Eye Evolution: Zhimbo vs Joralex

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:

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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".

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*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.

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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.

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For an eye to be useful, he indicates that at minimum you must have a
1) 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")

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Without all of this simultaneously appearing, even a hypothetical early "eye spot" is useless.

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*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

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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)

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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.

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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.

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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.

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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)

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""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.

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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."

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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 b. Light sensitive spot: c. Cup-shaped light sensitive spot: d. Pin-hole aperture eye cup e. Eye cup with lens 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.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:

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"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."

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Behe further states:

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"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."

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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:

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"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."

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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:

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"As the complexity of an interacting system increases, though, the likelihood of such an indirect route drops precipitously."

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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 informationIn 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 listedI 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 simultaneously
b) a functional system need not have all the components listedIf 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 that
a) 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.

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:

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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 :

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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?

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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!).

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In any event, I'll not quibble this point at all so let's move on.

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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.

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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)

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2. Irreducible Complexity (IC)In bringing up IC, I was curtailing any argument along the lines of:IC can’t evolve
System 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 sightI 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.