Talk:Evolution of the eye

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Related Article

I was searching around evolutionary related topics, and I found Cooperative_eye_hypothesis is orphaned. I wonder if it should be referred to from here. — Preceding unsigned comment added by 24.212.190.49 (talk) 00:24, 30 November 2012 (UTC)

Unclear statement

Not sure what this means: It is biologically difficult to maintain a transparent layer of cells as sizes, therefore the thicknesses gradually increased. Graft 07:09, 22 June 2006 (UTC)

Neither am I. The "as sizes" part is particularly baffling. I took the line (and much of the rest of the article's end) from Eye#Evolution of eyes. I think that the last two sections both need some significant cleanup and expansion; I couldn't find as many good sources for them as for the early stages of eye development, and the lens-formation stages are tricky to explain in layman's terms, so I gave up for the time being. -Silence 07:19, 22 June 2006 (UTC)

Very nice work, by the way. Graft 13:32, 22 June 2006 (UTC)

Almost 2 years, and no one has figured out what the "as sizes" means. I'm removing it. --Hordaland (talk) 14:06, 27 April 2008 (UTC)

Evolution of lenses

Completely disagree with the statement "The development of the eye is considered by most experts to be monophyletic". On the contrary, most experts would probably say that it seems to have developed at least 40 times independently. Perhaps the writer means the vertebrate eye.

In response to the request by Silence, I put together the diagram of major stages in the evolution of the eye. However, I'm not 100% happy with one of the diagrams, specifically diagram E, which shows the development of lenses. Some of the diagrams I looked at for reference (specifically this one and this one) appear to state that lenses derived from the cellular humor inside the eye, whereas the article itself states they evolved by "splitting" from the cornea. The diagram is not totally clear in this respect, but I'd like to know which of these is the most accepted. Were the diagrams I referenced out of date? Is there a difference of opinion over how lenses evolved? Did both situations happen in parallel? I'd like to make sure the diagram is as clear and accurate as it can be. I already raised this on Silence's talk page, but decided to throw it open to wider discussion here. ~ Matticus78 12:23, 10 July 2006 (UTC)

DJMcC (talk) 14:07, 27 July 2012 (UTC)

References

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DLH 18:05, 13 July 2006 (UTC)

Delete Undocumented Assertion

Propose deleting the following section as an assertion without support. The reference to Miller does not appear to mention the eye or vision and appears irrelevant.

Although the eye remains a common and popular argument among laypeople, some intelligent design and creationism advocates have abandoned the eye as an example of "irreducible complexity" because of the relatively thorough understanding of its evolutionary origins biologists now have, instead relying more on mollecular and microscopic structures such as the flagella, though recent developments have shed significant light on these structures as well.

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DLH 18:09, 13 July 2006 (UTC)

That sentence, and especially the one immediately following it, seemed to fail a NPOV test. Both sentences discuss evolution vs. ID and creationism, and do not really bring new information to the question of if and how eyes developed through natural selection. It is revealing to see people referred to as "laypeople" of evolution, as if it itself were a religion.

(this is getting pretty tangential, but this is a correct usage of "laypeople" -- see [1] -- and it has nothing to do with religion, except perhaps by distant etymology Montyy0 22:01, 10 December 2006 (UTC))

More to the point, the title of the article is "Evolution of the Eye" and not "Creation of the Eye". This article has no place for creationist ideology or claptrap and including it seriously degrades the credibility of the article as well as that of Wikipedia. — Preceding unsigned comment added by 76.88.5.219 (talk) 11:20, 15 August 2011 (UTC)

References

Review article in Science

Perhaps you are already familiar with this or it will not be helpful, but I came across a good review article in Science last month: “Casting a Genetic Light on the Evolution of Eyes”. Perhaps those more familiar with this topic might find something useful to add to this article. — Knowledge Seeker দ 03:01, 25 October 2006 (UTC)

primitive eyes

Unicellular invertebrates?

The earliest predecessor of the eye was a simple patch of photosensitive cells, physically similar to receptor patches for taste and smell, called an "eyespot". Eyespots can only sense ambient brightness: they can distinguish light from dark, but can not distinguish shapes or determine the direction light is coming from. Some organisms covered the spot in transparent skin cells for protection. Eyepatches are found in nearly all major animal groups, and are common among lower invertebrates such as the unicellular euglena. The euglena's eyespot, called a stigma, is located at its anterior end, has a red pigment, and allows the organism to move in response to light, often to assist in photosynthesis.[14][15]

This whole paragraph is a bit of a mess, but I haven't read enough to know how best to fix it. However, since Euglena is unicellular, it is not an invertebrate nor can it have a "patch of photosensitive cells." Also, it is inconsistent in terminology between "eyespot" and "eyepatch," and it's got a very strange voice, i.e. "Some organisms covered the spot in transparent skin cells for protection," rather than, say, "In some animals, the eyespot is covered by transparent skin cells for protection" or something. On a more detailed level, though, there are apparently even phototaxic prokaryotes, so claiming Eugelena as the fundamental precursor appears to be wrong. In overviews in some journals, there appears to be even some debate as to whether the eye arose independently numerous times, and there is a lot of evidence that the opsin proteins were not originally photosensing, and it's hypothesized (but I don't know that it's widely accepted) that prokaryotic rhodopsin evolved in archaea as a primitve form of photosynthesis. [2] and [3] are interesting reading in this area, but the latter needs a Science subscription for the full article.

Montyy0 21:56, 10 December 2006 (UTC)

It's more than a year since Monty pointed out that a patch of photosensitive cells could hardly exist on a unicellular organism. Duh. So I've sort of fixed it. Someone who is more knowledgeable in the field may well be able to fix my fix, but please don't just revert to the original paragraph which included (probably unintentional!) nonsense. --Hordaland (talk) 12:49, 23 December 2007 (UTC)

Thanks! My next target is the Backwards retina business... my recollection is that the vertebrate eye is "inside out" in that the photoreceptors are further back than the layer of supporting neurons and blood vessels and such, and that the cephalopod eye is not, and as a result the vessels and nerves don't have to pass through a blind spot as in vertebrates. Although I've seen some claims that the backwards-ness is a feature rather than a bug, I haven't read anything that seemed convincing that it wasn't just an accident of history. Anyway, if this is being discussed (and the octopus vs human eye seem to be brought up a lot in convergent evolution and creationism vs evolution arguments) it would seem like a good idea to describe how their eyes are morphologically similar but developmentally quite different: I can't find the reference just now, but I believe the cephalopod eye develops as a pit, while the vertebrate eye is an extension of the brain, so developmentally the eyes arise from different tissues. Cephalopods can also see polarization, and one squid, the firefly squid, has some color vision. Cephalopod eyes are also rhabdomeric, and can move around the pigment to accommodate for light levels (as well as adjusting their pupils sizes.)

Montyy0 (talk) 06:16, 25 December 2007 (UTC)

Sounds very interesting, hope you follow up.

See also section Circadian rhythms at the bottom of this page. There's more here than meets the eye. (Oh, can you forgive me for that?) Photosensitivity must first have developed for photosynthesis. Thereafter, I strongly suspect that photosensitivity first developed for the sake of circadian rhythms rather than for the sake of vision.

PZ mentions these two uses here (link to pertinent blog entry for the sake of myself and others, as I'm sure you already have it bookmarked) and here, but doesn't get into the which-came-first of it:

PZ: We vertebrates use ciliary photoreceptors in the image-forming part of our eyes; we have rhabdomeric receptors, too, but they're used in a more general way to sense light and dark, and play a role in circadian rhythms.

(BTW I found the source of the nonsense about multicellular patches on unicellular organisms in the article references and have written to <support@thinkquest.org> to ask them to correct or explain it.)--Hordaland (talk) 13:32, 25 December 2007 (UTC)

Degradation/loss of eyes

Is it worth mentioning the opposite process, where the eyes of an organism are reduced in size, covered over, or disappear completely? The mole is one example given by Darwin. I'm not sure if the opposite process is relevant to the evolution of the eye, but it is enlightening to know the process of eye formation isn't always beneficial to an organism. Richard001 08:35, 27 December 2006 (UTC)

Good idea. Other examples would be fish and insects that live in caves (big white eyes - I don't know the physiological difference).--naught101 (talk) 11:52, 3 September 2009 (UTC)

Paragraph needs context

Despite the precision and complexity of the eye, theoretical analysis of eye evolution, developed by Dan-Erik Nilsson and Susanne Pelger,[5] demonstrated that a primitive optical sense organ could evolve into a complex human-like eye within a reasonable period (less than a million years) simply through small mutations and natural selection.*Pro-intelligent design mathematician David Berlinski[6] criticized these findings, including a criticism that the work contained no computer simulations (something assumed by a number of scientists but disclaimed by the original authors), and criticisms of the scientific establishment in general.[7] The original authors and other scientists subsequently challenged Berlinski's criticisms.

