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| Author | Topic: Eye Evolution: Zhimbo vs Joralex | |||||||||||||||||||||||
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Admin Director  Posts: 13015 From: EvC Forum Joined: Member Rating: 1.9 |
Only Zhimbo, Joralex and moderators are permitted to post to this thread. Posts from anyone else will be deleted without saving or explanation. Moderators should immediately delete extraneous posts when encountered. Zhimbo and Joralex should ignore any extraneous posts they find that haven't yet been deleted. This debate has its roots in the Evolution of the eye? The myth goes on... thread where discussion on this topic began, and in the Existence of God thread where agreement to formal debate was reached. Moderators for the Debate I have had no Creationist volunteers, and so I am the sole moderator. If any qualified Creationist volunteers to help moderate after the debate begins I will add him at that point. Moderator list:
Percy (Member ID: Percipient) Comments about the Debate A parallel thread has been started in the Evolution forum titled Eye Evolution: Comments about the Great Debate. All comments, suggestions, feedback, etc, about the debate by non-participants should be made to that thread. Format of the Debate The debaters will alternate posts, but moderators will respond with comments and scoring after each post by a debater. This means that debaters should wait until the moderators have responded before posting their response. The moderator posts should prove very helpful to debaters by indicating where effort should be placed. By agreement reached in the Existence of God thread, Zhimbo will go first after November 17, 2003. Rules of Debate The Forum Guidelines will be in effect at all times. Time Limits Debaters have up to one week to respond after moderators post their assessments of the previous response. There is nothing hard and fast about a one week limit, and requests for more time made by email to Admin or by posting to this thread will be honored unless it becomes too much a habit. Any debater who disappears with no notice for more than two weeks will be deemed the loser by default. Judging the Debate Points will be awarded in this manner:
Note that it is possible to have a negative score. Like the legal system here in the US, the moderators are not on a quest for truth. Rather, they are seeking to assess the relative merits of the arguments presented by the debaters. Ending the Debate The debate will consist of 10 posts by each side. Whoever is ahead at the end of 20 total posts is deemed the winner of the debate. The debate may be extended by mutual agreement.
[Change comment thread title from text to a link. --Admin] [Add information about time limits. --Admin] [This message has been edited by Admin, 11-20-2003]
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Zhimbo Member (Idle past 6032 days)  Posts: 571 From: New Hampshire, USA Joined: |
This lengthy first post comes in three parts. Part 1 established the debate points, part 2 clarifies the scope of the debate, and Part 3 is where I argue for my position.
Parts 1 and 2 are not intended to be part of the debate, in that they do not require comment from Joralex. However, if Joralex believes I have misrepresented his position, then that may require comment. To visually separate the sections, Part 1 is in red, part 2 is in yellow. Part 3 is in standard white.
PART 1: Debate points First I will summarize the debate points: A. The simplest known eye is complex. Unfortunately Joralex did not specify what he considers to be the simplest known eye. (Context might suggest he considers the Trilobite eye to be a candidate, but I’m not convinced that was his intention).At any rate, I assume his main point is that there is a large chasm between "no eye" and the "simplest known eye". *This is an empirical question, about what is actually known. Joralex considers this a problem for evolutionary theory, but not a fatal flaw. My position is that I don’t think it is even a problem, and that a fine gradation of complexity of eyes can be demonstrated. B. In an argument he indicates is based on "irreducible complexity" (Michael Behe’s term), Joralex claims that multiple complementary subsystems must arise for an eye to be at all useful, therefore it could not have arisen gradually. For an eye to be useful, he indicates that at minimum you must have a1) Detector (e.g., eye) 2) transmission channel (e.g., optic nerve) 3) processor of information (e.g. brain) 4) proper reaction to information based on processing (e.g., the right "software") Without all of this simultaneously appearing, even a hypothetical early "eye spot" is useless. *This is an argument about what is possible in principle, and Joralex considers this to be a fatal flaw. My position is that it is easily shown that plausible scenarios exist for the evolution of a system which detects light and causes an adaptive change in the organism based on light detection. PART 2: Clarifications of scope of the debate A. These arguments could have a lot of overlap, depending on how you interpret them. I draw the distinction as:Argument 1 is about empirical knowledge of eyes. (large gulf between known eyes and complete lack of eyes) Argument 2 is about what is possible in principle with regards to the evolution of the visual system. (a complex visual system, including the eye, must arise all at once, and this is too unlikely to consider from the standpoint of evolutionary theory) B. This debate is not about the origin of life, or the origin of any biological system other than the visual system. This is a debate about how complete organisms that are blind may give rise to organisms with visual systems. C. "In Principle" should not be taken as "logically possible", rather it means that a hypothetical scenario is consistent with current scientific understanding. With regards to argument B from Part 1, it means that a hypothetical scenario is consistent with current, mainstream, evolutionary theory. A scenario inconsistent with natural law can not be considered at all, and a scenario which violates modern evolutionary theory does not counter argument B, from Part 1. I suppose one might argue that it is possible "in principle" that many multiple mutations could arise at once, just by chance. Technically this is "consistent" with evolutionary theory; it’s just extremely unlikely. However, even if this extremely unlikely event were allowed, our current understanding of the eye is that it may have evolved independently over 40 times, and therefore this extremely unlikely event would have to have occurred not once, but over 40 times! Any theory that relies on this sort of quasi-miraculous explanation is obviously on shaky ground, to put it mildly, so this type of explanation will not count as a counter to argument B. D. This debate does not concern the evolution of any specific eye, simply the evolution of any advanced eye. It is not my duty to explain the evolution of the eye for each of 40+ times it seems to have evolved in evolutionary history. PART 3: My opening statement. A. Is there a lack of intermediate complexity eyes? Originally, Joralex criticized the following text from a PBS website (Evolution: Library: Evolution of the Eye)
quote:Joralex wrote: "BTW, they forgot to end the article with ‘... and they lived happily ever after’" and described this scenario by putting the word "plausible" into scare-quotes, indicating his lack of agreement with its plausibility. He also stated that "the simplest known eye is not ‘simple’ at all.". A1. Far from being the fairy tale that Joralex implies, I will show that known examples of each type of eye discussed in the website quote exists. In fact I will start even more simply, with light sensitive organisms without an eye at all (age numbers refer to Cronly-Dillon unless otherwise specified):a. Light sensitivity without a specialized eye 1. the dinoflagellate Gyrodinium dorsum p 323
b. Light sensitive spot:
2. the pulmonate Lymnea stagnalis p 365 3. many gastropods, are light sensitive even after removal of the eyes p. 364-5 4. the marine gastropods Aplysia and Onchidium and the bivalves Spisula and Mercenaria have light sensitive neurons in their ganglia p. 366 5. the hydra (Duke-Elder, 182) 1. Many unicellular organisms have a specialized organelle, esp. eukaryotic algae (pp. 323+)
c. Cup-shaped light sensitive spot:
2. Leeches have small gatherings of light-sensitive cells (p. 20-21) 3. the bivalves Lima, Mya, and Tridacna (the giant clam) (p. 369) 4. the cockle, Cardium (p. 369) 1. turbellarian worm Planeria gonocephala p. 22
d. Pin-hole aperture eye cup
2. nemertime worm Drepanophorus p. 22 3. the limpet, Patella p. 25 1. the cephalopod Nautilus p. 374, Dawkins p. 152
e. Eye cup with lens
2. "marine snail" (Dawkins, p. 152) 1. abalone and ragworm have curved vitreous masses within their pinhole eye (Dawkins, p. 1520
