Evolution Question - The Eyeball

[bryant69]

This is an evolution question I've faced at times, and I'm curious if anybody has a simple answer to it?

Basically evolution happens as organisms make changes and those changes turn out to be productive. How does that work for an eye? Half an eye isn't going to be useful; it isn't going to be a survival mechanism is it?

I've heard explanations of this before; but they aren't coming out very clearly - so was wondering if anybody else had an answer off the top of their head?

Thanks

Bryant
Check it out --> http://politicalcomment.blogspot.com

[shoelace414]

1. Chaos Theroy tell us...

just one cell that is sensitive to light can after time.. (LOTS OF TIME) turn into an eye.

[rkc3]

17. Time. Lots of time. That's what's missing from a lot of equations.

The ID idiots, because their world is only 6,000 years old, neglect this part of the equation.

I can imagine that if Pat Robertson would live to be 10,000,000 years old, even he might evolve into a human being.

[phantom power]

2. Complex organs evolve via a mechanism called "scaffolding."

The "trick" is that over the course of the evolution of a complex thing, it's parts usually serve other functions during intermediary stages.

There was a great writeup of a scaffolding theory of eye evolution, if only I can find it out there...

[papau]

5. Do we have examples of known scaffolding theory type evolution?

:-)

[phantom power]

13. I've seen examples at the protein level.

At the protein level, the general scheme goes like this:

1) A gene that codes for some protein gets duplicated. This is often either benign or even beneficial: it just causes more of an existing protein to be created.

2) One of the protein-genes mutates. Since there is still one "good" copy, the organism is not necessarily damaged by the mutation.

3) the mutated protein is now "free" to evolve into something useful and new.

PZ Meyers recently posted a beautiful example of this sequence with regard to the evolution of alcohol metabolism in yeast, over at his "Pharyngula" blog. It comes complete with evolutionary clocking of protein mutations to date the event.

I'm less familiar with macroscopic examples at the "organ" level, but I imagine that if anybody has a good writeup it's somewhere on Pharyngula.

[papau]

36. I was aware of the mutation concept - and agree with it - but what

justifies it's extension to the eye (of course the opposite is also true - there is nothing that says it should not be extended to quite complex organs).

Indeed While I have heard of an organ that minus one gene no longer works, I have not seen any proof that the key gene could not have been one of the first to develop.

Indeed as I have said many times - When ID goes an inch beyond simple skepticism, it has gone too far and is no longer science.

[HereSince1628]

33. The origin of the insect wing is argued to be such a case

also the proton pumping capacity of the inner membranes of mitochondrial membranes...The proton gradient produced by this activity and used to generate ATP within the mitochondria is argued to have originally functioned to maintain red-ox balance in ancestral cells.

[papau]

37. Thanks - I learn a lot at DU! -- Now I need to remember this!

At least I have a conversation item for the next call from my Doctor Daughter!

:-)

[phantom power]

6. This isn't exactly the one I remember, but it's animated!

Nilsson and Pelger simulated a model of the eye to find out how difficult its evolution really is.

The simulation does not cover the complete evolution of an eye. It takes light-sensitive cells as given and ignores the evolution of advanced perceptual skills (which are more a problem in brain, than eye, evolution). It concentrates on the evolution of eye shape and the lens; this is the problem that Darwin's critics have often pointed to, because they think it requires the simultaneous adjustment of many intricately related parts.

Nilsson and Pelger allowed the shape of the model eye to change at random, in steps of no more than 1% change at a time. This fits in with the idea that adaptive evolution proceeds in small gradual stages. The model eye then evolved in the computer, with each new generation formed from the optically superior eyes in the previous generation; changes that made the optics worse were rejected, as selection would reject them in nature.

How long did it take?

The complete evolution of an eye like that of a vertebrate or octupus took about 2000 steps.

Nilsson and Pelger used estimates of heritability and strength of selection to calculate how long the change might take; their answer was about 400,000 generations. Far from being difficult to evolve, the model shows that it is rather easy.

http://www.blackwellpublishing.com/ridley/a-z/Evolution_of_the_eye.asp

[HereSince1628]

39. Do you see scaffolding as distinct from spandrels?

Just wondering

[Richard D]

3. Half an eyeball makes perfect sense . .

Think a rudimentary organ like collection of cells that can differentiate darkness from light. Shadows will then trigger an alarm reaction. Then over billions of years, it simply gets more and more refined as the evolutionary accidents that up-regulate this become more sophisticated leading to greater survival of the species that become more complex and have greater differentiation of variations of perception of qualities of light. Then comes focus, color differentiation, greater visual acuity, etc.