There are a couple of things wrong with this paragraph, not the least that the part in italics is almost information-free, only inferring some dispute, or controversy. David Berlinski has not published in a peer-reviewed journal, and it is misleading to infer a scientific controversy can be made. The criticism regarding a computer simulation is directed toward errors in popular reports of their work, not the original paper. I will replace the above with the following:

In 1802, William Paley claimed that the eye was a miracle of design. Since then, it has often been claimed that the eye is too complex to have evolved in any reasonable time-frame. To examine this claim empirically, Dan-Erik Nilsson and Susanne Pelger demonstrated that a primitive optical sense organ could evolve into a complex human-like eye within a reasonable period (less than a million years) simply through small mutations and natural selection. This paper has not raised any scientific controversy. Pro-intelligent design writer David Berlinski[6] has criticized the findings in the public arena, questioning the basis of the calculations. The original authors and other scientists responded by addressing Berlinski's apparent misunderstandings, including a challenge to submit a paper of his own to a peer-reviewed journal.Trishm 06:58, 3 February 2007 (UTC)

And the brain?

Shouldn't there be a section explaining how the brain could simultaneously manage to evolve to process new information an eye might send? NigelCunningham 06:22, 8 May 2007 (UTC)

Hmmm, possibly. It might just be worth adding a sentence to note that, alongside the apparatus of the eye itself, supporting infrastructure (brain, eyelids, muscles) would also be co-evolving. No point having a prodigiously complex and expensive eye if the brain using it can't use it to work out up from down. The current article does tend to focus (!) on the eye in isolation (it's implicit that other systems are evolving alongside it, but making this clearer might help). Cheers, --Plumbago 07:57, 8 May 2007 (UTC)

One potentially interesting reference for the this would be Georg Streidter's book Principles of Brain Evolution, as he discusses the principles that lead to brain development across a great number of species, including things like the development of a laminar LGN in mammals, which is the primary way station of visual information from the retina. Edhubbard 16:01, 22 July 2007 (UTC)

I've added PZMyers' review of a new paper to External links. It suggests, as far as this non-scientist can tell, that the eye actually can be considered to be a part of the brain. Or perhaps that it originally was. I recommend the review, at any rate, and don't miss the link to an animation showing the development of the eye. --Hordaland (talk) 11:38, 23 December 2007 (UTC)

Can I support the plea of NigelCunningham? There is definitely a view out there that the eye and brain could have co-evolved. "We now know that evolution progresses modularly, with different systems evolving in parallel and nearly independently" (Matt Young) in [27]. Further to that, an eye, without a means of processing the visual signals, would confer no advantage. The example of the cave-dwelling fish, which lose their "useless" eyes, is also applicable. Johnofdundee (talk) 06:43, 5 March 2009 (UTC)

Box jellyfish have complex eyes but no brains, so obviously brains aren't necessary to the evolution of eyes; the organism merely needs to be able to use the signals somehow. -- 71.102.128.42 (talk) 05:08, 26 November 2014 (UTC)

No, there shouldn't. It is not a purpose of this article to respond to bogus Creationist objections. -- 71.102.128.42 (talk)

Eyes only evolved once?

Right now, the article says "The common origin of all animal eyes is now widely accepted as fact, based on the shared features of all eyes.".

In 1992, in response to a Stephen Jay Gould book, John Maynard Smith wrote:

"In Gould's 'replay from the Cambrian' experiment, I would predict that many animals would evolve eyes, because eyes have in fact evolved many times, in many kinds of animal." -- From "Taking a Chance on Evolution", New York Review of Books, May 14 1992, pages 234-236

So which is it? Did ALL eyes evolve from a common ancestor? Or only the eyes of MODERN animals, with some extinct lineages having evolved eyes independently? If eyes evolved from scratch numerous times in multiple lineages, this is a major, encyclopedia-worthy fact. Bueller 007 14:45, 22 July 2007 (UTC)

I think the answer depends, to a certain extent, by exactly what level of specificity we are talking about. For example, in Climbing Mount Improbable Richard Dawkins discusses the "40-Fold Path to Enlightenment", and points out that eyes have evolved in at least 40 different ways, including compound eyes, standard lens eyes like most mammals have, and a variety of other manifestations. However, recent work on the genetics that lead to the development of eyes in individuals note that the same "toolkit gene", Pax-6, is involved in the formation of everything from fly eyes to human eyes (see e.g., Endless Forms Most Beautiful by Sean B. Carroll for an accessible treatment). This would suggest that these different evolutionary pathways for eyes have evolved from a common genetic signal, most likely based on a simple light-sensing spot (without lenses and optics) that would still give an evolutionary advantage over creatures that did not have the ability to sense light and dark. It is on the basis of this shared geneteic basis, and shared features such as the similarities in the light-sensitive rhodopsin molecules, that it is generally argued that eyes (in general) only evolved once, even if the various forms seen today have diverged greatly from that common eye-spot ancestor. Edhubbard 15:58, 22 July 2007 (UTC)

Thanks. That was what I had thought about the evolution of the eye before I read the Maynard Smith quote. But as I recall, I've seen the "eyes have emerged many times" claim repeated in Daniel Dennett's "Darwin's Dangerous Idea", Dawkins' "The Selfish Gene" and some other sources as well. Dennett, for example, used it to strongly suggest that if we were to encounter an alien lifeform that had developed locomotion through a transparent medium, it would almost certainly have eyes, since that seems to be a universal "good trick" that natural selection has stumbled upon independently many times on earth. This seems more true to my interpretation of the Maynard Smith quote (which Dennett himself uses.)

If I'm correct (and I'm hardly an expert) the current evolutionary theory seems to place the original emergence of the ancestor of all modern eyes some time around or before the Cambrian explosion. So the question is, I guess, did some of the Cambrian fauna of now-extinct lineages also develop eyes independently (perhaps in order to compete with the ancestor of the modern eye)? Bueller 007 16:32, 27 July 2007 (UTC)

Hi Bueller, your comment inspired me to go back to my copy of Endless forms... and look at exactly what Carroll had to say, in the hopes that it might clarify things. He notes that Pax-6 is associated with eye (or eyespot) development in creatures from flatworms to flies to frogs to humans, so this is most likely a highly conserved toolkit gene. It's hard to get all the references, since he only uses sparse endnotes (it's a popular audience book, after all) but he notes that the first experiments showing that the first studies that recognized that three different genes, eyeless in flies, small eye in mice and Aniridia in humans, were all part of the same Pax-6 family were:

Quiring et al., (1994). Science, 265: 785-789. and

Halder, Callaerts and Gehring (1994). Science, 267: 1788-1792.

Carroll's explanation of the Halder et al. study is especially interesting, as he notes that when small eye (the mouse gene) was transplanted into unusual regions of the flies, so that "it was also turned on in weird places in the fly [like the wings or legs].... The result was the same as the experiment with the fly gene - fly tissues were induced to form eye structures. However, it is important to emphasize that the tissues formed were fly eye structures, not mouse eye structures. So while each gene had similar effects, the final form depended upon the context of the species of the experiment, not the origin of the gene." (p. 67, emphasis in original). I think this is a very nice resolution of the forty-fold vs. single-evolution discussion (and see above on the top of the talk page, too).

In the footnotes, Carroll also notes that Gould himself had a commentary on this work, published as:

Gould, S.J. (1994). Natural History, 103: 12-20.

so, Gould was aware of these findings, but note that this is about five years after the publication of his book on the Brugess Shale and the Cambrian Explosion. Dawkins probably should have said more, but I don't have my copy of Climbing Mount Improbable handy. In any case, when discussing these findings, Carroll includes in his notes a nice laudatory comment about exactly the chapter of Dawkins' book that we were discussing above. If you have a copy, I'd be interested in hearing if there is any mention of Pax-6.

Going further, Carroll discusses the early evolution of life, during the time of the Cambrian, and notes that "[B]ased on the content and similar roles of the shared genetic tool kit in protosomes and deuterosomes, we can confidently add that the common ancestor of bilaterians (an animal that Eddy De Robertis at UCLA has dubbed Urbilatera, meaning primitive bilaterian) had a tool kit of at least six of seven Hox genes, Pax-6, Distal-less, tinman and a few hundred more body-building genes." (p. 143).

