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pmid: 22009640
Thirty years after Margulis [1] proposed her theory on endosymbiosis and almost a century since Fisher’s work [2] laid the ground for the modern theory of evolution, the question surrounding the evolutionary benefit of sex is still sparking great interest [3]. Several theories have been proposed to explain the maintenance of different reproductive strategies, be it sexual or one of the different forms of asexual reproduction. However, the different challenges and costs of the former still constitute a puzzling evolutionary issue to this day [4]. In an ever changing environment, one always argues that sexual reproduction generates beneficial diversity through allelic recombination, whereas reproduction of parthenogenetic species only leads to similar genomes being spread among descendants. From a purely cost-benefit and numerical perspective however, the exponential growth of an asexual population greatly outcompetes any sexual strategy. So clearly, the question remains: should sex be considered a solution for reproduction? Most proponents of Fisher [2] would answer yes but Lode [5] is tempted to say no. In his recent essay, the author proposed an alternative theory to explain the existence of sex. To do so, Lode uncoupled the concepts of sex and reproduction whereby the former is defined as a genetic exchange between two organisms through meiosis. In fact, Lode suggests that sex originated from an archaic gene transfer process among prebiotic bubbles. Considering important and primitive conditions such as the spontaneous formation of these prebiotic bubbles, the promiscuity of such bubbles allowing for the transfer of genetic material and the initiation of meiotic recombination, the author proposes the exploration of a new theory for the origin of sex, the libertine bubble theory [5]. Taken out of the context of reproduction, this gene transfer could be simply regarded as a trophic exchange [6] leading to the beneficial integration of DNA fragments which would then be selected or discarded due to genetic drift. The runaway process of sexual evolution, in which increased efficiency of genetic exchange provides adaptive advantages to sexual species, in turn selecting for more sexual exchange, is conventionally part of evolutionary textbooks and the core of the sexual evolution literature. Departing from the classical view that the advantages of sex in promoting variation are the main reasons for its maintenance, Lode’s hypothesis for the origin of sex presents some interest. First, it remains parsimonious only requiring an asymmetrical exchange of genes between hungry prebiotic bubbles. Second, the conceptual separation of sex and reproduction allows for a new research framework whereby cell, developmental and molecular biologists could shed new light on the origins of sexual mechanisms. However, while both the origin of sex and its maintenance are part of this essay, they would benefit from being dealt with separately. In fact, if the libertine bubble theory is ever proven true, it will not answer all the questions for the dual maintenance of sexuality and asexuality nor the combination of both strategies in organisms such as aphids [7]. Ultimately, the investigation of simple gene transfer mechanisms that may have provided circumstances permissive for the evolution of the highly complex and constrained sexual pathways will be a first step towards the advancement of the libertine bubble theory. Alternatively, phylogenetic studies of ancestral groups which diversified both in their asexual and sexual lineages (e.g. rotifers [8]) might help to disentanglewho came first andwhy theymaintain through evolutionary times.
Reproduction, Animals, Humans, Sex, Biological Evolution
Reproduction, Animals, Humans, Sex, Biological Evolution
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