Sunday, March 14, 2010
To be vestigial, or not to be vestigial. That is the question.
Throughout the first chapter in the book, Jerry Coyne explains the premise behind vestigial organs: that is, organs that are no longer of use to animals and are just evolutionary leftovers which have not been completely phased out of the body plan. The most prominent of such examples would obviously be the human appendix, which, simply, is thought to do nothing in the human colon. However, when reading an article on Wikipedia about the "Vermiform Appendix," it becomes clear that the appendix may actually serve a useful function. That function, at the risk of sounding gross, is thought to be the "safehouse" for healthy bacteria which help clean the colon after an episode of diarrhea. This begs the question, are all vestigial organs really useless in their current forms? Do they possibly serve some use that is insignificant yet still there? Also, when in the many phases of evolution would one finally call an organ vestigial? That is, when is something finally considered useless?
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It is difficult to determine when an organ can be definitely classified as vestigial. Humans are such a tiny part of evolutionary history that it becomes quite impossible to find the line between useful and vestigial. For example, the Cassowary (a flightless bird) has large wings. While it seems obvious that the wings are vestigial, for they serve no function in flying, scientists suggest that they may infact be used for balance while running and during courtship. Therefore, these wings, similar to the appendix, in my opinion cannot be considered vestigial because they are still attributed to having minor functions. However, if in the future these organs continue to shrink, then maybe they do not serve the function that scientists are speculating, and then they can be considered vestigial. Other animals, such as the whale, present organs that scientists have difficulty coming up with the smallest use for. For example, some whales today are seen to have a rudimentary pelvis and hind legs. While they cannot find a definite use for these organs, they have used these organs to attribute the whale to its ancestor the hippopotamus. According to the scientists who are responsible for this discovery: "...the hind limbs had become too small for locomotion but had joints and other signs that suggest they were still useful appendages. Perhaps, the scientists suggested, the limbs were used during copulation." As time goes on and whales continue to adapt, the whales with the hind legs and pelvis may begin to diminish. This is because it takes more time and energy during development to have these useless limbs. For this reason, it is possible that in the future, whales that lack these limbs will be naturally selected.if this does infact occur, then it is most likely that the limbs do not serve the purpose that the scientists are suggesting but rather that they are simply vestigial organs. Overall, it is difficult to determine if an organ is vestigial or not because scientists are coming up with new functions of these organs as time progresses. For example, according to Campbell, the appendix may serve a function in immunity. Other sources suggest that it may serve as a place for the "good bacteria" to dwell when they would otherwise be flushed from the intestines. Because our lifetime is insignificant compared with the time it takes for populations to evolve, it becomes very difficult to classify organs as vestigial because they may simply be organs with minimal function, as seen in the appendix, and in the wings of flightless birds.
ReplyDeletesource: http://www.nytimes.com/1990/07/12/us/whales-hind-feet-show-up-in-fossils.html?pagewanted=1
http://www.livescience.com/animals/top10_vestigial_organs.html
While vestigial organs may not appear to be the center of attention in breathtaking discoveries seen almost daily on the news, to consider all vestigial organs really useless would at the least be a drastic generalization. As Julia’s post touched on, “Humans are such a tiny part of evolutionary history.” Jerry Coyne paralleled this in a clever analogy that compared this picayune time on Earth to the time in a day humans would take up if all of evolutionary history was complete in 24 hours (28). Thus, this “uselessness” of vestigial organs have so many different evolutionary paths that lead to their lack of contribution to the human body that it would be practically impossible to assume they all are on the same level of lacking a job to do in the human body. In addition, the idea that their current forms render them useless is also an unsafe assumption to make because we don’t know what exactly would happen if people didn’t have them. Unlike the removal of a vestigial organ in one person, natural selection may favor the removal of one of these organs, but in terms of evolutionary time, this might prove disadvantageous in another way. So it’s relatively unsafe to assume that the “uselessness” of one vestigial organ is incomparable to another’s.
ReplyDeleteOn the contrary to popular belief, recent discoveries have actually proven that vestigial organs may not be as useless as commonly pointed out. For instance, a recent National Geographic report on July 30, 2009 claimed that, “the spleen… may be critical in healing damaged hearts” (Koerth-Baker). This is just one example of potentially many that show that what were once considered to be vestigial organs may lack an essential place in the human body, but nonetheless, hold a critical role in either homeostasis or other regulatory process. So in answer to your question, they not only may possess an important role in the body: they already do.
