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Author | Topic: Convergent Evolution - Reasonable conclusion? or convenient excuse? | |||||||||||||||||||||||||||||||
bluegenes Member (Idle past 2497 days) Posts: 3119 From: U.K. Joined: |
BobTHJ writes: 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. I don't. Let's help your picturing. Think of the times when you're trying to listen to something specific, but there's all kinds of background noise. The more background noise messages entering your brain, the harder it is to concentrate on what's important at the time. For every mammal, because of the specific way it operates in its environment, there will be an optimum position on the hearing frequency levels that's best for them, and also an optimum breadth of their range. An increase in the breadth of the range will only be selected for if the advantages of hearing the extra sounds outweighs the "background noise" disadvantages. Extending the breadth into higher frequencies could be an advantage for night flying hunters and swimming hunters in certain circumstances, but would be interference to those individuals of our own ancestors who mutated the characteristic, so it would have faced negative selection, rather than positive. If I'm not right about this, all mammals would have much broader hearing ranges than we actually do. Instead, natural selection has focused on the priorities of different creatures in different circumstances, and hearing is specialised, rather than just bringing in maximum noise to the brain, and giving us unnecessary headaches.
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Percy Member Posts: 22479 From: New Hampshire Joined: Member Rating: 4.7 |
Also, brains use more resources per ounce than any other body part. The processing centers for echolocation are relatively substantial, and there would be high selection pressure against this allocation of resources unless its utility for the organism was very high.
AbE: I just discovered that bats (and maybe dolphins, too) have techniques they must employ to avoid deafening themselves when they emit echolocation sounds. Also, both predators and non-predators would find their survival chances negatively affected if their echolocation signals gave away their position, so even if echolocation provided them advantages in some respects, it would have disadvantages in others. --Percy Edited by Percy, : Add AbE.
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Percy Member Posts: 22479 From: New Hampshire Joined: Member Rating: 4.7 |
BobTHJ writes: 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... What are the significant differences between a bat cochlea and, say, a human cochlea? What are the significant differences between bat vocalization and, say, human vocalization? Once you know the differences then you can better decide if any extraordinary difficulties would be involved in evolving them. My guess is that the differences are primarily shape, size, and (for the cochlea) number of hairs and the number of nerves traveling to the brain. How would you compare the odds of a process that we have observed and that is known to produce the precise type of phenotypic and genetic evidence we observe, to the odds of a process that has never been observed and whose details are therefore completely unknown. --Percy Edited by Percy, : Grammar, improve clarity.
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Dr Adequate Member (Idle past 305 days) Posts: 16113 Joined: |
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. Yeah, it's like the odds against two balls on the same slope independently rolling in the same direction and ending up in the same place. --- Sonar is better when frequencies are higher. So of course natural selection must favor similar adaptations in any species using echolocation. This is not something that happens at long odds, it's a certainty. What would take long odds would be the independent production of analogous organs and genes for this purpose so similar that they appeared homologous; which, of course, has not happened.
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? Because the selective pressure is only so high in species which use echolocation (because shorter wavelengths resolve finer details).
I have a hard time picturing a situation where hearing higher frequency sound wouldn't be an increase in fitness. Oh look, it's the Argument From Undesign! The ramshackle, hit-and miss process of evolution should have produced your idea of perfection. But it didn't --- it produced something you think is inadequate and imperfect, which we should therefore ascribe to a perfect, all-knowing, and benevolent God. --- The fact is that evolutionary adaptations to the genotype are unlikely to produce a perfect phenotype. There will usually be a trade-off. In this case, it seems reasonable to guess that adaptations to prestin making it better for the detection of high-frequency sounds make it worse for the detection of low-frequency sounds. But that's just the evolutionary explanation. Obviously the creationist view would have to be that God's screwed up again. Edited by Dr Adequate, : No reason given. Edited by Dr Adequate, : No reason given.
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 8.3 |
I have a hard time picturing a situation where hearing higher frequency sound wouldn't be an increase in fitness. Why? What survival benefit would we gain from hearing ultrasound? How about a dog? An elephant? Generally speaking smaller things make higher pitch noises, and the bigger you are the less interested you are in what small things are doing. Know the high pitch whine of various insects wings? Irritating, isn't it? But where's the benefit? Stick the threshold of hearing into the ultrasound and all you get is a load more insects whose wing-beats are an irritating whine intruding in your world but whose existence is entirely irrelevant to you. So I'm not seeing a big difference benefit to higher hearing thresholds. Now the cost. Hearing "hair" cells are arranged in the inner ear in order so you get the cells that respond to the lowest pitch first, and so on deeper into the ear until you reach the cells which respond to the highest pitch (IIUC the cells are similar, but the shape of the cochlea focus different sounds to different points but don't quote me on that). Increasing the auditory range would either mean altering the "step" on these cells, reducing the fidelity of the auditory input so you had less ability to distinguish sounds across the most useful part of the range or having a deeper cochlea with more cells. That means more cells, a bigger cochlea, more nerves to receive this input and more brain required to interpret the input. That's a cost in terms of energy to build and maintain. So, you see, a higher frequency hearing would have few benefits and non-zero cost so like so many other things, we see a trade off between costs and benefits. Something evolution works to optimise.
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BobTHJ Member (Idle past 5018 days) Posts: 119 Joined: |
quote: So, is your viewpoint: we can't really figure out a good statistic, so we'll just assume it happened?
quote: 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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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 8.3 |
So, is your viewpoint: we can't really figure out a good statistic, so we'll just assume it happened? No, you've got it backwards. This is how it goes: Science: the overwhelming consilience of evidence points to the evolutionary explanation.You: But Bats and Dolphins have similar proteins that's so improbable evolution can't have happened. Us: Show us the probability See how this is you being challenged to back your argument? We accept evolution because of the evidence for it. If you wish to challenge that position with a probabilistic argument you have to have some actual maths to back you up otherwise all you're doing is arguing from personal incredulity, and that's not terribly convincing at all.
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BobTHJ Member (Idle past 5018 days) Posts: 119 Joined: |
quote: Thank you, I appreciate the comprehensive reply!
quote: 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.
quote: 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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BobTHJ Member (Idle past 5018 days) Posts: 119 Joined: |
quote: 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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Taq Member Posts: 10033 Joined: Member Rating: 5.3 |
So, is your viewpoint: we can't really figure out a good statistic, so we'll just assume it happened? My viewpoint is that anyone who claims it is statistically improbable to the point of impossible is full of shit.
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Taq Member Posts: 10033 Joined: Member Rating: 5.3 |
The common Designer readily explains any convergence under ID.
So if we found examples of non-convergence this would be evidence against a common designer?
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BobTHJ Member (Idle past 5018 days) Posts: 119 Joined: |
quote: 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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BobTHJ Member (Idle past 5018 days) Posts: 119 Joined: |
quote: 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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BobTHJ Member (Idle past 5018 days) Posts: 119 Joined: |
quote: 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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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
Cases of common morphology without common genetics does not make common design an unreasonable conclusion. 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? TTFN, WK
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