Pharyngula

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I throw away a lot of creationist email; most of it is ranty and weird, or pious and dull, so it isn’t worth dealing with. Every once in a while (but sadly, not that often) one is polite and asks a simple question, and then I feel compelled to reply. If it’s short and sweet, I’ll just fire off a one-liner—for instance, when I was asked why I reject Intelligent Design creationism, I could simply say that I haven’t seen any evidence for it.

Some are a little more persistent, requiring a little more effort to answer, so they get posted here. I’ll answer this one to some degree online, tell the person where to find it, and let the commenters chew on it some more. Be nice and pretend this fellow is sincere, OK?

Here’s his question:

Thank you for your reply that there is no evidence for design. I am trying
to figure out as an impartial person why scientists say there is no
evidence for design.

I think species should have evolved first with only one eye. After
realizing that one eye cannot create depth perception, nature would have
generated another eye following thousands of years of evolution. We know
this is not true. Someone or something already knew that one eye would not
be enough.

Please tell me what is wrong with my theory?

I’ve seen this question before.

That’s right, it’s a Pinkoskiism!

i-2e03fd3b0e88fead75e679cd2540e1b4-pinkoski_asymmetry.jpg

This is precisely where some knowledge of development informs our understanding of evolution. Eyes (as the discrete, homologous organs with which we are most familiar) didn’t come first; the patterning information that establishes planes of symmetry—anterior vs. posterior, dorsal vs. ventral, and left vs. right—is generated before the eye field is established. We form eyes at the confluence of sets of interacting genes that turn on the Pax6 domain, and those genes have mirror symmetric patterns of expression. It takes additional, left-right specific patterns of gene activity to modify those domains selectively to turn off eye development on one side—in other words, it is easier to make two symmetrical eyes than one asymmetric eye.

His assumption is incorrect. The bilaterian ancestor would have evolved first with two eyes.

Comments

  1. #1 Jess
    March 29, 2006

    But you still haven’t explained PYGMIES + DWARVES!

  2. #2 ajr
    March 29, 2006

    So, following this creationist ‘logic’ would that mean animals like triops, horseshoe crabs, and spiders are all more advanced than us on account of their having more than two eyes?

  3. #3 Kristine
    March 29, 2006

    “After realizing that one eye cannot create depth perception, nature would have generated…” Nature doesn’t “realize” anything. Nature is not a person or being, and therefore “Nature” (capital N) is not a substitute for an all-omnipotent god. This is the trap that so many creationists fall into–if there’s no God, then Nature must be the Authority! Science must be the infallible Authority! What, “Science” (capital S) is not infallible and perfect? It’s all a lie! Etc., etc. These people never understood evolution or science in the first place–their scientism was merely the flip side of creationism.

    Instead of advancing his own theories regarding the formation of the eye, this person should study what evolution really is and respond to that. But that takes a lot of time and effort.

  4. #4 dcbob
    March 29, 2006

    Nor have you explained the evolution of monocles – the most obvious evidence in support of intelligent design around.

  5. #5 JoeB
    March 29, 2006

    But if this is true, how are there PYGMIES AND DWARVES??//!!1

    Oh…wait…they’re bilateral.

  6. #6 justawriter
    March 29, 2006

    The poor fellow is also very spinal-centric and doesn’t know about the copepod Cyclops not to mention other odd-eyed creatures such as Triops or that some creatures like the blue-eyed scallop which so delighted Euell Gibbons can have more than 100 eyes, they better to see you with. I have a theory that there is no lifestyle or bodily configuration so bizarre that it isn’t a standard feature in some family of invertebrates.

  7. #7 LBBP
    March 29, 2006

    Of course we all remember how short an existence Cy the one eyed Kitten had.

  8. #8 Observer
    March 29, 2006

    Where are all the one-legged or one-armed dinosaurs, too? What about the dinosaurs with only one front tooth vs two vs ten? What about the apes with one nipple instead of two?

    I’m constantly amazed that creationists don’t simply shut down due to all the infinite (useless) loops their thinking must irresistably lead to.

