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Evolutionary biologist Jianzhi Zhang Photo Credit: Courtesy of University of Michigan |
For a long time, evolutionary biologists have thought that the genetic mutations that drive the evolution of genes and proteins are largely neutral: they’re neither good nor bad, but just ordinary enough to slip through the notice of selection.
Now, a University of Michigan study has flipped that theory on its head.
In the process of evolution, mutations occur which can then become fixed, meaning that every individual in the population carries that mutation. A longstanding theory, called the Neutral Theory of Molecular Evolution, posits that most genetic mutations that are fixed are neutral. Bad mutations will be quickly discarded by selection, according to the theory, which also assumes that good mutations are so rare that most fixations will be neutral, says evolutionary biologist Jianzhi Zhang.
The U-M study, led by Zhang, aimed to examine whether this was true. The researchers found that so many good mutations occurred that the Neutral Theory cannot hold. At the same time, they found that the rate of fixations is too low for the large number of beneficial mutations that Zhang’s team observed.
To resolve this, the researchers suggest that mutations that are beneficial in one environment may become harmful in another environment. These beneficial mutations may not become fixed because of frequent environmental changes. The study, supported by the U.S. National Institutes of Health, was published in Nature Ecology and Evolution.