f. Human-like camera eye: humans, squid and octopi.2. polychaete worm Vanadis has a simple spherical lens (Duke-Elder, p 143) A large number of known eyes exist, ranging in complexity from highly complex camera eyes down to "eye spots" and even to simple diffuse light sensitivity without a dedicated anatomical structure corresponding to an eye. It is hard to imagine what chasm of complexity Joralex objects to - the gap between a spot and a cup? A cup and a pinhole? CONCLUSION: Known eyes span a huge range of complexity from no eye at all to highly specialized eyes such as the camera eyes of humans or squid, with no large gaps of complexity apparent. B. Does the visual system require the simultaneous appearance of multiple subsystems? B.1. IRREDUCIBLE COMPLEXITY fails as a general principle of sorting "evolvable" systems from "non-evolvable" systems. As defined by Behe irreducible complexity is:
quote: Behe further states:
quote: This argument is technically correct, but essentially irrelevant. There are many shortcomings with Behe’s thesis in his book, Darwin’s Black Box (all Behe quotes are from this book), but the major shortcoming is hinted at in the phrase "that is missing a part" in the second quote above. Using irreducible complexity (IC) as a way of sorting evolvable from non-evolvable mechanisms only works if the only possible evolutionary path is the addition of parts, and the individual parts do not change function over generations. If evolution can also occur via subtraction of parts, for example, then IC fails as a "filter". In fact, Behe has fully admitted that other pathways are possible:
quote: At this point, Behe should have scrapped the book and admitted defeat; instead he counters this obvious truth with a baseless assertion which reduces his whole argument to an Argument from Personal Incredulity:
quote: However, he does not offer any basis for this assertion. I have no need to counter a bare assertion, so I can only take Behe’s words as an admission of defeat. Pathways other than simple stepwise addition exist, therefore a system that meets Behe’s definition of IC may still be evolvable. CONCLUSION: Without the use of IC as a usable filter, one cannot point to a system that meets the definition of IC and argue that the system is un-evolvable solely by this criterion. B.2. FROM "EYE SPOT" TO CAMERA EYE. I believe it is trivial to dispense with this portion of the argument — the evolution of a camera eye (like the mammalian eye, or the eye of many cephalopods) from an eye spot. In addition to the known specimens given in a preceding section that fill in this transition, the simulations of Nilsson and Pelger have demonstrated the existence of an uninterrupted gradual series of anatomical constructs that bridge the gap between a simple "eye spot" and a camera eye, with each small step representing a beneficial change in image production. I do not go into detail here, for based on previous discussions with Joralex I do not think he disagrees with this argument — that such a series exists. I think he may doubt that this did in fact happen, and I think he questions the plausibility of the initial eye spot mechanism. If I am correct, then this argument (B.2.) does not need to be addressed by Joralex. Instead I use this section only to establish the idea that I need only to address the plausibility of the evolution of a visual system with a simple eye-spot detector. CONCLUSION: The possibility, in principle, of the evolution of a modern eye from a simple eye spot is not necessary to this debate. Rather the more fundamental issue is how a system with even a simple light detector can get established. B.3. HOW DOES EVOLUTION START A VISUAL SYSTEM? Joralex has stated that the following components, at minimum, are essential for a visual system:1. Light detector 2. Transmission channel 3. Processor of information 4. Software that gives an adaptive response to the light information In humans, these correspond to the eye, the optic nerve, the brain, and the proper connections within the brain. However, Joralex claims that any visual system will have analogous parts. For example, the transmission channel may simply be a chemical pathway, and not a specialized anatomical structure such as the optic nerve. To counter this argument, I can show either one of two things:a) the components need not all arise simultaneously b) a functional system need not have all the components listed I now present a scenario which involves a single genetic change in a functioning organism. Before the single change, the organism does not have an adaptive response to light. After the genetic change, it does. I consider it a given that a molecule can arise that is photosensitive — that it may react to photons. We know that many such molecules exist. We know of proteins that are photosensitive, and we know of photosensitive chemicals that can affect proteins. I do not consider this a controversial point, and I believe, based on past experience, that Joralex agrees. Consider a small, transparent, aquatic, motile organism. A molecule that is in a pathway that affects motility become photosensitive due to a mutation. (Alternatively, it may become sensitive to a photosensitive chemical already present in the cellular environment). Thus, when in light, the motility biochemical pathway changes. In the presence of light, the organism either 1) slows down or 2) speeds up. If the organism photosynthesizes, then option 1 is adaptive, as the organism now tends to stay in light and move out of shadow. Alternatively, if the organism, say, filter feeds but is more visible to predators in light, then option 2 is adaptive. The organism now tends to stay in shadow and move out of light. It can be seen that this simple sort of behavioral program is adaptive. Many known organisms have behavioral responses similar to the hypothetical example above — this sort of simple behavioral response can be seen in bacteria, flat worms, plankton, crabs, and fish larvae, among others; some of these have complex eyes, some have simple eyes, some have no eyes. The flatworm dendrocoelum changes direction periodically while swimming. The frequency of this directional change decreases with light, causing the flatworm to move in straighter lines; in dim conditions the frequency of the change increases, causing more circuitous paths. The net effect is that dendrocoelum tends to congregate in shady areas. (Specific examples in this paragraph are from Duke-Elder). Thus, I have presented a simple scenario which involves a single genetic change in which a formerly blind organism acquires an adaptive response to light. There is a detector (the photosensitive molecule), a transmission channel (the motility biochemical pathway), a "processor" (the same pathway), and a correct behavioral response (thus the correct "software"). The detector is the only "new" part of the system. The rest of the system was already in place and was useful without the detector. The exceedingly simple software", if you want to call it that, comes for free — if the wrong effect happened (up-regulation vs. down-regulation of motility), then the mutation wouldn’t stick. If the right effect happens, then it’s selected for. One could quibble over whether I’m cheating a little in using the labels "detector", "channel", "processor", or "software", and that in fact all these components aren’t present. It doesn’t matter to me. Remember, I needed to show at least one of the following: a) the components need not all arise simultaneouslyb) a functional system need not have all the components listed If my labels are correct, then I have shown that a visual system can arise without simultaneous occurrence of all of these parts. If my labels are incorrect I have shown that a visual system does not need all of the components listed. Given this, I see no insurmountable gap in forming a functional "eye spot" detector — now we have only to concentrate the detection to a portion of the animal, which can then lead to directional selectivity, for example. CONCLUSION: I believe that Joralex either needs to argue thata) there is, in fact, an insurmountable gap between this system and a light spot detector, or that b) my hypothetical scenario violates current evolutionary theory or natural law. References:Behe, MJ. Darwin's Black Box: The biochemical challenge to evolution. New York: Free Press, 1996. Cronly-Dillon, JR. & Gregory, RL., eds. Vision and Visual Dysfunction Vol. 2: Evolution of the Eye and Visual System. Boca Raton: CRC Press. 1991. Dawkins, R. Climbing Mount Improbable. New York: W.W. Norton & Co. 1996. Duke-Elder, S. System of Ophthalmology Vol. 1: The Eye in Evolution. London: Henry Kimpton, 1958. Nilsson, DE. & Pelger, S. (1994) A pessimistic estimate of the time required for an eye to evolve. Proceedings of the Royal Society of London, B, 256, 53-8.
