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Author | Topic: Convergent Evolution - Reasonable conclusion? or convenient excuse? | |||||||||||||||||||||||||||||||||||||||
BobTHJ Member (Idle past 5026 days) Posts: 119 Joined: |
As requested by Taq in Message 147 of Biological classification vs 'Kind', this thread is for the examination of case studies in convergent evolution to demonstrate the validity (or lack thereof) of the independent evolution of similar structures.
My assertion: Convergent evolution is a convenient way for darwinists to explain exceptions to the supposed nested hierarchy that forms the phylogenetic tree. When similar structures are detected in different clades darwinists rationalize it away as convergent evolution - instead of making the more reasonable conclusion that not all life fits into a neatly nested hierarchy of traits. As an initial case study for discussion, consider echolocation in bats and dolphins. According to this January 2010 Science Daily article both bats and dolphins share almost identical genes for echolocation. The statistical odds of the exact same mutations being selected in both species to form a working echolocating sense is nearly impossible - yet according to this research this seems to be the case. Wouldn't a much more reasonable conclusion be a common Designer re-using a created feature? I don't see anyone claiming recent common ancestry between bats and dolphins - yet genetic similarities of the same sort are used to show common ancestry between humans and chimpanzees. Why draw a conclusion of common ancestry for one case but not the other? Or is the data simply inconvenient because it doesn't fit the darwinian model? Edited by BobTHJ, : fix tag error
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Adminnemooseus Administrator Posts: 3976 Joined: |
Thread copied here from the Convergent Evolution - Reasonable conclusion? or convenient excuse? thread in the Proposed New Topics forum.
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Dr Adequate Member (Idle past 313 days) Posts: 16113 Joined:
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My assertion: Convergent evolution is a convenient way for darwinists to explain exceptions to the supposed nested hierarchy that forms the phylogenetic tree. A curious fantasy. What "exceptions"?
When similar structures are detected in different clades darwinists rationalize it away as convergent evolution - instead of making the more reasonable conclusion that not all life fits into a neatly nested hierarchy of traits. But this "more reasonable conclusion" is false --- it does. The occasional bit of convergence (an obvious prediction of evolutionary theory) is absolutely swamped by all the other traits one might consider.
As an initial case study for discussion, consider echolocation in bats and dolphins. According to this January 2010 Science Daily article both bats and dolphins share almost identical genes for echolocation. The statistical odds of the exact same mutations being selected in both species to form a working echolocating sense is nearly impossible ... Show your working. Oh, wait, you haven't done any, have you?
Wouldn't a much more reasonable conclusion be a common Designer re-using a created feature? Explanations involving magic are rarely "reasonable".
I don't see anyone claiming recent common ancestry between bats and dolphins - yet genetic similarities of the same sort are used to show common ancestry between humans and chimpanzees. But this is, of course, not true. The connection between humans and chimps is based on the honest scientific method of looking at all the data, whereas the connection you wish to establish between bats and whales is based on the dishonest creationist method of looking at one single tiny piece of evidence --- one single protein --- that you can misinterpret if you ignore all the rest of the evidence.
Why draw a conclusion of common ancestry for one case but not the other? Because evolutionists look at all the evidence.
Or is the data simply inconvenient because it doesn't fit the darwinian model? ... writes the man who just ignored the entire bat genome and whale genome with the exception of one single gene. Edited by Dr Adequate, : No reason given.
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined:
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Hi Bob,
This is interesting research, but I don't think it necessarily supports your contention.
The statistical odds of the exact same mutations being selected in both species to form a working echolocating sense is nearly impossible - yet according to this research this seems to be the case. Actually this isn't what it says, it says that the same amino acid substitutions seem to have ocurred. I'd suggest that what their paper (Liu et al., 2010) should talk about is Prestin protein having undergone sequence convergence since the gene sequence more normally refers to the DNA sequence. So the same amino acid substitutions are distinct from the same mutations. The same amino acid substitution can arise from a number of distinct mutations depending on the amino acid in question. There are multiple possible nucleotide sustitutions giving rise to the same amino acid substitutions so the chances of convergent amino acid substitution are considerably greater than those of convergent DNA nucleotide substitutions. In terms of the DNA sequences the paper specifically states ...