On edit: I would imagine that most people who refuse to acknowledge evolutionary processes have no idea how long a billion (or even a million) years actually is. Either that or they really believe dinosaur bones are a trick of god.

[HereSince1628]

30. But ID'er take half to mean half the existing components in their

present state. They wouldn't let you start at the beginning. They want to take things, especially things they use to argue irreducible complexity, as they are.

The part of the evolutionary history implicit in your notion of "more and more refined" (although if evolution is true, it undoubtedly true in some very general sense) would be discarded by ID'ers as empty of information.

[opihimoimoi]

4. Evolution will be here 50 years from now, a thousand, a million.

It is FACT.

ID/Creation is not fact. it is faith. it is not factual.

[bryant69]

12. Thank you

I'm grateful you took the time to repeat your catechism.

But for those who are not of your faith, that's not actually a very convincing argument. It's just a statement.

Oh and I do oppose teaching ID in schools and I believe in evolution (while also believing in a creator).

[HereSince1628]

7. The Coeloid (hollow cavity) eye of molluscs is almost identical

to the vertebrate eye, but it evolved independently.

The evolutionary history of the molluscan eye has left wonderful hallmarks among the extant members of the group.

Because the story of the molluscan coeloid eye is clearly explained as a product of classical evolution it provides an argument against the idea of the vertebrate eye as both irreproducibly complex and also as a structure with a uniquely executed design.

If you want a lesson on how eyes develop, you should check out almost any general Invertebrate Zoology text

[yellowcanine]

8. There is not a "simple" answer. How could there be? Here is a link.

http://www.origins.tv/darwin/eyes.htm

But I warn you that it is never going to be as "simple" as "God did it."

By the way, "half an eye" will be more useful than no eye. Half an eye could allow an animal to distinguish between light and dark, for example - thus there would be some ability to detect objects by the shadow they cast - that is useful.

[kay1864]

16. Shorter simpler answer...

From talkorigins.org:

The source making the claim usually quotes Darwin saying that the evolution of the eye seems "absurd in the highest degree". However, Darwin follows that statement with a three-and-a-half-page proposal of intermediate stages through which eyes might have evolved via gradual steps (Darwin 1872).

- photosensitive cell
- aggregates of pigment cells without a nerve
- an optic nerve surrounded by pigment cells and covered by translucent skin
- pigment cells forming a small depression
- pigment cells forming a deeper depression
- the skin over the depression taking a lens shape
- muscles allowing the lens to adjust

All of these steps are known to be viable because all exist in animals living today. The increments between these steps are slight and may be broken down into even smaller increments. Natural selection should, under many circumstances, favor the increments. Since eyes do not fossilize well, we do not know that the development of the eye followed exactly that path, but we certainly cannot claim that no path exists.

[havocmom]

9. Evolution of eyes would be determined by the environment

where the organism lived and operated wouldn't it? Nocturnal critters have more light receptors. Underground dwellers don't rely on vision.

Hunters have forward facing eyes which give better depth perception which in turn makes it easier to pounce on supper with greater accuracy.
Prey species have eyes turned more to the side allowing a wider field of vision, which helps see hunters about to pounce.

Critters in the Marianas Trench have lights. Birds that work mostly in daylight have small but very efficient eyes. Night hunters have big eyes.

Don't quite understand what you mean by 'half an eye'. Refering to poor vision? In the evolution of humans, those with vision problems might not live long enough to breed, which would tend to cut the numbers of any genetic vision problems (until we got organized.)

Our species has developed a social structure where by those who can't see to hunt or avoid being hunted were taken care of anyway by those who could. So vision became less important to survival than caring.

It is a lesson lost lately by those who tout Compassionate Conservatism and are BLIND to the need for communal effort for all to prosper.

Potatoes have eyes full of dirt.

[HereSince1628]

26. ID supporters fail to comprehend that anatomical evolution

not only results in the development of complex organs, but that as the organs become composed of more parts they also develop INTERDEPENDENCY upon the presence of the parts in particular relationships.

Complexity is easiest to understand as an emerging property as components increase in number and in variability in their properties. INTERDEPENDENCE is also an emergent property, a consequence of opportunities to try out possible supportive interactions and alternate roles. A feature of biological interdependence seems to be that independent function is lost.

