You may be aware that the Discovery Institute’s David Klingoffer just tried – and failed – to counter claims that the human spine couldn’t have been designed, because, if it had, said “designer” would’ve had to be rather bad at it. Today – in a post entitled Do Eyes Carry ‘Scars of Evolution’? – Brian Thomas of the Institute for Creation Research tries to do the same, but for eyes.
Eyes are a common topic in the great “controversy” between creationism and evolution. The earliest origins seem to lie in a certain oft-misquoted line in On the Origin of Species, where Darwin apparently states that the idea that the eye was evolved is “absurd”… until you read the rest of the paragraph. Creationists and their opponents alike have called the human eye incredibly and horribly designed respectively to further their points. Also, we know a route that they eye as it stands could have taken to evolve incredibly quickly – in merely a few hundred thousand years – given the right conditions.
And the word ‘eye’ is a not uncommon way for search terms to end up at this site – it is called Eye on the ICR after all. I don’t think that the people searching for neanderthal eye, updates about eye or head and eye embryology found what they were looking for, and I don’t think that this will help that, in the circumstances…
So what are the arguments that the eye has ‘evolutionary scars’? They mostly centre around the differences between the vertebrate and cephalopod versions of the organ.
As you can see in the diagram above, light entering the vertebrate retina must pass through successive layers of blood vessels and nerves to reach the light-sensing cells on the far right. Signals from these cells then travel back up (left) to the nerve cells nearer the surface of the retina, which travel along to the optic disk where they plunge into the retina, causing the blind spot.
Cephalopods, such as the Octopus, have the opposite arrangement. The light-receptors are on the surface of the retina, facing – as you would expect – the way the light comes in. Consequentially, they have no blind spot or any of the other problems that vertebrate eyes face.
Below is a diagram of the vertebrate eye (left) and the Octopus eye (right) illustrating the differences, along with its usual description on Wikipedia:
In the vertebrate example, 4 represents the blind spot, which is notably absent from the octopus eye. In vertebrates, 1 represents the retina and 2 is the nerve fibers, including the optic nerve (3), whereas in the octopus eye, 1 and 2 represent the nerve fibers and retina respectively.
There are other differences. The vertebrate eye is an outgrowth of the brain, while those of the Cephalopod are formed as “invaginations of the body surface.” Consequentially, they lack a cornea. They are also focused differently – in the human eye the lens changes shape to focus light, but in the octopus the process is more analogous to that of a camera, with moving parts. These differences are believed to be because of the different origins of the organs – after the eye had started off in one way or the other, there was no going back.
The reverse nature of the vertebrate retina has its problems. There is the potential for obscuration of light by the nerves and blood vessels – this is the primary argument, so more on that later. And also he poor anchoring of the retina due to this would increase the chances of a retinal detachment. This requires surgery – lazer surgery, generally – which leaves scars, hence the post title. The argument is that this is ‘bad design.’ From the evolutionary perspective we can say that the system chosen evidently “looked like a good idea at the time,” but, when it comes to making it better leaves design flaws that cannot be solved but must be worked around. The creationists must explain why these flaws exist themselves. Let’s see Brian Thomas try, shall we?
**SPOILER ALERT**: he doesn’t manage it.
Brian Thomas’ reason for the article is an article in the Scientific American by neuroscientist Trevor D. Lamb called Evolution of the Eye (you’ll need a subscription to get beyond the (lengthy) introduction). Lamb calls these problems of the eye the “scars of evolution.” Mr Thomas is responding to this part of the article, and not the description of how what we now know about the evolution of the eye “put[s] the nail in the coffin of irreducible complexity and beautifully support[s] Darwin’s idea.”
In a recent piece in Scientific American, neuroscientist Trevor Lamb wrote that vertebrate eyes contain numerous defects that he called “the scars of evolution.” He cited these “flaws” as powerful evidence that blind evolutionary forces are responsible for the “invention” of eyes.1But research has proven that these supposed defects are entirely fictional.
