Driving forces of Evolution

Depending on the relative importance assigned to the various forces of evolution, three perspectives provide evolutionary explanations for molecular evolution. Selectionist hypotheses argue that selection is the driving force of molecular evolution. Neutralist hypotheses emphasize the importance of mutation, purifying selection, and random genetic drift. Mutationists hypotheses emphasize random drift and biases in mutation patterns.

 

Selectionist hypotheses argue that selection is the driving force of molecular evolution. While acknowledging that many mutations are neutral, selectionists attribute changes in the frequencies of neutral alleles to linkage disequilibrium with other loci that are under selection, rather than to random genetic drift. Biases in codon usage are usually explained with reference to the ability of even weak selection to shape molecular evolution.

Neutralist hypotheses emphasize the importance of mutation, purifying selection, and random genetic drift. The introduction of the neutral theory by Kimura, quickly followed by King and Jukes' own findings, led to a fierce debate about the relevance of neo darwinism at the molecular level. The Neutral theory of molecular evolution proposes that most mutations in DNA are at locations not important to function or fitness. These neutral changes drift towards fixation within a population. Positive changes will be very rare, and so will not greatly contribute to DNA polymorphisms. Deleterious mutations will also not contribute very much to DNA diversity because they negatively affect fitness and so will not stay in the gene pool for long. This theory provides a framework for the molecular clock. The fate of neutral mutations are governed by genetic drift, and contribute to both nucleotide polymorphism and fixed differences between species.

In the strictest sense, the neutral theory is not accurate. Subtle changes in DNA very often have effects, but sometimes these effects are too small for natural selection to act on. Even synonymous mutations are not necessarily neutral because there is not a uniform amount of each codon. The nearly neutral theory expanded the neutralist perspective, suggesting that several mutations are nearly neutral, which means both random drift and natural selection is relevant to their dynamics. The main difference between the the neutral theory and nearly neutral theory is that the latter focuses on weak selection, not strictly neutral.

Mutationists hypotheses emphasize random drift and biases in mutation patterns. Sueoka was the first to propose a modern mutationist view. He proposed that the variation in GC content was not the result of positive selection, but a consequence of the GC mutational pressure. 

Related Conferences:

International Society for Evolution, Medicine & Public Health, North Carolina, USA- Population, Evolutionary & Quantitavie Genetics Meeting, FL, USA- IEEE World Congress on Computational Intelligence (IEEE WCCI 2016), Vancouver, Canada- Genetic and Evolutionary Computation Conference (GECCO 2016), Denver, USA- IEEE International Conference on Computational Intelligence in Bioinformatics and Computational Biology (CIBCB 2016), Chiang Mai, Thailand, Genetic & Evolutionary Computation Conference, CL, USA- EVOLANG-2016, The University of Southern Mississippi Gul Coast, New Orleans, USA- 2016 Ciliate Molecular Biology Conference, FL, USA- Population Genetic Group, Edinburgh, Scotland- New Model Systems for Linking Evolution and Ecology, Heidelberg, Germany.

  • Selectionist hypotheses
  • Neutralist hypotheses
  • Mutationists hypotheses

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