One of my favourite places to go is our local farm which inhabits a dizzy array of animals such as the ordinary laying hens, cows, sheep and pigs; but it is also houses a pair of gorgeous blue peacocks. The peacock, with its vibrant plumage, is often seen strolling around the enclosure with its tail wide open. Evidently the elaborate eye-shaped patterns and elongated train (tail feathers) will not protect the peacock from being the tiger’s supper, then why does it spend so much of its energy growing such a futile thing? Many people think that the peacock’s plumage is for attracting a mate but surely in the world of natural selection beauty is too luxurious to be its sole purpose. Therefore, what is the real reason for having such an energetically expensive feature?
The tail of the male peacock is a great example of sexual selection. Female peafowl are attracted to male peacocks with the largest and most ornate train. The ability of male peacocks to create a large train is related to their overall fitness. Testosterone is the masculine hormone involved in developing a large plumage, impressive main and significant antlers in male animals but it has a drawback- it suppresses the animal’s immune system. This is also why in almost all species (including humans) males have a lower life expectancy than females and are more susceptible to diseases.
Therefore, the quality of a male’s ‘ornaments’ reflects truthfully on the quality of its genes, especially its resistance to prevailing infections. The peacock with the largest tail is effectively saying ‘I can afford to grow a colourful tail at the risk of being infected by worms, and yet I am still alive and thriving’. For the quality of his ornaments depends on the level of testosterone in his blood: the more testosterone he has, the more colourful, large, songful or aggressive he will be. If he can grow a great tail despite lowering his immune defences, yet not catch disease, he must be impressive genetically even if he is a bit of a show- off…
Written by Rebecca, Upper Fifth/Year 11
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