Is convergent evolution evidence against common descent?

As crash noted the similarites in cases of convergent evolution are not all the way through.Excellent examples are both the convergence of sharks, dolphin and ichthysosaur and the convergence of mammals and marsupials.In both cases there are strong superficial similarities but a closer examination makes it clear that they are separate lineages. When the DNA is examined independently from the morphology we find that the separation is confirmed.It is, of course, harder to separate animals when all we have are fossils but, again, the bone structures are clearly different even when the external shape is similar. The shark, dolphin, ichthyosaur example supports this.Do you have examples where it is less clear?

I find this a bit confusingly worded. I hope you will try to reword it later.You are though suggesting that we might mistake a case of convergence as a case of common ancestry. Which is where this started.So far the examples put forward of convergence have all exhibited strikingly different ways of producing similar function. In other cases that do not show these differences we conclude common ancestry.You disagree with that conclusion. However, there are clearly two different kinds of situations here. They are in stark contrast.Perhaps you could develop this kind of sharp contrast into a way of, finally, defining "kinds" (as used by creationists) in some sort of specific and useful way. That is when there are these sharp contrasts of underlying support for a particular function then you might conclude that each of them was the result of a specially created "kind" and then subsequent hyper evolution from that kind (as many creationists suggest).Would you suggest that as an alternate explanation for the patterns shown?This message has been edited by NosyNed, 06-04-2005 06:59 PM

This is the pattern we see, of course. Initially, a couple of centuries ago, those who first understood this but accepted a single act of creation had to try to construct an alternative explanation. From that they devised a series of creation events.Is that your alternative explanation? What is that something then? Would you describe what you believe happened to produce the patterns we see in the fossil record and the forms of life alive today?

For science we work with the best we have. We only know to the degree that we have evidence and a model which fits that as well as we can. If the patterns we see in fossils and life are due to chance then that odds against it are astronomically huge. No, it does not just rest on the common traits. It rests on what we can see in life today. It rests on the particular patterns we see.You pointed out the pattern in the fossil record. If living things reproduced from other living things through the time the fossil record was being formed then the later, slightly different ones (as you pointed out) came from the earlier ones (unless you have a better explanation). This is common descent. I have no problem with your view then. You may decide that you don't know. Biologists may simply say they don't know for absolutely sure. However, given that there is not better alternative explanation and given how well the explanation we have works the degree of surity is rather high indeed.In the sciences we work with the best explanation that we have. We teach that explanation and the underpinings for it. We will also doubt and test the current model even without having another one. That is normal in the sciences too. However, we work with the one that works in the meantime.You may prefer to say "don't know" but that is heavily based on the fact that you know very, very, very little about the biology, physics, geology and paleontology involved. I might say you know microscopically little and much of what you do "know" is wrong besides. Under such circumstances "don't know" isn't an unreasonable position to take.Most of the time, when I know very, very little about an area I would have to both say "I don't know" and "I will go along with the experts until shown otherwise". I don't see any other position as being resonable.This message has been edited by NosyNed, 06-04-2005 08:32 PM

If not common descent then what? A chance happening?

And this explanation is?This message has been edited by NosyNed, 06-04-2005 08:35 PM

It certainly is presented that way! Right on! It is presented that way because after 150 years of work no one has come up with anything that even begins to match it and it has stood up to a great deal of work and examination.If the odds against any other explanation (like chance) are truly enormously huge then an explanation that doesn't require such unlikely occurances looks pretty good.(as an aside, if you want to play probabilty calculations please take that to another thread)In addtion, you have (again) a misapprehension of that true case. If you see the science only through the high school level presentations and popularizations then, of course, it is presented in a simplified form without all the details in the primary literature that allows one to separate the hypothosis, from the pretty likely and the very, very likely.The fact that life has evolved over time is "proven beyond all reasonable doubt". The explanatory model of neo-darwinism is correct as far as we have been able to push it. That is good enough for a popular presentation. I agree. When common forces act then common results can be expected. This gives some reason for commonality. What is your explanation for the differences then?So again, what is your explanation for the patterns seen? When 1,000's of individuals dig very deeply into the science and decades are spent and no one comes up with a robust alternative explanation we begin to conclude that the model we have is "beyond reasonable doubt". You may overthrow this by supplying the more robust equally explanatory model. Yes, somewhat similar. The difference is in the degree of digging into the data, the work done to get additional data, the amount of new data available and the approach taken. When you only have one explanation you go with it.I agree with your concern about teaching and popularization. I would like to see a lot more time spent on the basic evidence and only work up to conclusions at the very end. It is better for the student to draw there own conclusions.However, I am also practical. There simply isn't time to take someone not going into at least undergraduate level biology to really dig very deeply into the available evidence. That is unfortunate but also true of all the many some complex areas of knowledge that we would like citizens to be aware of.It is your opinion that it is taken on as dogma with a subjective view. It is my opinion that you have way to little knowledge of the subject to come to any such conclusion.

