The Kraken Wakes

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On 16 February Dr. Vincent Cassone debated Intelligent Design advocate Dr. Michael Behe. The debate was sponsored by the TAMU Veritas Forum.

Here is an outline of the debate. A number of issues caught my eye, but I will deal with one particular issue in this post.

“Behe’s rebuttal: The bad design argument [of the eye] is an argument from ignorance. May be reasons; in the case of retina, arrangement improves blood supply.”

No, it doesn’t. Behe shows his colours by giving a bad rehash of a bad creationist argument. I’ve briefly blogged the “blood supply” argument before, but I’ll put in a bit of detail this time.

Just to recap, vertebrates (like ourselves), Squid and Octopi have “camera eyes”. They differ in how the photoreceptors in the retina, the part of the eye that receives the image, is wired up to the brain. The vertebrate wiring system is often cited as an example of “bad”, or at least quirky, design that is explainable by evolution.

The vertebrate retina is wired “backwards”. That is the photoreceptors point to back of the retina, away from incoming light, and the nerves and blood vessels are on the side of the incoming light, this means that any image formed on the vertebrate retina has to pass though layers of blood vessels and ganglion cells, absorbing and distorting the image.

To get decent visual acuity, vertebrates must focus light on a small patch of retina where the blood vessels and nerves have been pushed aside, the fovea. This patch must be small because of the nutrient requirements of the retina. Also, the construction of the vertebrate retina means that blood vessels and nerves must pass through the retina, creating a “blind spot”, where no image is formed. Finally, the “backwards” retina means that vertebrates have a high risk of retinal detachment. Altogether this shows that having the nerves and blood vessels in front of the photoreceptors is less than optimal design.

Now consider the eye of squids, cuttlefish and octopi. Their retinas are “rightway round”, that is the photoreceptors face the light, and the wiring and the blood vessels facing the back (1). Squid and octopi have no blind spot; they can also have high visual acuity. The octopus also has a fovea-equivalent structure, which it makes by packing more (or longer) photoreceptors into a given area (1). Because it doesn’t have to create a hole in the supporting tissue it can have arbitrarily large “fovea”, and greater visual acuity. Cuttlefish have better visual acuity than cats (2) and because of their “rightway round” retinas; this level of acuity covers nearly the entire retina (1,2) unlike vertebrates where it is confined to the small spot of the fovea.

The vertebrate retina is a prime example of historically quirky “design”. The vertebrate retina is backwards because the development of the retina was first elaborated in rather small chordates, where issues of acuity and blind spots were non-existent, all subsequent vertebrates got stuck with this “design”. Vertebrates do very well with the limitations of the design of the eye, but it is clear that this is no system a competent designer would make. Naturally, this annoys the proponents of an Intelligent Designer, and they have been looking for ways to put a better spin on the kludged design of the vertebrate eye.

Behe, in using the “better blood flow” argument, invokes an argument that has been doing the rounds of creationists for a while. The True.Origins site (which is a rip-off of Talk.Origins) has a page that claims that the “backwards” retina improves the blood supply. It is probably the canonical page where these claims come from.

Unfortunately for Behe, this statement is completely wrong. Lets see why this is so.

In vertebrates, underneath the photoreceptors is a layer of pigment and pigment cells called the choroid (the squid, cuttlefish and octopus have similar arrangements - more on this later), this layer of pigment absorbs stray light that is not caught by the photoreceptors, which might reflect back and fuzz up the image.

In terrestrial vertebrates, the amount of light landing on the retina produces a significant amount of heat, enough to damage the retina itself (3,4). The True.Origins page gives the impression that it is light focused on the retina that produces the heat. The article implies that by having the most thermally sensitive bit of the photoreceptor bang up against a heat sink (the blood vessels of the choroid, whose rapid blood flow removes the heat, see below), vertebrates can tolerate light intensities that “right way round” retinas could not.

However, when one reads the paper they reference (3), a completely different picture emerges.

