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Author Topic:   Anatomical Vestiges -- Evidence of Common Descent
Chiroptera
Inactive Member


Message 5 of 34 (417358)
08-20-2007 2:07 PM
Reply to: Message 3 by EighteenDelta
08-20-2007 1:41 PM


Re: appendices
To sort of paraphrase Ned's link, the appendix has no known function. It does contain lymphoid tissue which serves an immunology function, but so does the rest of the digestive tract, and I can't see any reason why a lymphoid tissue needs to be contained in a blind sac. It certainly does not have any known digestive function. Some people are born without an appendix, some people have their appendix removed, and there are no ill effects that correlate with the absence of the appendix.
What the appendix is similar to is the caecum in other primates (and other mammals). In these animals, the caecum does have a digestive function: it helps in the digestion of a diet of green leafy stuff with a lot of cellulose. In these animals, not only does the caecum have a function, but it is larger than the human appendix, and it is located in the same place.
This is what makes it vestigial. It is clearly homologous to a functioning organ in closely related animals, but it no longer serves the same function, and, in fact, if it serves any function, the function is minor.

I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

This message is a reply to:
 Message 3 by EighteenDelta, posted 08-20-2007 1:41 PM EighteenDelta has replied

Replies to this message:
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 Message 21 by Doddy, posted 08-26-2007 2:47 AM Chiroptera has replied

  
Chiroptera
Inactive Member


Message 11 of 34 (417459)
08-21-2007 8:18 AM
Reply to: Message 10 by molbiogirl
08-20-2007 10:19 PM


And a fun one if we ignore the guest of honor.

I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

This message is a reply to:
 Message 10 by molbiogirl, posted 08-20-2007 10:19 PM molbiogirl has replied

Replies to this message:
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Chiroptera
Inactive Member


Message 18 of 34 (417642)
08-23-2007 3:22 PM
Reply to: Message 17 by molbiogirl
08-23-2007 2:44 PM


Re: Hammering tacks with a computer kekboard
Indeed. Here is an article on pseudogenes in general; Douglas Theobald's essay has a little bit on the broken vitamin C gene in humans and other apes that is a pretty popular subject in this vein.

I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

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 Message 17 by molbiogirl, posted 08-23-2007 2:44 PM molbiogirl has not replied

  
Chiroptera
Inactive Member


Message 22 of 34 (418087)
08-26-2007 10:39 AM
Reply to: Message 21 by Doddy
08-26-2007 2:47 AM


Re: appendices
Hi, Doddy.
We're not discussing why, given the existence of this particular organ, it should evolve to have extra lymphoid tissue. The purpose of this thread is to discuss the vestigial nature of the appendix. Creationists claim that the appendix is not vestigial because it has a purpose, and that it's purpose is that it contains lymphoid tissue important for the immune system. The question then becomes why God needed to create a holder for lymphoid tissue that was a blind sac, why a blind sac that looks for all the world similar to an existing, functioning organ in closely related species, and why a blind that can and does kill the person who has it.
Added by edit:
But maybe this is another case of where if I have to explain the joke, then it probably wasn't funny to begin with.
Edited by Chiroptera, : No reason given.

I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

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 Message 21 by Doddy, posted 08-26-2007 2:47 AM Doddy has not replied

  
Chiroptera
Inactive Member


Message 26 of 34 (418339)
08-27-2007 4:00 PM
Reply to: Message 23 by Fallen
08-27-2007 2:32 PM


