Convergent Evolution - Reasonable conclusion? or convenient excuse?

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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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.

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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.

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In terms of the DNA sequences the paper specifically states ...

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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.

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... 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.

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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.

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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.

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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 acids
14 convergent sitesSo, 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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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.

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Agree with your second sentence. However, this doesn't explain how both bats and dolphins independently developed a protein sharing the specific formatting required to make it sensitive to high frequencies - and yet other mammals did not.

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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.

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Agree. The problem becomes: how do you make the determination? How do you decide between "This similarity is a result of common ancestry" and "This similarity is the result of convergent evolution"? I'm still convinced the answer is "Which better fits our neatly organized phylogenic tree?"

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The nested hierarchy is deduced by looking at lots of traits - looking at one will give odd results.

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Were I a darwinist attempting to assemble a phylogenetic tree then I agree with this assessment. However, as I mentioned in my previous post, where do you draw the line? Not all traits fit neatly into a nested hierarchy.

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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.

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The overall evidence for a nested hierarchy is not high - the many cases of 'convergent evolution' demonstrate this. What does have a lot of evidence is the conclusion that creatures with similar morphological features will share similar genes. However, this conclusion does not support common ancestry and more than it supports baraminology.

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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.

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This does nothing to prove or disprove common ancestry - all it demonstrates is that there are multiple methods of expression for any particular outcome - the genetic code has told us this for quite some time.

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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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I would not dispute this statement.

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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

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I agree with the gist of this - and yes, were the prestin substitutions the only similarity then it might be feasible (though still improbable) that echolocation were to evolve convergently in separate species. But consider that both classifications would also need to separately evolve enhanced cochlea and a high-frequency sound emission system and we're suddenly increasing the complexity and subsequent odds substantially - even if the genetics may look different.Also, look at the inverse: if selective pressure for prestin is so high then why have not all mammals evolved the enhanced prestin of dolphins and bats? I have a hard time picturing a situation where hearing higher frequency sound wouldn't be an increase in fitness.

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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).

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Thanks for the NCBI link....I didn't realize that stuff was available online for free

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Are you saying that if two species share a common ancestor that they would NOT share common genes?

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No....common ancestry would imply a close genetic makeup.

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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.

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So, is your viewpoint: we can't really figure out a good statistic, so we'll just assume it happened?

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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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Yes, I'm sorry. I meant to say non-synonymous mutations are 70% deleterious - which is what fits with my math.

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Hi BobTHJ, and welcome to the fray.

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Thank you, I appreciate the comprehensive reply!

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While there are only 100 instances listed in the wiki article, and I don't call 100/1.9X10^6 = 0.005% a significant problem.

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I haven't looked, but it is probably safe to assume that the vast majority of these species are the result of recent variation (we may define 'recent' differently, but suffice it to say that they have very close relatives) so it seems your figure should be substantially less. I also doubt that the wikipedia article is comprehensive in nature as I've seen mentions of several hundred or more cases of convergency. As a result it is likely the percentage is substantially higher than .005%.As I stated in another thread - I suspect the phylogenetic tree to be a 95%+ accurate categorization of living organisms (ontology only - no common descent implied) - with these non-conforming cases composing the other <5%. Just stating this for the record so everyone knows where I stand.

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Where you draw the line is based on the preponderance of evidence at the detail level.

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Yes - and that seems to be what happens. Organisms are placed into the phylogenetic tree at the location where they show the most similarity to the surrounding organisms. This reflects a good ontology model - though it does lead to some inconsistency since some organisms classed in different clades still share similarities not shared by other closely classed organisms.

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How does ID account for what we see genetically in cases of convergent evolution, where the phenotypic similarity is belied by a completely different genetic underpinning?

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Does ID have something to account for or explain? Convergence is a (potential) problem for common-ancestry evolution, not ID. The common Designer readily explains any convergence under ID.

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Why did Carl Linnaeus, who died 80 years before Darwin published the Origin of Species and believed that all life existed in immutable forms laid down by God, place all animal life into a nested hierarchy then? Why does that system, laid down 250 years ago, broadly persist to this day? Why haven't the tens of thousands of taxonomists working since that time noticed that this nested hierarchy doesn't match reality as you assert?