I agree that Rrhain overstated the case there. ( a lot !).As for the rest:Yawn? sounds like you don't have an answer. You do exhibit a pattern of skipping the parts you can't handle.This message has been edited by NosyNed, 06-04-2005 10:12 PM

Good point about the topic. There are eduction threads you could take it to. You repeat this a lot but this form of mysticism isn't very convincing to me. As it is concerned with the cosomology and not biological evolution we can leave it to other threads. Absolutely agree. The question is how do these laws etc produce the patterns. Well, this is exactly one part of the laws producing the pattern and we agree on it. Agreed again. So far you seem to be backing current biological thinking in the same way any Christian biologists might. At the lowest level there are, of course, chemical "tendancies" that cause some of the behavior and patterns in genes. You may believe the nature of physics and chemistry is "pre programmed" if you wish. There is no evidence for an specific preprogamming beyond that.What are these tendancies and how do they cause the patterns we see? You have yet to even begin to answer the question. You are a good theist. I have no problem with you believing that if you so wish.Can you get around to answering Rrhains common question as to whether anything even the role of a dice, happens without God's intervention then?So far you have not offered a different explanation for the pattern of fossils and life that is the topic of discussion that is different from the accepted biological explanation with a God in the background somewhere.Again, what is your explanation for the pattern? This you may take to the convergence thread.

Why? Why should any two creatures be similar at all?If a wolf and tasmanian wolf are at all similar why shouldn't a shark and a dolphin be just as similar? You have not explaned this yet. Your only explanation so far was precisely the biological evolutionary reason for both the differences and similarities. I'm not clear, at this point whose responsibility it is to cover this. You suggested that there are few differences between the marupials and placental homologues. How many differences will it take to falisfy your statement? What will you accept as a difference? It is useless to list things that you will ignore. Done for the wolf and thyacine, see here:
http://www.naturalworlds.org/...ll/wolf_thylacine_skulls.htmJust from one of the views (dorsal) there are 10 or 20 obvious (to a non anatomist) differences in the details that are not driven to converge.

The issue is, as has been discussed before, the nature of the disparities.When all the differences and similarities are added up the wolf and the thylacine are further apart than the whale and dolphin in fact the wolf and the dophin are closer than the thylacine is to the wolf.That was recognized a long time ago.Now we dig down into the underlying DNA and we find that it is different in the same way and degree as we determined from morphology.Of course, a wolf and thylacine have a bunch of common traits as you point out, both being mammals.I think that we should retract the point about "few traits similar" because "few" was never quantified or made clear. However, when a wolf and cat are compared they will have more similar traits in detail than a wolf and thylacine. This means that the wolf and thlacine have "few" in comparison.The general form, that which is needed to fit the niche is similar but not the underlying details.Now here is the evolutionary prediction (I don't know if it has been done):
If a marsupial form is compared to a closly similar placental form (fitting the same ecological niche) then the DNA will be much less similar between them than between the placental form and all other placentals.What would your prediction be and why would you make such a prediction?

Is is surprising to me too. However, there is a general blending of forms all the way across the taxonomic groupings. There are places where (I understand) extremely similar and close relatives can not succesfully interbreed while others that are more dissimilar looking can to greater and lesser extents.Remember even species are "fuzzy" around the edges and there are a number of different ways of defining them. Normally, sucessfully, interbreeding in the wild is only one defintion. As you show it leaves room for surprises and there is fuzziness in the words used (like normal, and successful).All higher taxa only appear to be separated because we have lost the intermediaries. This will be interesting to look at. Hopefully we will come up with a few. If there is no viable alternative theory then only one will get taught.You are talking as if you have an alternative however. The explanation of it you gave a bunch of posts ago was simple, as far as I could see, evolution with a designer of universal laws, a misinterpretation of the word "observe" in QM writings and nothing new.Then on other occasions you suggest that the pattern is some sort of chance with unknown forces pushing things into similar patterns.If these are the sort of models you wish to put up against the TOE you have a lot of work to do. This however is a perfectly scientific prediction. It is best is surronded by the model which leads to such a prediction and supporting evidence and logic as well. Then it offers a chance to pick between competing hypothoses.It would be useful if you explained "not totally".

see:http://users.rcn.com/...ltranet/BiologyPages/T/Taxonomy.html
about 1.4 of the way down.HemoglobinsAn example of molecular homology.The numbers represent the number of amino acid differences between the beta chain of humans and the hemoglobins of the other species. In general, the number is inversely proportional to the closeness of kinship.
All the values listed are for the beta chain except for the last three, in which the distinction between alpha and beta chains does not occur.
Human beta chain 0
Gorilla ........ 1
Gibbon ......... 2
Rhesus monkey... 8
Dog ...............15
Horse, cow ..... 25
Mouse ................27
Gray kangaroo .. 38
Chicken ........45
Frog ........... 67
Lamprey 125
Sea slug (a mollusk) 127
Soybean (leghemoglobin) 124
The human beta chain contains 146 amino acid residues, as do most of the others.This message has been edited by NosyNed, 06-06-2005 05:30 PM

Well it is my opinion (first heard from Freeman Dyson in a talk) that one is not automatically entitled to opinions. One has to earn the right by become a small amount knowledgeable in the subject matter.If you make a charge of relying on false evidence you need to do two things:1) Actually understand the evidence
2) Be precise about why it is false.As far as conclusions being taught; you were invited to discuss that in the education thread. I'd be interested in seeing just what you would suggest teaching in a handfull of ten's of hours to students with little background and bombarded with misleading and even dishonest information by those in the ICR and AIG.That is an interesting article. It is an example of two things:1) When there isn't enough detailed information to sort out the exact branching patten of taxa from the fossil record the DNA studies can shed light on it.2) It requires more than one such study and it is wise (as these guys are) to be not too dogmatic in making sweeping statements. This is hard work; teasing out the relationships in a very complex world.I'm glad you found it interesting.This message has been edited by NosyNed, 06-06-2005 08:13 PM

That doesn't seem to me to be right.How about this?The distance from NYC to Miami is about 1800 miles, the distance from NY to Salt Lake is about 3200 miles. Does that mean that the distance from Salt Lake to Miami is 1400 miles?