So, based on this, the last common ancestor with most of the modern phylogenetic tree seems to already have had Pax-6. Based on this evidence, Carroll discusses what we can infer about the early evolution of eyes:

"Could Urbilatera have had eyes? Well, probably not the large pronounced eyes like those that we find on trilobites later in the Cambrian. Something that had large, complex eyes would probably have turned up by now in the fossil record. But, because the role of Pax-6 and other genes involved in eye development is shared in both major branches of bilaterians, we can deduce that Urbilatera probably had at least some kind of eyespot or light-sensing organ made up of photosensitive cells arranged in some geometry." (p. 144).

So, Carroll doesn't say that there was no other creatures that could have evolved eyes and gone extinct, but his line of reasoning certainly doesn't seem to leave much room for other creatures that we haven't detected. Of course, one difficulty with using the Pax-6 data to infer the presence of eyes in extinct species is that we have no way of looking to see whether Pax-6 would play a role in their development, since we have no way of observing the morphogenesis of an extinct animal. Sorry, this was longer than I intended, but hopefully there is some good material here for other editors to add to the article... or for me to do later, when I have more time. Edhubbard 20:10, 27 July 2007 (UTC)

Great. Thanks for the reply. Clarifies some things. It still hasn't explained the exact nature of the quotes, but your sources are newer than mine (except for Dennett, but he can hardly be expected to stay on top of the very cutting edge of evolutionary biology) so I suppose that Maynard Smith's claim may just represent the common assumption of his day, before the discovery of the common role of the PAX6 gene. Bueller 007 04:46, 28 July 2007 (UTC)

I too was under the impression that the eye evolved independently at least 40 different times. The eyeless gene doesn't build eyes, it merely specifies where the eyes should go, in effect, saying, "Put eyes here," without specifying what sort of eyes they should be. Zyxwv99 (talk) 13:59, 8 April 2012 (UTC)

Following Zyxwv99 I have removed the highly misleading and unsourced "Certain components of the eye, such as the visual pigments, appear to have a common ancestry: that is, they evolved once, before the animals radiated." from the lede. If there is a better place to make reference to that minutia, I've not found it. Fydfyd (talk) 14:49, 17 April 2014 (UTC)

Circadian rhythms

It's troubling that such a long and interesting article totally ignores the importance of photosensitivity to circadian rhythms! (Except for the half sentence which I just added, simply to get a mention in there.) Photosensitivity may likely have evolved first for this purpose, while it's use in vision came along later. It's now accepted that "knowledge" of the daily light/dark cycle is the basis for all seasonal, tidal, etc. rhythms, and it is common to and necessary for (virtually) all organisms. I don't think an article about the evolution of the eye can be anywhere near complete, when this aspect is ignored; the present article as it stands should rather be entitled Evolution of vision. --Hordaland (talk) 13:03, 23 December 2007 (UTC)

The development of the eye is considered by most experts to be monophyletic?

Not my field, but the above sentence, I think, needs correcting - firstly, I really doubt any sort of meta-analysis has been done on what opinions are on this. Worse, the citations used to support the statement are inappropiate - three papers by the same group of authors is not conclusive on acceptance of their claims. Finally, papers exist that contradict their statement. E.g. [4] suggests at least two independent evolutions of the eye, despite the shared PAX6 gene. Indeed, I think this subject is deserving of a separate section in the article, to give a fuller discussion of its nuances. Probably I am an inappropiate person to write it, though. Also, lazy. --Fangz (talk) 14:50, 31 January 2008 (UTC)

Neiher, Fangz, am I able to gauge the current consensus or not of "most experts"; yet it is evident that many particulars in the rest of the article and other related articles in Wikipedia and the well-publicized butterfly work being done by Briscoe et al especially within the last few years seriously explore the non-monophyletic possibilities with monophyleticism being itself as much an early (and legacy) speculation as simple descent of apes.

Editorially, getting the various parts of this article to relate, when even responsible, to meta-analysis statements and vice versa seems a fundamental review need in this article. Anyone wish to do it, please?

Pandelver (talk) 02:04, 5 March 2011 (UTC)

The evolution of "the eye" is only monophyletic if cyanobacteria had eyes! If you define "eyes" as optical imaging organs, then they are obviously far from monophyletic, even thouigh all may well be derived from the first opsin. DJMcC (talk) 15:52, 2 April 2012 (UTC)

This is so false as to defy belief that it made it into the article at all. Opsins might be monophyletic (although I'm not certain that every visual system out there employs opsins), but see below re: cephalopods for a clear example of the eyes' polyphyletic origin. Mammalian and cephalopod eyes have completely different physiology. Graft | talk 00:14, 5 April 2012 (UTC)

Berlinski vs Nilsson

First, 'misgiving' is used in connection with future events, according to the online Merriam-Webster.[5].

Second, it is important who replied to Berlinski.

Third, Nilsson's reply (ref 14 and 15), are not in a peer reviewed journal (something that would justify a 'scientifically proven that B. was wrong), but on a blog. Northfox (talk) 09:20, 5 April 2008 (UTC)

Berlinski's comments were not in a peer-reviewed paper (because they have no scientific grounding). Therefore no response can be published in a scientific paper. It is important that this article does not read as if Berlinski's comments have any weight (they don't), but on the other hand I feel that they should be mentioned, as they were well publicised. Neither Berlinski nor Nilsson's reply are "reliable sources" per Wikipedia, so I'm not sure what the best way forwards is... Suggestions, anybody? Verisimilus T 12:52, 5 April 2008 (UTC)

Please check Darwin quote

Something wrong with the sentence:

"...if [...]; if further, [...]; and if [...], then the difficulty of believing that a perfect and complex eye could be formed by natural selection, [...], can hardly be considered real."

What can hardly be considered real? Is it the difficulty of believing which isn't real? Perhaps they said things in that way in his day, but it looks strange. --Hordaland (talk) 20:47, 19 April 2008 (UTC)

You've read that correctly. Smith609 Talk 17:00, 1 May 2008 (UTC)

Thanks! --Hordaland (talk) 18:06, 1 May 2008 (UTC)

Evolution? Really?

Hi, (sorry for the bad english)

I'll be straight, Evolution is a theory. Which i believe is incredibly wrong.

So, don't say "Evolution", say "Theory of Evolution".

For me, Evolution is one of the biggest lies ever made. It's main goal, is that people stop believing in God, and unfortunaly for some, i can prove it.

NOT Even a single Protein would have come by accident, there is a chance on 10^950 that a medium sized protein would "appear". —Preceding unsigned comment added by Solidus18 (talk • contribs) 16:31, 1 May 2008 (UTC)

Hi, please review the link I've just added to the top of this page. You may also wish to view the wikipedia article on Evolution. For what it's worth, you are quite right, no proteins came about by accident. They all evolved. Smith609 Talk 16:59, 1 May 2008 (UTC)

This doesn't seem to be the right place to debate an issue, but just let me point out that a theory of something-or-other is a theory about that something-or-other; and a theory of something is different from that something. The theory of flight is not flight, and the theory of the earth is not the earth. Rather like a map of downtown Chicago is not downtown Chicago; the rules of the road are not the road; the evolution of the eye is not the eye. Evolution is something that happens in the world of life as we know it, and the theory of evolution offers explanations about how that happens. TomS TDotO (talk) 13:00, 7 May 2008 (UTC)

First of all, I must apologize for not being able to find a more suitable place to write this. Second, I must say I disagree with the theory entirely. BUT, even if I did agree with it, it would still be impossible for there to not exist SOME FORM of an intelligent creator. If these proteins all evolved, then what did they evolve from? And from where came the thing they evolved from? and then, in turn, where did THAT come from? an atom can only be cut in two so many times, likewise, one can only trace evolution back so far until he MUST come to the inevitable conclusion that there is, or at least was, an intelligent designer. To deny this would be illogical not only religiously but scientifically as well. This is the inescapable flaw of atheism. The flaw of evolutionism is that in order for an organism to evolve, it must be in a situation/enviroment where it cannot survive with it's current attributes, in which case it will DIE, not evolve. If it can survive (thus reproduce), then it still will not evolve, because it's genes will be able to be passed on. Even if the organism must struggle significantly to survive (example: an elephant in a new england forest), if it can reproduce it will not evolve, if it can't reproduce (because it died) it will not evolve. This cannot be explained away with the "random mutation" theory because random mutations are NEVER beneficial, EVER. Or at least not commonly enough to account for the staggering variety of surviving species on the earth (or outside of X-Men). Adaptations can occur, but these are distinct from evolution, example: a species' fur can adapt to become longer, shorter, darker, lighter, depending on the threats within it's enviroment, but the fur will NEVER become feathers, for the simple reason that in order to have the feathers, it would have to be in a situation where it could not survive (reproduce) without the feathers. For this to work, both a male and female of said species would have to SIMULTANEOUSLY AND RANDOMLY MUTATE A FULLY FUNCTIONAL PAIR OF WINGS!!! This example can be applied to anything, and disproves any evolution beyond minor adaptations. —Preceding unsigned comment added by 64.35.204.200 (talk) 03:21, 1 August 2008 (UTC)

