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Author
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Topic: Seemingly Unevolvabe Biochemical Systems
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Argon
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Member # 276
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posted 04. May 2004 00:12
I wrote:
"So when Scott suggests that Behe doesn't think the blood clotting system is IC, that is because Behe is mixing non-interchangeable definitions."
Scott replied:
"It's not a suggestion, it's a statement of fact. You even seem to be agreeing with me, in a sort of back-handed way.
Actually, I'll retract my original statement at least with regard to the exchange between Miller and Behe that RBH referenced. It does not appear that Behe is using an IC-mark-II criteria for evaluating the blood clotting system in that debate but the IC-version-I instead. Further, it does not appear in the exchange that Behe is saying the blood clotting system is not IC. What he is acknowledging is that some components (not all) of the blood clotting cascade can be redundant. The parts that cannot be lost comprise the IC system.
I wrote:
"Under the original definition, much of the blood clotting cascade is certainly "IC". The test? This was clearly specified in Behe's DBB: Simply remove or significantly alter one of its parts and see if fails to properly operate as a whole."
Scott:
""Much of..." does not make an IC system, and "fails to properly operate as a whole" is not any part of the definition of an IC system."
From the "ISCID Encyclopedia of Science and Philosophy"
quote:
Michael Behe's Original Definition:
A single system composed of several well-matched, interacting parts that contribute to the basic function of the system, wherein the removal of any one of the parts causes the system to effectively cease functioning. (Darwin's Black Box, 39)
Behe himself proposed the 'knockout test' as one means of evaluating whether a system is IC. Those parts that cannot be removed comprise the IC part of the system. The blood clotting system has such components and Behe describes some of them in his book. I do not see much evidence to suggest that Behe thinks the blood clotting system is not IC.
[ 04. May 2004, 23:27: Message edited by: Argon ]
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zenheadache
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Member # 1233
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posted 07. May 2004 20:42
I recently read Behe's book for the first time, and he devoted a whole chapter to the blood clotting cascade. He certainly appeared to this reader to be saying that the blood clotting cascade was IC.
Also, Behe has done an awful job of defending himself according to the links I read. Miller comes across as a blowhard lawyer with his questioning, and Behe as a pummeled witness. This is unfortunate, particularly since Miller exposes plenty of soft parts to attack in his own arguments against design. For instance, his argument that the mammalian eye is poorly designed because of its blind spot seems to be a classic fallacious ad ignorantium.
Research by Marcus Meister at Harvard suggests that the blind spot is actually a feature, not a flaw. And if so, then the eye is not poorly designed at all.
Where Behe erred with his notion of IC is that he thought he had the closed the deal where he merely had begun to bargain. If he continues to say that IC systems cannot be produced gradually, then he is defending a sinking ship. However, that does not mean that the gradual production of IC systems is natural and NOT designed, which I have explained in my Brainstorms post "What ID Proof Must Look Like." Where Miller is erring is that he seems to think that if he can show that IC systems CAN be built gradually, then he has refuted an ID explanation. That is not true either.
IC is a fact that isn't even arguable. The question is how do things get to be IC? By nature or by design? This is the issue in question. Behe has not answered it.
Neither has Miller.
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Rex Kerr
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posted 07. May 2004 20:55
I'm aware of a good deal of Dr. Meister's work, but none of the work I'm aware of seems to indicate that the blind spot is a feature. Can you be more specific as to which research you have in mind, and why it indicates that the blind spot is a feature?
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zenheadache
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posted 07. May 2004 21:26
Rex, the PDF's are here:
http://rhino.harvard.edu/Publications/index.html
Look for:
Soucy E, Wang Y, Nirenberg S, Nathans J, Meister M. 1998. A novel signaling pathway from rod photoreceptors to ganglion cells in mammalian retina. Neuron. 21: 481-493.
And:
Berry MJ, Brivanlou IH, Jordan TA, Meister M. 1999. Anticipation of moving stimuli by the retina. Nature. 398:334-338.
And for a discussion of Meister's research on this matter (by people who know more about the subject than I do), go here:
http://www.asa3.org/archive/evolution/199904/0181.html
I would be interested to know if you dispute the claims or think that Meister's work actually suggests that the blind spot could offer a useful advantage.
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Scott
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posted 07. May 2004 21:29
quote:
I recently read Behe's book for the first time, and he devoted a whole chapter to the blood clotting cascade. He certainly appeared to this reader to be saying that the blood clotting cascade was IC.
Indeed. And I was not disputing this, nor would I. Behe has, however refined his views on the clotting cascade. No "revisionist history" involved.
