The Eye: Testimony to Evolution and a Case of Creationist "Contraduction"
- Jon Peters
- May 6
- 13 min read
Updated: May 11
The claim from science: the vertebrate eye is poorly "designed'.
Without additional adaptations to the original structure
it would have severe functional limitations
Introduction
The vertebrate eye is poorly "engineered". The retina is inverted due to evolution compared to eyes that are not inverted. The vertebrate eye on the left has the light sensing cells not only pointing away from the incoming light but light needs to go through multiple layers of tissue before it even reaches the photoreceptors (see eye comparison diagrams below). This would be like placing a radio antenna or TV dish pointing away from the incoming signals, in the basement with all kinds of obstructions, and needing to run electricity down there because it needs extra support. There's a reason we put antennas on roofs with unobstructed views of the sky and pointed towards a satellite or tall source antenna. The octopus eye on the right does not have this limitation; the rods and cones are logically placed so they receive light (photons) directly and don't produce a blind spot where there are no receptors; all the nerves leave the retina to begin their path to the brain to form an image without producing a blind spot. See Figure 1.
Figure 1. "In vertebrate eyes (left), the nerve fibers route before the retina, blocking some light and creating a blind spot where the fibers pass through the retina. In cephalopod eyes (right; no blind spot), the nerve fibers route behind the retina and do not block light or disrupt the retina. 1 is the retina and 2 the nerve fibers. 3 is the optic nerve. 4 is the vertebrate blind spot."
Wikimedia Commons: From Wikimedia Commons: Caerbannog - Own Work, based on Image: Evolution_eye.png created by Jerry Crimson Mann 07:07, 2 August 2005 UTC (itself under GFDL).
Fair Use Attribution
In Figure 2, notice that the photoreceptors in the diagram not only are on the far side away from light entering the eye, but their orientation points away from the light photons, and there is a tremendous number of support cells and wiring required that the light must pass through to reach its final destination, the photoreceptors. Thus there are three major "design" issues from the beginning. Not shown in this figure is a fourth issue; as the nerves gather to exit the eye, that produces a blind spot where there can be no photoreceptors. Only nerves are shown. There is also a dense network of blood vessels and support cells that interfere with light transmission. This is not present in the cephalopod eye structure which evolved separately from the vertebrate eye. In addition the cephalopod eye has no need for an RPE.
Figure 2. From: https://www.brainkart.com/article/Retina_26069/
Fair Use Attribution
Various adaptations to lessen the vertebrate eye deficits
Comparative anatomy can help us conclude that the vertebrate eye is not only poorly constructed in its original form but that evolution has on numerous occasions applied "fixes" or workarounds to mitigate the deficits inherit to the vertebrate eye.
A. Pecten oculi in birds
Bird eyes are well known to provide them with better vision than other non-avian vertebrate species. The Retinal Pigment Epithelium (#10 in Figure 2) in vertebrates is a layer of support cells below the retina that provides nutrition and support to the photoreceptors. Due to their high visual demands birds have an added structure to supplement their vision needs, called the pecten oculi. It serves at least two functions. First, it provides extra nutrients and oxygen to the eyes and second this allows fewer retinal support vessels that would normally obstruct light passing through to the photoreceptors. This structure is present because it helps a problem with the vertebrate eye and its basic structure. See Figure 3.
Figure 3. From: Jfbleak. 2008. Updated 2013. Fair use attribution. Bird eye.
B. Conus Papillaris in some reptiles
Similar to the pecten oculi in birds, reptiles also have a structure to help their eyes function better called the conus papillaris. As in birds it lessens the thickness of the tissues interfering with light traveling to the photoreceptors and also provides extra nutrition and oxygen, supplementing the RPE. See Figure 4.
Figure 4. A - Reptile, lizard Conus papillaris. B - Pecten oculi, bird.From: Ringvold, Amund. 2022. The Function of Pecten Oculi. Conus Papillaris in Reptiles and it's Analog Pectin Oculi in Birds Evolved in Tandem with increasing Uric Acid in Serum. https://www.alliedacademies.org/articles/the-function-of-pecten-oculi-conus-papillaris-in-reptiles-and-its-analogue-pecten-oculi-in-birds-evolved-in-tandem-with-.pdf
For educational use only. Fair use attribution.
