Evolutionists Refute “Poor Design” Claim for Human Eye
Evolutionists have finally caught up with creationists: they show that
the octopus eye is not superior and the human eye is not “backwards”
by Jerry Bergman, PhD
One of the most common claims against creationists has long been the allegation that the human body is ‘poorly designed.’ And one of the most popular examples of this poor-design claim is the so-called backward vertebrate retina. The retina is the thin organ located at the back of the eyeball containing the light-sensitive rods and cones. The claim is made that the vertebrate eye is functionally suboptimal in a significant way. The reason for this claim is that the photoreceptors in the retina are oriented not toward, but away, from incoming light.[1] Oxford Professor Richard Dawkins considers this an example of poor design because, he concludes, that an
engineer would naturally assume that the photocells would point towards the light, with their wires leading backwards towards the brain. He would laugh at any suggestion that the photocells might point away from the light, with their wires departing on the side nearest the light. Yet this is exactly what happens in all vertebrate retinas. Each photocell is, in effect, wired in backwards, with its wire sticking out on the side nearest the light. The wire has to travel over the surface of the retina, to a point where it dives through a hole in the retina (the so-called ‘blind spot’) to join the optic nerve. This means that the light, instead of being granted an unrestricted passage to the photocells, has to pass through a forest of connecting wires, presumably suffering at least some attenuation and distortion.[2]
Professor Williams claimed the retina is not just an example, but one of the best examples, of “poor design” in vertebrates that proves a “blind watchmaker” created all life:
Every organism shows features that are functionally arbitrary or even maladaptive. . . . My chosen classic is the vertebrate eye. It was used by Paley as a particularly forceful part of his theological argument from design. As he claimed, the eye is surely a superbly fashioned optical instrument. It is also something else, a superb example of maladaptive historical legacy. . . . Unfortunately for Paley’s argument, the retina is upside down. The rods and cones are the bottom layer, and light reaches them only after passing through the nerves and blood vessels.[3]
This claim has permeated science to the degree that “One of the first things we find in textbooks when introducing the vertebrate retina is that it is ‘upside down’, ‘inverted’ or ‘back to front.’”[4] Usually, this argument includes mentioning that the “everted” retina of the octopus, with its photoreceptors aimed toward the light, is a “good design.”
Figure 1. The inverted eye with the retina compared to the cephalopod eye which shows the nerves behind the retina. Illustrations from Wikimedia Commons.
The Inverted Retina Is Actually a Good Design
Two evolutionists have now turned the tables on this claim. Tom Baden and Dan-Eric Nilsson write in Current Biology that vertebrate “eyesight is a compelling testimony to creative design.”[5]
Baden and Nilsson are not turning to creation by any means. But some of their language almost sounds like it. First, they echo the upside-down claim, mentioning the blind spot and the wires in the way. “From an engineer’s perspective, these problems could be trivially averted if the retina were the other way round, with photoreceptors facing towards the center of the eye. Accordingly, the human retina appears to be upside down.”[6] Continuing the poor-design story, they say that the “Cephalopods (octopus, cuttlefish and squid) have well developed eyes, superficially almost identical to vertebrate eyes” but their retina is not backward. So how did we vertebrates get stuck with a backward retina?
The two looked beyond the poor design claim and decided that what’s backward is the story. In contrast to the common narrative, they concluded “there are in fact plenty of reasons why an inverted retinal design might be considered advantageous.”[7] These reasons are discussed in some detail below.
