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the benefits of two separate sexes compared to hermaphrodites rather than to explain benefits of sexual forms (hermaphrodite dioecious) over asexual ones.
It has already been understood that since sexual reproduction is not associated with any clear reproductive advantages, as compared with asexual, there should be some important advantages in evolution.
There are a few species which have secondarily lost the ability to reproduce sexually, such as Bdelloidea, and some plants and animals that routinely reproduce asexually (by apomixis and parthenogenesis) without entirely losing sex.
The evolution of sex contains two related, yet distinct, themes: its origin and its maintenance.
For the advantage due to genetic variation, there are three possible reasons this might happen.
First, sexual reproduction can combine the effects of two beneficial mutations in the same individual (i.e. Also, the necessary mutations do not have to have occurred one after another in a single line of descendants.
Sexual reproduction must offer significant fitness advantages to a species because despite the two-fold cost of sex, it dominates among multicellular forms of life, implying that the fitness of offspring produced outweighs the costs.
Sexual reproduction derives from recombination, where parent genotypes are reorganized and shared with the offspring.
The concept of sex includes two fundamental phenomena: the sexual process (fusion of genetic information of two individuals) and sexual differentiation (separation of this information into two parts).
There are numerous species which are sexual but do not have a genetic-loss problem because they do not produce males or females.
Yeast, for example, are isogamous sexual organisms which have two mating types which fuse and recombine their haploid genomes.
Thus, in this formulation, the principal costs of sex is that males and females must successfully copulate (which almost always involves expending energy to come together through time and space).
Sexually reproducing organism only pass on ~50% of its own genetic material to each L2 offspring.