The creation-mutation-selection model: simulation and the advantage of sex

The creation-mutation-selection model makes predictions regarding the fitness of asexual and sexual populations in an environment that includes both positive and negative selection. However, for the asexual case, the model predictions depend upon the variance or skewness of the population log fitness distribution, something which the model does not provide. This makes the analytical comparison of the fitness of asexual and sexual populations appear to be intractable. Instead, simulation is required. The fitness of asexual and sexual populations is simulated over a range of plausible parameter values. The fitness is found to agree with the predictions of the creation-mutation-selection model. The cost of asexuality is found to exceed the cost of sex by a very large margin for eukaryotic species today, and probably for the first eukaryotes. Prokaryotes and the mitochondrion are viewed as asexual species for which asexuality incurs little cost.