Kimura's Theory of Neutral Evolution


Kimura's theory of neutral evolution and the theory of evolution are both ways of explaining how evolution occurs. The theory of natural selection says that individuals which are not well suited for an environment are less likely to reproduce than those that are well adapted. This leads to a population becoming more adapted to the environment assuming that the traits being selected for are heritable. For example, if you have a population of mice where 50% of the mice are brown and the other 50% are white. The white mice are much easier for hawks to see which makes the brown mice better adapted to the environment. After one generation the ratio might change to 75% brown mice and 25% white mice and after two generations it might be 90% brown mice and 10% white mice. After several generations, the population will either become 100% brown mice or closer to 95-99% brown mice depending on if brown fur color is a dominant or recessive trait. 

Kimura's theory of neutral evolution says that genetic variation doesn't necessarily impact an individual's fitness. If you have multiple alleles that code for one gene it doesn't matter if you have allele A or allele B because both lead to the same result and fitness. For example, if you are looking at a population of mice that has three alleles that code for fur color. The alleles abc code for a white mouse, ABC codes for a black mouse, Abc, aBc and abC all code for a light brown mouse and ABc, AbC and aBC all code for a dark brown mouse. There is still some natural selection occurring in this population because hawks are able to see the white and black mice more easily than the light and dark brown mice. However, neutral selection is occurring with the alleles because with the exception of abc and ABC all other allele combinations result in the same fitness. Unlike in natural selection, there will always be both white and black mice in the population and the ratio of white: light brown: dark brown: black mice will always stay relatively constant. 


Image credit: https://www.quantamagazine.org/neutral-theory-of-evolution-challenged-by-evidence-for-dna-selection-20181108/ 

Resources: https://evolution.berkeley.edu/evolibrary/article/0_0_0/misconcep_08 

Comments

  1. Hunter HiegertMarch 19, 2021 at 11:30 AM

    Awesome post Maddy! I enjoyed how although we have been studying the theory of evolution based on natural selection for awhile, you included details and even examples to clearly reflect how knowledgable you are on the subject! In addition to this you provided a well explicated description of Kimura's theory and even included examples again which I found both interesting and helpful.

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  2. Amy SchaulisMarch 19, 2021 at 9:30 PM

    You did a really good job on this blog post! I have heard about the example of the field mice and think it is really interesting that over time, their population eventually became mostly brown in color due to their predator being able to easily spot them. You also did a great job of tying both the Kimura's theory and the theory of natural selection into relating to one example yet clearly defining each one. Great job!

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