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Author Topic:   Convergent Evolution - Reasonable conclusion? or convenient excuse?
bluegenes
Member (Idle past 1717 days)
Posts: 3119
From: U.K.
Joined: 01-24-2007


Message 31 of 107 (564652)
06-11-2010 3:27 PM
Reply to: Message 28 by BobTHJ
06-11-2010 12:30 PM


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: 20770
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.1


Message 32 of 107 (564653)
06-11-2010 3:38 PM
Reply to: Message 31 by bluegenes
06-11-2010 3:27 PM


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: 20770
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.1


Message 33 of 107 (564657)
06-11-2010 3:51 PM
Reply to: Message 28 by BobTHJ
06-11-2010 12:30 PM


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 291 days)
Posts: 16112
Joined: 07-20-2006


Message 34 of 107 (564698)
06-11-2010 8:32 PM
Reply to: Message 28 by BobTHJ
06-11-2010 12:30 PM


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 (Idle past 1344 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 35 of 107 (564838)
06-13-2010 4:19 AM
Reply to: Message 28 by BobTHJ
06-11-2010 12:30 PM


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 4237 days)
Posts: 119
Joined: 06-02-2010


Message 36 of 107 (564839)
06-13-2010 4:24 AM
Reply to: Message 15 by Taq
06-09-2010 4:47 PM


Re: A good case study
quote:
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.

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

quote:
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.

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 (Idle past 1344 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 37 of 107 (564841)
06-13-2010 5:04 AM
Reply to: Message 36 by BobTHJ
06-13-2010 4:24 AM


Re: A good case study
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 4237 days)
Posts: 119
Joined: 06-02-2010


Message 38 of 107 (565038)
06-14-2010 1:07 PM
Reply to: Message 21 by RAZD
06-09-2010 7:55 PM


Re: superficial similarity but differences in the details
quote:
Hi BobTHJ, and welcome to the fray.

Thank you, I appreciate the comprehensive reply!

quote:
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.

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

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 4237 days)
Posts: 119
Joined: 06-02-2010


Message 39 of 107 (565079)
06-14-2010 5:15 PM
Reply to: Message 22 by Percy
06-09-2010 9:30 PM


Re: What is the ID Explanation?
quote:
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?

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: 8519
Joined: 03-06-2009


Message 40 of 107 (565084)
06-14-2010 5:26 PM
Reply to: Message 36 by BobTHJ
06-13-2010 4:24 AM


Re: A good case study
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: 8519
Joined: 03-06-2009


Message 41 of 107 (565086)
06-14-2010 5:28 PM
Reply to: Message 39 by BobTHJ
06-14-2010 5:15 PM


Re: What is the ID Explanation?
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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Replies to this message:
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BobTHJ
Member (Idle past 4237 days)
Posts: 119
Joined: 06-02-2010


Message 42 of 107 (565093)
06-14-2010 6:10 PM
Reply to: Message 23 by Dr Jack
06-10-2010 4:13 AM


quote:
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?

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.


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 4237 days)
Posts: 119
Joined: 06-02-2010


Message 43 of 107 (565096)
06-14-2010 6:20 PM
Reply to: Message 25 by Peepul
06-10-2010 6:23 AM


quote:
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?

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


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 4237 days)
Posts: 119
Joined: 06-02-2010


Message 44 of 107 (565098)
06-14-2010 6:24 PM
Reply to: Message 26 by Taq
06-10-2010 11:14 AM


quote:
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?

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 (Idle past 3334 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 45 of 107 (565102)
06-14-2010 6:34 PM
Reply to: Message 44 by BobTHJ
06-14-2010 6:24 PM


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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