One appropriate place to debate whether evolution actually happens is the Newsgroup talk.origins. Let me just point out a couple of things. First of all, there is nothing about evolution which denies that there is a creator. Secondly, this article on the evolution of the eye presents a counter-example to your unsubstantiated assertions about it being impossible. And, by the way, without a bit of detail on what your alternative explanation is, it is impossible to compare and contrast the relative likelihood of evolution with the likelihood of ... well ... of what?TomS TDotO (talk) 11:14, 1 August 2008 (UTC)

You are right, evolutionism does not deny a creator, but evolutionists do. An overwhelming majority of evolutionists are also atheists, and the two beliefs are as inextricably linked as PETA and vegetarianism, (theistic evolution is a pathetic joke from a Christian perspective and is perpetuated by people who don't understand true faith.) Also, my reason for mentioning my opinion of atheism was because a previous poster had already brought up the issue of evolutionism and atheism ("Evolution is one of the biggest lies ever made. It's main goal, is that people stop believing in God...") When you say "unsubstantiated assertions" you assume I must use science to provide proof for my assertion, but I was merely explaining the reasoning behind my opinion (yes, opinion. I don't claim to have ALL the facts.) I generally don't care if anyone is actually swayed by my statements (I was venting.) As for the counter-example, it proposes a process involving the eye actually gaining new abilities and not just adapting (A nearsighted, colorblind, creature with no depth perception will either survive, genes unchanging, or it will die, genes still unchanging. It will never need new abilities.) It is in no way a counter-example to my statements. Biased, pseudo-scientific speculation will always be defeated by cold reasoning and spiritual truth.

"when presented with an apple, one may look at it and conclude that is indeed an apple, or he may spend years trying to come up with a theory that will prove it is actually an expertly crafted fraud. I think it is probably just an apple" —Preceding unsigned comment added by 64.35.204.213 (talk) 01:16, 10 August 2008 (UTC)

Once again, I suggest that Wikipedia is not an appropriate forum for this sort of thing. Unless you have some alternative, so that there is something to discuss. Simply asserting that you don't like people who accept the reality of evolution, that is not something that can be discussed. TomS TDotO (talk) 13:14, 10 August 2008 (UTC)

When you are old and/or ill and on your deathbed, evolution will bring you absolutely no comfort. —Preceding unsigned comment added by 64.35.204.22 (talk) 01:06, 13 August 2008 (UTC)

Amusing non sequitur. Thanks for the laugh. --Hordaland (talk) 05:15, 13 August 2008 (UTC)

I wonder how much comfort anyone would get from any alternative explanation for the origins of the vertebrate (or invertebrate) eye. What is that alternative explanation? TomS TDotO (talk) 11:08, 13 August 2008 (UTC)

As long as our "advanced" society is able to provide you with the illusion that you are getting a sense of fulfillment out of life, you will be blinded from the truth. There are other beings on this planet who are similarly complacent and unreasoning. I usually eat them. They are called animals. They don't need a sense of fulfillment because they were created with only the desire to survive, unlike us. A wise friend of mine warned me of the futility of debating with people about evolution online. I should have listened to him. Do not bother responding, I am never going on to this talk page again. Sorry for wasting your time, I genuinely wish you well. goodbye. —Preceding unsigned comment added by 64.35.203.79 (talk) 00:15, 15 August 2008 (UTC)

Oh the supreme irony of being lectured about being blind to truth by someone who follows a theology that lauds the sheep-like behaviour of their followers. Having read through your postings, I accept your apology for having wasted my time. Ninahexan (talk) 01:13, 20 March 2009 (UTC)

Video from NCSE

Do you folks think that it would be appropriate to add a pointer to this recent video on the evolution of the eye from NCSE?

http://www.youtube.com/watch?v=fOtP7HEuDYA&eurl=http://www.expelledexposed.com/

TomS TDotO (talk) 12:34, 7 May 2008 (UTC)

As an atheist, I would like to point out that the above-linked video is fine for the particular subject of mollusc eye evolution, but not as fine as it claims to be for the evolution of the vertebrate eye. I claim that a better model for the early stages of the evolution of the vertebrate eye would use the hagfish, CONVEX, non-imaging eye-patch instead of the concave early mollusc eye. The advantage of the convexity is to increase light sensitivity in the deep, dark seas (away from sighted molluscs)rather than nascent imaging ability, which, for our evolutionary line, probably waited until the seas became shallower, about 410MY ago, forcing "us proto-vertebrates" to counter cephalopod attacks, by evolving an imaging ability of our own, some time after early molluscs had. (Protective hard materials, such as cartilage, then bone, came before imaging eyes, as nature's quick and easy initial response.) Thus, the evolution of "the eye" should not be treated as one single process, the way it is in the video, which unfortunately glosses over the significant differences between mollusc eyes and vertebrate eyes. There may have been just one evolution of photoreception, but there were a number of instances of imaging, of which our eyes and cephalopod eyes were but two. DJMcC (talk) 11:25, 2 April 2012 (UTC)

New References

Hi, thanks for adding new references to this article. Do consider using the references to expand the article, or to back up existing facts. References that are not explicitly referred to in the article are better placed under a "Further reading" header. Thanks again for your contributions! Smith609 Talk 13:29, 8 May 2008 (UTC)

Camera eye

The article looks promising, and I'm wikilinking to it from Cambrian explosion. I suggest a (sub-)section on the convergent evolution of the camera eye - I know of camera eyes in vertrbrates, cephalopods and box jellyfish, and I've read somewhere that the camera eye evolved independently about 40 times. Philcha (talk) 13:40, 28 June 2008 (UTC)

Types of eye

I think it would help both readers and editors if the article introduced the most common types of eye (camera, including pinhole; compound; basic light sensors, as in many jellyfish; whatever other types are significant) before looking at evolutionary paths. At present the article looks in danger of falling into the trap of considering only the camera eye. Philcha (talk) 21:51, 29 June 2008 (UTC)

In creationism and intelligent design)

If we're going to allow commentary such as that just added, wouldn't it also be appropriate to point out that other animals have a "superior design" to their vision? Squids don't have the "backward retina", mantis shrimp can detect a lot more colors, as well as polarization. Surely some quotable person has mentioned this. And, if we do that, wouldn't it be appropriate to mention that (at least some) creationists say that "design" doesn't necessarily mean "good/optimal design"? TomS TDotO (talk) 18:37, 5 July 2008 (UTC)

If we were going to mention everything that "some creationists" have said we'd be here all night. This article should really stick to the facts.

If we're going to have a "Creationism" section, we can have two approaches: one is to list "this creationist once wrote something about eyes" and "this scientist once wrote a book about eyes saying something different"; the other being "this creationist / group of creationists believes something about eyes" and "this scientist / science / the evidence showed that their beliefs are in contradiction to the available evidence".

We must be careful to present this encyclopaedia article as a summary of the facts, and avoid anything verging on personal opinion. If we present the facts, we can leave it up to the reader to decide if and how they wish to fit the facts around their beliefs; if we start inserting belief into the article, we'll end up with everybody wanting their own personal opinion listed, and the article will become a hodge-podge.