It is the choroid itself that generates the heat that threatens the retina! As noted above, the pigments in the choroid absorb light that is missed by the photoreceptors. This light is re-radiated as heat. 25-30% of the light falling on the retina ends up being absorbed by the choroid and re-radiated as heat (3,4). So we have the most thermally sensitive part of the photoreceptors bang up against the bit that generates the most heat. Good design? I think not.

To cool down the choroid, very fast blood flow through the tissues below and in the pigment layer is needed (3,4). But lets be clear about this, the Creationists have it back to front. The “backwards” arrangement of the vertebrate retina does not make possible fast blood flow, it requires fast blood flow to cool the tissue down. This is yet another area where vertebrate design is flawed, with the fragile photoreceptors hard up against the source of the damaging heat.

Of course, the question of why fish, which have more species than all terrestrial vertebrates combined, must suffer with a backwards retina so that terrestrial vertebrates can have high blood flows to an area that wouldn’t need them if the system was designed correctly in the first place, is never addressed. The other question is why terrestrial gastropods which have camera eyes have a “right way round” retina if invert retinas are important for terrestrial vision? Their camera eyes are relatively small compared to terrestrial vertebrates, and so should loose heat readily. However, arthropod eyes of this size are subject to light-induced retinal damage. See the references in this paper.

In squid, octopi, cuttlefish and terrestrial gastropods, the pigment layer is below the photoreceptors, in an area of dense blood vessels (1). This arrangement blocks stray light and provides sufficient blood flow to cool the tissue and provide nutrients without the added layers of ganglion cells over the top of the photoreceptors that distort and absorb the image. Even better, squid, octopi and cuttlefish do not have the most thermally sensitive part of the retina next to the source of waste heat, as it is in vertebrate eyes, needing an outrageous amount of blood flow to cool the system.

The vertebrate eye does very well indeed, but it is a kludge. The fovea is a cute trick to squeeze greater acuity out of a flawed design, but octopi and squid do it better. The cooling blood flow to the choroid is needed as the pigments of the choroid generate waste heat, but this is irrelevant to whether the photoreceptors are forward or reverse facing. The arrangement of the vertebrate eye does not improve the blood supply, and it looks like the vertebrate eye has to kludge up a high blood flow to the choroid because the vertebrate inverted retina is poorly designed to get blood to where it is needed.

Once again, the vertebrate eye fails as Intelligent Design. ID proponents loudly proclaim they are not creationists and one is left to wonder why Dr. Behe has appropriated a bad Creationist argument.

(1) Matsui S et al., Adaptation of a deep-sea cephalopod to the photic environment. Evidence for three visual pigments. J Gen Physiol. 1988 Jul;92(1):55-66 (2) Schaeffel F, Murphy CJ, Howland HC Accommodation in the cuttlefish (Sepia officinalis). J Exp Biol. 1999 Nov;202 Pt 22:3127-34. (3) Parver LM. Auker CR. Carpenter DO. The stabilizing effect of the choroidal circulation on the temperature environment of the macula. Retina. 1982, 2(2):117-20. (4) Parver LM. Temperature modulating action of choroidal blood flow. Eye. 1991;5 ( Pt2):181-5.

24 Comments

Here’s where I think the creationist rebutall comes from: our old pal Denton. Here’s his essay on the subject, which I assume Behe is thinking of: OH joy, your content filter doesn’t like the word retin_a. What a dirty, nasty word!

http://www.creationevolution.net/in[…]*etina*1.htm

Remove the stars in the above URL. Boy that’s annoying.

I should note that the Denton argument, now that I look at it, is a bit different. It claims that the ingenious design of the inverted eye (so ingenious that the reason it is found in fish is because it’s an intelligent PRE-adaptation!) is because it allows for… well here’s Denton:

“Taken together, the evidence strongly supports the notion that the inverted retina and its major consequence (the positioning of the photoreceptors in the outer section of the retina where they are in intimate contact with the choriocapillaris) is a specific adaptation designed to deliver abundant quantities of oxygen to the photoreceptor cells commensurate with their high energy demands–especially in metabolically active groups such as the birds and mammals. Rather than being a case of maladaptation, the inverted retina is probably an essential element in the overall design of the vertebrate visual system.”

