![]() In eukaryotes, true sexual reproduction by meiosis and cell fusion is thought to have arisen in the last eukaryotic common ancestor, possibly via several processes of varying success, and then to have persisted. The evolution of sex contains two related yet distinct themes: its origin and its maintenance.Īlthough Bacteria and Archaea (prokaryotes) have processes that can transfer DNA from one cell to another ( conjugation, transformation, and transduction ), these processes are not evolutionarily related to sexual reproduction in Eukaryotes. Sexual reproduction is widespread in the Eukarya, though a few eukaryotic species have secondarily lost the ability to reproduce sexually, such as Bdelloidea, and some plants and animals routinely reproduce asexually (by apomixis and parthenogenesis) without entirely having lost sex. Diversification into the phylogenetic tree happens much more rapidly via sexual reproduction than it does by way of asexual reproduction.Įvolution of sexual reproduction describes how sexually reproducing animals, plants, fungi and protists could have evolved from a common ancestor that was a single-celled eukaryotic species. Sex, however, has evolved as the most prolific means of species branching into the tree of life. Sex also halves the amount of offspring a given population is able to produce. And if the environment has not changed, then there may be little reason for variation, as the organism may already be well adapted. In reproducing asexually, no time nor energy needs to be expended in choosing a mate. Additional theories concerning the adaptive advantage of sex are also discussed below. Another prominent theory, also discussed below, is that a primary advantage of outcrossing sex is the masking of the expression of deleterious mutations. ![]() As discussed below, one prominent theory is that sex evolved as an efficient mechanism for producing variation, and this had the advantage of enabling organisms to adapt to changing environments. Currently the adaptive advantage of sexual reproduction is widely regarded as a major unsolved problem in biology. Sexual reproduction is an adaptive feature which is common to almost all multicellular organisms and various unicellular organisms, with some organisms being incapable of asexual reproduction. Pollen production is an essential step in sexual reproduction of seed plants. ![]()
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