Saturday, May 19, 2012

Sexual Selection: Birds of Paradise

Red Bird of Paradise (Paradisaea rubra)    © Tim Lama
Sexual Selection: 
Birds of Paradise 
Sarah Danser - Secular Students and Skeptics Society
Most birds of paradise are found in New Guinea, where each species has evolved to be uniqueThe males have bright, colorful plumage which they use to perform intricate mating displays

We're all familiar with the process of natural selection: only the most fit (strongest, best- adapted)  individuals will survive to reproduce. Those who are well adapted to the environment will survive. Because advantageous qualities are passed from parent to offspring, the species will evolve over time to best adapt to its environment.

Sexual selection is another evolutionary force which can lead species, such as birds of paradise, to evolve. Sexual selection functions in the same way as natural selection, in that only the most fit individuals will reproduce and pass on their genes. Unlike natural selection however, in which the environment determines fitness, sexual selection is in the hands (paws, claws, talons) of the species itself.

Male birds of paradise have evolved to be extravagant as a means of passing on their genes. Female birds of paradise, which are usually brown and do not display their feathers, choose males with the most impressive, most colorful, largest, or loudest displays (the handicap principle explains this preference). As an example, peacocks have very large, long tail feathers which are used for sexual display. Females selectively mate with the males with the longest tail feathers. Because of this, the next generation of peacocks will have longer feathers, on average, than did the previous generation. This process can lead, as you might expect, to the evolution of some very intricate physical features. 

Sexual selection is easily observed in many bird species, but is also observable in other animals including insects, reptiles, and even mammals. Many evolutionary biologists argue that the human species is in the process of evolution by sexual selection. From an evolutionary perspective, many human behaviors and cultural traits can be explained through sexual selection.

Conveniently, there in an easy example of human sexual selection which also takes place in Papua New Guinea, where both birds of paradise and humans use feathers to attract females. Tribesmen hunt birds and collect their feathers for headdresses which are worn to impress the women. Men with big, fancy feathers will attract the most (or the best) women.

Of course, most cultures do not exhibit this behavior and instead offer different sexually-advantageous traits, some genetic, others behavioral. People choose partners which they deem to be most fit in the given time and environment (culture). Fitness in humans may be indicated by social status, wealth, body type, etc. It has even been argued that the evolution of intelligence is more directly a result of sexual selection than natural selection: intelligent individuals were reproductively favored, and thus passed on the genetic quality of intelligence.

While of course this is only theory, it's a lot of fun to think about! Here's a question: In most species, the sexual selectors are female. Is this true for humans? Why/why not?
   - - - Sarah Danser; Sat May 19, 2012

What's with this guy?? He looks like a mushroom!

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