Lamb described the first “flaw” in vertebrate eyes:
The retina is inside out, so light has to pass through the whole thickness of the retina—through the intervening nerve fibers and cell bodies that scatter the light and degrade image quality—before reaching the light-sensitive photoreceptors.1
Light does indeed pass through the whole thickness of the retina, but it does not intersect the intervening nerve cell bodies. This is because special funnel-shaped Müller cells channel light through the retina directly to the photoreceptors at the back of the eye, so that the image quality is excellent.2 Far from being flawed, this arrangement serves to protect the photoreceptors from damaging UV light and allows them access to nutritive fluid.3
Cite 1 is to the SciAm article, 2 is to this study, and 3 is to this old DpSU, which does not back up either of the claims of that sentence at all. Consider that the octopus’ right-side-out eye still manages to get nutrients to the cells that need it – they are no further from the blood vessels that supply them, after all. And if the Müller cells help visible light so well, what obstruction do they pose to UV? It’s possible that they do, but you can still get trouble from UV in your eyes, and the article cited certainly has nothing to say on the matter.
And the idea is that the Müller cells shouldn’t be necessary at all. Better to remove the problem than to fix it. According to Mr Thomas’ next paragraph, the do apparently function over and above the call of duty – they apparently “refine incoming light, reducing scatter” – but this is still no justification for the inversion that requires them in the first place. Would it not be better for the layers to go:
- “refining” Müller cells
- photo receptors
- blood vessels, nerves etc
Much better ‘design.’ The best of both worlds (assuming that octopuses don’t already have the Müller cells, of course).
Skipping ahead to the next.
The second “flaw” Lamb offers is equally fallacious. He wrote, “Blood vessels also line the inner surface of the retina, casting unwanted shadows onto the photoreceptor layer.”1 The blood vessels are certainly there, but where is there any evidence of shadows? The Müller cells in vertebrate eyes act as optic fibers, literally bending light around blood vessels. Plus, without those blood vessels, there would be insufficient nutrient exchange. Inner-surface retinal blood vessels are only “unwanted” by those who don’t want to see their ideal fit in the eye’s internal structures.
You just covered the same point twice, you know… (I can’t tell who did it first, seeing as I can’t see the full article). I believe I’ve already covered this, so…
The last supposed defect Lamb noted was that “the retina has a blind spot where the nerve fibers that run across its surface congregate before tunneling out through the retina to emerge behind it as the optic nerve.”1 The retina does provide a tunnel for nerves to access the brain, but this is a necessary byproduct of having the optimal setup for the photoreceptors. And nobody with normal vision experiences a blind spot because it is fully compensated for by ingenious design features.
But you can still put the nerves behind and the Müller cells in front. And the point is that these “ingenious design features” shouldn’t be necessary at all, which is much better design.
For example, the entry point for the retinal nerve bundle has been purposefully offset. This way, the area of highest-intensity visual detection at the center of the retina, called the fovea, is undisturbed. Also, the optical processing software in the brain constantly generates a flawless “fill-in” image to mask the blind spot.
As it happens, if the optic nerve was in the centre it would have to be unnecessary longer to get to the same part of the brain:
Scroll back up to the comparison between the two kinds of eyes – you see the exact same thing in octopus eyes also, despite them not having the same problem.
By the way, in the first image at the top the fovea is in the centre, the optic disk on the left.
Not only do healthy eyes have no deficiencies, but even evolutionary researchers have recently admitted that they cannot be improved upon.6 This means that the supposed flaws listed by Lamb only apply to an imaginary, straw-man version of the vertebrate eye.
Those who insist that eyes have flawed construction should try making better eyes themselves. At the very least, they should get an updated education on the exquisite anatomy that they too easily criticize.
Look, for the last time, just because we can’t make something doesn’t mean Natural Selection can’t. And we can still point out design flaws, and they are everywhere. It seems that the eye and related machinery are only as “flawless” as, I don’t know, the bible?
I think I’ll call this “Type EYE: ‘You’re wrong!’ ‘No, you’re wrong'”