How does this change the argument?

He further claims that:

“The more deeply the design of the vertebrate retina is considered the more it appears that virtually every feature is necessary and that in redesigning from first principles an eye capable of the highest possible resolution (within the constraints imposed by the wavelength of light16) and of the highest possible sensitivity (capable of detecting an individual photon of light) we would end up recreating the vertebrate eye–complete with an inverted retina and a choriocapillaris separated from the photoreceptor layer by a supportive epithelium layer and so forth. (A more complete justification of this viewpoint is not possible here and is being prepared for publication elsewhere.)”

Is this so? Could we imagine a better design for the eye that would retain all its capabilities without being backwards and requiring all sorts of compensatory adaptations?

He further claims that:

“The more deeply the design of the vertebrate retina is considered the more it appears that virtually every feature is necessary and that in redesigning from first principles an eye capable of the highest possible resolution (within the constraints imposed by the wavelength of light16) and of the highest possible sensitivity (capable of detecting an individual photon of light) we would end up recreating the vertebrate eye–complete with an inverted retina and a choriocapillaris separated from the photoreceptor layer by a supportive epithelium layer and so forth. (A more complete justification of this viewpoint is not possible here and is being prepared for publication elsewhere.)”

Is this so? Could we imagine a better design for the eye that would retain all its capabilities without being backwards and requiring all sorts of compensatory adaptations?

But of course Behe’s claim doesn’t need to be correct or even supportable, because the debate format is not designed to require, encourage, or even reward correctness. Behe presented a refutation that sounds plausible, makes him look like he’s right on top of the facts, seems reasonably within his area of expertise, and is presented in language that’s scientifical and biological. Which is more than enough for the debate framework.

Meanwhile, and as always, the detail necessary to understand Behe’s response, and why it’s wrong, takes a great many words, requires a solid biological grounding, and is hidden away on an obscure forum none of the debate’s audience will ever read.

The last part, I’m convinced, we can do a better job of. Messages don’t get out there on their own. They have to be promoted. People need to get out there and spread references, call attention to the errors of someone like Behe, make noise, etc. They promote their nonsense. If our responses take longer, then that just means we have to work twice as hard as them to make sure they are out there.

Michael Denton (via plunge) Wrote:

“Taken together, the evidence strongly supports the notion that the inverted retina and its major consequence (the positioning of the photoreceptors in the outer section of the retina where they are in intimate contact with the choriocapillaris) is a specific adaptation designed to deliver abundant quantities of oxygen to the photoreceptor cells commensurate with their high energy demands—especially in metabolically active groups such as the birds and mammals. Rather than being a case of maladaptation, the inverted retina is probably an essential element in the overall design of the vertebrate visual system.”

I’m not an expert on physiology - in fact, I’m taking animal phys for the first time right now - but I don’t see how the higher basal metabolic rates of various groups would change the specific energy demands of the individual cells involved in vision. That prediction should be relatively testable, though. I would expect that groups that have photoreceptors with higher energy demands than other groups would show increased vascularization in that area.

That aside, my biggest problem with Denton’s argument is this: nobody is arguing that the visual system of vertebrates is a “maladaption”. Nor is anyone arguing that the inverted retinal is not “an essential element in…the vertebrate visual system.”. Vision is, has been, and will (for the forseeable future) continue to be of great benefit to the vast majority of vertebrates. The development of the vertebrate eye was clearly adaptive. The retina, even in its “inverted” state, is absolutely essential to the normal function of this system. Were either of those things not the case, the development of the vertebrate eye would in fact be a problem for evolutionary theory.

