Asexual reproduction evolution

As a search technique, using mutation and selection alone has several limitations. Evolution via asexual reproduction tends to build up deleterious mutations, ultimately limiting the potential of the experiment, an effect known as Muller s ratchet (Muller, 1964). This effect is exacerbated by high mutagenesis rates, as slightly deleterious amino acid substitutions can hitchhike with positive mutations. Recombination can act to remove neutral and deleterious mutations while allowing the accumulation of... 

Many evolutionary biologists believe that parasitism has had an important influence on the evolution of species. In a 2009 study of a species of snail from New Zealand, researchers found that in populations with high levels of parasites, the snails will switch from asexual reproduction (producing clones) to sexual reproduction, which produces genetically diverse offspring that are more resistant to infection. This discovery led the researchers to speculate that parasites may have been instrumental in the evolution of sexual reproduction. 

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