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The answer, of course, is that as a matter of fact life does form nested hierarchies. And the hierarchies it forms look very similar whether you look at genetics, morphology or fossil data.

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Let me clarify - as I really botched it earlier.95%+ of organisms fit nicely into a nested hierarchy. However, the hierarchy can not fully model that last <5% because there will be shared features/genes with other not closely grouped organisms.And, though I've posted it elsewhere I'll restate it here for completeness: nested hierarchy does not imply common ancestry - only a semi-reasonable ontological model.

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So, how much convergence would be expected to occur under the evolutionary scenario? How much convergence is there? How unlikely is that to have occurred by chance? iIf there is an excess, what leads you to think there is no natural mechanism out there to account for it?

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If you can answer these questions, you will be on your way to building a case.

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And I can not. In hindsight I started this topic without first doing the appropriate research to educate myself. I apologize to everyone. I'll add this to my growing list of topics to research in-depth.In the end here though I am accomplishing my goals for joining the discussion at this site. I'm learning a lot about science - including how to coherently defend my conclusions. I'm also learning about some areas where those conclusions seem to fall flat - so I will dig deeper into learning about those topics to see if my conclusions are unfounded. Thanks to all of you for assisting me in this endeavor.

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And again, we are looking at superficial resemblance. One of the better examples is the duck and the platypus. From the outside their bills do resemble one another. However, when you examine the underlying skeletal structure they are not alike at all. The platypus has a mammalian jaw complete with a single lower dentary bone and even cusped cheek teeth. The duck has a very standard bird jaw with multiple lower jaw bones and no cusped teeth. If you want to argue that a designer is reusing designs then why do we see a similar structure derived from such different sources?

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Common design is evident in all aspects of our universe - from the atomic to the astronomic. Grouping by similarity occurs at various levels in Biblical contexts as well. Cases of common morphology without common genetics does not make common design an unreasonable conclusion.

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So if we found examples of non-convergence this would be evidence against a common designer?

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If we failed to find significant similarity between life forms it would evidence against a common designer.

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Can you think of anything that would? And does it make a more reasonable conclusion than the one we already have which is supported by the material processes we can observe and understand?

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Of course - if organisms lacked significant similarity to each other then you would have evidence against common design. For example, if organisms didn't share a similar cell structure but instead most used a basic anatomical unit that was different from other organisms this would be evidence against common design. Or if organisms didn't all use DNA/RNA but instead each used its own method of storing data - that would be evidence against common design.Both are fairly reasonable conclusions - they both fit the data.

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Of course, and you also must realize that opinion is completely impotent at altering reality in any way. You are free to hold whatever opinion you wish, but if you are ignoring reality and evidence that contradicts your opinion, the only one you are fooling is yourself.

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Of course. You disagree with my opinion that the phylogenetic tree correctly models similarity (both morphological and genetic) to a degree higher than 95%? I didn't think many people would fight me on that assumption.

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Perhaps you would like to offer some evidence to show what you mean? Are you talking about lost traits?

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Sure, echolocating in bats and dolphins. They are not classed together in the phylogenetic tree (nor should they be if you want the most accurate ontological model possible) yet share a similarity not shared by other closely grouped organisms.

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With design there is no reason for these two trees to be the same.

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With evolution the two trees must be the same, and they are.

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A high degree of correlation between genomes and morpholocial features fits well with a design hypothesis. Just because darwinian evolution fails without that correlation doesn't mean it is the more reasonable conclusion.

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However, while such a hypothetical supernatural being might have done anything, evolution can only do a circumscribed set of things: and we find that those are the only things that we actually observe.

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Now, how are we to account for this?

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(a) By a complete coincidence, God's whims always led him to create just those things that the theory of evolution would predict.

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(b) God deliberately created the living world in such a way as to fool biologists into thinking that it was the product of evolution.

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(c) Evolution happened.

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Hmm...you see this as evidence for evolution. I see this as those who wish to deny the existence or involvement of God* devising the most reasonable naturalistic explanation to explain His creation. Not at all unlikely.*And because I know it's coming - no I'm not implying all evolutionists are atheists.