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Author | Topic: Evolution and complexity | |||||||||||||||||||||||
numnuts Junior Member (Idle past 6091 days) Posts: 19 Joined: |
I found this article and I thought I would post it here. I have not looked around to see if it has been done yet. It's a great article to help explain how evolution can work on a macro scale.
http://www.nytimes.com/2007/06/26/science/... I am also inserting a link to an unrelated picture I just found on My Yahoo of a horse/zebra cross breed. Nothing major just a cool pic. http://news.yahoo.com/...81/bccee8115b684ff8baf4a26cd3a944c6 I hope someone finds it interesting like me. Edited by AdminAsgara, : fixed url length to fix page width I think therefore I am...busy
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AdminWounded Inactive Member |
As it stands your post is pretty much just a couple of bare links. There certainly doesn't seem to be any clear connection to the topic. Would you have any objections if I moved this post to the 'Links and Information' forum instead, it looks like that would be a more suitable place.
TTFN, AW
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numnuts Junior Member (Idle past 6091 days) Posts: 19 Joined: |
Please do.
I posted the article here because it has to do with evolution. If you think it fits better somewhere else be my guest. I think therefore I am...busy
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jar Member (Idle past 395 days) Posts: 34026 From: Texas!! Joined: |
And fix them long ass links while you are at it.
Aslan is not a Tame Lion
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dwise1 Member Posts: 5930 Joined: Member Rating: 5.8 |
Basically, evo-devo looks a lot like what Dawkins was saying in The Blind Watchmaker. His Mac program, Blind Watchmaker (in Chapter 3), was based on the idea of small changes in the genotype resulting in large changes in the phenotype.
Slightly tangentially, it seems that a lot of standard creationist misrepresentations about mutations is that they concentrate largely on developmental mutations, in which the mutation is in the phenotype, not necessarily in the genotype. Rather the only mutations that are of interest in evolution are the mutations in the genotype -- ie those that will be carried in the genetic material in the gametes -- , because only those can be inherited. So part of the name of the game is that the only mutations that count are in the genotype, but selection does not act upon the genotype but rather on the phenotype. So how do we get the phenotype from the genotype? Through development. So in that sense, evo-devo is nothing new; we've known about it all along. What it does appear to contribute, though, is that it tries to figure out just how the genes direct development. Edited by dwise1, : Added the slight tangent.
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AdminWounded Inactive Member |
I have opened a new thread NY Times article on evo-devo for this derail.
Please reply to this topic there. This is off topic for this thread! TTFN, AW
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Simonsays Junior Member (Idle past 6105 days) Posts: 29 From: Ca., U.S.A. Joined: |
Percy,
Obviously I believe they are not correct, at least not in the the highly generalized way they are being applied. So what I'm really arguing is semantics, I guess. If the mechanism is supposed to be a general negative feedback cycle I can't picture/model that in my mind. If it is a special case (ie, one selective presssure affecting a single trait/character) then no problem... I think that you guys have clearly shown that that will lead to a stopping and not just a slowing down of change. I will address those other examples tomorrow hopefully, in replies to the posters who posted those analogies. Pesto and Nosyned,I believe. As to your improved Thermal analogy; I think you left off the selective pressure part, if it's meant to apply to the general case i'm objecting to. Continuing your analogy and using thermal energy as the selective pressue: I think I can improve upon the thermos analogy by substituting a temperature gradient, meaning things are at different temperatures. The laws of thermodynamics want to smooth out a temperature gradient so that everything is at the same temperature. Heat flows toward cold. So when a cup of coffee is at the same temperature as the air, then there is no heat flow. The cup of coffee doesn't have to know that it's the same temperature as the air, that's just the way heat flow works. This is analogous to a population that is well adapted to its environment. And when a cup of coffee is much hotter than the surrounding air, then there is a net heat flow from the coffee to the air. This is analogous to a population that is not well adapted to its environment. The flow of heat is analogous to change in allele frequencies in the population. --PercyAnd I take this coffee and pop it in the microwave... Turn it on high. Now The coffee and the surrounding air differentially absorb this microwave energy. That is the selectivepressure. Now, since they are at different temperatures, heat begins to flow again.Then changes in allele frequency happen again to the population(they continue to evolve)( Result-no stasis) Edited by Simonsays, : Word changes. Edited by Simonsays, : Punctuation errors, and typos. Added the word "Negative" and changed "keeping" to "using". Edited by Simonsays, : wording; flows-flow.
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Percy Member Posts: 22394 From: New Hampshire Joined: Member Rating: 5.2 |
Simonsays writes: I think you left off the selective pressure part... No, it's in there, but let's look at your own analogy first.
