The processes of evolution

Before I begin a new debate, I want to set some ground rules.1) No insults, no mockery and sarcasm. I will not respond to such letters.
I respect your believes, please respect mine.2) Please keep your replies short. I will also attempt to write short posts.3) And lastly a note. I will not be visiting this site on a daily basis, as I'm not all emotional on this subject. I'm simply curious how evolutionists will respond.There, thats done. Now I can get to my question:How did fish develop lungs?

well here's something I found;

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J Mol Evol 46:131-138 (1998)
1998 by Springer-Verlag New York, Inc.

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Conservation of Surfactant Protein A: Evidence for a Single Origin for Vertebrate Pulmonary Surfactant
Lucy C. Sullivan, Christopher B. Daniels, Ian D. Phillips, Sandra Orgeig, Jeffrey A. Whitsett

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Subscribers may view full text in PDF | HTML | HTML-Frames (see notes on formats here.)
Abstract

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Surface tension is reduced at the air-liquid interface in the lung by a mixture of lipids and proteins termed pulmonary surfactant. This study is the first to provide evidence for the presence of a surfactant-specific protein (Surfactant Protein A - SP-A) in the gas-holding structures of representatives of all the major vertebrate groups. Western blot analysis demonstrated cross-reactivity between an antihuman SP-A antibody and material lavaged from lungs or swimbladders of members from all vertebrate groups. Immunocytochemistry localized this SP-A-like protein to the air spaces of lungs from the actinopterygiian fish and lungfish. Northern blot analysis indicated that regions of the mouse SP-A cDNA sequence are complementary to lung mRNA from all species examined. The presence of an SP-A-like protein and SP-A mRNA in members of all the major vertebrate groups implies that the surfactant system had a single evolutionary origin in the vertebrates. Moreover, the evolution of the surfactant system must have been a prerequisite for the evolution of airbreathing. The presence of SP-A in the goldfish swimbladder demonstrates a role for the surfactant system in an organ that is no longer used for airbreathing.

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Thanks for your reply.I cannot say I understood exactly what you said as I don't have any tertiary education in science. I think I might have asked the question wrong. What I meant was WHY did they develop lungs. I think this is a question rather like "What came first: the chicken or the egg?". A fish swimming merrily in the ocean will have no disire to walk around on the surface, since it can't breath there. If it did, somehow, manage to get out to the surface, it would die within minutes. Therefore, before the fish got out on land, it had to develop lungs first. But why would it develop lungs, if its gills work just fine in its living environment?

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Originally posted by Hanno:
Thanks for your reply.

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I cannot say I understood exactly what you said as I don't have any tertiary education in science. I think I might have asked the question wrong. What I meant was WHY did they develop lungs. I think this is a question rather like "What came first: the chicken or the egg?". A fish swimming merrily in the ocean will have no disire to walk around on the surface, since it can't breath there. If it did, somehow, manage to get out to the surface, it would die within minutes. Therefore, before the fish got out on land, it had to develop lungs first. But why would it develop lungs, if its gills work just fine in its living environment?

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It's not hard to visualise advantages of being able to exist out of water for extended periods. Extra feeding opportunities, predator evasion etc. Lungfish do exactly this.Many fish have swim bladders which contain gas, uasually used to control bouyancy, but note that monkensticks abstract shows that the surfactant proteins that we have in our lungs are the same as fishes (or the same family, at least). The fishes have a ready made (but for another purpose) organ that could potentially double as a primitive lung, as is the case with lungfish. Consider a lineage which spends more time on land than in water, eventually gills will not be needed & will atrophy. In fact humans still possess gill slits at a particular stage of embryonic developement, they eventually go on to become part of the ear & pharynx.There are numerous examples of fish adaptions to terrestrial environments, lungfish being the most quoted. Mudskipper species are able to drag themselves around mudflats, in this case gaseous exchange is provided by gills.------------------
Occam's razor is not for shaving with.

[QUOTE]Originally posted by mark24:
There are numerous examples of fish adaptions to terrestrial environments, lungfish being the most quoted. Mudskipper species are able to drag themselves around mudflats, in this case gaseous exchange is provided by gills.
[/B][/QUOTE]Not to mention the snakehead fish in the news in the Washinton DC metro area. This fish can survive for about three days on dry land and can use this to migrate from one body of water to another.------------------
"Chance favors the prepared mind." L. Pasteur
Taz

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Originally posted by Dr_Tazimus_maximus:

Not to mention the snakehead fish in the news in the Washinton DC metro area. This fish can survive for about three days on dry land and can use this to migrate from one body of water to another.