  9. #9 wheatdogg
    March 29, 2006

    Easy explanation. The one-eyed herbivores were eliminated from the gene pool, after being attacked (on their blind side) by one-eyed predators. One-eyed predators did not eat as well as two-eyed predators, and also got eliminated from the gene pool. This happened so long ago that the fossil record lies deep, deep in the earth.

    Now, an intelligent designer would have put two eyes in the head straight away, since evolving one eye at a time is such a terrible waste of time. keeping critters away from doing more important things, like eating, sleeping and procreating.

    Meanwhile, in the Garden of Eden, Eve ate the apple because with her one-eyedness she ran into the tree so hard that she was knocked momentarily senseless. Adam and Eve were never embarrassed by their nakedness because they just turned a blind side to the other. Once they ate of the apple, they each gained an additional eye, becoming more like the Great Binocular God, Zeiss, who was mighty ticked off. Zeiss threw them out of the Garden, and the rest as they say is history. Their descendents developed agriculture, commerce and most importantly basketball, which is mighty hard to play with only one eye in your head.

    That’s my story, and I’m stickin’ with it.

  10. #10 Curtis Cameron
    March 29, 2006

    I think it’s interesting that this reveals Pinkoski’s (and this email writer’s) cartoonish view of evolution, that 1) species suddenly appear somehow, and 2) each time one does, it has to re-evolve everything again. Not just eyes, but “every other major organ of its body.” No wonder these people don’t believe evolution is possible!

  11. #11 Will E.
    March 29, 2006

    Ah, the origins of the “pygmies + dwarves” argument. I was always wondering what the heck you guys were talking about.

  12. #12 jbark
    March 29, 2006

    “After realizing that one eye cannot create depth perception, nature would have generated…”

    Actually it can. It’s certainly not as good as what we get from our binocular depth cues, but hey, you can still get your driver’s liscense with only one eye.

  13. #13 Drerio
    March 29, 2006

    What about the pineal or parietal eye in some vertebrates? The mystical third eye in the middle of the head! Next you’re going to tell some just-so-story about how the original expression pattern for eye-field genes includes the midline and that sets up eye-like expression patterns within the brain itself leading to photoreceptive cells being expressed outside the eyes. Like I’m going to believe experimental evidence when you can’t explain how there are trinocular animals + dwarfs.

  14. #14 Jeff Fecke
    March 29, 2006

    But you still haven’t explained asymmetrical PYGMIES + DWARVES.

    pwned!

  15. #15 BronzeDog
    March 29, 2006

    But you still haven’t explained asymmetrical PYGMIES + DWARVES.

    *hides a saw behind him* Nope, I have no idea how they got asymmetrical… you can’t prove anything.

  16. #16 Matt
    March 29, 2006

    I’ve never heard this explanation for 2 eyes vs. 1 (nor have I looked for an explanation before, nor have I heard this as a creationist/ID argument). But, since this seems to be a site where science questions will be answered, my question is: if the bilateral symmetry planes are predetermined before eye construction in the manner described, why don’t eyes connect symmetrically back to their respective hemispheres of the brain, instead of the anti-symmetrical connection they do have in humans (right eye connected to the left hemisphere, etc.). Secondly, is that just in humans, or do other animals have that antisymmetric connection too? I really am just curious how that plays out…

  17. #17 Michael Koppelman
    March 29, 2006

    It’s funny, too, that the writer puts forth this eye business as evidence of design! This is what they always do, take something that seems funny and claim that it is evidence of divine intervention.

    The whole point of science is that you leave until very, very, very last hitherto unknown forces or entities. Scientists are very skeptical of any explanation that requires new physics. Even with the overwhelming evidence for dark matter (for example) there are still physicists who balk at the idea that we need a new particle to explain what we observe. This is as it should be because clearly it is easier to say “God did it” or “it’s a brand new magical particle” than to figure it out in the context of known physics.