And I take this coffee and pop it in the microwave... Turn it on high. Now The coffee and the surrounding air differentially absorb this microwave energy. That is the selective pressure. So the microwave energy being absorbed by the coffee and causing the coffee to heat up is selective pressure. Hopefully I have this right and am just rephrasing what you just said. Let me know if I have this wrong, though, because there's no point in you reading on if I've got this part wrong. So you go on to say:
Now, since they are at different temperatures, heat begins to flows again.Then changes in allele frequency happen again to the population(they continue to evolve)( Result-no stasis) Is the microwave off now? Because if the microwave is the ultimate source of selection pressure, then turning it off removes the selection pressure, and once the selection pressure is gone there should be no change in allele frequency. Or is the microwave still on? If so, then why do you mention heat flow in connection with changes in allele frequency? In other words, I think you're confused about which part of your scenario is analogous to selection pressure. Is it microwaves or heat flow? If we go back to my analogy you'll see that it more neatly explains the situation. Don't worry about how the coffee got hotter than the surrounding air, it just is. The coffee will attempt to reach equilibrium with its environment by allowing heat to flow from it to the air. The heat flow is analogous to changing allele frequencies, and how close the temperature of the coffee and air are to each other is a measure of adaptation. Zero temperature difference corresponds to perfect adaptation where no more heat flows and allele frequencies no longer change. --Percy
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Simonsays Junior Member (Idle past 6105 days) Posts: 29 From: Ca., U.S.A. Joined: |
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quote: When I wrote... the selective pressure ... , I did not mean The with a capitol "T". As in one and only one selective pressure. I meant it to represent the more pressure (ie, more selective pressure) as in dwise1's quote. Here again is dwise1's quote that I took exception with:
quote: selection[/i] in his quote. However, I believe it was implied when he said quote:Likewise, I think dwise1 did the same thing with his adaptation analogies. quote: It as in one ? I think that's a special/unrealistic case.
quote: Sure. Microwave ovens have timers... They don't run forever.
quote: I never said it was the ultimate/only source.
quote: How so ? Your heat flow and my Microwave input are equivalent. They're both energy flows.
quote: Because you do. You compare (say it's analogous) to changes in allele frequency of a population.
quote: What's the difference here?
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dwise1 Member Posts: 5930 Joined: Member Rating: 5.8 |
I do not believe that selective pressure could be represented by a heat differential. Selective pressure would come from the survival requirements exacted by the environment. A lush environment in which food is relatively plentiful and predators are relatively few would exert a lower selective pressure; the standards would be more lax. A harsher environment would exert a higher selective pressure with tighter standards of what it would take to survive and reproduce.
Rather, what the temperature difference between the air and the coffee would represent would be how different a population is from an optimal set of characteristics for survival in that environment. The further away that population is from that optimal set of characteristics, the more rapidly we would expect it to move in the direction of that set of characteristics. But once it has arrived at that set of optimal characteristics, then selective pressure will hold it there. In that harsher environment, selective pressure never lets up, even though the perceived results of that selective pressure is different. Regardless whether a population is moving towards a set of optimal characteristics or it is holding tight to that set of optimal characteristics, it is as a result of the continuing application of selective pressure. Regardless of where the population is with respect to that optimal set of characterisics, selection happens! If you really feel so strongly that stasis is due to the absense of selective pressure, then perhaps you can offer an explanation for how evolution magically turns on and off. As in the thermos joke, how does evolution know when to turn on and when to turn off? My answer is, as in the case of the thermos, evolution never turns off.
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Simonsays Junior Member (Idle past 6105 days) Posts: 29 From: Ca., U.S.A. Joined: |
quote: Percy, I qualified my statement. You left this part out of your quote:
quote: I'm used to seeing selective quoting like this from Creationists, not evolutionists... I trust it was unintentional. Edited by Simonsays, : Words were ommitted when I submitted my reply.
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Percy Member Posts: 22394 From: New Hampshire Joined: Member Rating: 5.2 |
Simonsays writes: quote:Percy, I qualified my statement. You left this part out of your quote: quote: I'm used to seeing selective quoting like this from Creationists, not evolutionists... I trust it was unintentional. No, I left it out intentionally because my analogy applies to your "general case" objections. I think it must be a case of this particular analogy just not working for you, but let me give it one more shot. A population experiences changing allele frequencies when it is not well adapted to its environment. A cup of coffee experiences changing temperatures when it is not the same temperature as its environment. A population experiences relatively stable allele frequencies when it is well adapted to its environment. A cup of coffee experiences no change in temperature when it is the same temperature as its environment. In this analogy, a population is in equilibrium with its environment when it is well adapted to it. And a cup of coffee is in equilibrium with its environment when it is the same temperature as it. Changing allele frequencies are what happens to a population not in equilibrium with (not well adapted to) its environment. And net heat flow is what happens when a cup of coffee is not in equilibrium with its environment. The purpose of the analogy is to illustrate how organisms don't need to "know" they should change or stop changing. The change just happens through the application of the known physical laws of the universe. In the same way, the coffee doesn't need to "know" when it should start or stop changing temperature. The application of the known physical laws of the universe will cause the coffee to stop changing temperature as soon as it is in equilibrium with (same temperature as) its environment. And just as evolution doesn't stop just because a population is well adapted to its environment, heat flow doesn't stop just because a cup of coffee is the same temperature as its environment. But any minute change in the population away from equilibrium will put it out of equilibrium with its environment (it will be less well adapted), and the natural laws of the universe strive to restore equilibrium (restore good adaptation). And any minute change in the temperature of the coffee will put it out of equilibrium with its environment and again the natural laws of the universe will strive to return it to equilibrium, so that even though there might be minute temperature changes resulting from minute heat flows in and out of the coffee, the net heat flow will be zero. If this analogy doesn't work for you then we'll just move on to some other explanatory approach. --Percy