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Percy Member  Posts: 22480 From: New Hampshire Joined: Member Rating: 4.8 |
Eyes exist in nature across a broad range of complexity: +1
The irreducible complexity argument of Behe has little merit: +1 Joralex's four components are not all essential: +1 Score:
Zhimbo: +3 Joralex: 0 Note: The score immediately after the introductory post means little. Next week is Thanksgiving in the states, a national holiday, so Joralex should post a response by Monday, 12/1/2003. Reminder to everyone who isn't Zhimbo, Joralex or a moderator or administrator: please do not post to this thread. The thread for discussion of this debate is Eye Evolution: Comments about the Great Debate. --Percy
[Add reminder. --Percy] [This message has been edited by Percipient, 11-20-2003]
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Joralex Inactive Member |
Parts 1 and 2 are not intended to be part of the debate, in that they do not require comment from Joralex. However, if Joralex believes I have misrepresented his position, then that may require comment.
My response in YELLOW. PART 1: Debate points First I will summarize the debate points: A. The simplest known eye is complex. Unfortunately Joralex did not specify what he considers to be the simplest known eye.
I'm afraid that you didn't catch on that my "eye" is of a generalized form - this will be further elaborated in what follows. (Context might suggest he considers the Trilobite eye to be a candidate, but I’m not convinced that was his intention).
It wasn't -- the Trilobite eye is anything but simple. At any rate, I assume his main point is that there is a large chasm between "no eye" and the "simplest known eye".
No, that's not it. There is a huge chasm between the ability to "see" (in the generalized meaning) and not having this ability. Note also that "seeing" isn't merely receiving an electromagnetic signal since, if this were so, then rocks also "see". If you think about what "seeing" actually is then you realize that it involves the following: (1) The entity that "sees" must be a living entity.(2) The entity always begins at some ground state, Go ("unexcited"). (3) The signal alters the ground state from Go to Ge ("excited"). (4) The altered state, Ge, causes some change in the entity. (5) This change causes the entity to react in some way. (6) This usually leads to a cascade effect of changes/reactions in the entity. (7) The entity's "seeing" apparatus eventually returns to Go. Keep the above in mind - I'll refer to it as POINT 1. Note that POINT 1 applies whether we are talking about a photosensitive "spot" on some creature, a human eye or anything in-between. *This is an empirical question, about what is actually known. Joralex considers this a problem for evolutionary theory, but not a fatal flaw. My position is that I don’t think it is even a problem, and that a fine gradation of complexity of eyes can be demonstrated.
This is your first serious mistake (or maybe it's just a misunderstanding on your part). If we look around us (present or in the fossil record) we find all sorts of different 'eyes' and some are (or at least appear to be) more/less complex than others. However... ... this is NOT in dispute! Any knowledgeable Creationist accepts that in nature there are "different eyes exhibiting (real and apparent) degrees of complexity". B. In an argument he indicates is based on "irreducible complexity" (Michael Behe’s term), Joralex claims that multiple complementary subsystems must arise for an eye to be at all useful, therefore it could not have arisen gradually.
Essentially correct. However, you must extend your concept of an "eye" into the more generalized version (remember POINT 1). For an eye to be useful, he indicates that at minimum you must have a1) Detector (e.g., eye) 2) transmission channel (e.g., optic nerve) 3) processor of information (e.g. brain) 4) proper reaction to information based on processing (e.g., the right "software") Without all of this simultaneously appearing, even a hypothetical early "eye spot" is useless. *This is an argument about what is possible in principle, and Joralex considers this to be a fatal flaw.
Yes - when considered within the requirements and constraints, it is a 'fatal flaw'. DO NOTE : via ad hoc mechanisms it is possible to eliminate the 'fatal' aspect of the 'flaw' but then, this is always possible, isn't it? My position is that it is easily shown that plausible scenarios exist for the evolution of a system which detects light and causes an adaptive change in the organism based on light detection.
Let's see what that requires... PART 2: Clarifications of scope of the debate A. These arguments could have a lot of overlap, depending on how you interpret them. I draw the distinction as: Argument 1 is about empirical knowledge of eyes. (large gulf between known eyes and complete lack of eyes)
Correction : a large gulf between the ability to "see" (POINT 1 ) and lack of this ability. Argument 2 is about what is possible in principle with regards to the evolution of the visual system. (a complex visual system, including the eye, must arise all at once, and this is too unlikely to consider from the standpoint of evolutionary theory)
More precisely, all of the physical-chemical-interfacing infrastructure must be simultaneously present. This is a requirement by definition and it surprises me that some people cannot see this right away. For instance, I hand a blue crab a fully-formed human eyeball - is it of any use to the blue crab? Of course not - both the hardware and software are all wrong. To be of any use requires not just the hardware and software but also the interfaces with all appropriate infrastructure/subsystems. B. This debate is not about the origin of life, or the origin of any biological system other than the visual system. This is a debate about how complete organisms that are blind may give rise to organisms with visual systems.
I'll agree to this. C. "In Principle" should not be taken as "logically possible", rather it means that a hypothetical scenario is consistent with current scientific understanding. Agreed. With regards to argument B from Part 1, it means that a hypothetical scenario is consistent with current, mainstream, evolutionary theory. A scenario inconsistent with natural law can not be considered at all, and a scenario which violates modern evolutionary theory does not counter argument B, from Part 1. I'm not so sure about this part but I'll play it by ear. I suppose one might argue that it is possible "in principle" that many multiple mutations could arise at once, just by chance. Technically this is "consistent" with evolutionary theory; it’s just extremely unlikely. However, even if this extremely unlikely event were allowed, our current understanding of the eye is that it may have evolved independently over 40 times, and therefore this extremely unlikely event would have to have occurred not once, but over 40 times! Any theory that relies on this sort of quasi-miraculous explanation is obviously on shaky ground, to put it mildly, so this type of explanation will not count as a counter to argument B.
Okay ... for now ... D. This debate does not concern the evolution of any specific eye, simply the evolution of any advanced eye. It is not my duty to explain the evolution of the eye for each of 40+ times it seems to have evolved in evolutionary history. PART 3: My opening statement. A. Is there a lack of intermediate complexity eyes?
I've already addressed this question - this matter is NOT in dispute with the exception of changing the insinuation. IOW, what is in dispute is that you want to imply that these variants support an evolutionary path of "simple" eyes to "complex" eyes. We (creationists) see no such thing - we merely see eyes of different types. Originally, Joralex criticized the following text from a PBS website (Evolution: Library: Evolution of the Eye) quote:-------------------------------------------------------------------------------- ""Here's how some scientists think some eyes may have evolved: The simple light-sensitive spot on the skin of some ancestral creature gave it some tiny survival advantage, perhaps allowing it to evade a predator. Random changes then created a depression in the light-sensitive patch, a deepening pit that made "vision" a little sharper. At the same time, the pit's opening gradually narrowed, so light entered through a small aperture, like a pinhole camera.Every change had to confer a survival advantage, no matter how slight. Eventually, the light-sensitive spot evolved into a retina, the layer of cells and pigment at the back of the human eye. Over time a lens formed at the front of the eye. It could have arisen as a double-layered transparent tissue containing increasing amounts of liquid that gave it the convex curvature of the human eye." -------------------------------------------------------------------------------- Joralex wrote: "BTW, they forgot to end the article with ‘... and they lived happily ever after’" and described this scenario by putting the word "plausible" into scare-quotes, indicating his lack of agreement with its plausibility. He also stated that "the simplest known eye is not ‘simple’ at all.".
