Saturday, March 27, 2010
Vestiges
In Chapter 3, Remnants: Vestiges, Embryos, and Bad Design, Mr. Coyne talks about the vestigial organs of organisms, and how these vestiges never really disappear. He also takes note that we have not yet been able to discover the reason for vestigial organs, and why they aren't simply bred out of a population. On page 62, in the second paragraph, he gives several possible reasons for vestiges, but what do you think? What are other reasons certain organisms never lose particular traits?
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ReplyDeleteBecause traits are used for reproductive purposes,perhaps, there are certain,traits that inadvertently get passed from generation to generation, simply because they are neither helpful nor hinderance, thus become a permanent trait. Much like the human appendix, which doesn't contribute to much, but is a permanent feature. Permanent traits relate to the theme of continuity and change. Since the trait isn't really relevant and no radical event changes the trait, it continues to be passed down from generation to generation.
ReplyDeleteSome vestigial traits are actually useful; they just serve a different function from ancestral traits. Coyne gives the example of ostriches, which use modified wings for balance and mating displays. (This is another reason why ostrich wings aren’t bred out of the population; wings may give males a competitive advantage during mating displays (chapter 6, “How Sex Drives Evolution”)).
ReplyDeleteEven the seemingly useless eyes in the blind mole rat may have some purpose; the remnant eyes may register low levels of light, which can regulate the mole rat’s circadian rhythm (Coyne 60).
Coyne even admits that the human appendix may have some purpose (61). In humans specifically, the presence of an appendix may only relate to the modern application of surgery that prevents the application of natural selection, since more people survive even with appendicitis. (http://www.talkorigins.org/faqs/vestiges/appendix.html)
As Jessica said, the presence of vestigial traits relates to continuity and change, since the genetic information for the traits is inherited over many generations (Campbell 8). The presence of vestigial traits is further evidence of evolution because it shows how ancestral traits may have evolved from their original function to serve a different purpose in descendents.
Like Jamie said, there are many instances vestigial traits are useful, but maybe not in the same way as before. That is, vestigial organs just have a different purpose and use than they did before. For example, Coyne brings up the example of flightless birds having wings. Having these extra appendages that could be harmed and don’t serve for flight anymore seems useless; why do birds that don’t fly still have wings then? As Coyne says on page 59, “when the wings have assumed new uses, as in the ostrich, they will be maintained by natural selection, though in a form that doesn’t allow flight.” For example, Conye discusses penguins, and how these birds use their wings as flippers to help with swimming.
ReplyDeleteAnother instance is seen in the appendix. I disagree with Jessica when she said that the appendix “doesn’t contribute to much”. On the contrary, Coyne explains to us that the appendix “provides a refuge for useful gut bacteria when an infection removes them from the rest of our digestive system,” (61) and also has a small role in the immune system. (http://www.medicalnewstoday.com/articles/84937.php)
Like Jamie mentioned, vestigial traits show proof of evolution because of the change in ancestral traits over time. Also, another thing to note is having vestigial organs in the first place. Why would a creator put something in an organism if it was unnecessary? In terms of evolution, this makes sense because new organisms had to work with the ‘hardware’ of their ancestors, and in cases where that hardware was no longer needed for the old purpose (ex wings for flying), organisms found vestigial organs a new purpose. Like both Jessica and Jamie brought up, the theme of Continuity and Change relates because genes are passed on over many generations. Another relatable theme is the relationship between structure and function; specifically, one structure may find multiple useful functions, as seen in the different uses birds have found for wings other than flying.
Vestigial organs are organs that no longer performs the function for it evolved (Coyne 58). The organ may perform a different function but it no longer performs the same function as it used too. The traits may still remain in the organism because the organ or trait does something beneficial to the organism or removing the vestigial organ will harm the organism.
ReplyDeleteLike Jamie, Radhe, and Jessica had said, vestigial traits are evidence that evolution exists. Evolution is a long process and it takes a long time for one organism to evolve into another. Vestigial traits are the intermediate step from evolving from organism to another. An organism doesn't change overnight. The organism's organs and function changes slowly.
As Coyne had stated on page 57 ostriches have wings but don't use them for flying so the wings are considered vestigial organs. The wings were meant for flying in the ostriches ancestors but the wings aren't used for flying anymore in the ostriches. The wings however do still have function in ostriches. The wings are used for balance during running and are used in courtship displays (www.livescience.com/animals/top10_ vestigial _organs-1.html). The wings were left in ostriches because the wings still serve a purpose in ostriches.
As Jamie and Radhe had said, the appendix do still have minor benefits to the human body which may be why the appendix isn't fully removed from our body. Another reason the appendix isn't completely removed from our bodies is that a smaller appendix is even more harmful than a bigger one (Coyne 62). Evolution is a gradual change and to remove the appendix completely from the body will take many hundreds of years and the the appendix will have to become smaller and smaller for it to completely disappear. If the appendix becomes smaller, the appendix will become harmful to our bodies. Because the appendix at the size right now isn't harmful as long it doesn't become infected, there is no need for the appendix to be completely gone from our bodies.
I agree with all four answers. Like Jessica first mentioned, through reproduction, traits are passed onto offspring whether they are helpful or not. For this reason vestigial traits do not just disappear and are passed down from parent to offspring. I agree with Jamie (and Radhe and Anika), however, that vestigial traits like the appendix may sometimes be useful. Coyne specifically discusses the uses of some of these vestigial traits. The definition of a vestigial trait is "a feature of a species that was an adaptation in it's ancestors, but that has either lost it's usefulness completely or...has been coopted for new uses" (57). So a vestigial trait does not necessarily have to be useless. I agree with the ideas brought up that vestigial traits relate to the themes of continuity and change because of the method in which vestigial traits arise. Coyne later mentions in "The Engine of Evolution" that an adaptation only occurs when it increases the "reproductive output of its possesor" (120). He also discusses the fact that a gene that appears after reproductive age has no evolutionary dis/advantage. For the same reason I believe vestigial traits persist. Vestigial traits, whether useless or useful, do not provide a species with a certain advantage nor disadvantage. Also, traits that may endanger an individual after the reproductive age will continue to be passed on to offspring. The appendix is simply an exception. Coyne mentions that before surgeries, natural selection favored people with no appendix because ruptured appendixes killed so many people. The appendix could have been removed from humans all together due to natural selection, even though some people can survive with an appendix. Overall though, I think the major contributor to the existence of vestigial traits is that many of these traits are neither helpful nor hindering and so natural selection does not work for them or gainer them. These traits continue to show up even if they are useless. Like Jessica, Radhe, Jamie, and Anika all said, the appearance of these traits is evidence of evolution. Species possessing vestigial organs evolved from species that once used these organs for something else.
ReplyDelete