How Motoo Kimura's Neutral theory challenges NeoDarwinism


The neutral theory of molecular evolution, proposed by Motoo Kimura in 1968, is a theory that explains the evolution of molecular variation at the population level by random genetic drift rather than by natural selection. Kimura argued that most mutations are neutral, meaning that they do not affect the fitness of the organism, and that the fate of these mutations is determined by chance.

The neutral theory is based on the following assumptions:

  • Mutations are random and occur at a constant rate.

  • Most mutations are neutral, meaning that they do not affect the fitness of the organism.

  • The effective population size is finite.

  • Genetic drift is the primary force driving the evolution of neutral mutations.

Under these assumptions, Kimura showed that neutral mutations can become fixed in a population by random chance. This is because in a finite population, some alleles will be lost by chance, regardless of their fitness. Over time, this process can lead to significant changes in the molecular composition of a population.

The neutral theory has been controversial since its inception, but it has been supported by a growing body of evidence. For example, studies have shown that the rate of molecular evolution is relatively constant across different lineages, and that the vast majority of genetic variation within species is neutral.

The neutral theory has important implications for our understanding of evolution. It suggests that much of the molecular diversity that we see in the world today is the result of chance, rather than natural selection. This suggests that natural selection is not the only force driving molecular evolution.

The neutral theory has also had a significant impact on the field of molecular biology. It has provided a framework for understanding the evolution of genetic variation, and it has helped to develop new methods for estimating population parameters and reconstructing phylogenetic relationships.

The neutral theory of molecular evolution is a powerful and influential theory that has helped to revolutionize our understanding of evolution.

The neutral theory of molecular evolution, proposed by Motoo Kimura in 1968, challenges Neo-Darwinism in a number of ways. Here are 10 examples:

  1. The neutral theory posits that most genetic variation is selectively neutral, meaning that it does not confer any advantage or disadvantage in terms of survival or reproduction. This is in contrast to Neo-Darwinism, which holds that most genetic variation is subject to natural selection.

  2. The neutral theory predicts that the rate of molecular evolution should be relatively constant across different lineages. This is because selectively neutral mutations will accumulate at a constant rate, regardless of the environmental conditions. Neo-Darwinism, on the other hand, predicts that the rate of molecular evolution should vary depending on the strength of natural selection.

  3. The neutral theory explains the observation that most mutations are harmful or deleterious. This is because selectively neutral mutations are essentially random, and many random changes to a complex system are likely to be harmful. Neo-Darwinism, on the other hand, struggles to explain why so many mutations are harmful, given that natural selection should favor beneficial mutations.

  4. The neutral theory explains the high level of genetic diversity within species. This is because selectively neutral mutations will accumulate over time, adding to the overall genetic diversity of a population. Neo-Darwinism, on the other hand, has difficulty explaining how so much genetic diversity can be maintained, given that natural selection should tend to eliminate unfavorable alleles.

  5. The neutral theory provides a plausible explanation for the rapid evolution of some traits. This is because selectively neutral mutations can accumulate quickly in small populations, where genetic drift can play a major role. Neo-Darwinism, on the other hand, has difficulty explaining how rapid evolution can occur, given that natural selection is typically a slow process.

  6. The neutral theory is consistent with the fossil record, which shows that most species change very little over long periods of time. This is because selectively neutral mutations are unlikely to cause major changes in morphology. Neo-Darwinism, on the other hand, has difficulty explaining the long periods of stasis in the fossil record, given that natural selection should be constantly driving change.

  7. The neutral theory is supported by a wide range of molecular data. For example, studies of the human genome have shown that most genetic variation is selectively neutral. Neo-Darwinism, on the other hand, has difficulty explaining some of the molecular data, such as the observation that many genes have multiple copies.

  8. The neutral theory has led to a number of new insights into the evolution of complex traits. For example, the neutral theory has helped to explain how complex traits can evolve even if they are composed of many different genes. Neo-Darwinism, on the other hand, has difficulty explaining the evolution of complex traits, given the many constraints that must be overcome.

  9. The neutral theory has provided a new perspective on the role of natural selection in evolution. The neutral theory suggests that natural selection is not the only force driving evolution, and that chance events can also play a major role. Neo-Darwinism, on the other hand, has traditionally placed a much greater emphasis on the role of natural selection.

  10. The neutral theory has led to a new understanding of the relationship between evolution and development. The neutral theory suggests that many developmental changes are driven by selectively neutral mutations. Neo-Darwinism, on the other hand, has traditionally viewed development as being relatively independent of evolution.

It is important to note that the neutral theory does not challenge all aspects of Neo-Darwinism. For example, the neutral theory does not dispute the importance of natural selection in the evolution of major adaptations. However, the neutral theory does challenge the traditional Neo-Darwinian view that natural selection is the primary driving force of all evolutionary change.

In recent years, there has been a growing acceptance of the neutral theory. Many evolutionists now accept that both natural selection and genetic drift play important roles in evolution. However, the neutral theory has had a major impact on our understanding of evolution, and it continues to be a subject of active research.

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