Nathan Lents: Bad Design of the Eye?

On a TBD date, author and biologist Nathan Lents (@NLENTS) will be joining for conversation about the eye. Nathan recently published a book that is getting a lot of press, and also engagement across the spectrum:

His book has attracted wide coverage, including an opinion peice in the WSJ, and a flurry of 14 articles since April from the DI. In this book, Nathan catalogues several “glitches” in the human body, and stirred up an exchange over whether or not bad design disproves Intelligent Design.

Along with Nathan, I affirm evolutionary science and common descent, but I avoid bad design arguments entirely. There certainly is a long distinguished tradition of this reasoning that traces back to Darwin, and it arises today from Jerry Coyne and even Christians like Keith Fox. Lents is certainly consistent with this tradition, and I am the outlier here.

To be sure, I see the appeal. This one of those arguments that can get scientists rolling with the rhetorical beat of a preacher. It is one of those few places where academics feel the minutia of biology can engage and capture the crowd. I’m not sure this is a helpful way of engaging with audience skeptical of evolution.

I am concerned the “bad design” rhetoric is counter-productive, and if more neutral language would be wise. It might only be preaching to the choir, while undermining trust with others. It seems also to be a selective telling of science. Instead of the language of “bad design”, I prefer instead the more neutral language of his subtitle: “glitches”, and perhaps words like “surprises”, “quirks”, and “seams,” which might instruct us about the non-intuitive features of biology and how we came into being. I would not say loaded words like “botched”, “errors” and “bad design.”

That being said, I’ve noticed that Nathan’s rebuttals of the DI have been more measured. I also recognize that controversy is good for attracting attention around a book, regardless of what exactly is in a book. This brings me to my first question:

  1. Nathan, you’ve been back and forth with Discovery about the “bad design” argument. Is “bad design” really the point of your book? Or is there something more subtle going on? How would you most carefully explain what you are getting at in these exchanges.

Let’s look at a specific example, to make more clear. Nathan wrote about this on his blog (The Poor Design of the Human Eye – The Human Evolution Blog). He writes:

The human eye is a well-tread example of how evolution can produce a clunky design even when the result is a well-performing anatomical product. The human eye is indeed a marvel, but if it were to be designed from scratch, it’s hard to imagine it would look anything like it does. Inside the human eye is the long legacy of how light-sensing slowly and incrementally developed in the animal lineage.
The Poor Design of the Human Eye – The Human Evolution Blog

These sorts of posts were engaged by the Discovery Institute (Is the Human Eye Really Evidence Against Intelligent Design? | Evolution News). This seems like an unnecessary conflict to me, unless the goal was conflict itself. This gives a good place to focus in on some good questions about public engagement, and also to learn about the deeper questions that evolutionary science answers…

  1. Nathan, I have several questions on the science here, but will start with one. Do we really know that the retina is “wired backwards”? It seems that the flipped between humans and octopi might just as likely be neutral. And I can even see some very plausible reasons the flipped orientation should be preferred (and I can explain).

There are more questions on the science. Perhaps I will learn something. It seems to me, however, that neutrality on many if these internal details of humans is part of what gives us so much confidence in common descent. If it the retinal wiring is neutral, “design principles” (other than common descent of course) do not make good sense of why chimpanzee and human retinals are both wired backward.

  1. Nathan, several non-scientists on this forum have been asking about the evolution of the eye. This seems like a great way to begin this conversation too. We will save it for the end, but wondering if you can help map out how evolutionary biologists build the case for the evolution of the eye.

The eye loomed large in my story. It arises in anti-evolution arguments all the time, and it initially seems absurd to think it could have arisen by evolution. Raised as YEC, it seemed to be a clear defeater of evolution. The absurdity of seeing camera eyes in both octopi and humans was extreme.

Then, at some point, I tried to understand the reasoning from biology I had rejected. I learned more. I learned of the glitches, and also the lessons of comparative anatomy, and comparative genetics on the eye. It began to become clear. The claim was not nearly as crazy as I had thought. Of course, also, octopi eyes are only superficially like mammalian eyes; the two are very different in their particulars. This is just as we expect from evolution. The argument against common descent had the facts incomplete.

With those three questions guiding us, I’m really happy to have Nathan here. I expect some friendly disagreement, but also common ground. Nathan and I both are in the spotlight at Discovery right now, so this might get more attention than the usual exchange. As is usual for Office Hours, this thread will be tightly moderated.

Kind and respectful questions are welcome. Keep in mind, however, that this is not a forum for endless debate by non-experts. Instead, we encourage everyone to understand and be understood. Make this your goal, and we will all learn a great deal.

Come join the conversation on the grand questions here…


We are back to this conversation now. @NLENTS has begun to answer some of these questions.

The Point of His Book?

Two Questions:

But we are still left with a couple questions.

It seems to me this wiring is most likely neutral. There is also a plausible hypothesis for why it might be beneficial to have it wired “backward.”