    Although that race is about run when it comes to dark matter…

  18. #18 fusilier
    March 29, 2006

    Matt asks:…if the bilateral symmetry planes are predetermined before eye construction in the manner described, why don’t eyes connect symmetrically back to their respective hemispheres of the brain, instead of the anti-symmetrical connection they do have in humans (right eye connected to the left hemisphere, etc.).

    Matt, the 12 Cranial Nerves, specifically including the Optic Nerve, CNII, do connect ipsilaterally (same side) to the cerebral hemispheres. The contralateralization (opposite sides) you are thinking of occurs in the spinal nerves, because they exit distally (“downstream”) of a structure called the medulla oblongata where the motor and sensory tracts cross, or “decussate.”

    See any decent anatomy and physiology text. I use Ken Saladin’s since he uses evolutionary principles to explain these things.

  19. #19 Mis-nagid
    March 29, 2006

    This is why FSM’s pirates wear an eye-patch .-) AAARR!

  20. #20 BMurray
    March 29, 2006

    Dawkins’ discussion of symmetry in Climbing Mount Improbable is the most effective answer to this question I think.

  21. #21 Steve F.
    March 29, 2006

    “Adam and Eve were never embarrassed by their nakedness because they just turned a blind side to the other.”

    When they turned their blind eye, did they ever stop to think that they were creeped out because Eve only had one boob? Or Adam with only one testicle? Or, even better – by the creationist logic that two is better than one, do we say that god would have made Adam to the better standard and given him two penises?

  22. #22 Leon
    March 29, 2006

    To give the email’s author a straight answer (I think he deserves one):

    As some of the people posting here have implied, eyes didn’t appear wholesale as we know them and then multiply (ie, one eye appeared and then a second one appeared later). Eyes began as a small patch of skin that was sensitive to light–helpful to single-celled organisms that photosynthesize, like the euglena.

    Eventually they morphed into more complex structures that could distinguish some differences of shading and shapes, and into structures that could see, as we know it. Eventually color vision developed, increasingly sensitive vision developed, until we arrive at organs like the human eye, which is extremely sharp-eyed and sees a wide variety of color (though it’s not terribly good at night vision).

  23. #23 Peyre
    March 29, 2006

    Come to think of it, maybe this one-eye thing is the origin of turning the other cheek!

  24. #24 Jim H
    March 29, 2006

    Using the same argument, why did this not-so-intelligent designer only give us two eyes? If we are his greatest creation, why did he give other creatures more eyes, with a greater field of view, and in many cases a larger spectrum of visible light (at least visible to them). Damn it, I want eyes that cover the whole spectrum, like that guy on Star Trek (TNG). Oh yeah, and I’ll need a brain that can interpret all the extra data. And the same reflective gook in cat eyes that lets them see better at night.

    At least we know the FSM was drunk when he created us…that explains a lot.

  25. #25 chris
    March 29, 2006

    OK, devil’s advocate time. Quoth the creationist: “Since you claim that paired organs in bilaterians is a bye product of symmetrical body form, why do we only have one (asymmetric) heart, liver, pancreas, etc?”

  26. #26 Chris
    March 29, 2006

    You don’t mention the even bigger logic error in that cartoon: the contention that “EACH MAJOR LIFE FORM would have to EVOLVE ITS OWN EYES (as well as every other major organ of its body)!”

    That’s right, he’s denying that homology exists. Right there in black and white. Human eyes, monkey eyes, dog eyes, hawk eyes, frog eyes and shark eyes have to all evolve *separately*. Because the common descent of all those species from an ancestor with two eyes (and a heart, liver, endoskeleton, jaws, brain, etc.) is somehow irrelevant.

    Now, I’m not saying that eyes can’t evolve multiple times independently: they could and did. But each instance of eye “invention” was followed by radiation of multiple descendant species all using modificiations of the ancestral eye design. They did not each independently invent the eye from scratch.