Once upon a time, "simple" life was described as a "blob of undifferentiated protoplasm - a sort of JELL-O-like substance". Haeckel used the words, "simple little lump of albuminous combination of carbon" to describe "simple" life. Of course, this was before we had learned of the immense complexity that is in a cell - any cell. Applying this reasoning to "seeing" I find that history repeats itself yet again except that now the error is being made with sight. Here's part of what science has discovered regarding "seeing" - i.e., how the "simple" light-sensitive spot functions : "When a photon first hits the retina, it interacts with a small organic molecule called II-cis-retinal. The shape of retinal is rather bent, but when retinal interacts with the photon, it straightens out, isomerizing into trans-retinal. This is the signal that sets in motion a whole cascade of events resulting in "vision". When retinal changes shape, it forces a change of the protein rhodopsin, which is bound to it. The change in rhodopsin's shape exposes a binding site that allows the protein transducin to attach to it. Now part of the transducin complex dissociates and interacts with a protein called phosphodiesterase. When that happens, the phosphodiesterase acquires the chemical ability to cut a small organic molecule called cyclic-GMP in the cell, turning into 5'-GMP. There is a lot of cyclic-GMP in the cell, and some of it attaches to another protein called an ion channel. Normally the ion channel allows sodium ions into the cell. When the concentration of cyclic-GMP decreases because of the action of the phosphodiesterase, the cycli-GMP bound to the ion channel eventually falls off, causing a change in shape that shuts the channel. As a result, sodium ions can no longer enter the cell, the concentration of sodium in the cell decreases, and the voltage across the cell membrane changes." (Taken from : 'The Proceedings of the Wethersfield Institute, Vol. 9, 1999, pp. 113-150) The above system must, of course, "regenerate" - i.e., it needs to get back to the starting position (I call it Go in POINT 1) in order to be ready for the next incoming photon. For "complex" visual systems - beyond just a "light-sensitive spot" - the voltage change change across the cell membrane causes a wave of electrical polarization to be sent down the optic nerve to the brain. The brain must then interpret this electrical signal into the image that is seen. This, of course, is all happening in real time and at processing speeds that are adequate to serve the required purpose of the organism. HERE'S THE POINT TO THE ABOVE : Recall POINT 1. Even a single living cell that has "sight" must have a physical-chemical mechanism that parallels the major features discussed above. This IN PRINCIPLE is an inescapable requirement since anything less renders the entity 'sightless' (in the most general sense of the term). A rock, for instance, receives and absorbs photons but it doesn't "react" to them in the manner that a living cell with "sight" does. This cell receives the photons and reacts in some way. Extremely "primitive" vision, for example, may only detect a light source. But then that entity either moves towards the light source (maybe it's food) or evades it (maybe it's a predator). In either case there is a very complex infrastructure of reception, processing, reaction and readiness. A multitude of sub-systems must be connected in some way (as an example - a dog will salivate when it sees food ... how many subsystems must be connected to allow such a thing?). A1. Far from being the fairy tale that Joralex implies, I will show that known examples of each type of eye discussed in the website quote exists.
This is not in dispute. In fact I will start even more simply, with light sensitive organisms without an eye at all (age numbers refer to Cronly-Dillon unless otherwise specified): a. Light sensitivity without a specialized eye 1. the dinoflagellate Gyrodinium dorsum p 3232. the pulmonate Lymnea stagnalis p 365 3. many gastropods, are light sensitive even after removal of the eyes p. 364-5 4. the marine gastropods Aplysia and Onchidium and the bivalves Spisula and Mercenaria have light sensitive neurons in their ganglia p. 366 5. the hydra (Duke-Elder, 182) b. Light sensitive spot: 1. Many unicellular organisms have a specialized organelle, esp. eukaryotic algae (pp. 323+)2. Leeches have small gatherings of light-sensitive cells (p. 20-21) 3. the bivalves Lima, Mya, and Tridacna (the giant clam) (p. 369) 4. the cockle, Cardium (p. 369) c. Cup-shaped light sensitive spot: 1. turbellarian worm Planeria gonocephala p. 222. nemertime worm Drepanophorus p. 22 3. the limpet, Patella p. 25 d. Pin-hole aperture eye cup 1. the cephalopod Nautilus p. 374, Dawkins p. 1522. "marine snail" (Dawkins, p. 152) e. Eye cup with lens 1. abalone and ragworm have curved vitreous masses within their pinhole eye (Dawkins, p. 15202. polychaete worm Vanadis has a simple spherical lens (Duke-Elder, p 143) f. Human-like camera eye: humans, squid and octopi.A large number of known eyes exist, ranging in complexity from highly complex camera eyes down to "eye spots" and even to simple diffuse light sensitivity without a dedicated anatomical structure corresponding to an eye. It is hard to imagine what chasm of complexity Joralex objects to - the gap between a spot and a cup? A cup and a pinhole? CONCLUSION: Known eyes span a huge range of complexity from no eye at all to highly specialized eyes such as the camera eyes of humans or squid, with no large gaps of complexity apparent.
Again, the variety of 'eyes' that exist is not in dispute. Provide me with just ONE of these that you list where the 'sight' that any of these "eyes" provides is a 'simple' process. Refer to the condensed, incomplete description of the process of sight (from the Wethersfield Institute Proceedings) that science has thus far uncovered. Show me a 'simple' process of sight in ANY living organism. B. Does the visual system require the simultaneous appearance of multiple subsystems?
All you'd have to do here to 'prove' your case is provide one example of an entity that had the ability to "see" (refer to POINT 1) yet had that ability with nothing more than, say, a few simple chemical reactions. My position is that any 'sight' - even at the single-cell level, if you wish - is far from 'simple'. Yet, remove any critical component and by definition you do not have 'sight'. B.1. IRREDUCIBLE COMPLEXITY fails as a general principle of sorting "evolvable" systems from "non-evolvable" systems.
I disagree. As defined by Behe irreducible complexity is: quote:-------------------------------------------------------------------------------- "By irreducibly complex I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning." -------------------------------------------------------------------------------- Behe further states: quote:-------------------------------------------------------------------------------- "An irreducibly complex system cannot be produced directly (that is, by continuously improving the initial function, which continues to work by the same mechanism) by slight, successive modifications of a precursor system because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional." -------------------------------------------------------------------------------- This argument is technically correct, but essentially irrelevant.
I cannot follow your conclusion of "irrelevancy". There are many shortcomings with Behe’s thesis in his book, Darwin’s Black Box (all Behe quotes are from this book), but the major shortcoming is hinted at in the phrase "that is missing a part" in the second quote above. Using irreducible complexity (IC) as a way of sorting evolvable from non-evolvable mechanisms only works if the only possible evolutionary path is the addition of parts, and the individual parts do not change function over generations. If evolution can also occur via subtraction of parts, for example, then IC fails as a "filter".