C. Tapetum Lucidum
Nocturnal animals are hampered by very low levels of light compared to diurnal animals. Evolution has provided a structure for many of these species to amplify what light that is available for night vision. These species have a structure in the RPE called the tapetum lucidum. When we shine a night light at animals who have this layer, the eyes reflect light back to us and appear iridescent. The light that has passed through the retina is reflected back to the photoreceptors as a secondary stimulation to the photoreceptors. See Figure 5.
Figure 5. Tapetum lucidum reflecting light back from under the retinaFrom: https://www.reddit.com/r/Awwducational/comments/100uxki/the_reason_for_your_cats_reflective_eyes_in/
For educational use only. Fair use attribution
In July of 2023 Nathan Lents wrote in his blog* about the tapeta found in various species and that all indications point to attempts at minimizing the loss of available light in the vertebrate eyes who have it. A confirmation of this occurs in jumping spiders who have two types of eyes. The primary eyes have cephalopod like retinas but the smaller secondary eyes are wired like vertebrate eyes. Sure enough, only the secondary eyes have the need of a tapetum lucidum to improve light sensitivity!
As Lents writes, "tapeta is a compensatory co-adaptation for the sub-optimal nature of the inverted retinas". I would assert that it is only one such compensatory structure and joins several others as discussed in this blog.
From: Wikimedia Commons. Lukas Jonaitis* https://thehumanevolutionblog.com/2023/07/11/is-nocturnal-eye-shine-an-adaptation-for-the-backwards-retina/
D. Fiber Optic Cable System
In Michael Behe's book, Darwin Devolves, he mentions that the human eye is beautifully designed because it also has some cells that act as a "fiber-optic cable system" to channel light to the photoreceptors of the cell that are deep in the retina from the surface of the retina receiving light. He includes as photograph. Rather, that the retina has this is just more evidence that there are problems to the inverted retina that have been confronted by evolution. There is significant obstruction from all the support structures in front of the photoreceptors (see Figure 2) and natural selection has produced another compensatory work-around. Rather than a "neat" design, this is another example of a poor adaptation (inverted photoreceptors buried in the retina and pointing in the wrong direction) that needs help to function efficiently.
Anti-evolution objections
The attempts to claim that the vertebrate eye is wonderfully designed by most creationists tend to discuss cabling systems, the RPE, etc. as advantages and aspects of good "design". The blind spot is dismissed as not an issue. The RPE is said to supply nutrients and cooling and if we had a retina that was not inverted, the RPE would be in front of the photoreceptors. This is an error because cephalopods don't have or need an RPE. The vertebrate eye has it only because of the evolutionary constraints on the original "design" Similar to the evolutionary constraints of the recurrent laryngeal nerve. See here on this blog
A not uncommon anti-evolutionist response to counter the claim of the vertebrate eye being a poor design is to cite the 2022 article by Baden in Nilsson where they note in the evolution of both the vertebrate eye and cephalopod eye they both work very well. The authors note advantages to the inverted retina. In the 7th paragraph after Figure 4 the authors write, and the anti-evolutionist will often produce this quote: " In terms of performance, vertebrate eyes come close to perfect."
However just above this sentence which is usually never quoted is this: "So, in general, the apparent challenges with an inverted retina seem to have been practically abolished by persistent evolutionary tweaking. In addition, opportunities that come with the inverted retina have been efficiently seized."
The authors are not only saying that the vertebrate eye evolved and functions well but they confirm that the vertebrate eye only performs well because of evolutionary "tweaking" or workarounds that make it perform better, and not due to the original inverted retina 'design'. They also note that some species of fish, reptiles and bird cell bodies contain oil droplets in their photoreceptors to improve color vision and to help focus light. Thus, this is an example of dishonest or sloppy quote mining by the creationist. There are multiple structural compensations to the vertebrate eye necessary for improved vision not needed with the cephalopod eye.