Martin (Smith609 – Talk) 19:03, 5 July 2008 (UTC)

After some consideration I've carefully re-worded the section so it avoids expressing any point of view. I think we'll be okay to leave it at that, if the rest of the article is improved with mention of squid, shrimp, polarization and so on. Martin (Smith609 – Talk) 19:16, 5 July 2008 (UTC)

The section says nothing of any importance. It sounds like some evangelical evolutionist wrote it on a whim, and thats actually what I thought it was at first. It needs to be either expanded or removed. —Preceding unsigned comment added by 64.35.204.213 (talk) 01:19, 10 August 2008 (UTC)

I suspect whoever was writing this section made a mistake in aiming for NPOV by giving undue weight to false opinions. The section basically implies that both "theories" explain the evidence well. But the reality is that intelligent design proponents believe that the eye was created roughly in its present form by a creator. This section lies at the end of an article which sets out the overwhelming amount of evidence which points to the eye having evolved. I am changing this section to reflect this.Paul.rogers.1964 (talk) 14:30, 20 August 2008 (UTC)

Well done. --Hordaland (talk) 17:00, 20 August 2008 (UTC)

A useful source

• How vision begins: An odyssey (PNAS, 2008) is well worth a look - and incorporation! Martin (Smith609 – Talk) 15:18, 25 July 2008 (UTC)
• Saló, E (2002). "Genetic network of the eye in Platyhelminthes: expression and functional analysis of some players during planarian regeneration". Gene. 287: 67. doi:10.1016/S0378-1119(01)00863-0. --Philcha (talk) 13:44, 25 December 2008 (UTC)

Vertebrate and octopus eye

I've replaced the image with one that's colour-coded for ease of reading, and annotated via Template:Annotated image so that annotations can be moved or changed easily. BTW the bit in the old caption about the 2 variants of camera eye being inherited from a common Cambrian ancestor was nonsense for several reasons - one is that the camera eye has evolved independently about 40 times, including in box jellies!

the "arms race" in the evolution of the eye

The following extracts are from the article "Evolution of the Eye". (My CAPITALS)

1) ... the first predator to gain true imaging would have initiated an "arms race".[citation needed] Prey animals and competing predators alike would be FORCED to match or exceed any such capabilities to survive.

2) One of the many hypotheses for "causes" of this diversification holds that the evolution of eyes initiated an arms race that CAUSED a rapid spate of evolution.[citation needed]

3) As certain organisms benefited from the dramatic advantages given by full-fledged eyes, many other organisms were FORCED to evolve similarly advanced eyes in order to compete.[citation needed]

My understanding is that evolution occurs by way of random mutations, which may be favourable or not. In particular, evolution is not driven by need. An organism cannot adapt to a threat no matter how hard it tries. Thus, in the Cambrian, an eyeless organism either got lucky, or got eaten!

1) and 3) are similar. I propose to delete 3). 1) should be re-written as follows:

... the first predator to gain true imaging would have gained a significant advantage. Prey animals and competing predators alike would not survive unless they evolved similar capabilities.

On 2), I would appreciate your thoughts. It may well be TRUE, even if plainly WRONG. Johnofdundee (talk) 02:49, 13 February 2009 (UTC)

You'd need to phrase it more carefully, and should check what WP:RS (which should be cited) say. There are many modes of predation - ambush, passive (web spiders, some ctenophores, etc.), luring, mimicry, pursuit, etc. - and smell and vibration senses are generally more important than sight to invertebrate predators and to many vertebrate ones; OTOH and advantage is an advantage. There are also counter-measures that do not include improved vision - camouflage, nocturnal activity, speed coupled with heightened other senses, armour ("borrowed" in the case of hermit crabs), weapons and aggressive behaviour (rhino, water bufflao, both very short-sighted), unpleasant taste, poisonous / irritant spines / hairs, mimicking species that have nasty counter-measures - I suspect the list of defences is longer than the list of predator tactics. --Philcha (talk) 03:09, 13 February 2009 (UTC)

I've removed (1) and (3). Martin (Smith609 – Talk) 15:35, 14 February 2009 (UTC)

You've identified three statements spread throughout the article, all problematic, which probably should be gathered together in just one of those places, don't you think? That might be a first step, before rewording / hunting for sources. This article is fascinating and important. I applaud efforts to improve it. - Hordaland (talk) 13:02, 13 February 2009 (UTC)

An arms race can "cause" evolution to happen at a higher rate, if evolution is defined as 'change'. In the absence of an arms race, there is less selective pressure, so change happens more slowly. I've referenced the statement; the suggestion that eyes could have singlehandedly caused the Cambrian explosion is bogus for a swathe of reasons, but it is a widely held belief that arms races cause evolution to accelerate. Martin (Smith609 – Talk) 15:31, 14 February 2009 (UTC)

Argument from ignorance

Argument from ignorance is a technical term in logic, translated from the Latin "argumentum ad ignorantiam". It may appear to be more polite to change it to "argument from incredulity", but that is not the precise description. Perhaps we can compromise with the Latin expression? Myself, I would prefer just to revert the change, but if we don't get any discussion on this, I will change it to the "compromise" "argumentum ad ignoratium". TomS TDotO (talk) 11:08, 2 March 2009 (UTC)

OK, use Latin then. I'd just reverted 5-6 edits by one of these "but it's just a theory" types and don't see any need for provoking them unnecessarily. Do we need that paragraph at all? - Hordaland (talk) 14:36, 2 March 2009 (UTC)

I think plain English is better, and the "argument from incredulity" seems fine to me (it actually fits better than "ignorance" with what the linked article says). Yes, we do need the paragraph, although I would favor rewording it to be more helpful for anyone who is genuinely wondering about the issue (and remove the rather disdainful "supernatural"). It would be good to have a short para on the fact that it is well understood how all stages of eye evolution occurred, and it is believed to have happened independently around 40(?) times (with links). Yes, this repeats some of the article, but with suitable wording that would be best. I'll try thinking about this. Johnuniq (talk) 22:54, 2 March 2009 (UTC)

While plain English is better, I dislike the idea of substituting an incorrect term for a correct use of a technical term which might offend the sensitivities of some of the readers. The point being made when one says "argument from ignorance" is not "you are dumb if you argue this way", but that "you are drawing a conclusion from your claim that we do not know". "Argument from incredulity" is something else, something like "just because you can't think of a better answer", and it seems to me to be verging on being an insult. I notice that the article Argument from ignorance does draw a distinction between the two expressions. TomS TDotO (talk) 10:38, 3 March 2009 (UTC)

A technical term in Latin? C'mon this is EN.WP. "offend the sensitivities of some of the readers"? You mean Creationists? They get too many concessions already, and WP should not give Creationism any support at all, not even by failing to point out its weaknesses. --Philcha (talk) 14:01, 3 March 2009 (UTC)

I agree that trying to not offend creationists would not work, and would be misguided. However, there are two points that strongly support the "argument from incredulity" phrase. First (using an "argument from authority"), Richard Dawkins does not say "argument from ignorance" in some books I scanned. He does say "Argument from Personal Incredulity". Second, the linked Argument from ignorance article defines the two terms such that "ignorance" is not applicable, while "incredulity" is. I don't think TomS TDotO's statement that "incredulity" would be incorrect is really supported. Johnuniq (talk) 04:19, 4 March 2009 (UTC)

I notice that the reference given for the statement says "incredulity". Therefore, whatever my personal opinion is on the proper way to phrase it, I must not impose my opinion, but go with the reference. I withdraw my objection. TomS TDotO (talk) 11:35, 4 March 2009 (UTC)

rate of evolution of the eye

I refer to the following text:

Simple modelling, invoking nothing other than small mutations exposed to natural selection, demonstrates that a primitive optical sense organ could evolve into a complex human-like eye in under a million years,[7]* but this only provides a lower bound for the process.[7]

I am unable to access the original article [7], but I have read the various responses to Berlinski's critique. Thus "Nilsson and Pelger's paper provides an elegant capstone for this research, by providing a convincing calculation for an upper bound on the time required for an eye to evolve." (Jason Rosenhouse) and "Nilsson and Pelger concluded that an eye could have evolved in approximately 350,000 years." (Matt Young) Further, the title of [7] starts "A pessimistic estimate ..." which implies that an upper bound is intended. At the very least, pessimism and realism can be synonyms! So, should WP describe it as a lower bound?

If the estimate really is a lower bound, then the text above should be deleted. A lower bound is useless in this situation.