The argument that is being made is not that the vertebrate eye represents in some way a “bad” solution to the problem of how to see. From an evolutionary perspective, the vertebrate eye is just fine. The argument that is being made is that the design of the vertebrate eye is not the best possible design for an eye. That is, there are humans who could design an eye that did not suffer from as many disadvantages, and there are animals in another phylum that have an eye that does not seem to suffer from as many disadvantages. The “design” of the vertebrate eye therefore raises some serious questions for those who believe in “intelligent design”. In particular, it raises the question of why, if the designer is that intelligent, do vertebrates have an ass-backward visual system.

Well, that’s where we need someone like Ian, who knows enough about the structures to be able to confirm that the eye really could be designed the right way around without losing certain advantages someone like Denton could claim are impressive. The fact is, octopuses don’t need to see in the sorts of environments as humans. Denton et al could just argue that octopus eyes are wired in a way that gives them the sort of vision they need, but our vertebrate eyes have different needs that can only be met by resorting to the inversion trick.

I’m interested in this line of argument because in debates with creationists, this has come up a lot. I should have known better, but at one point I was seriously considering conceding the issue. I really want to understand if it is an example I can explain well, and is worth using. Should we really claim that the human eye is NOT the best possible design? Or is that claim fraught with problems and unknowns?

As I understand it, there used to be (still is?) a school of thought that if we find a functional or even non-crippling biological structure anywhere, it is the result of (invoking the ghost of Sagan) billions and billions of generations of refinement. If it seems like a kludge, this can only mean that we are not grokking the entire gestalt, as they used to say in the sixties. If the vertebrate eye seems inverted compared to how we would design it, this probably means that we have not factored in the full complement of biological and environmental fitness ramifications. Certainly all that evolution couldn’t get anything wrong.

This school of thought led to rather entertaining pontifications about how having two nostrils instead of one was a survival characteristic in some ineffable but very debatable way. Perhaps Denton attended this school at one time? And certainly the presumption that there must be some non-obvious but overriding advantages to what looks like lousy ad-hoc design plays on the creationist field. When the last ballot is tallied, it necessarily turns out that The Designer knew what He (uh, It?) was doing.

The point to get across is that evolution doesn’t deal with “getting it right” but rather in “better under the circumstances.” As Adam Osborne said, “Adequate is sufficient.”

Well, it strikes me that people like Denton are even more absurdly Panglossian than you give them credit for. Read that section on “pre-adaptation” in the article I linked to. Noses were designed so that we’d have a place to put our spectacles, after all. :0

You have to keep in mind that Creationists, like any good conman, always have a back up plan, and a back back-up plan, etc., for any direction the debate takes. Debate and misinformation is pretty much all they do. They have plenty of time and ten times the experience in these tactics. This can be overcome, but it’s not as easy as it often appears in retrospect. You have to be ready with a wide variety of contingencies covering pretty much every field of science held in memory, just as they are.

A friend of mine recently blogged a list of links to various creationist arguments regarding inverted retina.

I responded briefly to the arguments. However, I have no significant biological training, and my knowledge of the eye (other than basic details) was taken from the creationist articles themselves.

Seeing the topic came up here, I was wondering if the more knowledgable commentators could comment on my arguments, quoted below?

The various creationists have come up with different reasons as to why the inverted retina is not a design flaw. They fail to mention the full range of reasons why it is. In addition to blood vesels and nerves obscuring light, and the blind spot, the inverted retina is the major reason vertebrates suffer from detached retina.

Ayoub mentions the Retinal Pigmented Epithelium, which has three roles: regenerating photoreceptor pigments; recycling photoreceptor material; and absorption of excess light. Clearly the latter can be done by the RPE, or whatever layer underlies the retina, regardless of the orientation of the retina. It is, therefor, an irrelevant consideration. However, without the need for opacity related to this function, there is no reason why the RPE could not be transparent, performing the other functions while lying between the light and the retina.