This makes sense in terms of thermodynamic principles that attempt to minimize energetic costs. Supporting two sets of structures with the same function (particularly if one is "better"), is unnecessarily costly. Losing independence also makes sense if in the transition to functional interaction one or both components are modified to facilitate the emerging interdependence.

This is not at all difficult to conceptualize within the framework of existing evolutionary explanation. As so I can say that it is not necessary to invoke ID's concept of irreducible complexity and the necessity of a designer to arrive at the possibility of natural evolution leading to structures or functions which are dependent upon complex interdependent components.

[havocmom]

28. An many ID fans are farmers and ranchers who use selective breeding

to build better crops, domestic milk & meat animals. They are deeply involved in nudging evolution along, support 4-H so their kids can learn to do it, and then deny the whole concept.

Boggles my mind.

[HereSince1628]

31. All the ID'ers I've read, and most the contemporary Creationists I've read

accept modern notions of genetics, and all of the mechanisms of what biologists refer to as microevolution.

They don't see their position as hypocritical at all.

But they flat out reject the notion that those mechanisms produce new species. Which is to say they reject the notion of macroevolution, the processes that change the fundamental array of types of things on the planet.

[shoelace414]

35. Microevolution + 5 billion years = Darwin.

[HereSince1628]

38. Microevolution + time =Darwin isn't quite as nice and neat

as that post suggests.

If you are interested PM me and I'll send you some thoughts on that but there is no point in cluttering the board with what others feel is evolutionary esoterica.

[havocmom]

40. Cause they are short sighted and short lived

along with egocentric. They think if they don't see it, it don't happen!

[Ian David]

10. Here's some stuff on evolution and the eyeball...

Re: How do evolutionists explain how the eyeball evolved?
Date: Wed Sep 8 14:29:34 1999
Posted By: Dean Jacobson, Faculty Biology, Whitworth College
Area of science: Evolution
ID: 934919750.Ev Message:



Jen:
The eye is still a controversial subject among creationists and others
who do not believe evolution, but it is not a hard structure to explain.
The central idea is that if all creatures were originally blind, 1% of an
eye is better than nothing and will be preferentially selected. The best
idea of this apparent evolutionary change (a flat area of skin or epithelium
with light sensors, then folding inward to form first an open cavity and
later a closed cavity, first without a lens and then with a lens) is
illustrated in many evolution textbooks and popular books; checking the
index of library books on evolution might work. A technical paper (hard to
read, but with a good illustration) on this very subject appeared only 5
years ago:
A pessimistic estimat of the time required for aneye to evolve, by Nilsson
adn Pelger (1994), in Proceedings of the Royal Society of London, series B,
p. 256. (This is found only in the libraries of the largest colleges or
universities)

What is really neat is that we can find invertebrate animals like scallops,
worms, etc. that have eyes with each of these "intermediate" conditions
(i.e., open cavity with no lens, etc.). It is also neat that while our eye
and the octopus eye look very similar, our retina is inside out (the rods
and cones on the outside of the retina, *below* the blood vessels and the
neuronal wiring) while the octopus has a retina with the rods and cones on
the inside of the retina. (This is why we can see moving blood cells when an
ophthamologist shines a bright light into your eye.) It is clear that these
different eyes evolved separately.

A clue to the origin of eyes is also found in the protein structure of our
lens and those of other animals. Since these proteins, called crystallins,
are simply globular proteins that don't stick to each other (the lens is not
a crystal, but merely a fluid of nonattracting hard spheres, the proteins
themselves) it turns out that many types of proteins, originally used for
different metabolic functions in ordinary cells, were co-opted for use in
the eye. Crocodiles and some birds use a lactate dehydrogenase enzyme in
their lens (this enzyme removes a hydrogen from lactic acid, which you eat
in yoghurt and saurkraut), most birds and reptiles use argininosuccinate
lyase, and we and many other vertebrates use a heat shock protein, a helper
molecule called a chaperone that repairs other proteins if they get bent out
of shape (inproperly folded) after being exposed to excess heat. It is
amazing that so many types of metabolic enzymes have been used in the eye in
this structural role of focusing light, rather than a unique protein being
created just for this purpose. By the way, I have no trouble believing in a
supernatural creator who used evolution.

Cheers,
Dean Jacobson

More:
http://www.madsci.org/posts/archives/sep99/936884377.Ev.r.html

[bryant69]

14. Thank you for that informative response

Interesting.