Johnofdundee (talk) 05:26, 5 March 2009 (UTC)

That's tricky. A Creationist's argument (e.g. Paley's estimate would be that the lower bound for evolution of the eye without divine help would be infinate, i.e. it would never happen. So giving a lower bound that is pretty short by evolutionary standards si significant. OTOH placing an upper bound is aa really complicated busniess, as some things have not (so far) evolved on earth - e.g humans immune to appendicitis and vertebrates with more than 4 limbs. Estimating an upper boud has at least 2 prequisites: that each stage in the process is advantageous, so that it is favoured by natural selection; and showing that there are no constraints imposed by the previous developmental or evolutionary history of the animals. The advantage of each stage would have to be quantified, so that one could say that the lineage with the most advanced proto-eyes would replace those with none or less sophisticated ones in X generations, etc. That's a lot of assumptions. --Philcha (talk) 13:36, 5 March 2009 (UTC)

Can someone pull [7] and check to see what kind of bound is being claimed? Johnofdundee (talk) 01:32, 6 March 2009 (UTC)

An empirical upper bound for how long it takes an eye to evolve is provided by the article's second paragraph where it asserts "Complex eyes appear to have first evolved within a few million years". According to accounts I've seen, the Nilssen and Pelger (NP) paper makes various assumptions, for example, that the organisms have an environment where each incremental improvement has a (slight) evolutionary advantage. Philcha's above comment is (I think) pointing out that in general it is not possible to estimate an upper bound, because for example, there would be no natural selection to improve vision in organisms that live deep in a cave (in total darkness).

I have not seen the NP paper, but two books by Richard Dawkins (Climbing Mount Improbable and River out of Eden) make it clear that the NP paper is estimating an upper bound given certain pessimistic assumptions (pessimistic in the sense that NP calculate the worst-case or largest number of generations required to evolve an eye). I suggest that the phrase "but this only provides a lower bound for the process" should be omitted. Johnuniq (talk) 07:00, 6 March 2009 (UTC)

For some reason the sited DOI leads to a sales page. But here's the abstract:

Theoretical considerations of eye design allow us to find routes along which the optical structures of eyes may have evolved. If selection constantly favours an increase in the amount of detectable spatial information, a light-sensitive patch will gradually turn into a focused lens eye through continuous small improvements of design. An upper limit for the number of generations required for the complete transformation can be calculated with a minimum of assumptions. Even with a consistently pessimistic approach the time required becomes amazingly short: only a few hundred thousand years.

"An upper limit ...with a minimum of assumptions ... few hundred thousand years". --Philcha (talk) 07:18, 6 March 2009 (UTC)

As suggested by Johnuniq and Philcha above. Description of estimate as "lower bound" Deleted. Johnofdundee (talk) 07:01, 11 March 2009 (UTC)

Omitted ID portion, and why

I deleted the ID section until it can get some direct referencing going on, both from evolutionists and IDers. This whole article contains some heavy polemics, which is fine so long as it's referenced properly, is relevant, somewhat concise (or at least directly quotes if it's a lengthy point) and doesn't keep adding to a sentence in the manner of a kid trying to cut into the conversation: "Oh yeah?! Well here's so-and-such from Dawkins saying..." etc.

The charge goes both ways, I'm sure; for both sides.

And, the evidence is interpreted by both sides with +'s and -'s. Which is great - *both* sides should have a go with their interpretations of the evidence, so long as it's orderly, relevant to the main subject and/or whatever sub-headings/facets it finds itself under. AND, most importantly, so long as it is referenced. (I think even Dawkins is fine, so long as it isn't exclusively his musings on the subject, with no room for counter arguments from published sources.)

Whoever cited Dr. Glickman below has the right idea. I'm surprised that this wasn't included in the ID sub-heading, with attendant (and referenced) counter arguments if there were any.

Of course, asking for "neutrality" on wikipedia (or in the real world) is a pipe dream. I'm sure there are plenty of bright-eyed undergrads out there in their dorm rooms just itching to tell the world the truth about either macro evolution or ID, esp. in how it relates to the eye.

The best we can hope for in a polarized society (or here for that matter) is allowing the other side free speech, and to be responsible with one's own advocacy of ideas (Referencing relevant papers and books, people!) This is a public encyclopedia - something that is (at least I think) unparalleled in all of human history: People coming together from all walks of life, internationally, and from their own homes, to work together to collate knowledge....

In time, maybe we can add "responsibly and fairly" to that description, even over a contentious issue such as "eye evolution".

And that's it. From there, we can (hopefully) have a more informed and orderly wiki page on folks' interpretations/faith in how the eye came into being, from all sides of the coin. -kh123, March '09

I moved this section to here (it was recently added at the top of the page).

My instinct was to revert the removal of the "In creationism and intelligent design" section because we have to face the fact that "evolution of the eye" is a hot ID topic, and I don't find any part of the above comment to be a reason for removing the section. However, the article without the section looks pretty good, so I'm happy leaving it out. This is an article about the evolution of the eye so ID doesn't have a place, and the removed section wasn't going to convince anyone. Johnuniq (talk) 23:01, 8 March 2009 (UTC)

This article is still in Category:Creationist objections to evolution. Should it be? - Hordaland (talk) 01:04, 9 March 2009 (UTC)

Hmmm. I hadn't noticed that category. Let's leave things for a couple of days. If no objection, I think we should remove the category (although I have no problem if someone wants to remove the category now and/or restore the section now). Johnuniq (talk) 02:04, 9 March 2009 (UTC)

That sounds pretty contradictory to me, actually: It's a hot topic in ID, no reason it should be removed... however, since in your opinion ID has nothing to do with "eye evolution" (a fairly subjective yardstick, that) and since the section "wasn't going to convince anyone" (which is a pretty subjective statement unto itself)...

Well, like I said, I removed the section for the sake of clearing the air and hopefully getting the entire article reworked a bit more soberly (with references), precisely because subjective statements ("it doesn't belong" or "it ain't true!") were muddying the whole page up with hyperbolic retorts.

But anyhow, is a pipe dream to expect internet silversmiths to allow dissenting interpretations over their idols. -kh123, Dec '09

Evolution: Education and Outreach

The Journal Evolution: Education and Outreach has a specials edition regarding the evolution of the eye. Perhaps the content there is interesting as a reference for this article. 85.178.48.79 (talk) 06:03, 20 March 2009 (UTC)

Wow! Thank you! 26 articles, free access - I may waste the weekend on that link. And there certainly must be useful info, quotes and refs there. Looks like a fine resource. I've added it to the Further reading section. - Hordaland (talk) 12:27, 20 March 2009 (UTC)

Odd wording.

Can someone please correct this? I would, but I'm afraid I might inject some words that do not carry the full meaning, such as "process." As a chemical instead of mechanical adaptation, this may have occurred at any of the early stages of the eye's evolution, and the capability may have disappeared and reappeared, as organisms became predator or prey. It almost makes this read as if this starts off talking about a chemical and not chemical adaptation. The callback should be after and not before. Also, no comma is needed after "reappeared."Ukvilly (talk) 00:20, 3 May 2009 (UTC)

What exactly is the problem? I'm not a specialist here, but the text seems ok to me. Are you saying that it's not clear that "capability" is referring to color vision? The last comma could be omitted, but I rather like it. Johnuniq (talk) 01:44, 3 May 2009 (UTC)

Fixed, I hope. - Hordaland (talk) 13:31, 3 May 2009 (UTC)

Evolutionary baggage

In this section of the article, some recent edits replaced File:Vertebrate n octopus eyes.png with File:Evolution eye.svg, and correspondingly altered the caption. I think the change has some benefits but also some problems. The main issue is that the new image labels the retina as 1 in one eye, and as 2 in the other. That is unnecessarily confusing. It also necessitates some complex wording in the caption which would otherwise be able to simply talk about "the retina (1)...". I would be happy to redo the new svg image so 1 points to the retina (that is, change the lengths of the "1" and "2" lines in the octopus eye (and shift the "Octopus" title). However, maybe the old png image just using simple colors is better? Any thoughts? Johnuniq (talk) 08:16, 6 July 2009 (UTC)

As the uploader of the previous png image I'd prefer clearer colour-coding. If you redo it, please include the lines pointing to various parts but exclude all text excluding the numbers - I'll add these using {{Annotated image}}, so the same pic can be used in any language variant of WP. --Philcha (talk) 09:01, 6 July 2009 (UTC)

In my considered opinion, the supposed "poor design" of the vertebrate retina is a result of failure to take account all of the factors contributing to its evolution. I also deny that "The only limitations specific to eye types are that of resolution", as illustrated in (1). I would add "durability" as a significant limitation on invertebrate eyes, and sensitivity as a limitation on vertebrate eyes. I further deny that 'the eyespot depressed into a shallow "cup" shape, the ability to slightly discriminate directional brightness was achieved by using the angle at which the light hit certain cells to identify the source.' (2), because this was the way that the mollusc imaging eye evolved, but not necessarily how the vertebrate imaging eye evolved.