Eliminating Redundancy
To introduce their reevaluation, they begin by pointing out a significant economic benefit that the “backward” retina provides. They say,
[To] understand the merits of the inverted design, we need to consider how visual information is best processed. The highly correlated structure of natural light means that the vast majority of light patterns sampled by eyes are redundant. Using retinal processing, vertebrate eyes manage to discard much of this redundancy, which greatly reduces the amount of information that needs to be transmitted to the brain. This saves colossal amounts of energy and keeps the thickness of the optic nerve in check, which in turn aids eye movements.[8]
For instance, any spatially, temporally, and spectrally uniform scene, such as the blue sky on a cloudless day, is largely redundant. Keeping a large population of visual neurons constantly active recording a static scene
would be incredibly wasteful. A much more efficient representation is one that accentuates change. In this case, neurons ‘looking’ at this sky could be silent most of the time, but spring into action if anything were to change — for example, upon the sudden appearance of a bird’s silhouette. This is where the vertebrate retina truly excels. The extensive local circuitry within the eye — enabled by two thick and densely interconnected synaptic layers, achieves an amazingly efficient, parallel representation of the visual scene the signal gets to the ganglion cells that form the optic nerve, spikes are mostly driven by the presence of the unexpected. If there is nothing new to report, the nerve remains essentially silent.[9]
Figure 2. The vertebrate eye showing some of the main features.
Best Use of Space
Furthermore, they argue that, especially in the “smallest of perfectly functional vertebrate eyes, the inverted retina has allowed efficient use of every cubic micron of intraocular real estate.” The vertebrate eye puts preprocessing neurons in front of the photoreceptors where there is plenty of space. The information sent to the optic nerve, then, is sorted and condensed, saving energy and processing power in the optic lobe of the brain. Behind the retina, though, space for this is lacking.
This observation forced them to reassess the everted cephalopod retina. It now appears to have the more awkward orientation! This means that cephalopods have, at least in this respect, a less well designed eye. Contrary to the poor-design claim, then, the vertebrate retina is better designed, at least in some respects. Actually, they argue, both the inverted and the everted retinal design have their advantages and their challenges, depending on the environment:
The good points with the vertebrate way of making an eye is that it provides ample space close to the photoreceptors for early visual processing, and in very small animals, the visual system can be made extremely compact. Good points with the cephalopod everted retina are that there is no blind spot in the visual field, and the space in front of the photoreceptors is free of optically compromising neural tissue.[10]
In other words, the inverted system is the best design for vertebrates, and the everted design is the best design for cephalopods. Both are well designed.
What About Interference and Blind Spots?
Baden and Nilsson dispense with two of the main complaints about “backward” vertebrate eyes. Consider eye performance: vertebrates do really well with backward retinas! Viewing the world
through a layer of neural tissue may seem to be a serious drawback for vertebrate vision. Yet, vertebrates include birds of prey with the most acute vision of any animal, and …. vertebrate visual acuity is typically limited by the physics of light, and not by [claimed] retinal imperfections.[11]
Figure 3. Some details of a cephalopod eye.
The other often-noted downside of the ‘inverted’ retina is the blind spot. This is actually not a problem for several reasons. For one, it is tiny compared to the size of the entire retina. It’s an insignificant spot comprising less than 1% of the retinal surface. In addition, the blind spot falls into a region of binocular overlap. Consequently, the brain can fill in much of the missing data using information from the other eye. Thus, the two most serious challenges faced by the inverted retina are largely abolished. Baden and Nilsson then make this amazing statement: the design of “vertebrate eyes come close to perfect.”[12]
What about cephalopod eyes? Are they also close to perfect? This question is more difficult to answer because most details of cephalopod eye anatomy and physiology are still unknown. The lack of knowledge may lead to incorrect assessments. We can, however, gain performance clues from behavior. Baden and Nilsson comment, “anyone who has observed visually guided behavior in squid or cuttlefish, performance [of their everted eyes] appears in no way inferior to that of fish.”[13]
Clinging to Darwin
Having demonstrated that both the inverted and everted eye structures are extremely well-designed for their respective environments, the authors still support the view that such exquisite design is the handiwork of evolution by natural selection. Ironically, their evolutionary explanations frequently appeal to what amounts to magic: structures and designs “arose” or “emerged,” and complex cells also “emerged.” Personifying evolution is also common in the article: i.e., structures were “cleverly oriented the right way” and “persistent evolutionary tweaking” perfected, or “originated” some structure. Such language lacks empirical value and contributes nothing to understanding.