    Probably the cartoonist knows how ridiculous this statement is, and is dishonestly attempting to attach the ridiculousness to evolution itself, rather than his contrived misrepresentation of it. Evolution without common descent – each present-day (and fossil!) organism *independently* evolving from a *separate* instance of abiogenesis – would be far more unlikely (and would be expected to produce very different results than what we actually have).

    But nobody (that I know of) is seriously proposing such a theory – the widely accepted theories of evolution require common descent of all or almost all present day and fossil life on Earth, and acknowledge (rely on) the fact that features that first appear in one organism appear in many of its descendent species, often being modified, and the modifications are in turn passed on to descendents of the modifying species for further modification, etc.

    P.S. Wonder if he has ever heard of Opabinia, or what he would make of it.

  27. #27 MissPrism
    March 29, 2006

    The email commenter at least seems a bit saner than the cartoonist, who seems to thinks every species independently had to evolve first one eye and then the other – there’s just no answer to that kind of deliberate moose-ignorance.

    I’d invite the emailer to do some background reading on simple sense organs in invertebrates, which vary greatly in number and locations (eg http://staff.washington.edu/chudler/invert.html). But yes, the part he’s got fundamentally wrong is that neither development nor evolution are equivalent to building something out of Lego bricks.

  28. #28 george cauldron
    March 29, 2006

    What can we say about a scientific movement that gets all its information from comic books?

  29. #29 Mechanophile
    March 29, 2006

    Michael Koppelman says: “Even with the overwhelming evidence for dark matter (for example) there are still physicists who balk at the idea that we need a new particle to explain what we observe.”

    *gasp* You don’t mean that there are still physicists who deny the existence of the Jebon, do you?

  30. #30 KeithB
    March 29, 2006

    He actually begs the question a bit since most animals do *not* use multiple eyes for depth perception. It is much more advantageous to simply double the field of view.

    *Predators* need good depth perception.
    *Predator-chow* needs wide field of view coverage.

    Can you say chameleon? I can say it but can’t spell it. 8^)

  31. #31 Sean
    March 29, 2006

    This is why science rocks. It answers the questions. It is so easy to just cast the answer as a “well, god wanted it that way” but that never truly answers the question.

  32. #32 JP
    March 29, 2006

    Probably the cartoonist knows how ridiculous this statement is…

    Based on Pinkoski’s other stuff, I don’t think you can assume this at all.

  33. #33 John M Price
    March 29, 2006

    fusilier:

    Matt, the 12 Cranial Nerves, specifically including the Optic Nerve, CNII, do connect ipsilaterally (same side) to the cerebral hemispheres. The contralateralization (opposite sides) you are thinking of occurs in the spinal nerves, because they exit distally (“downstream”) of a structure called the medulla oblongata where the motor and sensory tracts cross, or “decussate.”

    Keeping with the eye, this is not correct. The visual fields do cross at the optic chiasm. The left visual field of both eyes goes to the right hemisphere, right field to the left. The axonal projections from the ganglion cells, then, are from the same eye and different visual fields before they reach the chiasm, but from both eyes and the same visual fields after their crossing at the chiasm.

    Crossing levels for the rest of the body are also different depending on the part of the nervous system being discussed. Much too long of a discussion for my present time. See Principals of Neural Science, and, perhaps, Carpenter & Sutton.

  34. #34 chris
    March 29, 2006

    Why stick with bilaterians? Cubozoan eyes are pretty awesome – 2 per rhopalium, so there are 4 little ones looking up and 4 big ones looking down! Eyes are old and eyes are easy.

    Also:

    Or, even better – by the creationist logic that two is better than one, do we say that god would have made Adam to the better standard and given him two penises?

    Squamates (including snakes) have two penises. So the tempting serpent was ‘built’ better than Adam. No wonder Eve chowed down the forbidden fruit. I wonder other forbidden items she tasted?

  35. #35 CousinoMacul
    March 29, 2006

    … then nature realized that the flounder didn’t need depth perception, so it evolved to put both eyes on the same side.

  36. #36 KeithB
    March 29, 2006

    “… then nature realized that the flounder didn’t need depth perception, so it evolved to put both eyes on the same side.”

