The Role of Sex

This essay aims to determine what the biological role of sex is in the natural world. As a result it is sensible to first define “sex”,

        “Sex n. either of two main groups (male and female) into which living things are placed according to their reproductive functions; fact of belonging to one of these; sexual feelings or impulses or intercourse.” (Oxford English dictionary, 1981).

        This definition suggest that two main areas should be discussed when writing an essay on this subject; why has evolution largely favoured species being separated into males and females, and secondly, why has evolution favoured sexual reproduction over asexual reproduction?

        Asexual reproduction accounts for the exponential growth of a species or colony. This can be easily demonstrated by spreading a culture of Streptococcus Pneumoniae on an agar plate with minimum medium (MM) then counting the resulting colonies twenty-four hours later. Sexual reproduction on the other hand is usually a slower process and requires a greater input of energy,...the small monkey flower (Mimuslus kelloggii), more than 20% of the energy from photosynthesis is used to make flowers (Moore et al, 1998), with fewer offspring than by asexual reproduction. Why, therefore is it that organisms, which reproduce by asexual means, have no completely over run sexually reproducing species in number?

        A theory known as “The Red Queen Hypothesis” is that sex is what evolution has come up with in order to combat the threat of parasitism. Sex forces the combination of the parental genotype to ensure a genetically unique offspring. This is in contrast to asexual reproduction, whose offspring’s are all clones of the original parent. Thus sexual reproduction enables a diverse gene pool to be established into each species such that in the event of any environmental change or parasitic attack on the species at least some of the offspring may survive due to greater diversity in the gene pool. For instance, if a lethal parasite invades a species of insect in a rain forest by attacking ATPase, some of the insects may have inherited a defence against this. This could be a slightly different enzyme composition and so at least some of the species would survive and pass on their genes.

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        “The fact that clonal offspring are genetically identical to their parents should make them highly susceptible to infection by coevolved pathogens. The Red Queen hypothesis predicts that clones are prevented from replacing sexual populations because infection by debilitating parasites erodes their intrinsic twofold reproductive advantage”  (www.sciencedirect.com, 2000)   

        This suggests that asexual reproduction is continually kept in check by the action of parasites, and than sexually reproducing individuals, although also susceptible to parasitic infections, are less susceptible as a species to parasites.

        One of the main proponents of the Red Queen hypothesis was Hamilton. In the late 1970s, with ...

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