Ecological context: In the relatively simply stuctured cephalopod retina, sensitivity and acuity (resolution) are the main factors determining the structure, probably because the cephalopod imaging eye evolved in the photopic environment throughout (except in the later, deep water species, such as the deep water collosal squid). However, the basal vertebrates are thought to have evolved their basic eye structure from a non-imaging, hagfish-type convex, scotopic eye-patch, by being forced from deep, dark water into shallower water at the end of the Ordovician period, in which the large land mass of Gondwana drifted across the south pole, allowing ice ages to have a dramatic effect on sea levels, especially between 410 and 400MYa (3), currently thought to be about the time of the first lampreys. Inevitably, some hagfish populations (or possibly other, now extinct agnathans, with only partially vertebrate eyes, evolved initially for detection of bioluminescence) would then have been under intense predation by shallow water predators, which did not previously encounter them.

It is also noteworthy that the only invertebrates that live for more than a few years are those which have a "work-around" for the opsin damage problem. For example, the collosal squid mentioned above simply avoids bright light; the queens of various ant species stay underground once they have excavated a nest, relying on cheap, throw-away workers (with eyes) to do the visual tasks for her; the 13- and 17-year cicadas also stay underground until they are ready to surface, mate and die; the American lobster has the unusual solution of having cheap, throw-away cylindrical stalk-eyes, which I suspect eventually fall off, and are replaced naturally, if not knocked off in a fight (as is already known).

Biological context: The process of structural change in the retina must have had two main stages: first, the invagination of the retina, while the environment is still scotopic (yet brighter than at the depths preferred by a hagfish). This is the only way to allow enough light to reach both the ganglion cells and the imaging photoreceptor layer. A crucial difference between the cephalopod eye and the vertebrate eye is the kind of cell backing the imaging photoreceptor cells. In the cephalopods, it is a ganglion cell, transmitting visual information to the brain. However, in the vertebrates, it is a retinal pigment epithelial (RPE) cell, which, among other things, helps maintain its associated photoreceptor cell against cumulative and irreversible photo-oxidative damage to the light-sensing chromophore-opsin complex by light entering the cell. It does this by chewing off the hindmost discs, on a daily basis, as illustrated in (4). This is part of a complex evolved mechanism by which the opsin discs are gradually cycled through the receptor cell, being generated at the front, working their way to the back, where they are returned to the blood-stream, via the choroid vascular layer. The effect of this process (unique to vertebrate eyes) is that the useful life of the photoreceptor is not limited by damage (even though that rate of damage is high (due to the oxygenated blood used by the RPE cells), and the organism can avoid being inexorably blinded by light within a few years. The RPE cell would not, of course, be able to function from in front of the photoreceptor, because it is higly pigmented, and would absorb nearly all of the light before it could reach the photoreceptor cell. The other main function of the RPE cells is rapid re-cycling of used retinal, a process which is not necessary in cephalopod eyes, because the photoreception cascade in them is photo-reversible (5) in any case.

I propose the above as an evolutionary model, in which the strange vertebrate retina ceases to be so mysterious.

1. http://en.wikipedia.org/wiki/Eye#Types_of_eye
2. http://en.wikipedia.org/wiki/Eye#Evolution
3. http://www.ncdc.noaa.gov/paleo/ctl/cliscibeyond.html
4. http://webvision.med.utah.edu/imageswv/photphag.jpeg
5. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781864/

PS, Sorry if this article seems to be in the wrong place, but I do not have the medical qulaifications for editing the main article. DJMcC (talk) 10:08, 29 March 2012 (UTC)

7 genes orchestrate eye creation in tadpoles

• Image, article at PLoS. --CopperKettle 06:32, 22 August 2009 (UTC)

Visual Spectrum

I haven't got the book in front of me, but Jackson's Electrodynamics (a well recognized textbook) contains a graph of water's absorption spectrum. It's transparent to what we call visible light. That should do for the "citation needed" at the end of "Early eyes," if someone can provide the page reference. Thanks. —Preceding unsigned comment added by Fcy (talk • contribs) 19:31, 3 April 2010 (UTC)

Please see, following upon this question, the succeeding heading on this talk page:

"Is the statement about which spectral wavelengths travel through water correct?"

Pandelver (talk) 01:58, 5 March 2011 (UTC)

In light of recent science

I believe the wording in the Evolutionary baggage section should be changed.

See: http://adsabs.harvard.edu/abs/2010PhRvL.104o8102L Quote: "The retina is revealed as an optimal structure designed for improving the sharpness of images."

So, it seems those arguments that the human eye is 'imperfect' have been proven wrong or at least called into major question. Cool! —Preceding unsigned comment added by 18.247.6.246 (talk) 00:42, 8 June 2010 (UTC)

The imperfections remain. The blind spot remains. Nothing important has been called into question. 75.155.158.11 (talk) 03:56, 3 October 2010 (UTC)

Implied directionality / improvement towards a goal.

Care should be taken to avoid language which either explicitly or implicitly suggests a target or progress towards a goal in the evolutionary process. Words such as 'primative' 'advanced' 'developed' 'progress' 'improvement' 'better' 'complete' should be used only with great care.

Evolutionary processes act to gradually optimises a gene pool for its environment in response to selection pressure. They do not act to drive the development of a target. It is important to note that a more simple eye is not necessarily 'worse' than a more complex one, it all depends on the organism which possesses it and what selection pressures they are experiencing.

I will not go through the article and fix this issue unilaterally since it will take some time and care, but it is an important point as sloppy use of language here would act to reinforce a common misconception about evolutionary processes. — Preceding unsigned comment added by Prosthetic Head (talk • contribs) 23:32, 10 January 2011 (UTC)

Is the statement about which spectral wavelengths travel through water correct?

In the Early eyes section, last paragraph:

"...only two specific wavelength ranges of electromagnetic radiation, blue and green visible light, can travel through water."

This seems incorrect since, as the Visible spectrum Wikipedia article points out concerning Roger Bacon, water is used like any lens to refract light and display, even after passing through the water, the full human visible spectrum. Of the articles cited as references for this section, the one which is available free in full online does not mention this posit. Furthermore, it is commonly demonstrated in recordings that humans see objects including fish in colors such as red, orange, and violet outside the mixing of blue and green and near neighbor yellow, even with the naked human eye. Clear sources, please, or overhaul of this part of this article?

Can anyone with appropriate knowledge of wave propagation of humanly visible spectra through water and other substances please answer here and then alter this statement in the article appropriately? I'd like to know myself, as such a radical posit, if fact, has great significance in evolution, optics, and in the statement which follows it in this text, the interrelationship between animal and plant radiations regarding sensation and processing as well as color generation via electromagnetism.

Pandelver (talk) 01:30, 5 March 2011 (UTC)

The statement in the article refers to two ranges (blue and green), whereas in practice the attenuation of light traveling in water would of course vary quite a bit depending upon the exact frequency of the light (so the article is referring to more than two precise frequencies). I thought I remembered seeing a nice article with some details, but I can't find it now, however red light is much more strongly attenuated than blue and green when light travels more than a few meters in water. The "blue and green" is just one range, with frequencies towards blue being less attenuated than frequencies towards green. That range is mentioned as two because of its significance to color vision: it is useful to be able to distinguish between blue and green. Red light can be detected under water, but only when close to the source. At any rate all this is tangential to the point in the article, which is that animal eyes only work well with those light frequencies that happen to pass without considerable attenuation through water. I am not able to offer any insight into this topic, and I suggest waiting to see if any responses occur here. If no response, one might ask at WT:WikiProject Evolutionary biology. An alternative would be to ask a specific question (much more specific than expressed above) at Wikipedia:Reference desk/Science. Johnuniq (talk) 03:17, 5 March 2011 (UTC)

Then Johnuniq, seems the statement being questioned is incorrect per se; it does not say these 2 frequency ranges propagate with less resistance or fall off nor that these 2 are more important for any particular reason, application, or topical perspective, and if the statement has value, even rather tangential as you note, it would have to be worked into that sentence within that para's point within the article.