Denton maintains that intement contact between the choroid and rods (and cones) constitutes good design in that it provides proper nutrition for light reception, and a cooling bath. However retinal cells have the following structure:

IIIIIIII M Cell body, where Is represent discs in which are embedded the visual pigment, and M represents the mitochondria. Discs are formed at the cell body end, and move progressively outward as they age. Molecules used for the energetics of light detection are formed in the mitochondria from blood born nutrients. Consequently, all blood born nutrients delivered by the Choroid in vertebrates must difuse past all the discs to the mitochondria to be used (and all waste difused in the reverse direction). Delivery from the cell body end would result in a shorter diffusion distance through less restricted space; ie, more efficient delivery. This point is born out by the fact that choroid oxygen tension drops by only 3% from artery to vein. In consequence, the retinal artery, though it only carries 5% of the blood supplied to the retina, carries 40% of the oxygen used by the retina. No wonder cephalopods require a much smaller blood supply to the eye.

As to a cooling bath, a more efficient procedure (for humans at least) would be a UV filter in the lense, eliminating the damaging but useless radiation in the first place.

Lindsay explores image processing in nerve cells in the eye. However, every function he mentions could be carried out if the nerves were behind the retina, just as well as if it were above it. This even applies to the light level detection of the ganglion’s light receptive capacity, used to adjust signal levels according to brightness. If these nerves were placed below the retina, but above the RPE, they would still be bathed in light, and be able to perform their function.

To conclude, the “advantages” suggested for the inverted retina are mostly nonexistant, in one case actually a disadvantage, and in no case more than of minor importance compared to the substantial disadvantages. The various creationists appear to make their case only be giving us partial information, and not thinking through the facts they present.

I notice that Ian did not deal with the nutrient issue that I discussed in most depth, and dealt differently (and better) with the over heating issue.

Here’s where I think the creationist rebutall comes from: our old pal Denton.

My understanding is that Denton himself has renounced all his previous anti-evolution criticisms, now accepts theistic evolution and views evolution as an “inevitable” part of nature, and has asked the Discovery Institute to no longer refer to him as an “Associate” . … .

Tom Curtis Wrote:

Ayoub mentions the Retinal Pigmented Epithelium, which has three roles: regenerating photoreceptor pigments; recycling photoreceptor material; and absorption of excess light. Clearly the latter can be done by the RPE, or whatever layer underlies the retina, regardless of the orientation of the retina. It is, therefore, an irrelevant consideration. However, without the need for opacity related to this function, there is no reason why the RPE could not be transparent, performing the other functions while lying between the light and the retina.

The various anti-evolution commentators usually don’t put in the time to understand the physiology of the retina in general, nor the comparative physiology of cephalopods and vertebrates. The RPE argument is a case in point. Most cephalopods have a transparent, non-pigmented epithelium that the photoreceptors are attached to. It is very hard to see it in the available online resources, but it is there. There is no reason it cannot do the recycling that the vertebrate RPE does (although this role is probably undertaken by processes from the supporting cells in the basement membrane). The absorption of excess light, as well as the nutrient function of the RPE/choroid, is undertaken by a layer of pigment cells and blood vessels in the basal membrane, that lies at the base of the light harvesting villi. You can see the blood vessels and pigments in this paper on the octopus retina.

Tom Curtis Wrote:

I notice that Ian did not deal with the nutrient issue that I discussed in most depth, and dealt differently (and better) with the over heating issue.

The nutrient issue follows directly from the heating issue. The blood vessels in the vertebrate eye are slightly distant from the terminal ends of the photoreceptor processes, and quite far from the cell bodies. The blood has to be pumped through at great velocity to cool down the choroid and to deliver nutrients to the distant retina. In the cephalopods the blood vessels are right next to the terminal parts of the photoreceptor process, the photoreceptor cell bodies and the pigment cells where it is needed. It is far more efficient than the vertebrate system for both cooling and nutrient delivery (this also takes care of Plunge’s concerns).

