XIII.3 There are four basic types of hypotheses explaining the emergence and persistence of sexual reproduction
While the disadvantages of sexual reproduction are mostly quite obvious, this is not as unambiguously true of its advantages.Simultaneously, the fact that, for a great many species and entire large taxa, such as birds and animals, it is the only means of reproduction, indicates that it should be an evolutionarily extremely advantageous process.The fact that asexually reproducing mutants do not gradually predominate in populations of sexually reproducing species also indicates that this is also an evolutionarily stable strategy (ESS) and that, in a population of sexually reproducing individuals, an asexually reproducing mutant is apparently in some way “penalized”, placed at an evolutionary disadvantage.
At the present time, a number of hypotheses attempt to explain the emergence and persistence of sexual reproduction.The first group of hypotheses assumes that sexual reproduction increases the evolutionary potential of the particular biological species.The second group of hypotheses assumes that sexual reproduction brings an advantage to its carrier, i.e. increases its direct fitness or inclusive fitness.The third group of hypotheses corresponds to a model that assumes that sexual reproduction can be maintained by the mechanism of an evolutionary trap and does not bring its carriers any advantage, while the fourth group assumes that sexual reproduction could have been forced on organisms from outside, and provides an advantage to other subjects of biological evolution at their expense.
A definite answer to the question of why and how sexual reproduction emerged is not yet available.We do not even know the answer to the question of why sexual reproduction persists in most species of eukaryotic organisms and why asexually reproducing mutants do not gradually predominate in the population.However, a number of hypotheses provide more or less probable answers to one or the other question.Nonetheless, because the individual hypotheses are not in any way mutually exclusive, it can be assumed that the proposed mechanisms could have been important jointly to varying degrees during evolution or could replace one another in the various taxa.