We could conceive Muller´s Ratchet, as the following: "An irreversible accumulation of DNA -harm- (in terms of mutations) due to the lack of recombination -genetic diversity-. So, we could say that lack of sexual reproduction, and a continuos style of clonal reproduction (that is, the same copy of the organism) with time accumulate harmful DNA changes. DNA changes (mutations) occur by chance, although their ocurrence is regulated by several mechanisms. But in asexual organisms, or when genetic diversity is low, it tends to accumulate a lot.