Creationists and the eye; Creationist "Contraductions" on display
In 2024 Dan Barker published a small book titled "Contraduction" with the intent to establish a new word for an apologist and creationist error he repeatedly encountered during his debates*. Several well known authors have praised the word and concept:"An ingenious word for an invaluable concept. Sharp, clear, and timely"
~ Steven Pinker, Professor of Psychology, Harvard
"Both a delightful read and a penetrating argument: Barker has invented an invaluable new concept, and puts it to work with clarity, wit, and above all conclusiveness."~ A.C. Grayling, Philosopher
"I am completely down with the concept of contraduction. It fills a need. False pattern recognitions pose a real danger to our survival. Well done!"~ Ann Druyan
What Barker had recognized and Druyan labelled are false pattern recognitions that completely and erroneously invert the conclusion to a set of observations. As Barker points out, an example would be if you are sitting in a train and you falsely note for a moment that you are pulling out of the station only to correctly understand a moment later that the train outside is what is moving and not you; you briefly had been the victim of a contraduction. He mentions other contraductions. Noses were created for glasses. The daily crowing of a rooster causes the sun to rise. Obviously, one of the most famous contraductions is that the sun revolves around the earth because it does appear that way until that conclusion is effectively tested.
Contraduction thus is defined by Barker as an informal fallacy that occurs before reasoning begins. It is a hidden fallacy, flipping and inverting the truth. The truth is opposite to what the person is thinking or asserting. "The verb 'contraduce' means simply to flip around" he notes.
The debates between scientists and apologists regarding the vertebrate eye are extensive on the Internet and are wonderful examples of creationist contraductions. The creationists will list the RPE, cabling systems, oil droplets in some photoreceptor cells, etc. as wonderful designs without realizing that a closer look at vertebrate eyes indicates it's just the opposite. They have inverted the truth; as in cosmology it is we who orbit the sun and not the other way around. In nature the vertebrate eye has had to undergo several "tweaks", "patches", workarounds, or compensatory changes to make it work well. When you come across a car with it's back tail light broken, the red duct tape someone put on it is not an original "great design" of the car.
Four compensatory adaptations through evolution have been discussed in the previous sections showing that the vertebrate eye is not well "designed"; rather, it has needed fixes and changes to make it work well. Creationists who list these adaptations and claim them as wonderful designs have tripped and fallen into a hole of contraductions. These co-adaptations really represent profound evidence of evolution attempting to lessen the evolutionary constraints of the vertebrate eye with its inverted retina.
* Barker, Dan. 2024. Contraduction. Hypatia Press, UK. 111pgs. Analogies for the eye and Intelligent Design advocates.
DISH TV. Arguing that all the needed compensatory adaptations necessary to make the vertebrate eye work well are original and good is like hiring a DISH TV installation. The technician arrives at your house. Instead of putting the antenna on the roof pointed at the satellite, they go to the basement and install it there (retina), point the antenna away from the signal (photoreceptors direction), place it so it will try and grab signals through several walls and floors (the support vessels and cells blocking the retina), run a long electrical cord down to the basement because there's not a wall socket for electricity (the RPE for support), adding a second antenna to make up for poor signal strength (the oil droplets), then punching holes in the walls and floors to try and get more signal in (the cabling system). You assert this is a great design? You'd recommend this tech person to your family and friends? Meanwhile your neighbor with their DISH antenna on their roof pointed at the satellite is wondering if you've lost your mind (cephalopod eye).
Broken tail light. The car you just purchased has a broken tail light. Someone has not replaced it but compensated only and patched it with red duct tape. You think this is a great original design to the car rather than use a better solution - replace the light (the cephalopod eye works without all those vertebrate eye "fixes")
Eyeglasses. Focusing on eyeglasses for vision instead of why they are needed for an eye with vision problems is like creationists declaring all the workarounds and compensatory structures for the vertebrate eye to have good vision wonderful designs instead of noting the fundamental eye problems requiring the eyeglasses to begin with. Contraduction - inverting the real reason for the observations.
Other Problems with an Inverted Retina
Novella has noted the inverted retina also causes problems for the vertebrate eye not mentioned discussed above.
The retina is prone to detachment. Novella notes, "the cephalopod eye does not suffer from retinal detachment because the axons from the photoreceptors anchor them to the layers beneath."A second issue is that the vertebrate eye is prone to macular degeneration. "The macula is that part of the retina that has the densest concentration of rods and cones for detailed vision. Within the macula is a smaller area called the fovea which contains only cones and has the highest density of these receptors. The very existence of the macula, however, is a partial fix for the “backward” arrangement of retinal layers with the nerve and blood vessels between the receptors and the direction of light. This limits the density of rods and cones, and so the partial fix is to have one small area cleared of nerves and blood vessels where rods and cones can be denser. However, if the human retina were designed like that of the squid and other cephalopods, this would not be necessary.