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Percy Member Posts: 22394 From: New Hampshire Joined: Member Rating: 5.2 |
dwise1 writes: I do not believe that selective pressure could be represented by a heat differential. I gather you say this is because you're thinking of selection pressure as independent of adaptation. For example, you say this:
Selective pressure would come from the survival requirements exacted by the environment. So if we consider a relatively unchanging environment, you would consider the selective pressure of that environment to also be a constant. I think you're probably saying this because there is always selection occurring, but what you're missing is that the net result of this selection is no change. It is net selection that's important, not the constant selection events that eliminate offspring that are too far from good adaptation. This constant selection that results in zero net selection is analogous to the coffee cup at the same temperature as its environment, since there is a constant exchange of heat with the environment back and forth, but no net heat flow, no temperature change. I think you're thinking of a population that is already well-adapted to its environment as being kept there by an active selective pressure, as if it were a force pressing in on it from all sides and keeping it in one place. But place a ball bearing in a bowl and it will come to rest at the lowest point where it experiences no forces. It is only when you give it a small nudge that it experiences forces that return it back to lowest point. So heat-differential does have some good analogous qualities to selection pressure. When there's no heat differential, there is no reason for temperatures to change, they're already the same. In the same way, when there's no selection pressure because the population is already well-adapted to the environment then there's no reason for the population to change. --Percy
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Modulous Member Posts: 7801 From: Manchester, UK Joined: |
...and opposite selective pressure...
Now The coffee and the surrounding air differentially absorb this microwave energy. That is the selectivepressure. Now, since they are at different temperatures, heat begins to flows again.Then changes in allele frequency happen again to the population(they continue to evolve)( Result-no stasis) If there is no physical constraints, the coffee could theoretically get hotter and hotter for ever. That doesn't happen of course, eventually the energy going into the microwave would equal the energy going out of the microwave. Eventually the coffee will vapourize. Physical constraints will mean that a stasis point will be reached - even as the mechanism that gave selective pressure remains the same. Other selective pressures will start to push in the opposite directions until the the two pressures cancel each other out and we get stasis. At some point during stasis we could remove one of the selective pressures, and then stasis would likewise go. For example, if we increased the pressure within the microwave sufficiently we could force the coffee back into a puddle of coffee on the microwave floor and we can continue heating it as a 'cup' of coffee. If we shielded the microwave better we could heat the coffee vapour up. If we turn the microwave off the stasis would be removed and the coffee would cool and condense (the pressure to equalize temperature with the rest of the universe would overcome the now non-existent pressure to warm the coffee up). This is the best way to take the analogy for evolution purposes: since selective pressures can drive a population to running faster, but eventually other selective pressures start preventing the population from attaining any more speed (animals have to save energy for things other than running fast or they will die without reproduction). Remove the pressure for running fast (turn the microwave off) and the population will probably begin to slow, using its resources for other things. Remove the need to spend energy on other ventures (increase the pressure in the microwave) and the population may continue to increase in speed. I realize that I've simplified. Coffee is dissolved in water so it isn't the coffee that will be vapourized for example (unless its one hell of a microwave oven!), but I trust you'll see the spirit in which the analogy was considered.
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dwise1 Member Posts: 5930 Joined: Member Rating: 5.8 |
..., but what you're missing is that the net result of this selection is no change. No, I haven't been missing that. That is exactly what I've been arguing for all along. Your earlier exposition in #87 makes a lot more sense now. However, no model or analogy is complete nor completely applicable.
I think you're thinking of a population that is already well-adapted to its environment as being kept there by an active selective pressure, as if it were a force pressing in on it from all sides and keeping it in one place. But place a ball bearing in a bowl and it will come to rest at the lowest point where it experiences no forces. It is only when you give it a small nudge that it experiences forces that return it back to lowest point. What I have been thinking of all along are two cases -- one where the population is not well-adapted to its environment and the other where it is -- and that the same evolutionary processes are active in both cases. But rather than the ball bearing being at equilibrium by coming to rest at a stable lowest point (what I recall as being called "static equilibrium"), it is at an unstable high point with the forces working to keep it there (which I recall as being called "dynamic equilibrium"). In the example of the coffee being at equilibrium with the surrounding air, we find that as the temperature of the surrounding air changes, the coffee's temperature will try to track it, but if the air remains at a constant temperature then the coffee will remain at in static equilibrium. But there all the changes that would throw the coffee out of equilibrium are changes in the environment, not in the coffee itself. But what I see as happening in a population is that the population itself will tend to throw itself out of equilibrium -- it is in dynamic equilibrium. With each generation, the population mean will drift away out of equilibrium. Selective pressure is needed to hold it at that equilibrium point. Instead of a ball bearing
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