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Author Topic: Darwinian evolution
maybe.logic
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Icon 1 posted June 28, 2006 08:58      Profile for maybe.logic     Send New Private Message       Edit/Delete Post   Reply With Quote 
For those who say evolution is entirely based on random, purposeless mutations -- not directed by some sort of coherent, orderly force -- I must ask: How could the first amphibious fish breathe atmospheric oxygen if the current theory of stochastic natural selection is true? How did lungs evolve entirely independently of the environment in which they would function? The modern theory of Darwinian evolution tells us that genetic mutations are completely random and that if a trait happens to be desirable and useful in the ecosystem it is quite by accident. But the theory also tells us that traits which will be used in a particular environment must have evolved in that environment. That is, environmental pressures for one ecosystem are generally quite different from those in another. So... if this theory is true, which most tenured biologists will swear by, how could the first land creatures have evolved lungs? An aquatic environment is obviously completely different from a continental one. The lungs must have evolved in the fish while they were still exclusively in the ocean. And if that is true, there are all sorts of interesting extrapolations to make. One could infer that the apparatus for breathing air was already programmed into the DNA. Furthermore, one could hypothesize that evolution is not at all purposeless and has a clear direction to higher complexity and constitutes a coherent process rather than stochastic chaos. Incidentally, this would also lend plausibility to Leary/Wilson's theory that neural circuits for a future state of humanity are already in some kind of chrysalis form in our brains.
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Mac D
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Icon 1 posted June 28, 2006 09:10      Profile for Mac D     Send New Private Message       Edit/Delete Post   Reply With Quote 
But what if the first creature to exsit on land was first in the mud near the shore?

It might have been there for protection from preditors in the water. It would be difficult for a preditor to get the creature in very shallow waters. And with tides going in and out and the like the first "Lung fish" may have indeed been in and out of the water for short periods of time and over hundreds to thousands of generations developed the lungs. And since plants would have devloped on land far before animals a food source would have been created.

Also laying eggs to protect the young could have been a reason. The parents could have died on the beach when laying eggs. We don't know how the tides worked on Pangia (Spelling?) Maybe during the winter or sumer the tides worked different so that the young could saftley hatch on the beach and go right to the water.

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TheMoMan
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Icon 1 posted June 28, 2006 09:33      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
maybe.logic_________________________there is a member of the cat fish family that has the ability to leave drying ponds (drought) and cross narrow land masses to get to deep water. Now this should not be possible if it must get its oxygen only from gills.

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maybe.logic
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Icon 1 posted June 28, 2006 09:37      Profile for maybe.logic     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by TheMoMan:
maybe.logic_________________________there is a member of the cat fish family that has the ability to leave drying ponds (drought) and cross narrow land masses to get to deep water. Now this should not be possible if it must get its oxygen only from gills.

This is an interesting answer to my question, but I don't really understand it very well. It seems to replace the original question with a new one. It's a bit like the general theory of relativity. Before Einstein, it was generally accepted that mass causes gravity. Nobody had any idea why. Einstein came along and showed that it is the curvature of spacetime in the presence of massive objects which, by its geometry, induces gravitational fields. Revolutionary, but, it replaces an old question with a new one. Instead of asking why mass causes gravity, now we must ask: why does mass bend spacetime? Applying the analogy to this thread, I still have to wonder how, ultimately, these lungs evolved at all. If the water ecosystem in which a certain group of fish live is too warm or stagnant to contain enough dissolved oxygen, how can the fish possibly have survived long enough to evolve lungs? Either there is enough oxygen, and the fish live, or there is not, and they die in less than one generation. It takes many hundreds or thousands of generations for new traits to develop according to most biologists (with the exception of Steven Jay Gould and his "punctuated equilibrium" model), so, even with momans explanation, I see no real resolution to my original question. The original question was: how did fish evolve lungs in order to breathe on land? The explanation: they needed more air, as there was not enough in the water. Now we've gone in a circle and have to ask another question: if they originally evolved lungs because there wasn't enough oxygen in the water for satisfactory metabolism, how could they possibly have survived long enough to develop the lungs and saturate the gene pool with the modification?
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Stereo

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Icon 1 posted June 28, 2006 09:56      Profile for Stereo     Send New Private Message       Edit/Delete Post   Reply With Quote 
They evolved by natural selection. That's what Darwin explained. Mutations occurs naturally. The fittest (read the individual having a mutation best adapted to its current evironment) have greater chance of success. The most successful reproduces, and pass its genes to another generation, until another mutation occurs. It's how species evolve. It takes millions of years, but guess what? Life on Earth existed for long enough to have supported many MANY mutations.