    Actually this *gave* the flounder the ability to have depth perception. Most fish do not have overlapping fields of view.

  37. #37 The Commissar
    March 29, 2006

    Interestingly, Vernanimalcula (for which MY blog is #1 on Google, eat your heart out Prof. Myers!), the earliest bilaterian found to-date, has pits, tentatively identified as proto-sensory organs, ON BOTH SIDES.

    Which is what science “predicted,” before Vern had been found.

  38. #38 TBroderick
    March 29, 2006

    I’ve talked with Pinkoski on the Comics Journal’s forums, and he’s completely serious about this stuff. He was challenged there too, btw.

    Here’s a better cartoonist: http://www.jayhosler.com/Sandwalk.html

  39. #39 Chris Braun
    March 29, 2006

    I’m not sure if someone brought this up already, but in fact the vertebrate visual system may have evolved from a single un-paired eye-field. Thurston Lacalli has argued that the frontal eye field of amphioxus is homologous to the eyes of craniates (vertebrates). In amphioxus, the light sensitive organ is roughly on the midline and unpaired. There are some debatable points to Lacalli’s homologies, but his reconstructions have shown a great deal of substantial similarities between this unpaired structure and the developmental field that gives rise to eyes in vertebrates (also median and unpaired at the neural plate stage in all living verts).
    So the creationist was correct. One eye preceeeded two within the vertebrates, and the same story might be repeated in other lineages as well.

  40. #40 Terrance
    March 29, 2006

    That was a very good question, but only because it produced an excellet answer.

    I just learned something new today!

  41. #41 James R
    March 29, 2006

    First; you do not have a theory. You have a question about something you do not understand. In order to have a theory you must understand something sufficiently well that you can state your theory in positive language. Someone else, anywhere else, in the world can take your theory and also prove it to be correct.
    Second; claiming it to be so does not make it so.ID is not science. There is no longer any dispute about this. ID is not a recognized science.

  42. #42 Steverino
    March 29, 2006

    “I think species should have evolved first with only one eye. After realizing that one eye cannot create depth perception, nature would have generated another eye following thousands of years of evolution. We know this is not true. Someone or something already knew that one eye would not be enough.”

    I take umbrage with that comment. I have one eye and I can perceive depth as well as the next asshole! I’m professional graphic designer, a 7 handicap (no pun intended) and one mean putter.

    I think the larger problem is “certain” people with two eyes cannot see the truth.

  43. #43 Carlie
    March 29, 2006

    “Great Binocular God, Zeiss”

    I so want to found a cult based on this God.

  44. #44 natural cynic
    March 29, 2006

    Take a good look at the sweater on the guy asking the questions. It’s good to see that that master of befuddlement, good ol’ Charlie Brown, has finally grown up.

  45. #45 impatientpatient
    March 29, 2006

    Not being a scientific person, I read with interest this post. It twigged in me something about mirror neurons, and glia that sends signals from one part of the body to the same part of the body on the other side facilitating pain conditions. I have no idea if this contributes to this discussion in any way, but it does seem to fit with what PZ is saying in the sense that our bodies seem to be designed with genes that are express things in a mirror pattern.

  46. #46 BronzeDog
    March 29, 2006

    As I understand it, we (using “we” broadly for pretty much all bilaterally symmetrical life) essentially have in our DNA “program” a statement of “Mirror all these objects unless told otherwise”. For, say, fiddler crabs, they have a gene that says “make the right claw really big” that overrides the default mirroring.

    Noticed PZ fixed the spelling in the title. I was wondering if the double ‘s’ was intentional. Guess not.

  47. #47 yagwara
    March 29, 2006

    Matt:

    As far as I remember, (certainly one of the friendly biologists here will correct me if I am mistaken), the octopus has none of the “crossing” of optic nerves we see in humans. It connects up left to left, right to right.
    (As previous commenters noted, to say the optic nerves cross, as some kids’ books do, is an oversimplification.)