"The dependence of the human eye on the macular for sharp vision creates a vulnerability, for any problem with that small area will have a dramatic effect on visual acuity. The rest of the retina will not be able to adequately compensate for the loss or compromise of the macula because the density of rods and cones is just too diffuse."
Third, the human eye is prone to glaucoma. This occurs because there is a narrow space between the iris and cornea called the anterior chamber which can become blocked and disrupt the flow of fluid through this chamber, producing narrow angle glaucoma. The eye configuration makes the eye more prone to this problem. "The most susceptible populations are Asians and Inuit. There is speculation that the narrow angle may have been a thermoregulatory adaptation to colder climates—a compromise exacerbating an already existing design weakness."
Other Problems with an Inverted Retina
Novella has noted the inverted retina also causes problems for the vertebrate eye not mentioned discussed above.
The retina is prone to detachment. Novella notes, "the cephalopod eye does not suffer from retinal detachment because the axons from the photoreceptors anchor them to the layers beneath."A second issue is that the vertebrate eye is prone to macular degeneration. "The macula is that part of the retina that has the densest concentration of rods and cones for detailed vision. Within the macula is a smaller area called the fovea which contains only cones and has the highest density of these receptors. The very existence of the macula, however, is a partial fix for the “backward” arrangement of retinal layers with the nerve and blood vessels between the receptors and the direction of light. This limits the density of rods and cones, and so the partial fix is to have one small area cleared of nerves and blood vessels where rods and cones can be denser. However, if the human retina were designed like that of the squid and other cephalopods, this would not be necessary.
"The dependence of the human eye on the macular for sharp vision creates a vulnerability, for any problem with that small area will have a dramatic effect on visual acuity. The rest of the retina will not be able to adequately compensate for the loss or compromise of the macula because the density of rods and cones is just too diffuse."
Third, the human eye is prone to glaucoma. This occurs because there is a narrow space between the iris and cornea called the anterior chamber which can become blocked and disrupt the flow of fluid through this chamber, producing narrow angle glaucoma. The eye configuration makes the eye more prone to this problem. "The most susceptible populations are Asians and Inuit. There is speculation that the narrow angle may have been a thermoregulatory adaptation to colder climates—a compromise exacerbating an already existing design weakness."
The evolution of the vertebrate eye - a few comments
Why then did the vertebrate eye evolve like this? One reason could be that early eyes were in a water environment and an inverted retina has space saving advantages. Kroger and Biehlmaier discuss how studies support this view: https://www.sciencedirect.com/science/article/pii/S0042698909003162#fig2
A key protein needed for vertebrate eye function has been found to be of bacterial origin, acquired by horizontal gene transfer in the distant past. At least 45% of our genome is derived from viruses or duplicated viral products and genes. All of this is consistent with evolutionary explanations and best explained through evolution:
"Here, we describe the essential contribution of bacteria to the evolution of the vertebrate eye, via interdomain horizontal gene transfer (iHGT), of a bacterial gene that gave rise to the vertebrate-specific interphotoreceptor retinoid-binding protein (IRBP). We demonstrate that IRBP, a highly conserved and essential retinoid shuttling protein, arose from a bacterial gene that was acquired, duplicated, and neofunctionalized coincident with the development of the vertebrate-type eye >500 Mya."
[additional discussion and explanation]
Conclusion
Debates surrounding the vertebrate eye as an example of poor design over the years have produced many competing articles from both sides. The case of the vertebrate eye being poorly structured for vision is a strong one because when comparing various vertebrate eyes we find compensatory adaptations to lessen the vertebrate eye deficits. These include the RPE which an eye with an everted retina does not need, the pecten oculi in birds, the conus papillaris in many reptiles, the tapetum in many vertebrates for night vision, a cabling system to shuttle photons more cleanly to the photoreceptors, and oil droplets in some vertebrate eye photoreceptors.
Instead of realizing these vertebrate eye structures are a result of evolution diminishing and attenuating problems with the eye, creationists and apologists have inverted their true meaning, falling victim to contraductions. The problems with the vertebrate eye are a result of the evolutionary inverted retina constraint imposed upon it. The irony is that what they think will defend their views, actually represents powerful evidence for evolution. In addition, an example of creationist quote-mining is discussed that is often encountered in debates with creationists regarding the inadequacy of the vertebrate eye. Without tweaks and patches to make it work efficiently the vertebrate eye is hardly intelligently and wonderfully "designed".
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