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The better known common eel (of Sargasso Sea fame) is able to travel overland between waterways, too.Mark------------------
Occam's razor is not for shaving with.

[QUOTE]Originally posted by Dr_Tazimus_maximus:
[B][QUOTE]Originally posted by mark24:
There are numerous examples of fish adaptions to terrestrial environments, lungfish being the most quoted. Mudskipper species are able to drag themselves around mudflats, in this case gaseous exchange is provided by gills.
[/B][/QUOTE]Not to mention the snakehead fish in the news in the Washinton DC metro area. This fish can survive for about three days on dry land and can use this to migrate from one body of water to another.[/B][/QUOTE]Yes. Millions of years ago there may have been a time when large bodies were slowly drying up and those fish which could survive for longer periods of time out of water, while looking for another body of water big enough to support them, would have passed this trait along to the next generation.[This message has been edited by nos482, 10-07-2002]

Actually, the best explanation shows swim bladders developed from lungs, not the other way around. Lungs adapted from pharyngeal structures originally functioning in filter feeding (which in turn developed from gill pouches) in Ostracoderms (bottom feeders — by the Devonian they were extinct). Remember that there doesn’t have to be anything fancy here — just a moist membrane that allows gas diffusion from an area of high concentration to an area of low concentration. Some modern amphibians, for example, breathe through the skin or swallow air and use just such gut pouches as "lungs". There are also a number of modern fish — especially in fresh water subject to periodic low oxygen content (but also some salt water fish like many of the Gobiidae) that gulp air, then hold the bubble in their mouths for diffusion. Obviously, a thin epithelium in the mouth is worthwhile at this stage — thinner epithelium means easier cross-membrane diffusion. Development of small pharangeal pouches came next. Look at the anatomy of either Polypterus or Polydon species — each have small pharangeal pouches attached to their gut surrounded by capillaries — just like modern lungs, except these are still attached to the gut. Fossils discovered of the early fresh water teleosts (Cheirolepis, for example) show skeletal adaptations similar to the modern fish mentioned.There are enough modern analogs of freshwater fish that rely on air when their ponds/streams/mudholes/intertidal pools dry up or turn anoxic showing the full range of adaptations (from mouth bubbles to lungs) that this is one of the easier transitions to visualize. With paleoecology showing a long Devonian drought, it makes sense that critters who could use some air would be better adapted - and survive - over the ones who couldn't.Hope that answers your question.

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Originally posted by Quetzal:
Actually, the best explanation shows swim bladders developed from lungs, not the other way around.

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Hey thanks Quetzal!!!Basically, you said nothing I didn't know, but said it in such away that it all came together beautifully. I had visions! You're and angel.... oh, wait... that can't be right ------------------
http://www.hells-handmaiden.com

Quetzal,Interesting, do you have a cite? I came across this once before but dismissed it as a teachers thought experiment, & investigated no further.Mark------------------
Occam's razor is not for shaving with.

Hanno writes:

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1) No insults, no mockery and sarcasm. I will not respond to such letters.
I respect your believes, please respect mine.

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This is a moderated site, you should have no worries in this regard. Please see the Forum Guidelines.--------------------EvC Forum Administrator

All the examples shown here are of fish that already possesses the capability to live outside water. Their breathing system is already adapted for it. I am aware of their existance. However, evolution dictates that this capability is not automatic, but that it must have been develop. Therefore, I wish to concentrate on fishes that does not have this capability. Lets take a fish that cannot survive outside water, and cannot use its fins to move around outside water. Acording to evolution, this is what the precursors of land animals must have been like. The question is, how do these fishes get the capability to move on land? Remember, the genetic code to create lungs does not exist yet, so this process cannot be compared with the live cicle of an amphibian, whos genetic code already contain the information to form lungs.I do not agree with the arguement that it was food that lured them out to land. When a whale beaches itself, only animals that can move on land will come out from the water to feed on it. You do not see fishes (such as sharks) that cannot live above water, struggling out to join the feast. If this was the case, evolution is feasable: The fish that can crawl out better, is more likely to survive and pass on their genes. But this is crearly not the case. They simply don't come out. Similarly, the lush plants of the tropics do not lure fish that can not move on land. Science assume that things worked in the past as they work today. Therefore, we can savely descard the theory that propose that fish were "lured by the advantages of walking on land". This advantage, however great it might be, cannot change the genetic makeup of animals, because genetics is chemistry, and habitat advantiges is not.If evolution did happen, then there must be some other mechanism thatcaused it.

