Neutral theory of molecular evolution

The neutral theory of molecular evolution (also, simply the neutral theory of evolution) is an influential theory that was introduced with provocative effect by Motoo Kimura in the late 1960s and early 1970s. Although the theory was received by some as an argument against Darwin's theory of evolution by natural selection, Kimura and most evolutionary biologists today maintain that the two theories are compatible. The theory attributes a large role to genetic drift.

The "neutralist-selectionist" debate

A heated debate arose on the initial publication of Kimura's theory, in which discussion largely revolved around the relative percentages of alleles that are "neutral" versus "non-neutral" in any given genome. Contrary to the perception of many onlookers, the debate was not about whether or not natural selection acts at all.

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After flirting with the idea that slightly deleterious mutations might be quite common (Ohta, 1973), Tomoko Ohta, Kimura's student, made an important generalisation of the neutral theory by including the concept of "near-neutrality" (Ohta, 1992, 2002), that is, genes that are affected mostly by drift or mostly by selection depending on the effective size of a breeding population. The neutralist-selectionist quarrel has since cooled, yet the question of the relative percentages of neutral and non-neutral alleles remains. Graur & Li (2000), go as far as to say; "There are only two predictions we are willing to make about the future of molecular evolution. The first concerns old controversies. Issues such as the neutralist-selectionist controversy or the antiquity of introns, will continue to be debated with varying degrees of ferocity, and roars of "The Neutral Theory Is Dead" and "Long Live the Neutral Theory" will continue to reverberate, sometimes in the title of a single article."

Related Topics:
Tomoko Ohta - Kimura

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As of the early 2000s, the neutral theory is widely used as a "null model" for so-called null hypothesis testing. Researchers typically apply such a test when they aready have an estimate of the amount of time that has passed since two species or lineages diverged--for example, from radiocarbon dating at fossil excavation sites, or from historical records in the case of human families. The test compares the actual number of differences between two sequences and the number that the neutral theory predicts given the independently estimated divergence time. If the actual number of differences is much less than the prediction, the null hypothesis has failed, and researchers may reasonably assume that selection has acted on the sequences in question. Thus such tests contribute to the ongoing investigation into the extent to which molecular evolution is neutral.

Related Topics:
2000s - Null hypothesis - Radiocarbon dating - Fossil - Selection

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