Liu et al., 2010 writes: Trees based on nucleotide alignments from this larger dataset strongly supported the accepted species tree topology ... ... so in fact the gene sequences, the level at which the mutations actually occur, don't show convergence, but the protein sequences, the higher level phenotype, do. We are talking here about 14 amino acid substitutions and it is worth noting that value is a collective one between all the dolphins and all the bats. In other words there is no single bat-dolpin pair you could pick that would show those 14 convergentamino acid changes. So I would echo Dr. A's suggestion that if you really feel that this is still nearly impossible you should show your workings. And remember that the basis of that calculation should not be 'The statistical odds of the exact same mutations being selected in both species' but rather the statistical odds off the same amino acid substitutions occuring in such a pattern that between 14 species of bat and 4 dolphin species they can find 14 well supported convergent sites. It is also worth noting that when the authors include the sperm whale in their analysis your whole premise falls apart. Suddenly the dolphins end up back in their usual place in the phylogenetic tree. So in fact this research still supports the Darwinian model and indeed seems to fit in with the traditional nested hierarchy. The only way it doesn't is if you leave out some of the data.
yet genetic similarities of the same sort are used to show common ancestry between humans and chimpanzees. The thing is this simply isn't true; the sequence similarities between human and chimpanzee are orders of magnitude stronger than the ones shown in the paper stretching across the whole genome and are at the more relevant actual genetic sequence level. TTFN, WK Edited by Wounded King, : used wrong term swapped conserved for convergent. Edited by Wounded King, : Added link to abstract.
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
Looking again at that issue of Current Biology I see that there were in fact 2 papers on the same topic. The other paper (Li et al, 2010) has a less extensive analysis but shows essentially the same pattern.
The one particularly distinct analysis they do is to instead of just looking at the whole nucleotide sequence for the gene look at specific subsets of nucleotides, those leading to synonymous and non-synonymous substitutions. They show that looking at the non-synonymous substitution sites alone also produces an anomalous tree position. I don't see that this has much bearing on my previous comments though in terms of genetic support for the nested hierarchy. TTFN, WK
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RAZD Member (Idle past 1433 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hi Wounded King,
I don't see that this has much bearing on my previous comments though in terms of genetic support for the nested hierarchy. There's another element to consider. From the first abstract: Convergent sequence evolution between echolocating bats and dolphins - PubMed
quote: If the changes result in sensitivity to certain frequencies used in echolocation, it could be a matter of resonance fitting: the amino acid substitutions changing the resonance response. For the same response in other species, the same substitutions would result in the same resonance fitting, while different substitutions would not. Selection for the resonance response would result in selection for the same sequences. Enjoy. Edited by RAZD, : /qs we are limited in our ability to understand
by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined:
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I'm not sure how that is another element to consider, since it is the whole point of both articles. They both posit convergent protein sequence evolution of Prestin as a result of selective pressures associated with echolocation.
But as I have been pointing out, protein sequences and amino acid substitutions are not really genetic data in and of themselves. Selection for the resonance response only selects for the same amino acid sequences not the same DNA sequences. While this selection will affect the DNA sequences to some extent it still allows a lot more variability than at the amino acid level. For Bob's argument to make any sense the nested hierarchy really needs to fall apart at the genetic level, it is no good him just choosing an arbitrary phenotypic level and then saying, look at these supposedly convergent traits they blow a major hole in the darwinian nested hierarchy approach. TTFN, WK Edited by Wounded King, : Fixed ridiculous spelling error
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Asking Junior Member (Idle past 5066 days) Posts: 19 Joined: |
Key points in the article
1) The gene linked with hearing is known as prestin2) There are a limited number of ways that prestin can change to make it responsive to high frequencies (When expressed) 3) There was a selective pressure which conserved these limited number of mutations that occured that made individuals of both species better at hearing high frequencies. With these points in mind its innevitable that we should find similar genes in bats and dolphins. Given the nature of this gene it would be suprising if we'd found that there was a significant different between them. ------------------------------ Of course there is an important lesson to be learned from this research and that is that when determined how related various species are from their genes care should be taken in interpretation of results. Of course this is already addressed as they don't just rely on one gene to make these phylogenetic tree's. As for your alternative theory I don't think it warrants serious consideration. Edited by Asking, : No reason given. Edited by Asking, : Rehashing Edited by Asking, : No reason given.