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Originally posted by Hanno:
However, evolution dictates that this capability is not automatic, but that it must have been develop. Therefore, I wish to concentrate on fishes that does not have this capability. Lets take a fish that cannot survive outside water, and cannot use its fins to move around outside water. Acording to evolution, this is what the precursors of land animals must have been like.

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Yes and no, Hanno you actually came very close to putting your finger on a very important but often ignored point of evolutionary biology. Evolution often occurs by an organism taking advantage of secondary traits, ie gas exchange through a membrane/organ where that is not it's principle function, or the use of feathers for something other than thermoregulation. This occurs in a different manner in biochemical systems as well; proteases which can act in mutliple ways ranging from digestion to clotting, the use of a bacterial defense system in open circulations as a basis for clotting in closed circulations (this one is from the LAL system derived from the horseshoe crab). The ability to breath out of the water likely derived from this form of a start.

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I do not agree with the arguement that it was food that lured them out to land. When a whale beaches itself, only animals that can move on land will come out from the water to feed on it. You do not see fishes (such as sharks) that cannot live above water, struggling out to join the feast.

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How about to escape predators. This is a more likely scenerio, and the reason that it happens less now (it does happen some) is that now there are predators on the land as well who have evolved.

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Science assume that things worked in the past as they work today.

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Um, slight correction here, science assumes that the processes which operated in the past operate today. While it might seem like a small distinction it is quite important to understand the difference between processes and specific events or things that worked then vs things that work now.

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This advantage, however great it might be, cannot change the genetic makeup of animals, because genetics is chemistry, and habitat advantiges is not.

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Again, yes and no. NS does notchange the genetic makeup. it acts as a filter. And a fish with better gas exchange and stronger, stouter fins is more likely to be able to "go where no fish has gone before" ( please imagine Star Trek voice). This fish has a greater chance to live longer and have an increased chance of leaving its genes. As genes are chemistry, think of it as a scrubber, certian genes are scrubbed out but others are not.------------------
"Chance favors the prepared mind." L. Pasteur
Taz

Hanno,I understand what you mean, but as has been pointed out already, only things that pre-existed already, were used. Let me explain. Getting a Mackeral to walk is looking like a poor proposition. It has very flimsy ray like fins. BUT, not all fish had ray like fins. Some were "lobe finned", that is, they already had an adaption (for something else) that predisposed them to having stronger limbs than ray finned fishes. Anything that provides a selective advantage for stronger fins will mean stronger fins/limbs over time. Absorbtion of oxygen simply requires a wet membrane, as has been pointed out. A fish, yesterday. "The evolution of the skeletons of the earliest amphibians (top) from Devonian lobe-finned lungfish (bottom) did not require major modifications in structure and the skulls have a great many similarities as well."You can see the extreme similarity in morphology between lungfishes & amphibians in the image above.All of that said, modern fishes (even ray finned) DO have terrestrial adaptions, so perhaps you would do better by looking at extant fish that are able to go "feet dry", to answer your question "why".Mark------------------
Occam's razor is not for shaving with.

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Originally posted by mark24:
Quetzal,
Interesting, do you have a cite? I came across this once before but dismissed it as a teachers thought experiment, & investigated no further.

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Mark

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Hey Mark.I think it's pretty much concensus these days. Here's one cite: Mallatt, J. (1984). Early vertebrate evolution: pharyngeal structure and the origin of gnathostomes. Journal of Zoology, 204, 169-183. I don't have the original paper, but my "marginal notes" say this discusses the evolution of pharyngeal pouches from gill structures. Caroll talks about the lung -> swim bladder adaptation in "Vertebrate Paleontology" (1988). Most comparative anatomy/zoology courses that talk about fish evolution are saying it these days, afaik.