  48. #48 Carlie
    March 29, 2006

    Just stumbled across this on CafePress… is it from someone around these parts, or is Pinkoski reviled far and wide for the pygmy argument?
    http://www.cafepress.com/pygmies_dwarfs

  49. #49 Carlie
    March 29, 2006

    Just stumbled across this on CafePress… is it from someone around these parts, or is Pinkoski reviled far and wide for the pygmy argument?
    http://www.cafepress.com/pygmies_dwarfs

    By the way, the one-eyed dinosaur would make an awesome t-shirt.

  50. #50 Matt
    March 29, 2006

    Thanks to all the responders about the eye/brain crossing question I posted… I’ll check out the books that were recommended here, or talk to my old college roommate who is now a doctor. He’s newly out of residency, so I’m pretty sure he needs some good drinkin’ time.

    This is a great place to come for solid arguments for the theory of evolution (and debunking the ID side)… and it’s nice to have a community already wired up to answer some of my biology questions to boot…

  51. #51 dAVE
    March 29, 2006

    another question to ask is:
    Why is the vertebrate retina backwards?
    Light goes through a few layers of neurons before hitting the photoreceptors, then the signal travels back down the neurons where they bundle to form the optic nerve. Where the optic nerve forms at the back of the eyeball, there is no room for photoreceptors, and, hence, a blind spot.

    A designer surely would not have done things this way.

    Cephalopods have a similar eye to vertebrates, but with the layers of the retina in the right order, and no blind spot.

    Evolution is the explanation that provides for “eh, good enough” solutions to problems, and developmental cul-de-sacs that are difficult, or impossible, to evolve out of. This is a problem that a designer could get out of.

    A few weeks ago, PZ had a post about mammals having seven cervical vertebrae, and how this looks like it’s tied to developmental processes – I don’t remember the details, but it looks like, in mammals, a change in the basic developmental genes (or gene controllers, whatever) ends up causing cancer in the embryo and it dies.

  52. #52 Andrew Wade
    March 29, 2006

    As some of the people posting here have implied, eyes didn’t appear wholesale as we know them and then multiply (ie, one eye appeared and then a second one appeared later).

    It’s possible for eyes to appear wholesale (well, pairs of eyes anyway). The genome does have a hierarchical structure of a sort, so the possibility exists of a mutation activating a pre-existing “eye subroutine” where one wasn’t activated before. Scientists have had great fun doing this sort of thing with flies (duplicating wings, putting legs where eyes should be…). Now, I grant you such mutations probably wouldn’t work out too well in complicated vertebrates (they don’t work too well for flies either). But this hierarchical structure does have other consequences more relevant to the question. Because it is not the case that each copy of a structure has to be evolved anew. If “you want” another vertebrae, “you” don’t have to evolve bone all over again for it, “you” just duplicate an existing vertebra. If “you want” to add an alpha-helix to a protein, “you” don’t have to evolve an alpha-helix all over again, “you” just insert a stretch of DNA coding for an alpha-helix in the right spot. If “you want” another pair of eyes, “you” just need to create the right indicator molecules at the right time and desired location. The results are probably not going to work too well with humans, but if you’re working on a slug it may not turn out to badly, and if you’re mutating a clam that already has 20 pairs of eyes, an extra pair may in fact be a bonus.

  53. #53 BrianT
    March 29, 2006

    After reading the original post and the comments, I’m left feeling that the poor creationist still won’t know which end is up. It seems that, when trying to get his brain around evolution, he’s still stuck on the POOF! idea: species and body parts come into existence suddenly, out of nowhere, from nothing, fully formed. Isn’t a more direct answer to his confusion that species change gradually over time and that species have two eyes because their ancestors had two eyes?

  54. #54 The Brummell
    March 29, 2006

    As far as the backwards vertebrate eyes go, I seem to remember reading something (sorry, no references) about early vertebrate eye evolution, and how this backwards arrangment is actually an adaptation for night vision. The argument goes something like:

    – Rods are very sensitive to light intensity, and are good for vision in low-light conditions
    – This same sensitivity makes them vulnerable to radiation damage at high light intensities
    – Placing the rods (photoreceptors) at the back of the retina allows a protective structure to partly cover the rods during periods of high light intensity, and withdraw during periods of low light intensity.

