Asexual Reproduction

Asexual reproduction is the production of offspring from a single parent without the genetic contribution of a second individual. Common forms include binary fission, budding, fragmentation, and parthenogenesis — the development of an embryo from an unfertilized egg. Asexual reproduction is evolutionarily advantageous in stable environments because it preserves well-adapted genotypes intact and avoids the metabolic and ecological costs of finding mates.

But the advantage is short-term. The Muller's ratchet theorem predicts that asexual lineages will accumulate deleterious mutations irreversibly and eventually suffer mutational meltdown. This theoretical prediction is consistent with the rarity of long-lived asexual lineages in nature: most complex organisms reproduce sexually, and the celebrated exceptions — such as bdelloid rotifers — appear to have evolved elaborate alternative mechanisms for purging deleterious variation.