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zenheadache
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posted 07. May 2004 22:10
Rex, sorry I didn't answer the first time. The reason why I think Meister's research indicates the blind spot is actually a feature is because the ganglion cells seem to have a "predictive" effect which would not exist in the absence of the peculiar mammalian construction. It seems to me that this "predictive" effect could provide a performance advantage in mammals.
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Rex Kerr
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posted 08. May 2004 02:24
Fine, but what does this have to do with the blind spot? There are no ganglion cells in the blind spot. The spot is blind because the axons from the ganglion cells collect in one spot to form the optic nerve that leads to the LGN (in the thalamus).
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zenheadache
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posted 08. May 2004 03:46
Sorry Rex. Excuse my imprecision.
The alleged fault of the eye is that the axons collect in that region of the retina creating the blind spot.
I should not have said that the blind spot itself were the feature, but the consequence of a valuable feature that would not be present if the eye followed the invertebrate model.
But the point is that Miller and Dawkins both could not imagine a good reason for this arrangement, and so they pronounced it bad design, and from this inferred that there was no design.
Have I misunderstood Meister's work?
[ 08. May 2004, 03:52: Message edited by: zenheadache ]
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Rex Kerr
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posted 08. May 2004 15:22
Added in edit:
Somehow I missed your first post so when I said
"You didn't reference any work, so I'm not sure if you're misinterpreting it."
that was, er, just plain wrong.
I continued on to say, accurately:
The part of Meister's work that I'm familiar with deals with information processing by the retina. This processing is independent of the orientation of the retina--it's a consequence of lateral connections made by bipolar and amacrine cells.
Now that I've looked at the papers, I still come to the same conclusion. They don't, as far as I can tell, have anything to do with the blind spot or the orientation of the retina. There are aspects of the retina that are designed well, but nothing that Meister talks about would differ if the layers of cells were inverted, or if the optic nerve was placed further away from the fovea, or if it was distributed, or if the rods and cones sent were above the rest of the retina but there were a layer of pigment cells immediately below, etc. etc..
All things considered, our vision works pretty well given the rather odd design, but the design is still odd.
[ 08. May 2004, 18:51: Message edited by: Rex Kerr ]
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Krauze
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posted 08. May 2004 15:37
Hi Zen,
I've only looked at the abstracts of the Meister articles, but it doesn't seem to me as if his work has any relevance to the orientation of the vertebrate retina. In the post you linked to, Loren Haarsma suggests a good explanation for the arrangement, without connecting it to Meister's work. As Elsberry points out in another post (click on "Thread" in Haarsma's post), the issue of ganglion processing is unconnected to the issue of retinal orientation.
Have you read the articles you're citing? If so, perhaps you could provide some quotes from them to support your point? As an ID proponent myself, I would very much like it if there was experimental evidence against the suboptimality argument, but from what I've seen so far, this doesn't appear to be the case.
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zenheadache
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posted 09. May 2004 01:34
First of all, I goofed. I read these about 6 months ago and didn’t reread them before posting the links. I thought there were TWO relevant Meister papers, and I was mistaken. Only the NATURE article is relevant to this discussion. The Soucy reference is irrelevant here.
Second of all, before we get any further on this, I want to be clear to correct any mistaken impressions I may create that Meister and his work is focused on the suboptimal design debate. Meister himself isn’t at all concerned with these questions in the referenced work, and I don’t want to create the false impression that he is a player in the Darwinism-Design debate, or that he is a proponent of design . What I am saying is that some of Meister’s findings suggest that what Miller and Dawkins consider bad design actually provides an evolutionary advantage that outweighs in importance the “problem” that having a blind spot creates.
Rex, in the vertebrate eye, incoming light hits the ganglion cells before the actual photoreceptors, right? And what Meister’s findings show—in the NATURE reference—is that the ganglion cells fire off signals to the brain before the light reaches the photoreceptors, which allows us to anticipate the future location of a fast moving object.
If we can anticipate the future location of fast moving objects, then we can respond to them quicker, and this is important for survival because fast reactions are often a matter of life and death.
So if incoming light did NOT strike the ganglion cells first, then the anticipatory advantage would be gone, would it not? And it could not have this benefit if it were NOT constructed as oddly as it is, correct? So it might be the case that the accuracy of the imagery resolved by the eye, some of which is lost by this arrangement, is less important that being able to anticipate the future locations of fast moving objects, especially in reference to the perceiving creature. Criticisms of the eye's design as poor have assumed that the eyes primary purpose was to resolve imagery as accurately as possible, and that because we could imagine better ways of creating sharper imagery, then the design must be flawed. That assumption seems to be false. Imagery resolution only has to be good enough, not perfect, and if we can get “good enough” in a design which also offers anticipatory benefits at the same time, then this seems to be better than having perfect resolution at the expense of the predictive coding effect.