Will wait with you. And am glad to learn more about how the WikiProject groups work and respond. We go to the main talk page for a Project with purvue over an article in which we find an issue to question, at least if there's no patrolling or random response at that article's talk? Pandelver (talk) 17:33, 5 March 2011 (UTC)

I did not give due emphasis to the reference desk link above. There are some seriously clever people there who are very likely to give a good response to a clear question (the better the question, the better the answer). I suggest you ask there, and I would be interested to see the result. Johnuniq (talk) 01:11, 6 March 2011 (UTC)

The above issue bothered me while I did some copy editing today on the article. If blue and green wavelengths pass through water so easily and red does not (which any scuba diver who has dived to 60 feet in daytime with a flashlight can verify), and if this fact is of evolutionary importance, then why do we see into the red part of the spectrum and not into the ultraviolet or further into the (infra)red? I think the article should at least briefly address this because many readers will immediately wonder, I think. Comet Tuttle (talk) 00:15, 14 May 2011 (UTC)

"safely in a cave"

The article currently states that eyespots are useful "enough to know when they are safely in a cave, for example...". There is a cited source that I don't have access to. This is unlikely. Any mobile creature that's primitive enough to only have photoreceptors is unlikely to want to go into a cave. "Under a rock", maybe. Could someone flesh out this statement with an example of an actual, non-hypothetical animal? Comet Tuttle (talk) 00:09, 14 May 2011 (UTC)

96 percent

The article currently says that only six of the "thirty-something phyla" can discriminate the direction of light to within a few degrees, and that

However, these phyla account for 96% of living species.

I think it means to say that these phyla account for 96% of the organisms on Earth, not 96% of the species count, but since I'm not sure, I'll ask a more knowledgeable editor to clarify this sentence. Comet Tuttle (talk) 00:11, 14 May 2011 (UTC)

Cephalopods

Under "Evolutionary baggage", it's stated that cephalopods' eyes develop "as an invagination of the head surface whereas in vertebrates they originate as an extension of the brain." This is close to the end of the article, but it's the first time this apparently important fact is menioned. Could a more knowledgeable editor discuss this point earlier in the article, presumably at the point where it's mentioned that eyes have evolved several times, and in any case outside of the "evolutionary baggage" section it's currently in? Comet Tuttle (talk) 00:18, 14 May 2011 (UTC)

pair of eyes

This article fails to explain evolutin of two eyes. — Preceding unsigned comment added by Fattyjoe (talk • contribs) 04:42, 19 September 2011 (UTC)

Bias

This article only discusses the evolution of camera-type eyes. An article titled "evolution of the eye" should also include information on the evolution of compound eyes, which are just as widespread. — Preceding unsigned comment added by 50.131.184.173 (talk) 19:34, 27 May 2012 (UTC)

I agree that this article seems to focus on the evolution of the camera eye. I feel that outlining the basic characteristics of the different types of eyes would be a great contribution to this article. Including distinctions such as compound v simple, aquatic v. terrestrial, ect. would allow readers to really understand the different types' components and their advantages/disadvantages. The article Eyes lays out some major types from this source.

http://www.annualreviews.org/doi/abs/10.1146/annurev.ne.15.030192.000245 Kreinbrink.31 (talk) 02:26, 2 October 2014 (UTC)

Does the box jellyfish have a blindspot as well?

I'm sort of cheating here, as it's primarily just my curiosity, but I think it could make an interesting addition to the article in the blind spot/baggage section, if someone finds out. So it's not 100% cheating. --Extremophile (talk) 17:56, 23 January 2013 (UTC)

History section ??

The history section is misnamed. It is simply a brief mention of the "intelligent design" paradigm, which has been discredited (specifically in the case of eye evolution, to keep things simple). As of 2013, we are able to show successive "steps" of development, each more adaptive (potentially) than its predecessor. Unfortunately, the ID people will no doubt want to neuter any facts which contradict their dogma. Withing the last 2 years, I read a review article in Science magazine (AAAS) which dealt with eye evolution. It is in the references? It should be. Anyway, if there is significant controversy still (from the ID crowd) then that is a valid part of the article. But it is a small part of the history of the science and does not belong, imho, in the histroy section. My recollection of the Science article was that some of the work (arthropods or crusteceans? ?) was very recent. This seems to put into question the claim that "SOON" after Darwin wrote that quoted paragraph he was vindicated. 150 years is not "soon".173.189.78.110 (talk) 18:53, 10 February 2013 (UTC)

Darwin Quote

The old text didn't make sense "if numerous gradations from a perfect and complex eye to one very imperfect and simple"; evolution happens from simple to complex.

Anyway I updated the text and this is the reference. Imad marie (talk) 16:54, 16 October 2013 (UTC)

Human

In the section, "One origin or many" the sentence read, "the PAX6 gene controls where the eye develops in organisms ranging from to mice to humans to fruit flies." But mice and humans are both mammals, which diverged only ~15% as long ago as did mice and fruit flies, and which, according to the referenced articles, use PAX6 genes identical in amino acid sequence. I changed it to read, "the PAX6 gene controls where the eye develops in organisms ranging from octopuses to mice to fruit flies" because octopuses, mice, and fruit flies all diverged at nearly the same time, close to 530 million years ago, they represent three utterly distinct lineages of animals, and yet they still all use PAX6 to control the development of their eyes. I provided a peer reviewed reference for octopuses using PAX6 in eye development.Nick Beeson (talk) 14:02, 30 June 2014 (UTC)

History of Research needs to be renamed & updated

I agree with the previous post that this section has to be given a new title. The current one is very misleading to the reader, as there is no talk of historical research in that paragraph. It is simply the classic intelligent design vs evolution debate, and a new section should be created for this if we wish for it to be included. A possible title for it could be "Classic Source of Debate" or "Darwin's Impact".

I still think that we should include some aspect of research in this article, though. Perhaps a section titled "Modern Research" would be fitting. There is all sorts of modern research going that aims to discover different genes and mechanisms involved in the eye's evolution. One prominent author is Dan-E. Nilsson. Although his earlier works are much more famous, particularly his paper explaining the timeline for the evolution of the eye, there are several that have been published more recently. I think modern applications with any topic is a subject of curiosity for readers and would be a good addition.

Fink.182 (talk) 02:37, 30 September 2014 (UTC)

Detail in "Rate of Evolution"

In this section, the first paragraph is good. However, the second one seems like it was added without much thought put in. The paper used as a reference (reference #7 in this Wiki article) has tons of detail in describing the evolution of the eye and I think a little more detail would be helpful. To begin, I will include what Nilsson's paper actually includes, which is the pessimistic approximation of 364,000 generations needed for the development of the camera eye. Also, the authors clearly state that the eye doesn't evolve on its own, independent of the organism. The actual number of generations needed for the eye to evolve in different species can we wide ranging, but their pessimistic estimate is the best we have.

Feel free to add more content after me. Fink.182 (talk) 02:56, 30 September 2014 (UTC)

Please go ahead. I won't be able to help as this is not my area, but updates are good. Johnuniq (talk) 03:01, 30 September 2014 (UTC)

Imperfections in the vertebrate eye

The section titled "Evolutionary Baggage" is off to a good start, yet could use some improvements and added detail. It mentions the most common description of the way the photoreceptors are located behind many other cell layers, and how this is a result of evolution. Another main piece of baggage that is not mentioned is the blind spot, where the optic nerve exits the eye. Here are some links to a blog that was written by a physician named Steven Novella on the disadvantages that the vertebrate eye has due to its evolution:

http://theness.com/neurologicablog/index.php/the-not-so-intelligent-design-of-the-human-eye/

http://theness.com/neurologicablog/index.php/the-not-so-intelligent-design-of-the-human-eye-part-ii/

^^ These can be used to comprehensively cover the flaws the vertebrate eye has and how these are a consequence of evolution by natural selection.

Fink.182 (talk) 03:22, 30 September 2014 (UTC)

Selection Pressures

This article does touch on some selection forces such as eyespots allowing for circadian patterns, higher resolution aiding in survival/predation, and better recognition with color vision. However, I feel it has some gaps in evolutionary forces and their effects. I think the article could benefit from further explanation in the evolutionary baggage category. This topic is very interesting, but I think it could be more informational with some additions as suggested in the “Evolutionary baggage” category of this talk page. The article also points out that the earliest photosensitivity was developed aquatically. In addition to the light filtering effects of water, the refractive indexes would be different for an organism in air. I feel it would be a useful addition to include some information about how these forces worked on the original aquatic eye. Kreinbrink.31 (talk) 02:26, 2 October 2014 (UTC)

Moulting Example

I made an addition to the Early Eyes section. I was interested in how the layers allowing for specialization in transparent humour or air and water operation, could be involved in moulting. I thought it could be an interesting addition to include an example.

http://onlinelibrary.wiley.com/doi/10.1111/j.1502-3931.2008.00138.x/abstract;jsessionid=794AD37010C17B485C06DD42029A308E.f03t04 Kreinbrink.31 (talk) 02:26, 2 October 2014 (UTC)