Evolution of Eyes

Understanding eye evolution is easy. Begin with a small change, then add changes, each giving an advantage, until what you have can be called a “new organ”.First, start with regular temperature sensitive nerve cells (we can evolve their presence in steps too if you like). Now, a mutation causes them to fire when exposed to light instead of heat - not hard since light produces heat anyway. Now there are a clump of light sensitive cells, which are advantageous because sensing light is better than not sensing it - this may allow the little creature to hide under a rock, etc. Now a mutation causes that clump to be depressed in the skin - thus protecting it. Similarly, you can see that the opposite mutation - causing it to bulge up, would be selected against, so the “depressed in” mutation survives. Now the cup with light sensitive cells can sense light direction too! Mutations that cause a transparent cover of cells, and later thicken this layer to make a lens, or add muscles that allow the eye to move are all accumulations of small steps, each being advantageous, up to the eye you possess. That's understandable. Let's look at it closely. Say a mutation causes a thin layer of clear skin to cover the eye (outer, thin layers of skin are often clear). That has the advantage of protecting the eye, an so seems clear that it would be selected for. That would automatically fill the middle with a fluid due to normal growth (embryos grow in fluid, not in air). Is that what you were unclear on, or is there some other step in the useful image on post #9 that is still a little foggy?Eye evolution was recognized as easy even 150 years ago - Darwin described the process in post #9, long before we found living transitional forms of so may intermediate steps.Have a good day-Equinox

It helps to keep in mind that a fossil is a snapshot of the organism existing at the time. Fossilization is a very very very rare event. So rare that most species that have ever existed never got fossilized at all and the knowledge of their existence lost forever and ever, Amen.An example is the dodo. They're extinct now and yet we have not a single one of their fossil. Another example is the passenger pigeon. There were once hundreds and hundreds of millions and millions of them over our skies. They're extinct now. We don't have a single fossil of them.Now, what is even much rarer is us finding the relatively few fossils that are out there. Just use your common sense. It's like finding a needle in the haystack.Going back to the snapshot concept, imagine this. You want to take a tour of Europe. You first land in London and take a picture of yourself at the airport. You then decide to visit the whole country before going through the tunnel into France. All this time, you continue to take snapshots of your trip. You make your way through France and into Italy. You visit Rome and the various cities all the while taking random snapshots of your trip. You continue to do this until you get to Russia. By now, you've created quite a few snapshots of your trip. You then come back to the States.You show your photos to the people you know. Some get thrown around. Some are lost. Some are forgotten.Five generations later, only a few random photos out of your original collection have survived. Your descendants want to piece together where you'd been in Europe. Out of the 2 thousand or so photos that you took, only about 100 survived, and most of these were snapshots of you in the countryside somewhere in Europe (in other words, not very identifiable). But a few were pictures of you in Paris, Rome, Munich, etc. In other words, your descendants might not know exactly what roads and what train routes you took, what hotels you stayed at, what restaurants you ate at, what people you talked to, etc. But with the hundred or so photos that survived, they were able to piece together relatively what places you've visited and perhaps where you probably stopped at. For example, since they had a photo of you in London and another in Paris, I think it's reasonable that they could just assume you went through the tunnel. Since they have a picture of you in Rome and another in Germany somewhere, they could probably assume that you at least went through Switzerland.What creationists like you are doing is equivalent to claiming that those few photos that survived just proved that five generations ago you used a transporter from the star trek series and transported yourself from place to place. Why? Because someone somewhere along the line found a book on the star trek universe and decided to create a religion out of it.Fossilization is very very very rare. Having the luck to find fossils are even rarer. Will we ever find enough fossils to piece together exactly how so-and-so species came about step by step? Probably not. Can we piece together how they generally came about? Sure.

This is a really helpful reply. Thank you.Alright, still on the "c" and "d" part. How would the fluid start to secrete? You said it would start automatically due to normal growth. Are you saying that it would be something like trapped embryo fluid or something like that inside? Or are you saying that something will secrete the fluid into the space? The embryo fluid one seems more plausible because the automatically secrete thing would be like cupping your hands, sealing them, and then they would suddenly fill with fluid in the space between them. Can you clarify this part for me please?

But aren't they both just a cluster of lenses that group together to form an eye? The placing is different, as they are different species, but to me they sound like the same general idea.

My words were "curious" not "see, your wrong because it doesn't make sense". I wanted an understanding of how it happened, or as you would say, how scientists pieced it together.