[Ian David]

27. You're very welcome! I think one key thing to remember is...

a single photo-sensitive chemical molecule inside a cell is still an eyeball to some creature somewhere. And while it's not "perfect" it is still an eyeball and still evolved naturally- most likely from something that was used for something else.

Think about all the things you have in your house that you bought for one purpose but learned to use for other purposes. Did you know that Lemon Pledge works better than WD-40 for lubricating things like hinges?

Organisms do the same things during the course of Evolution. All the way from the way they use their body parts on down to the way they use individual molecules within their cells. Things they already have in their toolbox can be re-purposed, multi-purposed, or modified to work in new ways.

Anyone who has ever played with a large box of Legos or Tinker-Toys should get that.

I'm glad to help!

[mcg]

41. "co-opted"

"it turns out that many types of proteins, originally used for
different metabolic functions in ordinary cells, were co-opted for use in the eye"

So where's the statistical chance involved with this? There isn't any, this is not Darwinian evolution, yet atheists still think it is reasonable to think this happened 'by Chance'. Chancedidit. No matter how unlikely it seems, no matter how unreasonable or counter-intuitive it seems, chancedidit.

Atheists are in denial.

[YOY]

11. Also don't forget the first creatures withe eyes have no where near

the complexity of higher lifeforms. The simple photo sensors of many lifeforms evolve with the creature.

Of course they eye as a developed organ cannot function as a half...it has not evolved to do that. If partial eye loss were a constant risk from the very beginning of the evolutionary process, then it might have done so.

It has evolved to take in and differentiate color, alter itself to permit better vision via dilating in response to light strength, and even protect itself with a thin layer of flesh that prevents moisture seepage and removes particles.

[Teaser]

15. I've always found this argument incoherent.

An eye is built of lots of things. Photoreceptors. Retinae. vitreous humour.

It's not hard to first envision an early organism developing photoreceptors on a circular surface.

Then, imagine over time it is advantageous for the circular surface to involute (become concave). Perhaps the concavity becomes such that only a small aperture is left. It may then become advantageous for clear tissue to grow between the aperture edges. Once that happens some kind of fluid will provide structural support to the eye, so one could see how that adaption might take place.

It was probably also advantageous, early on, for the musculature under the original photoreceptor surface to be able to angle the flat surface to some degree and one can create a similar picture for musculature.

[BillZBubb]

18. The eye isn't a problem for evolution.

Let's assume the organism has already developed cells that are sensitive to heat and connected to the central nervous system. Those would be valuable to the organism to keep it from frying itself. To do so, it would be best if they were close to the outside surface of the organism, so the overheat warning would come ASAP.

Heat is energy at a certain wavelength. Now suppose through mutation some of those cells are able to detect other wavelengths as well. It's not too far a stretch to get into what we now call the "visible wavelengths". Being near the surface of the organism means only a few layers of skin cells are between the heat/light sensitive cells and the source of light. Those skin cells would be somewhat tranparent.

Then you have a rudimentary eye. It could detect light/no light and movement in light. That would be a huge advantage to the organism. It would be highly selected for.

Over time, the structure would become refined due to natural selection. A single receptor cell would be replaced by multiple receptor cells. The skin layer covering the cells would become more transparent and develop a focusing mechanism. Etc, etc.

[Ian David]

19. From Wikipedia

Evolution of eyes

How a complex structure like the projecting eye could have evolved is often said to be a difficult question for the theory of evolution. Darwin famously treated the subject of eye evolution in his Origin of Species:

To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real.

Despite the precision and complexity of the eye, computer models of eye evolution, developed by 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.

Eyes in various animals show adaption to their requirements. For example, birds of prey have much greater visual acuity than humans and some, like diurnal birds of prey, can see ultraviolet light. The different forms of eye in, for example, vertebrates and mollusks are often cited as examples of parallel evolution, suggesting that the development of eyes through evolution might not be so improbable as it might seem. However, the development of the eye is considered to be monophyletic; that is, all modern eyes, varied as they are, have their origins in a proto-eye believed to have evolved some 540 million years ago (Mya). {That bit about the pro-eye isn't universally accepted}

More:
http://en.wikipedia.org/wiki/Eyeball#Evolution_of_eyes

[Ian David]

