcephalin, a Gene Determining Human Brain Size." 13.11 (2004): n. pag. 2004. Web. 10 Feb. 2014.
Zhang, Jianzhi. "Evolution of the Human ASPM Gene, a Major Determinant of Brain Size." (2003): n. pag. Genetics Society of America, 2008. Web. 10 Feb. 2014.
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