Cup your hands in the way you're talking about for a good 10 minutes and hold them like that.What covers your hands now? Sweat? That would be a secretion.When you get a blister, where one layer of skin is separated from the rest, what happens (as long as the blister remains sealed so nothing leaks out)? It fills with fluid.The body tends to fill voids like that with some sort of fluid. It may not be ideal for an eye all the time, but then, evolution has never been about the "ideal," just "good enough" and sometimes "better than my parents."

Not very much seeing as to how it is the first stage of the evolution of eyes according to the photo. That would be like asking "are apes human?" I know that there is signs of life before the Cambrian time period. That is, however, simple life. If you want answers to everything to message 5, here you go: This part is contradicted by you. I said Cambrian is the oldest with complex life, you said no, Precambrian has simple life. This would be like someone going "Hey, this is the oldest painting found" then someone else going "Nope, google statues". That would make the guy confused because he was talking about paintings (IE complex organisms). Now if he said "this is the oldest art (oldest life)" then you would have a reasonable argument. The only other sentence in this half of your post is proof about Precambrian that I don't need.As for the other half of your post: What is there to say to this? You say it may be hard to identify, but they have identified a type of eye in Trilobites. I'm not saying that eyes don't exist (in which you would have a reasonable argument if I did). Then you say eyes have evolved or re-evolved several times. I say good, that's why we are here: to discuss that, not debate if it happened or not. I want to know how it would have happened (and Equinox gave a very nice answer for that).Is this a long enough answer for you?Enjoy.Edited by Lyston, : Misquote

Thanks for the quick response (and short too!). As for what you are saying, would organisms back them sweat? And wouldn't that sweat be because of the heat your hands generate? What if it was very cool inside that space? I don't think you would still sweat. As for the blister part, that would make sense, but if that were to happen, would the thin membrane have to pop every so often to let fluid out or something? But that would be our (the human) bodies. We make blisters, but they can't stay because the growth of our skin will push them out or shed it. I'm not doubting this, btw, just curious and unable to see it clearly.

There are several different kinds of compound eyes.Please read the material I post more carefully.To repeat: To suggest that "they're the same, just positioned differently" is akin to suggesting that graphite and diamonds are "the same", the atoms are just "positioned differently".For more information about compound eyes, check wiki:Compound eye - Wikipedia

In a discussion about eyes, pretty much everything is going to sound like "the same general idea."When we say that the eye of one species is "completely different" from the eye of another, we are saying that their structure and the way they work is different, not that they aren't eyes. After all, with regards to the evolution of eyes, all we're really talking about is the increasing specialization of light-sensitive features in organisms over time. Many organisms have evolved eyes on completely separate paths (the eye of a squid, for instance, while still and eye, is completely different from your eye). Eyes are an extremely useful and beneficial structure, so it really isn't surprising to see them pop up in so many wildly different species.Specifically, when you say that the Brittlestar eye and trilobite eye are "the same general idea," you're correct in that they are both compound eyes. The eyes of the Brittlestar are probably the closest living example to eyes like trilobites had, but the fact that the body of the Brittlestar is essentially one giant compound eye is very, very different from trilobites who, depending on the specific species, had anywhere from one to t a few thousand lenses contained in just a few eyes.You could say that the mammalian eye and the eye of an Eagle are "the same general idea" as both examples consist of a lens, a retina, etc, but really, the particular structure is very, very different.

I get what you are saying, but to me they sound like the same KIND of compound eyes. Maybe, instead of graphite and diamonds, I'm looking at gold and fools gold. Can you explain the differences to me please? I'm looking at this as Cat Eye vs Dog Eye (I know you won't like this example as the two kinds of eyes right there are very different, but to me, the form is very similar).

You posted before me, but I think you just answered my post. That's weird. Alright, I get what you are saying. Trilobite eyes and Brittlestar eyes are generally similar, but not the same.

You're taking the analogy too far. The point of the analogy is not to suggest that the first example of eyes fulled with a humor would have been filled with sweat or any other specific fluid, but rather to show you that bodies tend to fill voids with fluid. That's all.Sweat is increased due to heat, but your body secretes through the skin all the time. You don't notice because it typically evaporates away, and you (I hope ) take regular showers to wash away the excess oil and such your skin secretes. With a covering to prevent the fluid from escaping, you'd notice that your body secretes an awful lot of fluid, pretty much constantly. Yes, I know it's gross.And again, we're talking about a structure that already has a cavity. A simple mutation would be all that's necessary to create an extra layer of skin to cover that cavity, and it would as a matter of course fill with some kind of fluid (just like any other cavity in your body). Further mutations in that organisms descendants can refine what the specific fluid is made of, what the covering is made of, etc.The key with evolution is to think small, and don't carry an analogy farther than it's intended. Individual mutations will be extremely slight modifications almost all of the time. It's only over many generations that the particular structure will further specialize into something far more complex than the tiny cluster of light-sensitive cells its ancestor had.