    I’ve seen diagrams of this rod-protecting-pigment-structure-thing for Salmonid eyes, and I’ve heard it’s present in all (most?) vertebrates.

    I think the idea is that vertebrate eyes evolved in highly light-variable environments, so having sensitive detectors that could be protected was favoured. I guess this means that cephalopod eyes, with their straightforward, Minolta-like setup, evolved in an environment of fairly constant light levels (ie, consistently pretty dark).

    Of course, a designer could simply make rods that were resistant to high light intensities, and put them in a place that doesn’t require a blind spot. This has been done – I already mentioned Minolta, I’m sure other camera / optics corporations employ designers. I believe in the existence of these designers, and feel they prefer to be called “Engineers”. But I won’t proseletyse here about the Canon of the Church of the Opto.

  55. #55 Andrew Wade
    March 29, 2006

    OK, devil’s advocate time. Quoth the creationist: “Since you claim that paired organs in bilaterians is a bye product of symmetrical body form, why do we only have one (asymmetric) heart, liver, pancreas, etc?”

    Because the heart, liver, pancreas, spleen, etc, all originate on the midline of the body. As to why the symmetry is broken, I would assume that is to fit the organs in the abdominal and thorasic cavities. Except for the heart, where the two sides perform different functions.

  56. #56 Geoffrey Brent
    March 29, 2006

    After realising that one eye cannot create depth perception

    This is rather overstating things. Having two eyes certainly helps depth perception, but there are several ways to achieve depth perception and only one requires binocular vision.

    – Focus. The closer an object is, the more focal power your eye needs to yield a sharp image. Useful up to about 2 meters; for focal purposes, anything past that is pretty close to infinity.

    – Stereo vision. Using parallax differences between the eyes’ images to gauge distances. Useful up to maybe 10-20 meters; after that, the differences are too small to be much use, which is why missing an eye isn’t as big an obstacle to golf and marksmanship as many folk think. Ideally involves two eyes, but with practise a one-eyed person can replicate it to some degree by moving their head and watching how things shift.

    – Comparison with known objects. If I know how big a 10-cent coin really is, and how big it *looks*, I can gauge how far away it is. Useful at all distances.

    – Haze. The further away something is, the more visibile is the intervening haze. Only useful at very long distances for us, but can be significant at much closer ranges underwater.

  57. #57 malcolm
    March 29, 2006

    You have all missed the essential creationist point. If God had not created our two eyes, two ears and one nose in just the right relationship, glasses would never have worked. How unlikely is it that glasses would work on some random facial structure? How far-seeing is our creator!

  58. #58 fusilier
    March 29, 2006

    John M. Price.

    Thanks for the points – however, I didn’t wish to bring up the notion of hemidecussation at the optic chiasm, nor the spinal roots of the Accessory nerve, CNXI. I was addressing Matt’s misunderstanding as a common one I see in my classes for allied health students.

    You are quite correct that the visual fields overlap – but I’m not 100% sure that this is not secondary in development, to the primary ipsilateral formation.

    fusilier
    James 2:24

  59. #59 Dr. Marco
    March 29, 2006

    Teleology lies deep in the creationist mind. “We have eyes so that we can see”, they will say, instead of “we see because we have eyes” They believe there is a purpose in everything, i.e., a creator. For example: “The appendix is there so that we can have appendicitis” or “so that future surgeons can practice”. Those are examples of the teleology of the concrete creationist mind

  60. #60 miko
    March 29, 2006

    Hi Matt,

    Not just eyes, but a huge percentage of the nervous system is cross-wired. Why? It’s hard to say exactly, but there is no shortage of theories. If you have access to an academic library, here’s a review (though it’s by MDs, so they get some biology wrong).