What? So you're saying that with evolution we are able to "lose everything until we have it all"? First, the feature/part must have had to evolve and then it has to be discarded. Theoretically possible (as are many things) but you're stepping on some thin ice here and asking people to believe in a lot that has never been observed. Where I thought you were heading was towards the theory of Co-Option (Co-option : where a part/structure that was employed for function A was later used for functions B, C or D through evolutionary adaptations). The problem with this (Co-option) is that, as an example, of the 40 or so proteins that make up the bacterium flagellum, less than a third (going on memory here) have been discovered to exist in other structures (this supports Co-option). However, the remaining have NOT been found anywhere else (Co-option is useless here). The fact remains that without ALL of the 40 proteins present and in their precise structure, their is no flagellum - period! In fact, Behe has fully admitted that other pathways are possible: quote:-------------------------------------------------------------------------------- "Even if a system is irreducibly complex (and thus cannot have been produced directly), however, one can not definitely rule out the possibility of an indirect, circuitous route." -------------------------------------------------------------------------------- At this point, Behe should have scrapped the book and admitted defeat;
I fail to see why you'd say this. Saying that something is "possible" doesn't imply that this "possibility" happens to be the best alternative available. Tell me : is it possible that life was planted here on Earth by aliens from another galaxy roughly 600 million years ago? Well, if it's 'possible' then why don't you subscribe to that position? Answer : because it isn't the best alternative as far as you are concerned. Likewise, Behe may be conceding the 'possibility' but this concession doesn't trash his position. instead he counters this obvious truth with a baseless assertion which reduces his whole argument to an Argument from Personal Incredulity: quote:-------------------------------------------------------------------------------- "As the complexity of an interacting system increases, though, the likelihood of such an indirect route drops precipitously." --------------------------------------------------------------------------------
As I've just stated, Behe is perfectly logical in this statement. I believe it is you that is arguing from Personal Incredulity, Behe was merely being thorough (and overly kind, if you ask me). However, he does not offer any basis for this assertion.
I just offered one alternative based solely on common sense. I have no need to counter a bare assertion, so I can only take Behe’s words as an admission of defeat. Pathways other than simple stepwise addition exist, therefore a system that meets Behe’s definition of IC may still be evolvable.
Yes and don't forget, ET may also be in your family tree. So, why aren't you defending that position? CONCLUSION: Without the use of IC as a usable filter, one cannot point to a system that meets the definition of IC and argue that the system is un-evolvable solely by this criterion.
IC is a good filter but I prefer the one by Dembski - it is more general in nature. Behe recognized this and stated so in the Foreword to Dembski's book Intelligent Design - The Bridge Between Science and Theology. In fact, Behe felt "silly" (and says so) for not having seen the generalization himself. B.2. FROM "EYE SPOT" TO CAMERA EYE. I believe it is trivial to dispense with this portion of the argument — the evolution of a camera eye (like the mammalian eye, or the eye of many cephalopods) from an eye spot. In addition to the known specimens given in a preceding section that fill in this transition, the simulations of Nilsson and Pelger have demonstrated the existence of an uninterrupted gradual series of anatomical constructs that bridge the gap between a simple "eye spot" and a camera eye, with each small step representing a beneficial change in image production.
One last time : the existence of variety is NOT in dispute. But you are begging the question : How does the existence of different "eyes" 'prove' (or even support) the hypothesis that "eyes" somehow began and then evolved in complexity and variety? Not even Darwin wanted to posit anything regarding the beginning of 'sight'. You are committing the fallacy of most Naturalists/evolutionists : assuming that "because we are here then that 'proves' that evolution happened". No! : all sorts of "eye" variations exist but this doesn't lend any support to "they evolved that way". That is precisely what we are disputing here : is it more reasonable to think of the eye as a created structure or as an evolved one? Alternatively : is it more rational to think of the eye as having evolved or as having been created? I do not go into detail here, for based on previous discussions with Joralex I do not think he disagrees with this argument — that such a series exists.
A "series" implies a progression and I do not subscribe to this. I do submit to the evidence of a set of 'varied eyes'. I think he may doubt that this did in fact happen, and I think he questions the plausibility of the initial eye spot mechanism. If I am correct, then this argument (B.2.) does not need to be addressed by Joralex. Instead I use this section only to establish the idea that I need only to address the plausibility of the evolution of a visual system with a simple eye-spot detector. CONCLUSION: The possibility, in principle, of the evolution of a modern eye from a simple eye spot is not necessary to this debate. Rather the more fundamental issue is how a system with even a simple light detector can get established.
No, you need to consider that little word : "simple". B.3. HOW DOES EVOLUTION START A VISUAL SYSTEM? Joralex has stated that the following components, at minimum, are essential for a visual system:1. Light detector 2. Transmission channel 3. Processor of information 4. Software that gives an adaptive response to the light information In humans, these correspond to the eye, the optic nerve, the brain, and the proper connections within the brain. However, Joralex claims that any visual system will have analogous parts. For example, the transmission channel may simply be a chemical pathway, and not a specialized anatomical structure such as the optic nerve. To counter this argument, I can show either one of two things:a) the components need not all arise simultaneously b) a functional system need not have all the components listed I now present a scenario which involves a single genetic change in a functioning organism. Before the single change, the organism does not have an adaptive response to light. After the genetic change, it does.
Zhimbo : you do know that everything reacts to light, right? You correctly employ the more proper language of "an adaptive response to light" and that's a start but now you must finish the thought. Let's see what you do... I consider it a given that a molecule can arise that is photosensitive — that it may react to photons. We know that many such molecules exist. We know of proteins that are photosensitive, and we know of photosensitive chemicals that can affect proteins. I do not consider this a controversial point, and I believe, based on past experience, that Joralex agrees.
Here you seem to be reverting to not knowing that ALL matter reacts to electromagnetic energy (photons) in some way. But this does NOT constitute "sight". Consider a small, transparent, aquatic, motile organism. A molecule that is in a pathway that affects motility become photosensitive due to a mutation. (Alternatively, it may become sensitive to a photosensitive chemical already present in the cellular environment). Thus, when in light, the motility biochemical pathway changes. In the presence of light, the organism either 1) slows down or 2) speeds up.
Consider my POINT 1 and think about the complexity contained therein. If the organism photosynthesizes, then option 1 is adaptive, as the organism now tends to stay in light and move out of shadow.
Consider my POINT 1 and think about the complexity contained therein. Alternatively, if the organism, say, filter feeds but is more visible to predators in light, then option 2 is adaptive. The organism now tends to stay in shadow and move out of light.
DITTO! It can be seen that this simple sort of behavioral program is adaptive.
I don't disagree at all but you are hand-waving over a huge amount of complexity. The devil is in the details and you're skipping over most of them. Many known organisms have behavioral responses similar to the hypothetical example above — this sort of simple behavioral response can be seen in bacteria, flat worms, plankton, crabs, and fish larvae, among others; some of these have complex eyes, some have simple eyes, some have no eyes.
Agreed and regardless of the situation you will find a very complex response mechanism linking a great deal of the organism's infrastructure. You seem to want to broad-stroke your way out of the requirement for the immense amount of complexity that is present. The flatworm dendrocoelum changes direction periodically while swimming. The frequency of this directional change decreases with light, causing the flatworm to move in straighter lines; in dim conditions the frequency of the change increases, causing more circuitous paths. The net effect is that dendrocoelum tends to congregate in shady areas. (Specific examples in this paragraph are from Duke-Elder).
