Evolution of the Eye

[Moontanman]

Originally Posted by LJP07

I understood all of that anyway Moonman...the question is how can say a sheet of perfectly normal skin...just say you had a sheet of skin 20cm x 20cm and each area of that sheet is exposed to the same degree of light, what determines HOW those cells evolve into photosensitive cells and at the SAME time, what governs its location on the sheet assuming the sheet is similar to say the face.

First of all you are not looking at the question from the correct perspective. There were photosensitive areas before there was sheets of skin and eyes before there was sheets of skin. Eyes didn't evolve in higher animals, eyes were already present and then incorporated into higher organisms as they evolved. Single celled protozoa have eye spots, the ability to sense light has a huge evolutionary advantage and was selected for early on in evolution.

[LJP07]

Yeah, makes a lot more sense again now...

[mynah]

Box jellyfish have 24 eyes, ranging from simple to amazingly complex. Why, when they don't even have brains?

[Moontanman]

Originally Posted by mynah

Box jellyfish have 24 eyes, ranging from simple to amazingly complex. Why, when they don't even have brains?

I'm not so sure they do not have a brain, they have a neural net that is found through out the their body and it serves the same purpose as brain does in a more complex organism. The best way I can answer why they don't have central brain is they don't need one, their neural net works well for them.

[mynah]

Interesting article:

Precursor of eyes found in the brain

[jab2]

Originally Posted by Thunderbird

Or its just a series of fortuitous mistakes.

Looking at the ratio of beneficial to non-beneficial changes on DNA of any organism you wish to choose, your statement might be much nearer to the truth than you would ever imagine.

[doggone]

Cyclopoida (cyclops) exist in cold polar water and deep dark water. Another possibility is that light sensitive tissue was used to lead protozoans away from the light and away from being eaten...Then again, ordinary plant cells are light sensitive. The growth of plants has been shown to follow the sun’s movement across the ecliptic.

Overall, I’m not convinced with the current evolutionary concepts for the eye. I believe the eye can evolve in innumerable ways AFTER one gets up and running, but the hitch is that there’s no reason for the eye to have ever gotten off the drawing board.. The theories I read about, offering ideas on the reason for ‘eye’ evolution, always suggest a measurable degree of perception that plants and single-celled organisms just aren’t capable of.. No plant, microbe, or protozoan has the wherewithal to know that the guy next to him is his enemy. They do not have the moxie to know that the morsel over yonder is food. An eye is of no use to such an entity and the evolution of such would lead nowhere.

[Boerseun]

Doggone, that's just plain wrong.

You don't need any "moxie" to determine if something is food or not.

For a predator, movement might indicate something not naturally part of the background. It is chased and eaten, whether it be food or not. The junk found in shark stomachs shows that there is no consideration for the edibility of it - car numberplates have been found in shark stomachs, and a varied collection of other human-made crap, none of it edible. But in nature, moving stuff not part of the background is more likely to be edible than not.

Similarly for prey: Anything moving against the background has a higher chance of being a predator out on the hunt than not. So you freeze or run away. Chickens run like hell when airplanes fly overhead, with a silhouette and movement pattern that doesn't even remotely resemble that of an eagle. It's an instinctive response that has nothing to do with the reality of what they perceive - but it's clear that those chickens will have a higher chance of survival, cause if you run like hell for anything in the air, you'll be better prepared when the actual eagle pitches up. But you have to be able to perceive that movement, whatever your reaction to it will be.

In both cases, perceiving that movement requires eyeballs. And the minimum for determining the distance of the threat/possible morsel is two eyeballs, giving you nice stereoscopic vision. There are exceptions.

Up to this point of development, there are, as yet, no requirement for any "moxie", or intelligence of any sort. Simply instinctive reaction to the input of even very rudimentary light-sensitive cells is required. But given the above, it is also very clear that those with the best-developed or most effective light receptors are the most likely to survive.

And there you have it.

[doggone]

Hi Boerseun:
All of your examples support my earlier statements, and you’re still not addressing the subject of this page. You’re using examples of organisms that already sport the basic ‘eye’. I already talked about that, and for that ‘eye’ there’s no end to where that evolution can go. I’m not talking about chickens, sharks, or eagles, I’m talking about the “plant, microbe, or protozoan” entities....., where the so called ‘eye evolution’ would have begun.

To fill in the blank spaces of our theories, and to abbreviate our arguments, we try to humanize our theories: “It would become advantageous for the creature to be able to run from, or to, a determined goal and the eye now allows that”... That’s from a textbook, and its wrong, and its how all these theories are reduced. A level of reasoning power, even if it’s a small amount, is needed to interrupt food or danger from any distance. The plant, microbe, or protozoan, is unable to do that. A chicken, yes, a single-celled brainless protozoan, no. Light sensitive tissue might be an advantage to the proto-type, but an eye would be of no use.

I’m not saying someone, someday, won’t come up with a working theory for how the eye could have evolved into being. I’m just saying that it doesn’t exist now. Not even close.

[Moontanman]

Originally Posted by doggone

Hi Boerseun:
All of your examples support my earlier statements, and you’re still not addressing the subject of this page. You’re using examples of organisms that already sport the basic ‘eye’. I already talked about that, and for that ‘eye’ there’s no end to where that evolution can go. I’m not talking about chickens, sharks, or eagles, I’m talking about the “plant, microbe, or protozoan” entities....., where the so called ‘eye evolution’ would have begun.

To fill in the blank spaces of our theories, and to abbreviate our arguments, we try to humanize our theories: “It would become advantageous for the creature to be able to run from, or to, a determined goal and the eye now allows that”... That’s from a textbook, and its wrong, and its how all these theories are reduced. A level of reasoning power, even if it’s a small amount, is needed to interrupt food or danger from any distance. The plant, microbe, or protozoan, is unable to do that. A chicken, yes, a single-celled brainless protozoan, no. Light sensitive tissue might be an advantage to the proto-type, but an eye would be of no use.

I’m not saying someone, someday, won’t come up with a working theory for how the eye could have evolved into being. I’m just saying that it doesn’t exist now. Not even close.

If you haven't found a working theory of the evolution of the eyes you are not looking very hard. I found a whole page on google. here is one of them.

Evolution of the eye - Wikipedia, the free encyclopedia