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The Role of Sex

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Introduction

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? ...read more.

Middle

The least resistant hosts and the least virulent parasites were killed in each generation. Now the asexual population no longer had an automatic advantage. It was predominant most often if there were lots of genes that determined resistance and virulence in each creature. In the model, as resistance genes that worked would become more common, then so too would the virulence genes. Then those resistance genes would grow rare again, followed by the virulence genes. As Hamilton (1978) put it, "antiparasite adaptations are in constant obsolescence." But in contrast to asexual species, the sexual species retain unfavored genes for future use. "The essence of sex in our theory, is that it stores genes that are currently bad but have promise for reuse. It continually tries them in combination, waiting for the time when the focus of disadvantage has moved elsewhere." (Hamilton, 1978) Another theory suggests, "The mutation accumulation hypothesis predicts that sex functions to reduce the population mutational load" (Evolution: Vol. 52, No. 2, pp. 604-610.) According to this idea, sexual lineages persist because they are more efficient than asexual's at clearing their genomes of mutations. With the onset of time, asexual lineages are expected to be eliminated due to the build up of a large mutation load. Potentially, this idea is sound but would require there to be extensive mutation of the order of one per genome, and the mutations would have to affect fitness in a very specific way. ...read more.

Conclusion

This tends to give rise to the more traditional male/female sex roles." (http://www.pbs.org/wgbh/evolution/library/01/6/quicktime/l_016_04.html) This suggests that the role of the male/female system is to allow the female to choose a mate. The idea is that the males will all compete for the females, and so the female has the best opportunity to choose a suitable mate, i.e., the fittest male. In many animal species there are strict sexual rituals that the males must go through to be able to pass its genes onto the next generation, by impressing the female. In some species this involves a fight between the males whereby the strongest will mate with the female. This is so the female will combine with genes from the male who is bigger, stronger and faster. In other species, the ritual may involve elaborate displays, such as the giant peacock, which displays its wings to the female. All in all these rituals serve to maintain a strong gene pool in a population, which can only be maintained by there being two sexes. Overall, the favour of evolution towards sexual reproduction and the sexes that make it possible, seems to give the species a greater chance of survival by maintaining a rich and diverse gene pool. The evolutionary pressure and species interactions that are forced onto species have resulted in these processes, in each species drive to remain alive and abundant. ...read more.

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