Hi Krauze. Read the Nature reference I posted. Its not very long and much of the relevant details are in the graphs which I am not sure how to post here from a PDF.
Also, it seemed to me that Elsberry was dismissive and might have been considering what was already known, not understanding what Meister’s discovery was, whereas Haarsma was not. I think Haarsma had the final word on the question when she posted:
“We spent some time over lunch discussing whether or not Meister got a
big publication out of saying something which everyone has known for
decades -- namely, that most ganglion cells have a strong transient
signal. We decided that Meister really did show something a bit more
than that. (His results showed that this "predictive coding" effect --
which was a well-known psychophysical phenomenon for quite a few years
and was widely assumed to happen entirely in the visual cortex --
actually happens (to at least some extent) in the retina before signals
even reach the visual cortex.”
Unless I am misreading or misinferring something (yes, that is possible, even for me), then the predictive coding effect is made useful by the peculiar construction of the eye, with the ganglion cells positioned in front of the photoreceptors.
You also wrote: In the post you linked to, Loren Haarsma suggests a good explanation for the arrangement, without connecting it to Meister's work.
You must mean this:
“Is the invertebrate eye designed better? Actually, that's not clear.
The "backwards" arrangements of the vertebrate retina allows the
photoreceptors to be in contact with the pigment epithelium. This
tissue not only blocks further transmission of light into the head, it
also helps recycle the photoreceptors' used photopigments. Recycling
used photopigments is a metabolically intensive process. So there's an
advantage to having the photoreceptors right next pigment epithelium.
This arrangement allows tight spatial packing of photoreceptors, and
allows rapid recycling of photopigments.”
Yes, she does offer an explanation of the arrangement without referencing Meister, but she does nothing to dispute the claim, as Elsberry does, that the vertebrate design offers an important benefit by the predictive coding effect, so I would suggest that the predictive coding effect is an additional benefit to the arrangement. The vertebrate eye might have advantages in its peculiar design in a number of ways, one of which is the predictive coding effect, and another of which might be photopigment recycling.
And I am not the first in claiming that the predictive coding effect has a distinct advantage, but am merely following Meister himself in the Nature paper:
"In general, an animal is likely to benefit from anticipating the future position of an object, for example to pounce on it or to evade it. This is particularly urgent when the primary sensory data are delayed. In principle, this delay could be compensated anywhere within the behavioural loop, even within the motor system that executes the response. However, it is advantageous to perform the correction early, before different sensory pathways merge."
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Rex Kerr
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posted 09. May 2004 15:30
Zen, you misunderstand the article. The ganglion cells fire by "predicting" future input (e.g. from a moving pattern) as a result of lateral connections.
Ganglion cells have no photoreceptor pigments, and the picosecond it takes for light to travel from the ganglion cells to the rods and cones is utterly negligible when compared to the tens of milliseconds it takes for a response to light. The orientation of the structure is irrelevant.
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zenheadache
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posted 09. May 2004 21:38
Rex, okay, I see what you mean and where I was wrong regarding the lateral connections. But doesn't the predictive effect still depend on the ganglions being available to the light, without considering photoreceptor positioning? Would they be AS available if the construction were inverted, or would the difference also be negligible?
[ 09. May 2004, 21:40: Message edited by: zenheadache ]
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Rex Kerr
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posted 09. May 2004 23:59
Ganglion cells don't detect light, so it doesn't matter whether they're exposed to light or not, as far as we know. All of Meister's results can be accounted for by network properties, assuming rods and cones as the only directly light-sensitive cells.
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zenheadache
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posted 10. May 2004 18:31
Understood.
Now why have some biologists maintained that the eye is suboptimally designed given the role of RPE and the greater problems that would result by trying to "improve" the design by changing the location of the RPE relative to the photoreceptors to remove the blind spot?
I mean, given everything we DO know, if we cannot imagine how to improve the vertebrate eye's design, then it seems nonsensical to maintain the eye could have been designed better.
We would actually have to show how to fix the blind spot problem without creating worse problems in the process. If we can't do that, then it seems Miller and Dawkins are making—dare I say it?—sensationalist claims.
[ 10. May 2004, 18:33: Message edited by: zenheadache ]
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