Hi, Prodi.
The evidence that has been presented here is evidence against a particular version of creationism....
Sure. That's the only way evidence can be used against an idea -- you need particulars in order to figure out what you should see in the world around us, and then to check whether the evidence supports or refutes those particulars. It isn't evidence against something vague like someone, somewhere, did something -- no evidence can refute something so vague. That is why creationism isn't science. Creationists refuse to pin themselves down to definite specifics that can be tested.
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...not evidence in favor of evolution.
Oh, but it is. Do you know what evidence is in science? One makes predictions based on one's theory, and then checks to see whether those predictions are observed. If the predicted phenomena are observed, then that counts as evidence in favor of the theory. If the predicted phenomena aren't observed, then we have a potential falsification.
Once common descent is recognized and once the phylogenic tree is more or less worked out to some degree, then one can make definite predictions about vestigial organs and see if one observes the predicted phenomena.
Theobald explains how this works. Assume gradual evolution, then if the members of a species begin to take advantage of a new niche where a certain organ is no longer necessary (at least for its original "purpose"), then mutations that disable its use will no longer be selected against. And, even if it is harmful to carry a useless organ, it will take time for natural selection to eliminate it completely. Therefore, we should actually see vestigial organs in nature. And we do!
Also, these vestigial organs should be similar to organs that had a function in a recent ancestor. We shouldn't, for example, see frogs with vestigial wings -- frog ancestors didn't have wings. It is possible that some birds would have vestigial wings (and they do!), it is possible that some bats would have vestigial wings (which none do, as far as I know), but no frog should have vestigial wings. If a frog with vestigial wings were found in nature, that would be a problem for evolution.
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Smart designers don’t create hundreds of entirely independent concepts.
Sure. No matter how smart a designer is, there is a limit to her imagination. Thinking up a totally new design takes a lot of time and effort on her part. Smart designers have limited resources available to them, so it makes sense that they will save time and money by re-using old designs.
This makes no sense for God creating the world ex nihilo unless we postulate that God wasn't so smart, and that he was forced to work within a budget. But most creationists assume that God is omnipotent and omniscient, so these limitations wouldn't apply. God is omniscient, so he already knows all the possible designs that he could use; he's omnipotent so he can make them come into being. It wouldn't be dumb for an omniscient, omnipotent God to make every creature with radically different designs. That fact that the number of designs is limited seems to be evidence that God isn't as omniscient or as omnipotent as his followers would have us believe.
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The reason for this principle of engineering is simple - if you only make one kind of a design, you waste a lot of potentially useful similar designs.
Exactly. Because real designers are limited in imagination (no matter how clever they are, there are limitations to their cleverness) and in the budgets within which they must work. As you said before, this is evidence against a particular version of creationism, namely the version that has an ominpotent, omniscient creator.
This is evidence, perhaps, that God was a very limited entity. He was forced to reuse old designs. When he created ostriches, he couldn't figure out how to eliminate wings -- they were too hardwired into the developmental processes, and so ostriches have wings that can't fly.
God couldn't figure out how to make primates without appendices, so when he created humans, he had no choice but to include a useless tiny sac in the basic human design.
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Likewise, in your example, the designer probably used the appendix design to make a workable addition to the immune system.
But the immune system works fine without the appendix. They have studied people without appendices -- either because they were surgically removed, or because they were born without an appendix. No ill effects whatsoever correlate with the lack of an appendix. This has been studied.
And even if there were some immune function, an omnipotent God could presumably figure out how to include extra lymphoid tissue without embedding it in a blind sac branching off of the intestine. Maybe by making a solid organ embedded with lymphoid tissue, or including extra lymphoid tissue in the rest of the intestine.
But God was stuck with a basic primate design that included a caecum. God couldn't figure out how to change the embryonic development of humans to eliminate it -- he was working under deadline, apparently, and didn't have enough time to work it out and didn't have a large enough budget to make the necessary changes anyway (hey, you are the one who wants to compare God to real designers!), so even though humans don't eat a cellulose rich diet consisting mainly of leaves, he was stuck with the caecum. Oh well, at least it makes a handy place to put some extra lymphoid tissue.
My guess is that this is not the sort of God that most creationists think that they worship. Yet here is the evidence. The evidence seems to be in favor of a god with rather limited powers.
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Well, this isn't true either, because the important thing isn't the similarities, but pattern the similarities exhibit. This is actually my favorite piece of evidence, but it unfortunately is off-topic here.
Edited by Chiroptera, : Missed a typo.

I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

This message is a reply to:
 Message 23 by Fallen, posted 08-27-2007 2:32 PM Fallen has not replied

  
Chiroptera
Inactive Member


Message 33 of 34 (418645)
08-29-2007 4:15 PM
Reply to: Message 30 by Fallen
08-29-2007 11:45 AM


