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Friday, July 08, 2011

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Genetic Material Itself Drove the Evolution of Sex

Julian O'Dea

The basic problem with previous theories to explain the evolution of sex is that they focus on the wrong levels of selection, namely at the individual or population level. I think it is more productive to focus on what about sex is advantageous for the genetic material itself, for example the chromosomes.

To follow up my previous post of 4 April 2011 on this issue, I want to broaden my argument a little. I have already published the basic idea and it has been cited in the Journal of Molecular Evolution. Further thought leads me to have confidence that I am on the right track. Sex evolved because it is to the advantage of the genetic material in a cell or organism to combine with that from a different cell. The reason is that this allows the genetic material to constantly find better environments by escaping from poor quality genetic material (e.g. damaged chromosomes, serious mutations).

To take a simple example, consider two cells with several diploid chromosomes. Assume each cell has one of its chromosomes in a pair with a serious defect. For most of the genetic material, it is easy to see that following sexual exchange of chromosomes between two such cells, there is a 25% chance that it will be found in a cell with both defects, a 50% chance of still being in a cell with one defect and a 25% chance of being in a cell with no defects. The last case is crucial. This new cell will have a major adaptive advantage. Putting it another way, its genetic material is likely to survive and thrive.

The advantage for normal genetic material in coding for sex, rather than asexual reproduction, is that it permits the genetic material to constantly escape from damaged and deleterious genes and chromosomes.

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