Thanks for the response, Lyston. Not really (though I'd be interested in why you think so, but that could be another thread).We are talking about using the sense of sight - that's what eyes are for. A light sensitive patch senses light. The benefit of an eye is that it allows the owner to sense something and organism without one can't. Thus if a patch of light sensitive skin offers an advantage to an organism it will be selected for, and any modifications that improve it will also tend to be selected.The question thus comes down to what qualifies as an eye. What would a most primitive eye be like.Then you need to consider if you could find evidence of that kind of eye development in the fossil record, and here it would be difficult to do for pre-cambrian life. You equate the precambrian with complex life, and this is false. Life existed before, and had similar "complexity" to cambrian life, just not shells and hard parts.But if you really want to get into distinctions between complex and simple you are going to have to define what you mean by "complex" and where you start. Is a two cell organism complex? Three?Given that there are several different kinds of single cell organisms that can sense light, and that daily rise and fall in a water column in response to light, the development of an "eye" starts with a single cell organism.How complex an organism do you need? or is it just a matter of perspective. In other words you didn't do it, you did not look to see how complex pre-cambrian life actually is. Even with the links I gave you in Message 5 and repeated in Message 12.HINT: You are wrong. Here's just ONE example:Spriggina

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The striking Vendian fossil Spriggina (shown here) and its close relative Marywadea make up the Spriggina, a clade of soft-bodied organisms that are restricted to the Precambrian. Spriggina is known largely from the Ediacara Hills of south Australia, near Adelaide. The organism had a crescent-shaped head and numerous segments tapering to the posterior end; it is only about three centimeters long.

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Spriggina was described as an annelid (segmented worm), but it now appears to be related to the arthropods, although Spriggina had no hard parts, and it is unclear exactly what kind of appendages it had. Compare it to our pictures of trilobites and see what you think!

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Do you think Spriggina may have had eyes like trilobite eyes? And there are as many answers to how eyes evolved as there are different kinds of eyes.From Investigator: Eye's Silly Design (from the Silly Design Institute):

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Copepod:

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This is a little critter that (shown here as a larvae) has a single eye and a single photoreceptor ... and yet it has a lens.

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Why would it have a lens with only one photoreceptor (that is basically an on\off signal processor)? Because the photoreceptor is at the end of a little stalk that can move back and forth and up and down, covering the area that a more complete retina would cover with this single sensor. The stalk dances for the light.

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Copepods are predators and use this dancing eye to build up a picture of their surroundings in much the same way that a laser light show can produce an image with one dancing light, or a television can produce an image with a dancing beam (of course both examples are commonly used to expand the intelligence of their viewers ... or is it just for silly entertainment?).

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Again this comes down to the question of how complex is complex again. In Message 1 you said: So what we see is evidence of organisms complex enough before the cambrian to evolve eyes. What we see is that eyes are simple.You also quoted a pamphlet that said:

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This fossil fact (and thousands others) falsifies the Theory of Evolution by complex systems appearing suddenly without any transitions.

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And the evidence we have, is that this statement is totally false. Not only are there transitions TO cambrian trilobites, there are transitions with eyes.We can easily believe that their "thousands others" are also equally bogus misrepresentations of the reality. Did you learn anything in order to write it? If not, then my answer is no.Enjoy.

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I know this has been answered a few times already, but I figured I'd throw in my little bit too.What's cool about this diagram is that you can actually see just about every step of it today in living molluscs. See the diagram on this Encyclopedia Brittannica article (I don't think you need a subscription to see this, but you might). This doesn't really have any bearing on the evolution of the vertebrate/human eye, but there isn't much reason to assume that our eyes are somehow uniquely "irreducibly complex," when mollusk eye evolution from pigment patches to morphologically-complex cephalopod eyes--with lens, cornea and humor--is this easy to see.To add to this, when a squid is preserved in formalin, the outer covering of the eye turns opaque, and takes on the same color as the rest of the skin, and hides the eye behind it.Here's the image molbiogirl put up for reference: Edited by Bluejay, : Added dashes for easier reading

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There was a point to this [post], but it has temporarily escaped the chronicler's mind. -modified from Life, the Universe and Everything, Douglas Adams