Hi, Prodi.
If my understanding is correct, staying on topic is an important issue on this forum. Would you mind moving this discussion to a more appropriate topic so that this thread stays clean and simple?
I was simply replying to a point in your post. Moderators tend to allow individual points to be answered and step in when those points look like they're beginning to dominate and derail the main topic.
I'll just say that I'm not much interested in Intelligent Design. It just seems like the old Argument from Incredulity to me; Intelligent Design exhibits much of the same sloppy thinking that characterizes Young Earth Creationism, except that people like Dembski and Behe realize that their thinking is sloppy and so they obfuscate the issue as much as possible to hide it. I've yet to see a discussion on Intelligent Design that didn't make my eyes cross.
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Any number of vestigials (or complete lack of vestigials) can be explained as being due to the randomness of mutation and uncertainties about what selective pressures were at work.
Actually, that's not quite true. As I pointed out, it would be unlikely that every single species that we see would have, in every single case, have completed the evolutionary processes that would have eliminated unused organs (or completely adapted them to other purposes so completely to hide their original use (like the way a jaw joint became adapted into middle ear bones in mammals). Surely, with all the species that we see, a least a few would still be in the process of adapting to an evironment in which an organ possessed by the ancestor is now unnecessary?
So, sure, often we wouldn't see vestigial organs (since they would, like gills in mammals, been long eliminated), but sometimes one should see vestigial organs since there should still be organisms in the process of adapting to new environments and new niches that their ancestors didn't inhabit.
Incidentally, if you read The Structure of Evolutionary Theory, Stephen Jay Gould points out that it was a problem for the theory of natural selection that whales didn't have vestigial legs. Not for macroevolution, since that alone wouldn't suggest that we should see vestigial organs in each and every case, but it did for the theory of natural selection as the mechanism for evolution. At one point, one would naively think, when the leg became really, really small, say 5 millimeters long and embedded within the body, surely natural selection wouldn't distinguish between a vestigial leg 5 mm long and one 4 mm long. This was one of the reasons that natural selection wasn't universally accepted as the mechanism for evolution until the 1940s and 1950s, when genetics and developmental biology provided the answers to this particular question. So the lack in of vestigial organs was considered a problem in certain cases.
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If we found a frog with vestigial wings, people would see it as an organ “on its way in” rather than “on its way out,” and possibly even use it as further evidence for evolution.
Well, it it was on the "way in", then it wouldn't be vestigial. Natural selection does not select for useless organs. It can only select for features that make a positive contribution to the survival of the organism. Even if a frog wing was truly vestigial, without a use, right now then it must have originated as a feature that was useful in an ancestor and so had a definite use. So the ancestors of that particular frog must have had wings. Since the wings would have had to have been well-developed for them to be identified now as wings, then it must have evolved over some long length of time. So closely related species must also have wings; if a frog had vestigial wings, then there should be indications that its ancestors had wings, either through direct fossil evidence, or by the possession of wings (functioning or vestigial) in closely related species.
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For example, flying fish have wings...
...which aren't vestigial, so they aren't particularly relevant here.
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First, we have no way of knowing the goals and intentions of the designer of life on earth, so any assumption about them is just that: an assumption.
But I'm not the one making assumptions about the designer. It is the "reuse of similar designs" people who are. By comparing the tendency of the creator of life to reuse common designs with the same tendency of human engineers, the creationist/intelligent designist is making the implicit assumption that the goals and reasoning of the two are similar.
Why would the creator of life reuse designs? That is the question. Why would the creator of life reuse designs? To point out that human designers reuse designs is to imply that the answer is for the same reason that human designers do. Why do human designers reuse designs? Because it is too expensive and takes too much time to come up with totally new, innovative designs from scratch. So, when someone answers this question with this answer, then they are saying that creating innovative new designs from scratch is too expensive, too time consuming, and too difficult for the creator of life.
If the creator is reusing designs for reasons different from human designers, then the comparison is useless and misleading and should not be made.
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According to him, an all powerful being would by default have to create a more radically diverse array of designs than what scientists observe in our world.
No, I am saying that it is not possible to say what a designer would do until one has an idea of how and why a designer does what it does. One needs a theory.
The theory of evolution is an explanation of the similarities and the pattern of similarities, and it has great explanatory and predictive power.
Why is the appendix like the primate caecum? Because that is what the designer wanted. Why is the retina of the human eye behind the capillaries suppying its blood? Because that is the way the designer wanted it. Why do birds have feathers and no other animal? Because that is what the designer wanted. This has no explanatory or predictive power at all. It may be comforting theologically, but it is useless scientifically.
Edited by Chiroptera, : Totally awful typo.
Edited by Chiroptera, : Another typo.

I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

This message is a reply to:
 Message 30 by Fallen, posted 08-29-2007 11:45 AM Fallen has not replied

  
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