Summary
This has been a good illustration of the fact that poor-design arguments fall apart when investigated. It also demonstrates that evolution is the science stopper, not creation! When evolutionists embrace the ‘poor design’ story, thinking that structures are the result of a bumbling evolutionary history, they lose motivation to look for reasons why things are the way they are. Creationists would ask “why do differences exist between what is extant and what actually should exist.”[14] It’s prejudicial to think that retinal rods and cones should face the light and not face away from the light as in the cephalopod eye. A good scientist would ask why that should be assumed. Are there reasons for the differences? As noted, both designs perform exceptionally well in their respective habitats.
Evolutionists have assumed for decades that the answer was ‘poor design’ based on their own imaginations of what “should” be or what a good engineer “should” do. Creationists consider that good reasons must exist for what appears to be poor design, with a hunch that upon further research, the existing design will be found to actually be superior.[15] Curiosity motivates further scientific investigation, rather than dismissing a phenomenon as poorly designed. If creation had been the dominant worldview in science (as it was before Darwin), the arguments for good design described in this paper might well have been made much earlier.
References
[1] Ayoub, George. 1996. “On the Design of the Vertebrate Retina.” Origins and Design 17(1): 19-22, Winter, p. 19.
[2] Dawkins, Richard. 1986. The Blind Watchmaker. New York, NY: W.W. Norton, p. 93.
[3] Williams, George C. 1992. Natural Selection: Domains, Levels, and Challenges. New York. NY: Oxford University Press, p. 72; emphasis mine.
[4] Baden, Tom, and Dan-Eric Nilsson. 2022. Is our retina really upside down? Current Biology 32: R295–R310, April 11. https://www.cell.com/current-biology/fulltext/S0960-9822(22)00335-9.
[5] DeYoung, Don. 2002. Vision. Creation Research Society Quarterly 38(40): 190.
[6] Baden and Nilsson, 2022, R301.
[7] Baden and Nilsson, 2022, R301. Emphasis mine.
[8] Baden and Nilsson, 2022, R301.
[9] Baden and Nilsson, 2022, R301. Emphasis added.
[10] Baden and Nilsson, 2022, R301-R302.
[11] Baden and Nilsson, 2022, R302.
[12] Baden and Nilsson, 2022, R302.
[13] Baden and Nilsson, 2022, R302-R303.
[14] Bergman, J. 2000. “Is the Inverted Human Eye a Poor Design?” Journal of the American Scientific Affiliation. 52(1):18-30, March.
[15] Bergman, 2000.
Figure 1 The inverted eye with the retina compared to the cephalopod eye which shows the nerves behind the retina. From Wikimedia commons.
https://upload.wikimedia.org/wikipedia/commons/8/86/Vertebrate_n_octopus_eyes.png.
Figure 2. The vertebrate eye showing some of the main features. FromWikimedia Commons.https://upload.wikimedia.org/wikipedia/commons/1/1e/Schematic_diagram_of_the_human_eye
Figure 3 Some details of the cephalopod eye. From Wikimedia Commons. https://www.earthlife.net/inverts/cuttlefish-anatomy.html
Dr. Jerry Bergman has taught biology, genetics, chemistry, biochemistry, anthropology, geology, and microbiology for over 40 years at several colleges and universities including Bowling Green State University, Medical College of Ohio where he was a research associate in experimental pathology, and The University of Toledo. He is a graduate of the Medical College of Ohio, Wayne State University in Detroit, the University of Toledo, and Bowling Green State University. He has over 1,300 publications in 12 languages and 40 books and monographs. His books and textbooks that include chapters that he authored are in over 1,500 college libraries in 27 countries. So far over 80,000 copies of the 40 books and monographs that he has authored or co-authored are in print. For more articles by Dr Bergman, see his Author Profile.