But with such an uncertainty of whether or not an organ is truly vestigial, this debate begs the question, “When can one conclude that an organ is ultimately vestigial?” In truth, unfortunately, there probably is no answer to that question. As with the example of the spleen’s recently discovered function in healing the heart, vestigial organs have functions that may not be apparent to humans because either researchers don’t look into connections between organs that may exist but aren’t what we consider natural or a certain molecule or other key detail that would lead to a given function’s discovery hasn’t been discovered. In addition, natural selection may favor a useless vestigial organ for a given reason leading to the development of the function that was never apparent. On a molecular scale, this is seen in the relationship between ATP synthase and Flagella: “On a molecular scale, apart from ATP synthase, only bacterial flagella are known as a rotary motor” (Yoshida et. al.). As we’ve discussed in class, the rotary motor may have been an evolutionary development that had an unforeseen connection to an enzyme. Similarly, this can be predicted of in vestigial organs, a natural selection procedure that favors the use of an organ that isn’t in use right. Therefore, in terms of evolutionary time, unless a given vestigial organ ceases to exist, its potential uses are endless.
Sources:
Jerry Coyne, Why Evolution is True
http://news.nationalgeographic.com/news/2009/07/090730-spleen-vestigial-organs.html
http://dipbsf.uninsubria.it/dbsf/seminars/fotosint/yoshida.pdf
In my opinion, no organ can truly be labeled as useless. At one point or another, it was arose for a specific purpose and could have been of great help to the organism. It, however, is very possible that the environment of the organism has changed and therefore the function that this organ once provided is no longer necessary. Coyne says that an organ “is vestigial not because it’s functionless, but because it no longer performs the function for which it evolved” (58). The appendix may be practically useless to some people, but to others it may still have a function. For instance, as Dr. William Parker of Duke University discovered, a small function of the appendix is a safe house of good bacteria. He stated that when “diseases such as cholera or amoebic dysentery...clear the gut of useful bacteria...the appendix’s job is to reboot the digestive system.” (Examiner). Although these two diseases are not nearly as common as they once were, they still affect a large number of people. A human doesn’t need the appendix to regain good bacteria because it has other ways of doing so now. But before purified drinking water was available, it was not uncommon for diseases like that to sweep through an entire community, making it a challenge to find external sources of good bacteria. That is when the appendix came in handy. But today, clean drinking water is a far more readily available item. It’s taken for granted. Therefore, for people with easy access to clean water and who are less vulnerable to disease, the appendix maybe seem to be a vestigial organ. But to those where clean water is a rarity, such as in struggling third world countries, calling the appendix useless is not correct, because it’s function in bacteria storage is still very important. Finding sanitary water sources is a difficult task and when it is not found, the inhabitants of such an area have to drink water that is not considered “drinkable”, at least not on an American standard, and that’s when diseases arise and threaten the population. Hence, the appendix truly is useful to help clean the colon after an episode of diarrhea or some other disease.
ReplyDeleteI think that an organ can finally be considered useless when an organism’s habitat has changed to such an extent that the original function is incapable of being performed. Also, it can truly be considered useless once its presence has a possibility of only causing harm, instead of any benefit. For example, in the year 2000, there were nearly 300,000 appendectomies performed in the U.S., and 371 deaths from appendicitis. (About.com) In fact, last spring break, I was supposed to go on a sailing trip with my friend to the British Virgin Islands, and two days before the trip she was rushed to the hospital with appendicitis, and our vacation together was unfortunately ruined. If it wasn’t for her appendix, we could have been sailing the Caribbean! If the appendix has no major function then even its minor one will most definitely not be missed. Some doctors even say it would be better to remove it completely instead of waiting for the off-chance that it might rupture on its own. When an organ has a potential negative effect and no major positive impact on an organism, then I think it can be considered useless.
ReplyDeleteThe appendix is just one example of a vestigial organ, but there are many more that are considered to be “functionless” also. Like Julia stated, wings on flightless birds appear to be vestigial because they serve no function in flying, however, they play a role in running and during courtship. Although the wings’ function isn’t a major one, it still plays some role in the bird’s life. Another example of a vestigial organ could be wisdom teeth in humans. They clearly seem to have no function and they are simply “remnants from their large jawed ancestors” (Livescience). The wisdom teeth are trying to grow into a jaw that has shrunk during its evolutionary path. It no longer fits its function, which was to help humans’ ancestors chew their food, and therefore its structure no longer fits either (emphasizing how important an organ’s function is when compared to its structure). Wisdom teeth tend to cause immense pain and they usually need to be removed, once again pointing out how an organ can have a negative impact on an organism and hinder its well-being and survival. Hence, wisdom teeth can truly be considered useless in my opinion. The line between being useless and simply just used for a different function is very fine. On the evolutionary scale, humans have lived for a very short time when compared to the rest of the organisms and therefore it is very difficult to determine which vestigial organs can truly labeled as useless.
sources:
http://www.livescience.com/animals/top10_vestigial_organs-1.html
http://atheism.about.com/od/evolutionexplained/a/VestigialOrgansAppendix.htm
http://www.examiner.com/x-1242-Science-News-Examiner~y2009m8d21-The-appendix-not-as-useless-as-we-originally-thought