Wonderful - this is supporting my position perfectly! The visual perception and locomotion (muscles, metabolism, etc... etc.) must be interconnected in this example you give. These are but two of the many subsystems that must be interconnected in this flatworm in oredr for it to respond to its environment as it does. Thus, I have presented a simple scenario which involves a single genetic change in which a formerly blind organism acquires an adaptive response to light.
Formerly "blind"? As I have stated, everything has some response to electromagnetic radiation - especially living things. Shine light on any living organism - eyes or no eyes - and you will get a reaction - guaranteed! So, where do you get "formerly blind"? There is a detector (the photosensitive molecule), a transmission channel (the motility biochemical pathway), a "processor" (the same pathway), and a correct behavioral response (thus the correct "software"). The detector is the only "new" part of the system.
Maybe I'm missing something (?). The rest of the system was already in place and was useful without the detector. The exceedingly simple software", if you want to call it that, comes for free — if the wrong effect happened (up-regulation vs. down-regulation of motility), then the mutation wouldn’t stick. If the right effect happens, then it’s selected for.
Again you use the word "simple". Show me "simple" ... there's nothing "simple" about 'sight' when you consider POINT 1. One could quibble over whether I’m cheating a little in using the labels "detector", "channel", "processor", or "software", and that in fact all these components aren’t present. It doesn’t matter to me. Remember, I needed to show at least one of the following: a) the components need not all arise simultaneouslyb) a functional system need not have all the components listed You fail right at the outset - you begin with an entire series of components and then merely 'adapt' them for the purpose that you need. This is begging the question since it is an extraordinary coincidence (I hope you will agree) that all of these components are perfectly suited to the task that is required of them. If my labels are correct, then I have shown that a visual system can arise without simultaneous occurrence of all of these parts. If my labels are incorrect I have shown that a visual system does not need all of the components listed. Given this, I see no insurmountable gap in forming a functional "eye spot" detector — now we have only to concentrate the detection to a portion of the animal, which can then lead to directional selectivity, for example. CONCLUSION: I believe that Joralex either needs to argue thata) there is, in fact, an insurmountable gap between this system and a light spot detector, or that b) my hypothetical scenario violates current evolutionary theory or natural law. I may or may not have done this ... Zhimbo, this was an extremely long post to respond to. I have a small request : please try and limit yourself to a point or two at a time. Given the length of this post I honestly wasn't able to put in the time responding to your argument that I would have wanted to (and it still took me a few hours). Thanks in advance. Joralex
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Percy Member Posts: 22480 From: New Hampshire Joined: Member Rating: 4.8 |
First, a few words about the way I'm moderating this debate. When judging the merit of a rebuttal I plan to be circumspect about my reasons. I will refrain from any analysis or significant commentary on content, since to do so might provide assistance to one side or the other. I will often times not be specific about what part of an argument I found unconvincing or unpersuasive, because it is up to the debaters themselves, not me, to identify the weaknesses in each other's arguments.
Second, the way Joralex composed his response prompts me to request that he consider these questions:
This isn't to say you can't quote everything, only that there are some issues to consider. I'm puzzled regarding Joralex's expressed concern about the length of Zhimbo's introductory post. While I'm sensitive to the issue of length of posts, it was Joralex who requested that Zhimbo begin the debate. Because the debate on this particular topic can only begin once the Creationist position is outlined, Zhimbo was forced to first state Joralex's position, then rebut it. That it was long seems only natural. An attempted clarification: Joralex several times draws a distinction between eyes and the ability to see. Since for the purposes of this discussion it seems not only reasonable but imperative to consider that the organ that enables an organism to see is called an eye, no matter what structure and implementation that organ may have, that this is therefore merely an issue of individual preference regarding terminology. Sometimes a mere reference is sufficient rebuttal, sometimes not. Just to assist the debaters in future posts, this to me is insufficient rebuttal:
Consider my POINT 1 and think about the complexity contained therein. Unless something is really obvious, debaters should actually go through the trouble of constructing rebuttal arguments. Zhimbo points summary:
Joralex points summary:
Score:
Reminder to everyone who isn't Zhimbo, Joralex or a moderator or administrator: please do not post to this thread. The thread for discussion of this debate is Eye Evolution: Comments about the Great Debate. --Percy
[Add reminder. --Percy] [This message has been edited by Percipient, 11-22-2003]
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Zhimbo Member (Idle past 6032 days) Posts: 571 From: New Hampshire, USA Joined: |
1. Simplest eyes:
It is my understanding from Joralex’s post that he does not object to the point that eyes exist on a nearly continuous scale of complexity from simple light reactivity, without specialized eyes, to complex camera eyes such as in humans or squid. Instead, he claims that even the simplest generalized eye — which I assume means something like adaptive light sensitivity even without any dedicated organ to call an eye — is a large gap away from no generalized eye. As I originally framed this point in terms of the complexity of the light detection organ (eye), this changes the debate somewhat. I originally framed the question in this way in order to keep the two main debate points, originally posed by Joralex, distinct. Furthermore, here is Joralex’s version of the argument in his own words, complete:
quote: Since he is talking about the simplest known eye and referring to fossil evidence, it seems unlikely the original point was about biochemical pathways, since biochemical pathways are not fossilized. I can’t see how to take this statement other than talking about the evolution of the specialized light detection organ called the eye. From this standpoint, I have shown that the simplest known eye is very simple — no specialized eye at all. Joralex has agreed, but shifted the argument to a generalized eye, a shift not justified, in my view, by his own original statement. Rather, it is a new point: not that a large gulf exists between simplest eye and no eye, but that a large gulf exists between adaptive light sensitivity (my wording) and no adaptive response to light. As an argument he supplies a quote from The Proceedings of the Wethersfield Institute. In Joralex’s words, Here's part of what science has discovered regarding "seeing" - i.e., how the ‘simple’ light-sensitive spot functions : (see above for quote) Unfortunately, his example is of the retina — not a simple light spot, a fairly major mistake. But, even given that, every single step of the pathway he then describes is either found in other systems, or is a minor variant of an analogous protein from another system — this from a full-blown retina, not a simple light spot. The g-protein (GTP-binding regulatory protein) pathway described is in no way unique to vision. Thus, in a debate on how a blind organism attains vision, these pathways do not require any special explanation, as they are clearly already part of the biochemical machinery, being used for other purposes. Actually, they are being used for the same purpose as in other cell types, it’s just that in the case of the retina, the initial signaling event is a photo-chemical reaction.