  61. #61 Matt
    March 29, 2006

    Hi All,

    Thanks for the additional comments. The picture on the following page jars my high school memory of the original ‘eyes cross hemispheres’ idea that i had:

    http://neuro.med.harvard.edu/site/dh/b14.htm

    So, I can accept the argument that “genetically, it can be easier for two eyes to arise rather than one,” but it did make me wonder how, in the paralance of the knowledgable of this post, how does the eye get both ipsilateral and contralateral symmetries? I suppose that it is both an evolutionary question and a developmental question (that is, how does evolution account for getting eyes w/both these types of symmetries, and deveolpmentally, how are the two symmetries implemented genetically?)

    just curious, if people are still reading the comments of this post…

  62. #62 Jonathan King
    March 30, 2006

    Our host writes:


    His assumption is incorrect. The bilaterian ancestor would have evolved first with two eyes.

    Just to be excruciatingly correct about this for a moment, does that really follow? Cnidarians are not in Bilateria, but some of them have eyes. Similarly, echinoderms are in the phylum Bilateria, but have a radically different and eyeless body plan. Finally, scallops have way more than two eyes (and beautiful mirror eyes at that!), and that needs to be accounted for. I think there’s a better argument to be made concerning the way patterning genes work in general; note that it’s not even Pax6 that seems to be most basic here, since (last I knew) Cnidarians don’t really have Pax6 but something related to PaxB.

    But please correct me on this if I’m wrong; my excuse is that I’m just a psychologist. 🙂

  63. #63 Keith Douglas
    March 30, 2006

    So, what’s the relationship between this Pinkoski and Jack Chick?

  64. #64 darukaru
    March 30, 2006

    So, what’s the relationship between this Pinkoski and Jack Chick?

    Pinkoski is ignorant enough to be funny.
    Chick is barking, frothing mad.

  65. #65 BronzeDog
    March 30, 2006

    Out of curiousity, how litigitious is Pinkoski when people parody his stuff?

  66. #66 Y. Khan
    March 30, 2006

    Thank you all of you who answered my question about two eyes. I learned something from it.

    I have a few more questions up my sleeve in favor of ID but I am afraid to ask them in an open forum like this. I believe my questions will given more ammunition to religious leaders against science.

    Y. Khan.

  67. #67 darukaru
    March 30, 2006

    I have a few more questions up my sleeve in favor of ID but I am afraid to ask them in an open forum like this. I believe my questions will given more ammunition to religious leaders against science.

    Oh, please don’t throw us in that briar patch.

  68. #68 Carlie
    March 30, 2006

    Jonathan,
    Eyes evolved many times in different organisms – there’s more than one way to capture light. However, the argument is that bilateral organisms are most prone to having two eyes (or another even number) rather than some odd number because of the basic body plan. Not impossible, but it’s more likely to have two than one, in opposition to the one-eyed dinosaur argument.

  69. #69 PZ Myers
    March 30, 2006

    Y. Khan is the person who sent me the question, by the way.

    I’d like to see what other questions are up his sleeve.

  70. #70 dude
    March 31, 2006

    What is the experimental evidence for the “Big Bang Theory”? Is someone able to reproduce that result?

    How long does it take to evolve from a single cell to a multicellular organism? Has someone able to reproduce this result?

  71. #71 Owlmirror
    March 31, 2006

    What is the experimental evidence for the “Big Bang Theory”? Is someone able to reproduce that result?

    Have you read this?

    http://www.talkorigins.org/faqs/astronomy/bigbang.html

    Or are you seriously asking for a thumbnail abstract of the past century of astronomical observations, combined with advances in other fields, such as optics, chemistry, and electronics?

    If you think there’s a better theory based on testable observations of reality, by all means publish it.

    How long does it take to evolve from a single cell to a multicellular organism? Has someone able to reproduce this result?

    I’ll let the real biologists tackle this one, but the fact that single-celled and quasi-multi-celled organisms (cooperative groups and quorums, such as Volvox) exist implies that true multicellularity is just the next logical step.

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