20. More about Eyeballs

<snip>

From: Gaspode ® 10/10/2002 08:17:01
Subject: re: Suprise have an eyeball post id: 198927
Part of a formed eyeball isn’t useless. There are a huge range of animals out there with what you would term partly formed eyeballs. AT the lowest end we have flatworms with a spot of special pigment cells on either side of their ‘had’ These do nothing at all except detect whether there is light hitting them or not. They enable he animal to hide under cover during daylight. From there we move to more advanced worms where these pigment cells are arranged into cup like depressions. By doing this they are able to detect the direction the light is coming form and so the animal can move around without moving into the light directly. Arthropods then follow this by placing a clear protective cover over these pigment cups to protect them from damage. Form there it’s a relatively easy matter to thicken he centre of the protective plate to form a lense that focuses all the light from a large area onto he pigment cells, allowing far more sensitive detection of light, such as might be caused by a predator moving. Then other animals have an ring that can vary in size around he collection of pigment cells so that so that they can adjust the amount of light getting to the cells. This enables it to work at night as well as in daylight. So we now have a retina, a lense and an iris. By improving the data processing abilities of the brain and improving control we have a fully functional eye, all by a series of small steps.

So which of these partly formed eyeball do you think is useless? They are all indispensable to the creatures that have them.

From: TheDreamOf ® 10/10/2002 08:17:37
Subject: re: Suprise have an eyeball post id: 198929
>> A photon detector is a simple eye?

Yes - just imagine a scenario where a beastie has two simple photocells - and so knows where light is and where light isn't - such an adaptation would aid survival over beasties that didn't have it.
From: Dark Orange ® 10/10/2002 08:21:04
Subject: re: Suprise have an eyeball post id: 198932

Half a modern day eye is essentially useless to us who are used to perfection.

To those who aren't used to perfection and have only very limited vision will no doubt contradict our beliefs. Limited vision can still inform you of your surroundings, if there is an object/wall in front of you, the general location of a doorway etc.

The eye has likely evolved from basic photoreceptors like those found in starfish, (uh-oh, a shadow has just passed over me, time to defend myself!) to groups of receptors, then to groups of receptors within a single enclosure of the right shape...


From: Kath ® 10/10/2002 08:21:30
Subject: re: Suprise have an eyeball post id: 198934
TheDreamOf
I didn't know animals had photocells. To be honest they are new to me. Single cells that detect light? What animals have them today?
Kath


More:
http://www2b.abc.net.au/science/k2/stn/archives/archive33/newposts/198/topic198916.shtm

[Village Idiot]

21. WOW! I was just thinking about this issue on the weekend!!!

I was wondering how far back the evolutionary change happened to produce the eye. Definetely before we left the oceans, at any rate...

and WHY the heck did it happen? There are so many advanced organisms that do not rely on vision and have no eyes...

[benburch]

22. It actually evolved four times!

There is the Mammal/Reptile/Bird eye that we have.

There is the Octopus eye.

There is the Chambered Nautilus eye.

There is the Insect/Arthropod eye (which is quite different)

All four are different, and all evolved separately.

The Chambered Nautilus eye shows part of the process; it has no lens and not aqueous humor; It is a pocket filled with light sensitive cells and a small aperture that makes it a pinhole camera.

A pit viper has a heat sensing organ on its "nose" that is directional in the same way; It is a pocket of IR sensitive cells that are most sensitive when the pocket is pointing at the warm prey.

The Octopus eye is even designed better than ours; On our retinas, the light sensitive cells are BELOW the layer of nerve cells that connect them to the optic nerve. Light must pass through these cells and this is a quite inefficient process. In the Octopus, the light sensitive cells are in front and, it is to be presumed, work better for it.

But this is very instructive with regard to how evolution with natural selection works; It produces few totally perfect "designs", but over millions of years selects for whatever gives, on average, an advantage in survival and reproduction. And it always works with whatever it has. All subsequent evolution from a certain point is based on extrapolation of the body features that already exist.

[benburch]

23. I take so long on these replies that people have made most of my points...

*sigh*

[Ian David]

24. Richard Dawkins on the Eyeball- The Message from The Mountain

Climbing Mount Improbable
By Sir Dr. Richard Dawkins
http://www.powells.com/biblio/17-0393039307-0


Excerpts from Chapter 3 - Message from the Mountain

Mount Improbable rears up from the plain, lofting its peaks dizzily to the rarefied sky. The towering, vertical cliffs of Mount Improbable can never, it seems, be climbed Dwarfed like insects, thwarted mountaineers crawl and scrabble along the foot, gazing hopelessly at the sheer, unattainable heights. They shake their tiny, baffled heads and declare the brooding summit forever unscalable.