quote: 2. Irreducible Complexity (IC) In bringing up IC, I was curtailing any argument along the lines of: IC can’t evolveSystem X is IC System X can’t evolve. I was not arguing that systems don’t meet the definition of IC. Many systems do. I was arguing that the premise IC can’t evolve critically depends on evolution ONLY proceeding by simple stepwise addition. If you allow any other possible path — subtraction of parts was my particular example — then the premise is simply not true, and the argument fails. Co-option is yet another possibility, mentioned by Joralex, in addition to subtraction of parts. He then argues against co-option by referring to the bacterial flagellum. The flagellum itself is irrelevant. We aren’t debating the flagellum. However, Joralex illustrates precisely my point: it is not enough show that system X is IC. You must go to specific evidence that a particular system could not have evolved by paths other than stepwise addition. Whether I agree with Joralex’s point on the flagellum or not, the fact that he makes this additional argument itself shows that IC is an insufficient criterion. My problem with Behe’s argument is that he argues that alternate paths are too unlikely, but doesn’t offer any justification for this statement as a general principle. Again, it might be the case that a specific system is too unlikely, but one can’t simply assert this to be true for all cases. Joralex: Can you show that vision could NOT have evolved by circuitous pathways? For example, can you show that the elements of the biochemical pathways have no counterparts in other systems, and thus co-option is not a valid evolutionary pathway? I’ve already argued to the contrary, and I doubt you can make such an argument. 3. Scenario for evolution of sight I presented a hypothetical scenario for how vision might first emerge in post 2 of this thread. My scenario stands perfectly. Joralex repeatedly refers to his Point 1 as a rebuttal, but my scenario fulfills all aspects of point 1 . Point 1 by Joralex is:(1) The entity that "sees" must be a living entity. (2) The entity always begins at some ground state, Go ("unexcited"). (3) The signal alters the ground state from Go to Ge ("excited"). (4) The altered state, Ge, causes some change in the entity. (5) This change causes the entity to react in some way. (6) This usually leads to a cascade effect of changes/reactions in the entity. (7) The entity's "seeing" apparatus eventually returns to Go. 1) is a given. Of course we’re talking about living things. It’s been agreed that the origin of life is not a part of this debate.2,3,7) are all part of the definition of a chemical being photosensitive. It does make explicit a point that has only been implicit so far, and that is that the photo-reaction is reversible. This is not an extra step, but just specifies a subset of all photo-reactions. 4,5,6) are all the same point — the photo reaction has an effect on the organism. Change and react are synonyms, and 6 is optional according to Joralex’s wording, and probably inevitable in any biochemical system. So, point 1 asserts that a reversible photo-reaction(2,3,7) has an effect(4,5,6) on an organism (1). My scenario fulfills all of these requirements.
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Joralex Inactive Member |
1. Simplest eyes:
It is my understanding from Joralex’s post that he does not object to the point that eyes exist on a nearly continuous scale of complexity from simple light reactivity, without specialized eyes, to complex camera eyes such as in humans or squid. I wouldn't word it that way. There exists an immense variety of eyes - this much is clear. It is then the claim of the evolutionist that this observation supports the hypothesis that complex eyes evolved from simpler eyes which, in turn, came from no eyes. IOW, the evolutionist takes this variety and sequences them in some order that suggests A --> B --> C --> D --> etc... The logical/scientific necessity of such a progression is ... missing. Instead, he claims that even the simplest generalized eye — which I assume means something like adaptive light sensitivity even without any dedicated organ to call an eye — is a large gap away from no generalized eye.
The simplest "generalized eye" (i.e., the capacity to "see") is a huge gap away from seeing. In stronger language, I say that the only way to bridge this gap is by believing that it is possible and that it did occur (long ago and far away). There is no evidence for this since the "simplest" eye that exists in the fossil record is a far cry from simple. Hence, the evolutionist is forced to assume the evolutionary progression : 'no eye - simple eye - complex eyes'. As I originally framed this point in terms of the complexity of the light detection organ (eye), this changes the debate somewhat.
I wouldn't mind hearing (again?) - in simple language so that even I could understand it - exactly what it is that you're trying to advocate here. Furthermore, here is Joralex’s version of the argument in his own words, complete: quote:-------------------------------------------------------------------------------- The argument for the evolution of the eye typically begins with some cell becoming light-sensitive and then evolving through various stages until 'complex vision' is attained. There are at least two problems with this, one "solvable" and the other, IMHO, not : 1. The simplest eye known is not "simple" at all. Even those that are 'reconstructed' from (supposed) ancient fossil evidence (e.g., Trilobites) are highly complex, although they (supposedly) go back 1/2 billion years. So, did the complexity of the Trilobite eye evolve very quickly, as some suggest, in less than 1/2 million years? If so, where are the intermediate stages of the highly complex Trilobite eye? Of course, the "solution" here is to say that no 'intermediates' have been preserved in the fossil record for us to examine (how convenient... way to squirm out of that one!). In any event, I'll not quibble this point at all so let's move on.-------------------------------------------------------------------------------- Since he is talking about the simplest known eye and referring to fossil evidence, it seems unlikely the original point was about biochemical pathways, since biochemical pathways are not fossilized. I can’t see how to take this statement other than talking about the evolution of the specialized light detection organ called the eye.
I hope to have clarified my position but, if not, I'll be happy to try again. From this standpoint, I have shown that the simplest known eye is very simple — no specialized eye at all. Joralex has agreed, but shifted the argument to a generalized eye, a shift not justified, in my view, by his own original statement.
When I provided what science has learned concerning the process of sight (from The Proceedings of the Wethersfield Institute), it was to demonstrate that what you are calling "simple" (in regards to 'seeing') is nowhere near "simple" at all - in fact, it is immensely complex and we still don't have the complete process. I have not agreed to any "simplicity" in the capability of sight. As for "shifting the argument" - my argument has been exactly the same all along : there is no basis - other than belief - to support an evolutionary progression of "simple" eyes to complex ones and, furthermore, the notion of a "simple" eye is as mythological as is the notion of a "simple" cell. The alleged "simplicity" is a function of ignorance, not fact. Rather, it is a new point: not that a large gulf exists between simplest eye and no eye, but that a large gulf exists between adaptive light sensitivity (my wording) and no adaptive response to light.
No, not a new point at all as I hope that I've demonstrated. As an argument he supplies a quote from The Proceedings of the Wethersfield Institute. In Joralex’s words, Here's part of what science has discovered regarding "seeing" - i.e., how the ‘simple’ light-sensitive spot functions : (see above for quote) Unfortunately, his example is of the retina — not a simple light spot, a fairly major mistake. But, even given that, every single step of the pathway he then describes is either found in other systems, or is a minor variant of an analogous protein from another system — this from a full-blown retina, not a simple light spot. The g-protein (GTP-binding regulatory protein) pathway described is in no way unique to vision. Thus, in a debate on how a blind organism attains vision, these pathways do not require any special explanation, as they are clearly already part of the biochemical machinery, being used for other purposes. Actually, they are being used for the same purpose as in other cell types, it’s just that in the case of the retina, the initial signaling event is a photo-chemical reaction.
However, there is much more to this as you have observed (below)... quote:-------------------------------------------------------------------------------- Visual pigments belong to a very large family of structurally similar transmembrane proteins that act as receptor molecules in a wide range of different cell types: all function through the activation of a G-protein that binds guanosine triphosphate (GTP). The family includes not only all the visual pigments, but also acetylcholine muscarinic receptors (of which there may be at least five pharmacologically distinct subtypes), noradrenergic receptors (again at least five subtypes), serotonin or 5-hydroxytryptamine (5-HT) receptors (at least 3 subtypes), dopaminergic receptors and probably many others. (Bowmaker, The evolution of vertebrate visual pigments and photoreceptors, in Cronly-Dillon/Gregory, eds., Evolution of the Eye and Visual System) -------------------------------------------------------------------------------- Zhimbo - did you read your own material? Tell me, what do you find "simple" in this process? In my last post I used the words "or a process that parallels this". Yes, what I described concerned the retina, but any other 'seeing process' - even a single-celled variety - involves a series of very specialized and complex chemical reactions just to enable "seeing". Then, what is "seen" must (if it is to satisfy the definition of sight) invoke a response and a cascade of changes in the organism (e.g., moving towards or away from a light source) and, finally, the "seeing" apparatus must return to its ground state to enable it to be in the receive mode once again. There is absolutely nothing "simple" about this and your above example only serves to accentuate this point further. 2. Irreducible Complexity (IC) In bringing up IC, I was curtailing any argument along the lines of: IC can’t evolveSystem X is IC System X can’t evolve. I was not arguing that systems don’t meet the definition of IC. Many systems do. I was arguing that the premise IC can’t evolve critically depends on evolution ONLY proceeding by simple stepwise addition. If you allow any other possible path — subtraction of parts was my particular example — then the premise is simply not true, and the argument fails.
