MangyTiger
Member (Idle past 90 days) Posts: 989 From: Leicester, UK Registered: 07-30-2004
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Message 301 of 303 (138453)
06-03-2005 11:55 PM
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Reply to: Message 300 by randman
06-03-2005 10:40 PM
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Similarities and convergent evolution
| randman writes: Next, we should consider the possibilities of any examples where 2 species are highly similar, but genetically are farther apart. Take the concept of 2 people that look-alike, who would appear to be a sibling, but they are not. If it can be shown that greater similarity can be produced without greater similarity genetically, then that undercuts the claim that similarity corresponds to genetic relatedness. So if you do not have the DNA, for example, maybe the appearance of similar traits in species in the fossil record does not indicate genetic similarity or common ancestry. |
I'm not an expert by any means (and would welcome input from those who are!) but your use of the word similar doesn't seem right to me, especially in the context of convergent evolution. Although convergent evolution can lead to two species which are not closely related to each other being similar, this similarity is not much more than skin (or fur, or scales etc. :)) deep. A quick Google suggests that placental and marsupial moles are a good example. External examination suggests they are very similar, indeed MSN Encarta says: | For example, the marsupial mole of Australia looks very much like the placental moles found on other continents, yet these animals have evolved entirely independent of one another. The explanation for the moles’ similar appearances lies in the principles of convergent evolution. Both species evolved to exploit similar ecological niches—in this case, the realm just beneath the surface of the ground. Over the course of millions of generations in both marsupial and placental moles, natural selection favored adaptations suited for a life of burrowing: tube-shaped bodies, broad, shovel-like feet, and short, silky fur that sheds dirt or sand easily. The most striking difference between placental moles and marsupial moles is the color of their fur. Placental moles are usually dark brown or gray, a coloration that enables them to blend in with the soil in their habitat. Marsupial moles burrow in the golden or reddish sand of Australia, so natural selection produced golden or golden-red fur. |
Closer examination will show considerable differences between the two. Apart from the obvious reproductive differences most (all?) marsupials have a number of features that differentiate them from placental mammals, as described in the Animal Diversity Web site from The University of Michigan Museum of Zoology. As I understand it these are the sort of similarities used in cladistics. | randman writes: And really, the more I think about this, genetics and DNA are going to be problematic for arguing for common descent regardless of the findings because if we see that species can be similar but with a wider difference genetically than species that are not as similar, that undercuts the guiding principle entirely since what that will have shown is that similarity can be produced without common ancestry. But on the other hand, if we find that species that are more similar are indeed more similar genetically, then that undercuts common descent even more since convergent evolution posits similarities can be produced without common ancestry. |
So convergent evolution only results in superficial external similarity which you wouldn't expect to see reflected in the DNA. I would expect (he says sticking his neck out way beyond his knowledge!) that the marsupial mole is genetically much more similar to another marsupial - probably any marsupial - than it is to the placental mole.
Oops! Wrong Planet
| This message is a reply to: | | | Message 300 by randman, posted 06-03-2005 10:40 PM | | randman has not yet responded |
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Hrun
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Message 302 of 303 (138454)
06-04-2005 12:43 AM
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Reply to: Message 300 by randman
06-03-2005 10:40 PM
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Re: Hmmm....
Randman, I do not want to necessarily disregard what you posted, but to come to an understanding, I think it would be helpful if you stay within the confines of the examples that I gave. Especially, since I did not use terms liek 'theorized ancestors', 'closely related cousins', 'common descent' or 'fossil record'.Essentially, I asked very specific questions: Do you think that with the methodology I described (one that does not rely on genetics) we can determine the relatedness between species. Specifically, I asked whether you agree that a dolphin should be related closer to other mammals than to fish and if marsupials among each other should be closer related that marsupials with mammals. I know that in your post you brought up questions that may or may not question DNA as a measure of common descent, but before we get to that we have to see on which points we agree or do not agree. So, sorry if I kinda disregard your message 300, but please come back to my message 295 and lets see specifically on which points we agree and on which points we disagree. Only that way will we actually make any headway.
| This message is a reply to: | | | Message 300 by randman, posted 06-03-2005 10:40 PM | | randman has not yet responded |
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