Our mountaineers are too ambitious. So intent are they on the perpendicular drama of the cliffs, they do not think to look round the other side of the mountain. There they would find not vertical cliffs and echoing canyons but gently inclined grassy meadows, graded steadily and easily towards the distant uplands. Occasionally the gradual ascent is punctuated by a small, rocky crag, but you can usually find a detour that is not too steep for a fit hill-walker in stout shoes and with time to spare. The sheer height of the peak doesn't matter, so long as you don't try to scale it in a single bound. Locate the mildly sloping path and, if you have unlimited time, the ascent is only as formidable as the next step. The story of Mount Improbable is, of course, a parable. We shall explore its meaning in this and the next chapter




..To this day, and in quarters where they should know better, Darwinism is widely regarded as a theory of 'chance'. It is grindingly, creakingly, crashingly obvious that, if Darwinism were really a theory of chance, it couldn't work. You don't need to be a mathematician or physicist to calculate that an eye or a haemoglobin molecule would take from here to infinity to self-assemble by sheer higgledy-piggledy luck. Far from being a difficulty peculiar to Darwinism, the astronomic improbability of eyes and knees, enzymes and elbow joints and the other living wonders is precisely the problem that any theory of life must solve, and that Darwinism uniquely does solve. It solves it by breaking the improbability up into small, manageable parts, smearing out the luck needed, going round the back of Mount Improbable and crawling up the gentle slopes, inch by million-year inch. Only God would essay the mad task of leaping up the precipice in a single bound. And if we postulate him as our cosmic designer we are left in exactly the same position as when we started. Any Designer capable of constructing the dazzling array of living things would have to be intelligent and complicated beyond all imagining. And complicated is just another word for improbable - and therefore demanding of explanation. A theologian who ripostes that his god is sublimely simple has (not very) neatly evaded the issue, for a sufficiently simple god, whatever other virtues he might have, would be too simple to be capable of designing a universe (to say nothing of forgiving sins, answering prayers, blessing unions, transubstantiating wine, and the many other achievements variously expected of him). You cannot have it both ways. Either your god is capable of designing worlds and doing all the other godlike things, in which case he needs an explanation in his own right. Or he is not, in which case he cannot provide an explanation. God should be seen by Fred Hoyle as the ultimate Boeing 747.

The height of Mount Improbable stands for the combination of perfection and improbability that is epitomized in eyes and enzyme molecules (and gods capable of designing them). To say that an object like an eye or a protein molecule is improbable means something rather precise. The object is made of a large number of parts arranged in a very special way. The number of possible ways in which those parts could have been arranged is exceedingly large. In the case of a protein molecule we can actually calculate that large number. Isaac Asimov did it for the particular protein haemoglobin, and called it the Haemoglobin Number. It has 190 noughts. That is the number of ways of rearranging the bits of haemoglobin such chat the result would not be haemoglobin. In the case of the eye we can't do the equivalent calculation without fabricating lots of assumptions, but we can intuitively see that it is going to come to another stupefyingly large number. The actual, observed arrangement of parts is improbable in the sense that it is only one arrangement among trillions of possible arrangements.

Now, there is an uninteresting sense in which, with hindsight, any particular arrangement of parts is just as improbable as any other. Even a junkyard is as improbable, with hindsight, as a 747, for its Parts could have been arranged in so many other ways. The trouble is, most of those ways would also be junkyards. This is where the idea of quality comes in. The vast majority of arrangements of the parts of a Boeing junkyard would not fly. A small minority would. Of all the trillions of possible arrangements of the parts of an eye, only a tiny minority would see. The human eye forms a sharp image on a retina, corrected for spherical and chromatic aberration; automatically stops down or up with an iris diaphragm to keep the internal light intensity relatively constant in the face of large fluctuations in external light intensity; automatically changes the focal length of the lens depending upon whether the object being looked at is near or far; sorts out colour by comparing the firing rates of three different kinds of light-sensitive cell. Almost all random scramblings of the parts of an eye would fail to achieve any of these delicate and difficult tasks. There is something very special about the particular arrangement that exists. All particular arrangements are as improbable as each other. But of all particular arrangements, those that aren't useful hugely outnumber those that are. Useful devices are improbable and need a special explanation.