So, adapted to your question, a fish had a mutation that gave it the first step to having lungs. Mabe that gene was already present before, but didn't gave any specific advantage, while not disadvantaging the individuals having it, so is spread somewhat in the population. Then a change of environment (a drought? being chased away by predators/fitter specy for the previous environment? other?) suddenly gave an advantage to the individuals having it, ensuring further spreading. Then another mutation occured, spread, etc. until the point where descendant of the original specy had full grown lungs as we know it now.

Enough of an answer, or you want me to dig the lastest studies on the subject?

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Xanthine

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Icon 1 posted June 28, 2006 10:07      Profile for Xanthine     Send New Private Message       Edit/Delete Post   Reply With Quote 
I've got work to do so I'll be brief. It is that nature of science to replace on question with a few dozen more. This is not a flaw. To understand the natural world, you must ask questions and challenge the answers. I find it rather exciting and stimulating myself.

First of all, catfish and lungfish aren't the only fish that need air. Betta fish also need to breath from the surface, which is why if you shouldn't have too many plants near the surface of your betta's tank.

Second of all, you seem to misunderstand evolution. Yes, mutations are random, but not completely random. Out of one desirable trait come others. Imagine you have a bag of bags of bags. You take out one bag at random, open it up, take out another bag at random, open that bag and so on. The contents of each bag is different from the contents of the other bags.

Finally, while ecosystems are different, there are some constants. There's air at the surface of every body of water. Ice floats in every body of water. There is usually mud and plant at the shore of any given body of water. Unless you're in a cave, there's sunlight as well. And gravity works the same wherever you go.

MacD, I'd lay money on the tides being more or less the same on Pangaea as they are now. There was a moon back then and, AFAIK, gravity does not change.

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littlefish
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Icon 1 posted June 28, 2006 10:09      Profile for littlefish   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Either there is enough oxygen, and the fish live, or there is not, and they die in less than one generation.
Which assumes that all the fish are the same, and the habitats are the same. And this assumption is rubbiish.

Natural variation within the species means that some have a better ability to absorb oxygen, possibly through having a rougher skin, which gives a greater surface area for transport across the membrane. This is probably also detrimental, in other areas, say it makes it easier for a predator to spot the bumpier fish.

So, you have smooth fish, bumpy fish, and everything in between, due to no two fish being identical. What is likely to happen is that the smooth fish die as they suffocate. The bumpy fish get eaten, and the in-between fish live to breed. Thus a mix of bumpy and smooth offspring are again produced.

Now imagine that the environment changes. If the oxygen level in the water drops, all the smooth fish die. Many in-between fish die. This leads to a population predominated (but not exclusively) by the bumpier fish. These breed, producing slightly bumpier offspring than the previous generation. If the oxygen keeps dropping, the bumpiness can keep increasing, until the gills form. This change happens over a huge number of generations.

If you are really interested, read "The Selfish Gene" by Dawkins.

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TheMoMan
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Icon 1 posted June 28, 2006 10:43      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
Darwin____________________________Lets see. I have taken to liking the Siberian Husky breed, These are by far the best hunters in the world untill you fire the gun, They are then headed for home. I like to Ice fish and on some days the dog will not go out on the Ice, I take that as she knows something I don't and that I should stay of the Ice, I do know that if I take a tray of Ice cubes out of the freezer and twist it to loosen them that the dog goes nuts and is looking for cover.

I say that the Siberians that made it into the breeding pool did so because their owners got off the Ice.

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The Famous Druid

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Icon 1 posted June 28, 2006 15:53      Profile for The Famous Druid     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by maybe.logic:
The modern theory of Darwinian evolution tells us that genetic mutations are completely random and that if a trait happens to be desirable and useful in the ecosystem it is quite by accident.
Yes.
But the theory also tells us that traits which will be used in a particular environment must have evolved in that environment.

Um, no.
Traits may have evolved in environment A, which allowed the species to move into environment B. If you then observe the creature in environment B, you'd be wrong to assume those traits evolved there.


An aquatic environment is obviously completely different from a continental one. The lungs must have evolved in the fish while they were still exclusively in the ocean.

It's the word 'exclusively' that has tripped you up here.
As pointed out by other posters, there are many intermediate environments between ocean and land, mangrove swamps for example. There are several species of swamp fish that can breathe air for long enough to cross a few metres of mud when stranded by low tides or drought.

And if that is true, there are all sorts of interesting extrapolations to make. One could infer that the apparatus for breathing air was already programmed into the DNA. Furthermore, one could hypothesize that evolution is not at all purposeless and has a clear direction to higher complexity and constitutes a coherent process rather than stochastic chaos. Incidentally, this would also lend plausibility to Leary/Wilson's theory that neural circuits for a future state of humanity are already in some kind of chrysalis form in our brains.