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Peepul Member (Idle past 5046 days) Posts: 206 Joined: |
quote: The nested hierarchy is deduced by looking at lots of traits - looking at one will give odd results. The overall strength of the argument for a nested hierarchy is very high - that's why scientists don't overturn it in the face of examples of convergence. It's supported by a large number of statistically significant studies of relationships based on morphology and / or genetics. If the majority of traits indicated that life does not fit into a nested hierarchy - then we would have to throw away that concept. But that's not the case. So, it is reasonable to retain the nested hierarchy based on what we know. Changes are happening now to our understanding of convergence, as genetic data overturns some previous thinking based on morphology. The genetics gives a better picture of what is truly convergent. Features that are based on different genetics but look similar are clearly convergent - and there are examples of this. Here's a case where evolution of blue eyes in humans and lemurs is shown to have a different genetic basis. Blue eyes in lemurs and humans: same phenotype, different genetic mechanism - PubMed This isn't always the case of course, but this kind of result does demonstrate that at least some convergence is only phenotypic.
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Taq Member Posts: 10084 Joined: Member Rating: 5.1 |
My assertion: Convergent evolution is a convenient way for darwinists to explain exceptions to the supposed nested hierarchy that forms the phylogenetic tree. If separate creation were true then the exceptions should be the rule. They aren't. What we see with the prestin gene in bats and toothed cetaceans is 10-14 common derived amino acid substitutions out of hundreds. Given the importance of the prestin gene in audition (knock out mice have a >100-fold decrease in hearing, source), it is not too surprising that amino acid substitions are highly constrained and would be strongly selected for.
According to this January 2010 Science Daily article both bats and dolphins share almost identical genes for echolocation. False. They share 10-14 of the same derived amino acid substitions. You can go to NCBI and search for the genes themselves. A search for "prestin bat" or "presting dolphin" will give you the results you need. You will find that the genes are not identical. In fact, there are fewer differences between dolphins than there are between dolphins and bats. They are far from identical. It's a bit tough to show these comparisons on internet forums, but if you want I can try to figure something out (or someone else with better http skills can give it a try).
The statistical odds of the exact same mutations being selected in both species to form a working echolocating sense is nearly impossible Let's see the math.
Wouldn't a much more reasonable conclusion be a common Designer re-using a created feature? Since when is magical poofing reasonable?
I don't see anyone claiming recent common ancestry between bats and dolphins - yet genetic similarities of the same sort are used to show common ancestry between humans and chimpanzees. Are you saying that if two species share a common ancestor that they would NOT share common genes? Edited by Taq, : No reason given.
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Dr Adequate Member (Idle past 313 days) Posts: 16113 Joined: |
One point that perhaps should be made is this. Creationists are quite happy with taxonomy and the methods of taxonomy up to a certain level (or perhaps I should say an uncertain level.) When they want to identify cats as one "kind" and humans as another, they've got no problem with the results produced by real scientists, or with the taxonomic methods favored by real scientists to identify.
They do not, for example, focus in on one single isolated feature like eye-color, and declare that the concept of a "kind" is incoherent because some cats and some humans share the property of being blue-eyed, and that this is an "exception" to their concept of a "kind". No, in that case they'd be quite happy to look at all the data, because they have no religious objection to the conclusion they'd come to by doing so. But because they have a religious obligation not to accept all the results of taxonomic methods, they also need a way to misunderstand these methods when it suits them ... i.e. when one is considering any clade larger than a "kind". This seems to me to be stupid, hypocritical, dishonest, and, in a word, creationist.
