Sexual Attractiveness in Male Rats

This arms race is essentially what drives great genetic variation because with little to no variation, parasites can adapt easily to its hosts’ genes. However, in order to avoid this, hosts must evolve just like the parasites do, and the individuals who do not adapt will fall victim to the parasites. This is called a coadaptation cycle. Hamilton and Zuk discovered that in many species of birds, increased showiness (plumage and song) led to increased resistance to parasites.

In the context of evolution, birds which are more resistant to parasites and are therefore more viable are able to demonstrate this viability via secondary sex traits such as showier plumage. Contrary to the 2015 Lopes study however, this study demonstrated that individuals that were more showy were also more viable as seen in their greater resistance to parasites. In the Lopes study, mice which became sick downregulated their testosterone and darcin levels, indicating a tradeoff between immune response and secondary sex traits.

In the Hamilton-Zuks study, however, it was discovered that instead of a tradeoff, the individuals which exhibited greater ornamental traits could afford to do so because of being overall more healthy. Discussion Through analyzing both the sexy sons hypothesis and the pathogen avoidance model, it is inconclusive whether one is more viable than the other as both have their justifications and their weaknesses. For the most part, both theories were backed up by numerous studies.

However, instances where certain sons should have been more viable indicated that the sons were in fact less healthy due to other influences such as paternal care and other environmental factors. Additionally, it should be noted that the nature of the secondary sex traits is still unknown. There is either a tradeoff between the ability to exhibit ornamental traits and the ability to remain healthy, or there is no tradeoff and instead, males who are showy are actually overall more healthy.

This difference distinguishes between risk vs reward in attracting mates and overall higher quality (survival of the fittest). The value of these traits in attracting mates is undisputed, but to what extent evolution has stressed species into balancing risk and reward is still unclear and is still open to research. Also, the discrepancy of many species who partake in monogamy and those which are polygamous is interesting because it shows that the same theory has many small details branching from it, requiring more specific analysis.

In conclusion, both of the theories are backed by strong evidence but what needs to be realized is that there are many factors not encompassed by the theories that have been discovered, with more to likely come.

Works Cited

Fisher, Ronald Aylmer. The Genetical Theory of Natural Selection. New York: Dover, 1958. Rosenberg, Alexander and Bouchard, Frederic, “Fitness”, The Stanford Encyclopedia of Philosophy (Fall 2015 Edition), Edward N. Zalta (ed. ), URL = <http://plato. stanford. edu/archives/fall2015/entries/fitness/>. Schacht, Ryan and Bell, Adrian. The Evolution of Monogamy in Response to Partner Scarcity.

Egan, Andrea L. , Kristin Hook A. , H. Reeve Kern, and Vikram Iyengar K. Polyandrous Females Provide Sons with More Competitive Sperm: Support for the Sexy-sperm Hypothesis in the Rattlebox Moth (Utetheisa Ornatrix). 2013 Nelson, A. C. , Colson, K. E. , Harmon, S. , & W. K. Potts. Rapid adaptation to mammalian sociality via sexually selected traits. BMC evolutionary biology. 13(1), 81. Kumar, Vineet, Anand Vasudevan, Linda Jing Ting Soh, Choo Le Min, Ajai Vyas, Maha Zewail-Foote, and Fay Guarraci A. Sexual Attractiveness in Male Rats Is Associated with Greater Concentration of Major Urinary Proteins.

A study performed in 2005 claims to have acquired results that do not support the sexy sons hypothesis like the 2013 Nelson study did. The study performed by Lars Gustafsson and Anna Qvarnstrom showed that collared flycatchers did not inherit …

Darwins’ theory of natural selection suggested that all species were motivated by ensuring their survival. From this idea, came the concept of ‘survival’ of the fittest, through which only ‘adaptive’ traits and/or characteristics would be ‘naturally selected’. Darwin came to …

As I have stated before, polygamy plays a very crucial role in the sexy sons hypothesis as females will optimally mate with several males if “better sperm” is found. Females must be selective with the males they mate with and …

Darwin noticed that there were certain features that he could not explain by Natural Selection  Such as differences in size, body form, colouration and behaviour between males and female of the same species – why are females often smaller and less …

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