Or one could lie down and have a rest until one is thinking a little more clearly. [Wink]

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Astronomer Jedi
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Icon 1 posted June 28, 2006 20:00      Profile for Astronomer Jedi   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by Xanthine:
MacD, I'd lay money on the tides being more or less the same on Pangaea as they are now. There was a moon back then and, AFAIK, gravity does not change.

Mm, gravity itself doesn't change, but the Earth-Moon system is changing. The tides are gradually getting longer and the Moon will eventually become tidally locked with Earth.

I did read Dawkins' The Blindwatchmaker a while back. That was very interesting.

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Colonel Panic
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Icon 1 posted June 29, 2006 21:04      Profile for Colonel Panic         Edit/Delete Post   Reply With Quote 
"We" have not gone in a circle, maybe.logic, you have.

You build a house of cards, so you can knock it down.

Lungs did not evolve as a response to an environment, they evolved randomly. Nor, did lungs have to evolve as a single incident, they may have evolved time and again, until the proper conditions existed for them to succeed.

You may be having difficulty understanding the concept of billions and bilions of years.

As an aside, I was married to a molecular biologist for 20 years. She received her doctorate from a very well-respected Jesuit institution. As she was working on her degree, I had the opportunity to have some enlightened conversations with some brilliant theologians and biologists. There I learned that science and faith are not exclusive. It is those who seek to discredit science to bolster their own faith, that are the ones who are both weak in faith and in science.

Faith by its own definition is something that cannot be proven.

The religious texts were never written as scientific documents.

CP

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GrumpySteen

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Icon 1 posted June 29, 2006 21:32      Profile for GrumpySteen     Send New Private Message       Edit/Delete Post   Reply With Quote 
maybe.logic wrote:
How could the first amphibious fish breathe atmospheric oxygen if the current theory of stochastic natural selection is true? How did lungs evolve entirely independently of the environment in which they would function?

Let's see... a gill is a collection of membranes which expose a large number of small capillaries to an oxygen bearing substance and allows the creature to extract oxygen from its environment.

A lung, on the other hand, is a collection of membranes which expose a large number of small capillaries to an oxygen bearing substance and allows the creature to extract oxygen from its environment.

You're so right. How one could have ever evolved from the other is completely beyond the realm of logical explanation and obviously must involve divine intervention.

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Xanthine

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Icon 1 posted June 29, 2006 22:48      Profile for Xanthine     Send New Private Message       Edit/Delete Post   Reply With Quote 
Some interesting stuff on the evolution of lungs and fish can be found here.

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And it's one, two, three / On the wrong side of the lee / What were you meant for? / What were you meant for?
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Sirius
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Icon 1 posted June 30, 2006 06:10      Profile for Sirius     Send New Private Message       Edit/Delete Post   Reply With Quote 
Iím no expert on this subject so apologies if this is completely off the mark but I always assumed that the transition from sea to land dwelling creatures (assuming one even took place) happened due to a sea dweller spending short breaks out of water, perhaps to escape from a predator. These breaks being short enough for most to withstand without mutations.

As these breaks became more a part of the species daily routine they would be mimicked by the next generation and at an earlier stage at their development allowing them to develop some sort of mutation that allowed for longer excursions and so on over x number of years.

Obviously this is an overly simplified viewpoint but nevertheless, once my time machine is finished I shall post the definitive answer [Beard of Peter Gabriel!]

as for idea of random mutations I have no idea. [ohwell]

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Stereo

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Icon 1 posted June 30, 2006 08:08      Profile for Stereo     Send New Private Message       Edit/Delete Post   Reply With Quote 
Sirius: I worry you got the evolution process at individual level reversed. It's the same as the "chicken or egg" question.

By the way, you know some PHD finally ended up with a definitive answer? The same I've been saying for a long time? Egg first. But from what I understood in the news report, his reasonning is wrong (IMNSHO): he said the genetic code doesn't change in an idividual*, so the genetic change that led to the first chicken must have happened in the egg, when the fetilized egg evolves into an individual chicken. I say the genetic code doesn't change from conception till death*, so the change must have happened at conception, when one genetically mutated spermatozoid from a not-quite-rooster fertilized an ovule from a not-quite-hen (or the other way around), producing the first real chicken. Mutation at the cell level happens all the time. That's what most cancers are about. Spermatozoids and ovules are single cells. Mutation at the body level doesn't happens.

So mutations happens first (at conception), at random. Then the mutation that gives an advantage to the individual having it get passed to the next generation, while a disadvantaging mutated gene will most likely cause early death to its individual, before it can pass it on.


*Unless something very bad happens, like irradiation or absorbtion of a teratogenous** substance, and still, the mutation isn't the same for every cell in the whole body.

**Just for the fun of it: the greek (I believe) root "tera" stands for monster. So "terabyte" could be translated to "a monstruous amount of byte". So when you'll buy your first computer having a TB-sized hard drive, be sure to name it after a famous monster.

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