7. Kimura's Theory of Neutral evolution vs Natural Selection

 A theory first put forward by M. Kimura in 1969, called Neutral theory, provided a conceptual framework for developing methods that detect the action of selection within a species genome. This method proposed at a molecular level, most evolutionary changes within a species are not caused by natural selection. Instead, it happens with random genetic drift, mutation, and is not selected for. This means that everything is random, and these drifts and mutations that are introduced will be randomly fixed as well. “For example, one strong prediction of the neutral theory is that at selectively neutral sites, the rate of substitution is equal to the rate of mutation,” (Duret, 2008). After researching more about Kimura’s theory, he “compares the amino acid sequence of hemoglobin a and cytochrome c in several mammalian species and found that the number of mutant substitutions was too large to be tolerable within Haldane’s theory of natural selection if the substitution number was extrapolated to the total genome” (Ohta, 2013). Deviations from neutral assumptions in genes associated with diet, climate, and infectious diseases. In class, our professor gave examples of positive selection on lactose genes associated with domesticated cattle. As for the theory of evolution by natural selection, first formulated by Darwin in 1859, is a process in which organisms change over time in order to increase fitness level and change in physical or behavioral ways. Much variation in DNA is hardly affected by selection at all. Mutations escape selection if they are not affecting the phenotype. Some of those mutations could be non-synonymous and synonymous, that are not really a subject to selection but rather a subject to the forces of genetic drift. Neutral mutations become fixed in populations at a roughly regular rate all due to genetic drift. This is the idea that most portions of our DNA are randomly getting fixed over time due to genetic drift. If that is true, the genetic drift between two species should be correlated from the last splitting ancestor.These two theories are very different, but both assume there and beneficial and deleterious mutations that affect a species. 

 

 

Ohta, T., et al., Neutral Theory. Science Direct. www.sciencedirect.com .2013

 

Duret, L. (2008) Neutral theory: The null hypothesis of molecular evolution. Nature Education 1(1):218