There are lots of discussions about the maintenance of sex. Seeing many species get along perfectly well without males, why is sex still important? Unless something stops them, asexual species can grow exponentially – one, two, four, eight, sixteen …They can produce clones of themselves and some of them can have over 1 million descendants after only a few days. So, why does sexually reproducing still necessary?
The picture above shows the different between sexual and asexual reproduction. This is the main reason why sexual reproduction is important for evolution. Theoretical evolutionary research has put forward more than 25 hypotheses in the 1970s and 1980s to explain the advantages of sexual reproduction in evolution. The hypotheses can mainly be divided into two groups, both of them point out that sexual reproduction reduces the risk of extinction.
First, sex provides novel genetic variation in offspring by reshuffling genes during recombination and meiosis. Thus, it will provide opportunities for novel fast adaptations. Only sexual reproduction can reshuffle genes because the offspring will mix the feature of both parents, asexual reproduction will have offspring identical to parent. Also, sex removes negative deleterious mutations through meiosis and recombination.
Overall, although sex appears costly, it will do well to offspring for most species. Rather than asking why we need sexual reproduction, we may want to ask how those asexual species exist during the evolution.