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RAZD Member (Idle past 1433 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hi Wounded King, it's just a thought.
I'm not sure how that is another element to consider, since it is the whole point of both articles. They both posit convergent protein sequence evolution of Prestin as a result of selective pressures associated with echolocation. It's the issue of resonance, like a vibrating string ...
quote: Presumably the hair vibrates in response to sound. This is how sound is normally sensed, yes? Different mutations would cause different resonance frequencies (length, folding, weight distribution of the protein and change the hair), so selection for specific frequencies would result in selection for specific amino acid sequences.
But as I have been pointing out, protein sequences and amino acid substitutions are not really genetic data in and of themselves. Selection for the resonance response only selects for the same amino acid sequences not the same DNA sequences. While this selection will affect the DNA sequences to some extent it still allows a lot more variability than at the amino acid level. I would not be surprised if you could compare any convergent species and find some similarities at this level (rather than the genetic level).
For Bob's argument to make any sense the nested hierarchy really needs to fall apart at the genetic level, it is no good him just choosing an arbitrary phenotypic level and then saying, look at these supposedly convergent traits they blow a major hole in the darwinian nested hierarchy approach. I would think there would have to be a failure of any other nested hierarchy. If evidence of some kind of intelligent design "reuse" of features is being sought, then there should be multiple examples of features "borrowed" from multiple other species, to the point where no consistent nested hierarchy could be derived. Enjoy. we are limited in our ability to understand
by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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BobTHJ Member (Idle past 5026 days) Posts: 119 Joined: |
quote: You are correct. I needed to brush up on my genetics and misinterpreted this article initially. I agree that the selection of certain amino acids are far more likely than the selection of specific nucleotides.
quote: Statistics is not my strong point - and I shouldn't have made a sweeping general assertion as to the odds in question - but let's see if I can take a stab at it: 20 base amino acids14 convergent sites So, the base odds are 20^14, correct? Of course, selective pressure would reduce this by eliminating deleterious mutations over time. I recall reading recently that studies have shown approx. 70% of mutations to be deleterious. Selective pressure isn't fool-proof by any means, but for the sake of a conservative estimate let's assume that it eliminated all 70% of deleterious mutations - leaving only neutral or beneficial mutations remaining. That gives us final odds of 1 in 4.9152 10^17 which is still overwhelmingly improbable - or am I missing here? Edit: Oh, and this doesn't take into account mutations that would disable the gene - such as new stop codons. Edited by BobTHJ, : noting gene disabling mutations
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Modulous Member Posts: 7801 From: Manchester, UK Joined: |
So, the base odds are 20^14, correct? If you want to know the probability of guessing a random amino acid fourteen times in a row, you are looking in the right direction. But that's not the problem facing you - it is much more fiendish than that, I'm afraid:
quote:
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Taq Member Posts: 10084 Joined: Member Rating: 5.1 |
Statistics is not my strong point - and I shouldn't have made a sweeping general assertion as to the odds in question - but let's see if I can take a stab at it: 20 base amino acids14 convergent sites So, the base odds are 20^14, correct? For all mutations occuring at once in a single individual, yes. But that isn't how it happened. These mutations occurred separately among millions of individuals over millions of generations. Using your view of statistics no one should ever win the lotto since the odds are against them, and yet someone always seems to win on a regular basis. What you need in order to do the statistics is the population sizes, mutation rate, time period in which these mutations occurred, and the percent increase in fitness conferred by each mutation.
I recall reading recently that studies have shown approx. 70% of mutations to be deleterious. Highly doubtful. You yourself carry between 75 and 150 mutations. Most of these occur in non-coding DNA so have little to no effect. Of the mutations that change the amino acid sequence (about 3% if memory serves) I wouldn't be surprised if 70% are slightly deleterious. However, this leaves 30% that are either neutral or beneficial.
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