To which I respond with two counter-arguments : First, the "subtraction of parts" argument presumes a great deal such as the parts first had to evolve and then the "correct" ones had to go away in order to generate a novel feature (in this case, sight). But the most serious response that I have against your argument is that addition or subtraction of parts is only one aspect of a complex system. What I mean is that, for example, suppose I were to hand you all of the individual parts that make up a Space Shuttle. Okay, now hand me an operational Space Shuttle. You see, even if all of the parts are present, they require a very specified assembly for functionality. Failure of just one of those parts may render the entire system 'non-functional' (as we have tragically witnessed). That 'specification' is part of what constitutes information and this information has no known natural origin. Hence, we don't even have to get into the parts issue - this argument alone stops you dead in your tracks. Co-option is yet another possibility, mentioned by Joralex, in addition to subtraction of parts. He then argues against co-option by referring to the bacterial flagellum. The flagellum itself is irrelevant. We aren’t debating the flagellum. However, Joralex illustrates precisely my point: it is not enough show that system X is IC. You must go to specific evidence that a particular system could not have evolved by paths other than stepwise addition. Whether I agree with Joralex’s point on the flagellum or not, the fact that he makes this additional argument itself shows that IC is an insufficient criterion.
My last statement may be inserted here with equal application. My problem with Behe’s argument is that he argues that alternate paths are too unlikely, but doesn’t offer any justification for this statement as a general principle. Again, it might be the case that a specific system is too unlikely, but one can’t simply assert this to be true for all cases.
Science is often reduced to making determinations based on probabilistic considerations (in fact, I would say almost always!). The justification that you demand is almost a given in science, namely, an 'inference to the best explanation' should be based on justifiable expectation more than on anything else. The alternate pathways that Behe discards are discarded based on what science knows today (rather than retaining them based on what science may discover tomorrow). Behe is simply following the available evidence to its best conclusion. Your objection to this is mystifying. Joralex: Can you show that vision could NOT have evolved by circuitous pathways? For example, can you show that the elements of the biochemical pathways have no counterparts in other systems, and thus co-option is not a valid evolutionary pathway? I’ve already argued to the contrary, and I doubt you can make such an argument.
I'm afraid that you've got the procedure all mixed up, Zhimbo. If you wish to support your position, this is not accomplished by asking me to show that your allegation could NOT have occurred. I once read a hilarious (yet genuine!) request to "demonstrate that the Oort Cloud doesn't exist!". Requesting a proof of 'non-existence' is naive, at best. My main response to you (to repeat it concisely) is that EVEN IF I were to grant you co-option or any other evolutionary pathway, this gives you only the parts but not at all the instructions for assemblying those parts in the precise sequence necessary to bring about a highly complex function (e.g., sight). Remember, DNA must encode this process if it is to be passed along to the next generations or else it ends right there. How is the process encoded the first time? Regardless, I must also remind you that while partial co-option has been supported, there is no known instance of total co-option. For example, about 10 of the proteins in the bacterium flagellum have been found in other cellular structures used for other functions. But the other 30 or so proteins are unique to the flagellum; i.e., have been found nowhere else. Co-option is thus, so far, only marginally able to explain IC structures. 'Faith' that it happened in then used to fill in this gap. 3. Scenario for evolution of sight I presented a hypothetical scenario for how vision might first emerge in post 2 of this thread. My scenario stands perfectly. Joralex repeatedly refers to his Point 1 as a rebuttal, but my scenario fulfills all aspects of point 1 . Point 1 by Joralex is:(1) The entity that "sees" must be a living entity. (2) The entity always begins at some ground state, Go ("unexcited"). (3) The signal alters the ground state from Go to Ge ("excited"). (4) The altered state, Ge, causes some change in the entity. (5) This change causes the entity to react in some way. (6) This usually leads to a cascade effect of changes/reactions in the entity. (7) The entity's "seeing" apparatus eventually returns to Go. 1) is a given. Of course we’re talking about living things. It’s been agreed that the origin of life is not a part of this debate.2,3,7) are all part of the definition of a chemical being photosensitive. It does make explicit a point that has only been implicit so far, and that is that the photo-reaction is reversible. This is not an extra step, but just specifies a subset of all photo-reactions. 4,5,6) are all the same point — the photo reaction has an effect on the organism. Change and react are synonyms, and 6 is optional according to Joralex’s wording, and probably inevitable in any biochemical system. So, point 1 asserts that a reversible photo-reaction(2,3,7) has an effect(4,5,6) on an organism (1). My scenario fulfills all of these requirements.
Many people have "created" scenarios by which this or that may have evolved - that is not at issue here. It's the plausibility of said scenarios in light of present scientific knowledge and understanding that's at issue. I'll grant you your scenario but you are obliged to grant me that your scenario fails to explain (without making assumptions that exceed the limitations of our present science) how molecular parts managed to assemble themselves into the precise structure necessary to generate sight (at any level). This is the crux of my argument and is further expanded in this post. Finally, I wish to re-iterate that maybe I'm not directing myself at the crux of your argument. If this is the case then I wish to remedy this. Provide the crux of your argument for me again, please. Jorge
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Percy Member Posts: 22480 From: New Hampshire Joined: Member Rating: 4.8 |
Rule violation!
Premature posting, moderator hasn't assessed previous message: -87356 points! Just kidding!!  Hi Joralex, Sorry I've been remis in evaluating Zhimbo's post. Thanks for staying on the ball and replying anyway. It wasn't the way I imagined things working, but I'm in a busy period and this is helpful. Zhimbo, I think I can assess both yours and Joralex's post sometime this weekend. If you feel I'm slowing things down too much then go ahead and reply. --Percy
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Percy Member Posts: 22480 From: New Hampshire Joined: Member Rating: 4.8 |
Zhimbo points summary:
Joralex points summary:
Score:
Reminder to everyone who isn't Zhimbo, Joralex or a moderator or administrator: please do not post to this thread. The thread for discussion of this debate is Eye Evolution: Comments about the Great Debate. --Percy
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Percy Member Posts: 22480 From: New Hampshire Joined: Member Rating: 4.8 |
Zhimbo points summary:
Joralex points summary:
Score:
Reminder to everyone who isn't Zhimbo, Joralex or a moderator or administrator: please do not post to this thread. The thread for discussion of this debate is Eye Evolution: Comments about the Great Debate. It is Zhimbo's turn to reply. --Percy
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Percy Member Posts: 22480 From: New Hampshire Joined: Member Rating: 4.8 |
In the opinion of the judges (me), Zhimbo has had adequate time to reply but has not posted a response. Joralex is therefore declared the winner by default.
Congratulations, Joralex!
--Percy
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