This is another way of saying that objects such as these cannot be explained as coming into existence by chance. As we have seen, to invoke chance, on its own, as an explanation, is equivalent to vaulting from the bottom to the top of Mount Improbable's steepest cliff in one bound. And what corresponds to inching up the kindly, grassy slopes on the other side of the mountain? It is the slow, cumulative, one-step-at-a-time, non-random survival of random variants that Darwin called natural selection. The metaphor of Mount Improbable dramatizes the mistake of the sceptics quoted at the beginning of this chapter. Where they went wrong was to keep their eyes fixed on the vertical precipice and its dramatic height. They assumed that the sheer cliff was the only way up to the summit on which are perched eyes and protein molecules and other supremely improbable arrangements of parts. It was Darwin's great achievement to discover the gentle gradients winding up the other side of the mountain.




Also:

<snip>

Dawkins: Well, there's that, but I think there's also the fact that again if you look at complex elegant beautiful adaptations which have many parts, all fitting together, they — it's really back to the point I referred to, the sense in which Darwin was a gradualist. If you think about the evolution of a really complex adaptation like an eye or an ear, then precisely because it cannot have come about as a single chance step it had to have come about as a gradual improvement. The first eye could hardly see anything at all, and successive eyes saw a bit better, a bit better, a bit better. Progressively, each aspect of the eye came in as a step building upon previous ones. That's progressive, without any doubt at all, and the same thing must be true of any complication adaptation. Any really well-adapted animal, whether it's adapted as a predator, or to escape predation, whether it's a plant well-adapted to pick up sunlight or to pick up water from the ground, all those adaptations must be progressive. The sense of progress that Gould objected to, I would of course agree; the idea that evolution was directed towards humans. And that was why I wrote that book backwards; precisely because I didn't want to give that impression.

More:
http://www.powells.com/authors/dawkins.html

[bryant69]

25. That's an interesting article

Thanks for posting it.

[grumpy old fart]

32. Self delete...misread an earlier post.....

[SteppingRazor]

29. Evolutionary explanation for the eyeball...

While it hjas been posited by ID proponents that the eyeball is too complex to have evolved, that's simply not the case.

Imagine a single-celled organism that, through mutation, develops the ability to distinguish light from dark. Now, as that ability helps it avoid predators, soon that becomes the norm. It's not long before the ability refines itself to the ability to distinguish color. In incremental steps such as these, you can seee how a logical progrssion would eventually come to the ability to see one's surroundings.

[hunter]

34. If the human eye is evidence of God's design...

...then you've got to wonder.

The eye is not a masterpiece of optical science, it is more like a hodge-podge of things tossed together into something that works. What we have is a very complicated image processing system distilling some sort of sense from a rather shaky and dodgy image data stream.

Some of the flaws in our visual system are quite delightful. You can amuse yourself for hours with a book of optical illusions.

The other flaws in the system are not so pleasant, as they sometimes lead to mayhem, death, and blindness.

talkorigins.org is always a good source for this sort of thing, but in many forums you don't want to link to them unless you are an experienced flame warrior.

http://www.talkorigins.org/indexcc/CB/CB301.html

BTW, has anyone seen my glasses?

[FM Arouet666]

42. Sounds very irreducibly complex, yet

I have seen the eye mentioned in the ID debate. The notion is that the eye only functions with a host of intricate chemical and physical processes, missing any one of which would render a non-functional eye.

Simple, god made it.

The argument fails when you consider that "half and eye," as you mention, is useful. What does the eye do for us? The brain interprets light via a host of sensors, there by allowing us to better survive to reproduce.

An organism with no light sensory organ may not do as well as one with some light sensation. Half and eye is better than no eye at all. I am talking early organisms, not Stevie Wonder.

The irreducible complexity issue fails because the "theory" assumes that any earlier form which bares little resemblance to the "final product" cannot logically occur. The flagellum which doesn't whip about is useless? Perhaps not, a tube for transfer of nutrients, a static defense, a host of things other than god made it so. The eye argument is easier, earlier forms which offer sensory information superior to competing organisms may prove to be a survival benefit.

Earlier forms of the eye should not be mistaken to be "half an eye," the connotation being that the early form was useless to the organism, unable to function in the capacity of the "final product." Early forms did function to the advantage of the organism, and the joy of science is to find out how these forms evolved. Saying "god did it" ends the discussion, robbing mankind of the grand intellectual pursuit we call science.