Evolution of the Eye

Yellow_Number_Five
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Evolution of the Eye


Supplemental reading: http://www.don-lindsay-archive.org/creation/eye_time.html
Feel free to ask me any questions.

I am against religion because it teaches us to be satisfied with not understanding the world. - Richard Dawkins

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Kelreth
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I have a question pertaining

I have a question pertaining to human and possibly mammalian eyes. In my general biology course biol 001 (not idiot bio, first bio course, my school is strange -_-) my teacher commented on how the human eye is backwards. The receptors are on the opposite side of where the light comes in. I dont remember why this is "bad" persay, but some other creatures have better developed eyes. Do any scientists know/guess accuratly why the human and possibly mammalian eye developed this way when there is a more efficent form?


Yellow_Number_Five
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Well, as you mentioned, the

Well, as you mentioned, the human eye is actually a rather inefficient way to go about seeing. The eye has evolved many times and in many different ways.

http://www.don-lindsay-archive.org/creation/eye_time.html

No eye is "perfect".

The reason why we don't have better eyes? The eyes we have are good enough.

We don't need to pick out prey from 1,000 feet above as an eagle does. We don't need to see the ultraviolet spectrum. We don't need to see underwater as an octopus does. We don't need a 270+ degree field of vision a chameleon has and we don't need compound eyes like insects.

We have the eyes that billions of years of selection gave us.

Please don't confuse this with teleology, or I will go ape shit.

Give us the necessary selective pressures and the time to evolve however....

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gnat
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eye

i don't understand what your teacher ment by "opposite side"
does that mean opposite the lens? if so..it wouldn't make much sense to produce many light reseptors there (on the lens)...1. they'd get fried, 2. the light would be intercepted before it has a chance to land on the retina where it goes directly into the brain.

the spot where light can be most concentrated and densely focused is called the central fovea...it's in the dead center of the macula lutea. this makes sense because the shape of the eye has a chance to ingest and concentrate (with the help of muscles) all the light with litte escaping.

this spot is a distance from the optic disc ( the site where the optic nerve leaves the eye)...this area is called the blind spot. there are no receptors there.


Kelreth
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i think she meant that light

i think she meant that light comes in one side, the retina and then has to cross a space then it hits the receptors

not meaning for you to go ape shit yellow, but what is teleology? I have never heard of it before and am not sure if I should know what it is


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Quote: what is

Quote:
what is teleology?

http://en.wikipedia.org/wiki/Teleology

- Brian Sapient


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Randalllord
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Kelreth, What your teacher

Kelreth,
What your teacher meant by the "eye is backward " is that the light receptors (cones and rods) are at the far side of the retina. Light has to pass through the blood vessels and axons before reaching the light sensors.

Being "backwards" is not necessarly bad or evidence of a poor design.

Religion is regarded by the common people as true, by the wise as false, and by the rulers as useful. - Seneca


Kelreth
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o, ok, i thought it was

o, ok, i thought it was somehting along those lines. Thank you


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While not 'bad' or

While not 'bad' or necessarily evidence of bad design, it does illustrate quite clearly that natural selection does not favour the obvious or the more efficient ways of doing things- It favours anything that WORKS.

If you want evidence of 'bad design' all you have to do is think for one second. Acne, back problems, failing eyesight, menstruation, arthritis . . . . stupidity . . . . these are all things that a god could have avoided.
but i'm straying that is another topic.

We are animals. Skin and bone and teeth and blood and hair. Intelligent animals, but animals nonetheless.


LeftofLarry
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to further comment on this,

to further comment on this, let's not forget how eyes become less and less useful for organisms that do not need them anymore, such as deep sea dwelling fish, mole rats etc... The remnants of eyes are there, however, due to selective pressure, they are rendered useless. If an animal were to have been designed for life in the dark, why would a designer design an animal with a half ass eye? or...perhaps why not give it a super eye or even no eyes at all (genetically or phisiologically).

Also, if you look at animals that can see infrared or ultraviolet, the reason why they can see in those wavelengths is because of a single mutation within the gene. If selective pressures allow those organisms to be more "fit" within their environemnt, that mutation gets passed down. So....it is not in fact...a design, it is in fact...selection...natural selection, over time....

And one more thing....next time you're at a pet store look at an iguana's head. at the top of the head you'll see a "scale" that looks a bit paler...this is a parietal eye.

The parietal eye is a photosensory organ connected to the pineal body, active in triggering hormone production (including reproduction) and thermoregulation. It is sensitive to changes in light and dark, it does not form images, having only a rudimentary retina and lens. It is visible as an opalescent gray spot on the top of some lizard's heads; also referred to as "pineal eye" or "third eye."

so you see...rudiments of eyes are found throughout nature....and selection...is what dicatates whether...these eyes adjust, change, diminish, or enhance. And we see REDUCIBILITY of eyes all over the animal kingdom.

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Thanks for putting this

Thanks for putting this video up. My biblically inclined family is always going on about irreducible complexity, and the eye is their favourite topic (they haven't quite moved on to the flagellar motor stage yet, but I'll be ready). I've tried explaining it to them, but I don't think I'm clear enough. (Or maybe they aren't bright enough) Perhaps I'll use this.


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Additional videos

I also recommend these videos:

Dawkins: Lecture 3. Climbing Mount Improbable ( 4 of 8 )
http://www.youtube.com/watch?v=sezfMGjRQEg

Dawkins: Lecture 3. Climbing Mount Improbable ( 5 0f 8 )
http://www.youtube.com/watch?v=iT5gDA_QNhs

"Ridicule is the only weapon which can be used against unintelligible propositions. Ideas must be distinct before reason can act upon them; and no man ever had a distinct idea of the trinity. ..." -- Thomas Jefferson


Alt Ctrl Delete
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It says the video is no

It says the video is no longer availible