Typically, most of the arguments for the “superiority” of the vertebrate “back-to-front” retina are irrelevant. Other commentators in this thread have pointed this out giving a number of examples. Vertebrate photoreceptors can detect a single photon, great, but so can cephalopod photoreceptors, and they are not covered with gunk that absorbs or scatters the incoming photons. Cephalopods occupy many niches, from shallow water tidal zones with high light intensities to the abyssal depths where every photon counts, some are ambush predators, and some are active hunting predators. Some see in black and white, some see in colour, some see polarized light (which vertebrates can’t). Many have visual acuity equivalent to many vertebrates; cuttlefish have equivalent visual acuity to cats. All this without an invert retina. When Denton says

Denton Wrote:

“that in redesigning from first principles an eye capable of the highest possible resolution (within the constraints imposed by the wavelength of light16) and of the highest possible sensitivity (capable of detecting an individual photon of light) we would end up recreating the vertebrate eye”

he is just plain wrong.

The pre-adaptation concept is nonsense. We are to expect that an intelligent designer will give the marine vertebrates, which are significantly more numerous in species and population than the terrestrial vertebrates, a poorly designed retina so that a very few percent of all terrestrial vertebrates can have supposedly superior vision? This is a definition of “good design” of which I was not previously aware.

Tom Curtis Wrote:

As to a cooling bath, a more efficient procedure (for humans at least) would be a UV filter in the lens, eliminating the damaging but useless radiation in the first place.

.

Not really, most of the damage is coming from heat generated by ordinary visual spectrum photons being absorbed by the pigments in the choroids (and superoxide radicals generated by the visual cascade itself), a UV filter would help, but would only reduce some of the damage. Cephalopods manage the cooling system better than vertebrates.

Plunge Wrote:

Should we really claim that the human eye is NOT the best possible design?

Yes, because it isn’t. The vertebrate eye works, and works rather well (one merely has to contemplate the visual acuity of the eagle to see that the “design” works well). But it is a suboptimal Heath Robinson “design” where the limitations of the original invert retina setup (which were irrelevant to amphioxus and the small chordates in which the vertebrate eye evolved) are worked around by kludges. It is like claiming that the misground Hubble mirror with its correcting lenses is the “best possible design” because it gives clear pictures.

Which way would one expect a Designer to design the eye of an eyeless cave critter? I don’t know to what extent their eyes develop, but has anyone identified whether blind cave fish photoreceptors are frontwards or arsy-tursy? Evolutionists can predict which way the eyes would develop, but on what basis could IDers make such a prediction? And what is the point of designing eyes for an organism if they never grow into working organs?

Ian Musgrave Wrote:

The pre-adaptation concept is nonsense. We are to expect that an intelligent designer will give the marine vertebrates, which are significantly more numerous in species and population than the terrestrial vertebrates, a poorly designed retina so that a very few percent of all terrestrial vertebrates can have supposedly superior vision? This is a definition of “good design” of which I was not previously aware.

Not only that, but it requires some rather bizarre assumptions about the Designer. Apparently, the Designer was capable and motivated to design the vertebrate eye – to swoop down and stick said eye into early fish-like vertebrate ancestors. But it was not capable or motivated to insert said eye into terrestrial vertebrates. Why not just give fish the cephlapod eye, and then insert the backwards vertebrate eye a bit later on? That would give both fish and terrestrial vertebrates optimal eyes, and it wouldn’t require little if any additional effort. The notion that a Designer would give fish a suboptimal eye only so that later on down the road, it would work out well for terrestrial vetebrates, just boggles the mind. Did the Desginer plan on not being around when terrestrial vertebrates evolved? Was it too much effort to give fish a certain kind of eye that doing it again for terrestrial vertebrates was out of the question? He’s a weird, wacky guy, that Designer.

Ian, thanks for that! I would strongly suggest that you organize both the original article and your long post into a single, punchy response to the whole shebang that can be used as a further resource the next time something like this crops up.

“Was it too much effort to give fish a certain kind of eye that doing it again for terrestrial vertebrates was out of the question? He’s a weird, wacky guy, that Designer.”

Sure: and apparently, seeing single photons is necessary to humans, but having eyes that can handle reading without tremendous strain or commonly degredation to the point where reading becoems impossible: that feature just wasn’t in the offing. :)

Mike Dunford Wrote:

In particular, it raises the question of why, if the designer is that intelligent, do vertebrates have an ass-backward visual system.

oh, this is very strong evidence in support of (not-so)intelligent design! This sort of phenomenon is quite common in software engineering. “oh, man, why did we do it that way…sheesh…well, can we get it to work? Yeah, but I wish we had done it the same way they did over there…”

I mean, c’mon, WINDOWS is an example of intelligent design :-D

I think that what they really mean is “omniscient” design…

Mike Dunford Wrote:

In particular, it raises the question of why, if the designer is that intelligent, do vertebrates have an ass-backward visual system.

oh, this is very strong evidence in support of (not-so)intelligent design! This sort of phenomenon is quite common in software engineering. “oh, man, why did we do it that way…sheesh…well, can we get it to work? Yeah, but I wish we had done it the same way they did over there…”

I mean, c’mon, WINDOWS is an example of intelligent design :-D

I think that what they really mean is “omniscient” design…

Ian, thanks for that! I would strongly suggest that you organize both the original article and your long post into a single, punchy response to the whole shebang that can be used as a further resource the next time something like this crops up.

I will, eventually, when I get time.

Re: UV filter. I’m pretty sure the lens DOES filter UV to some extent. It’d be good if I had a source, though. Anyway visible light is perfectly capable of heat production when absorbed by a dark surface like the choroid. Why I never would buy a car with a dark interior.

1. The human eye does filter UV to some extent. I don’t have any references, but I know from clinical experience that some people who have had lens replacements for cataracts say that they can perceive UV patterns that were not perceivable before. The extent of the filtering, I’m not sure of. It may not be enough to change the argument.

2. This is an old game. I saw the same sort of arguments used by YECs to counter the vestigial nature of the appendix. They argued that it was full of Peyer’s patches, and was therefore invaluable to the gut’s immune system (thereby ignoring the fact that Peyer’s patches are sprinkled throughout the gut and are simply part of the design). Then they argued that people who had their appendix removed were at a higher risk of cancer, which proved it was not a vestigial organ. This was despite the fact that the concern over post-appendicectomy risk of cancer was a statistical aberration that was shown to be a furphy by dozens of papers that were readily available at the time of the writing. Behe is really doing no more than that.

3. I love the fact that Behe “rebutted” the bad design of the retina by claiming it was an argument from ignorance. Just because you don’t know why a design is optimal doesn’t mean it isn’t. For some reason, this has nothing in common with arguing from ignorance when it comes to IC. If you can’t think of how flagellae evolved, in Behe’s view, that proves that they didn’t.

4. I think there is a place for detailed rebuttals of ID claims. This is a good forum, for instance. But when it comes to 35 minute public debates, then what you need is unfortunately soundbites. The trick is to come up with the single most powerful rhetorical argument – not the most logical or best-referenced, but the argument that can engage the public imagination the best. In the instance of retinal design, I feel that the clear favourite would have to be the argument already bandied about here questioning why the Designer would give terrestrial retinas to non-terrestrial organisms just so that they could evolve into terrestrial organisms and take their retinal designs with them.

5. The other thing the debater needs is a large database of such quick rebuttals to all the dozens of fallacies the ID crowd can throw.

regards, Chris

Whoops. Forgive me for using the word “design” when I should have used “basic pattern”.

regards, Chris

Get hammocks…Great blog by the way..

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This page contains a single entry by Ian Musgrave published on March 15, 2005 1:53 PM.

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