This is something that will be helpful to a lot of people, and I know that both @Patrick and @Michael_Callen have been wanting to learn more about this.

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A post was merged into an existing topic: Side Comments on Bad Design of the Eye

Let @NLENTS and I go back a bit, and lay things out. Then definitely jump in with follow up questions. If you have some sub questions on the inference to eye evolution, you can concisely ask them now.

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3 posts were merged into an existing topic: Why don’t bad design arguments work?

A post was merged into an existing topic: Side Comments on Bad Design of the Eye

So @NLENTS, I’m going give a brief summary. There are several questions there. If you can humor me there, I think it will tease out some of the finer points.

Common Ground

First off, I think we are on agreement on several things.

This is an important point. It is unfortunate the main point of your book was lost in the acrimony.

That’s exactly right. There are range of weird features of biological systems that are best explained as common descent. Of course, God have de novo created us to be like this, but it wouldn’t explain why he did it this way.

So What Is the Problem?

I’ll try and map out the key issues here, at a high level.

  1. It rhetorically argues that the beauty and complexity is “poorly” designed, which doesn’t even match our own experience as scientists as we are in awe of it all. In this way, it is a very hard argument to emotionally win.

  2. Is our belly button an example of poor design? Not at all. Rather it bears testimony to an important function that our bodies once had, but no longer do. In the same way, a broken GLUO gene is not poor design if common descent is true, because it had a real function the past. So from an evolutionary point of view, is not actually bad design.

  3. The fact that it requires adopting a non-evolutionary point of view, makes it susceptible to being a straw man, and in fact I think it is. It requires presuming a specific narrow range of design models to be valid (i.e. rejection of common descent).

  4. Ultimately it is a theological argument because you have to come back to “what God would or wouldn’t have done.” Scientific arguments should stay out of careless theology (or maybe all theology) like this. If we are going to talk about God would have or wouldn’t have done, we need to start engaging other disciplines (philosophy, theology, etc.) and specifying which God we are talking about (Christian, Hindu, etc.). Messy territory for secular science. I oppose this sort of mixing of theology into scientific argumentation.

  5. For people like me, that draw on the pre-ID concept of “creation” by common descent, as a the way God designed us, it puts us in an awkward position. We end up dodging between the rhetoric of both sides. Thankfully, scientists are smart enough to know we aren’t their opponents.

  6. This adopts the biased rhetoric of anti-evolutionists. They want evolution to be incompatible with “design”/“creation” so they can rely heavily on a fallacy of an excluded middle. From a persuasion point of view, arguing “this is a better version of design” will always be more effective than “design is false.” Adopting there rhetoric, rather than turning it, ends up substantially weakening its persuasive power.

  7. Perhaps most importantly, quite often this argument leads to lazy thinking about biology, and often the facts are fudged to serve the preacher-roll of the argument’s narrative. The eye is a good example of this. I’m not sure, for example, if your arguments about the eye being poorly designed are scientifically accurate.

  8. Narrative’s like bad design can work against scientific curiosity. When we see an oddity in life, we should ask why? Perhaps it is neutral? Perhaps is positive? Perhaps it is negative? However, for the bad design argument, it only works if the quirk is negative. This by its nature constrains to an a priori view of mysteries in biology. This is not how science works, so it misrepresents the spirit of science to the public. In many ways, it can be as much a show stopper to scientific thought as ID arguments can be.

All these reasons, in my opinion, are why we should back away from both ID and bad design arguments in science. They seems to be a well-intentioned but misguided rhetoric for engaging the public.

Quirks, Seams, and Questions

I think there is a better way. In its place, I would suggest an alternate invitational rhetoric that better matches the spirit of science. For example, these make the same point, and make it more persuasively to religious audiences.

  1. These are quirks and mysteries about how life is arranged we are trying to figure out. Here are many of them are explained by common descent.

  2. These are seams or breadcrumbs, pointing to a deeper history of how things came into being though common descent.

  3. There is an open question about the importance of this quirk and this is how we are trying to make sense of it. Maybe it is helpful, or maybe it is harmful, but perhaps it is most likely it is neutral

  4. What might seem like bad design right now had a important purpose and role in a different context. Maybe this quirk is a lot like the belly button of our species as a whole.

This sort of language, still points to common descent and shared history. It avoids many of the pitfalls of the bad design approach.

Once again, I acknowledge that I am the outlier here. I still hope this can be making some sense.


All of your points are solid and I agree with basically everything you say as your justification, but… I think what it comes down to is this…

1.) what you call seams, quirks, and questions, others call glitches, flaws, or poor design. In general, I like your terminology better, but we agree what it says (and what it doesn’t say). The GULO gene is only “poor design” if you think humans WERE designed. As you say, we weren’t, so its an echo of long ago past. But I call it a flaw because it also has physiological consequences. Many people have died agonizing deaths because of scurvy. The mutation that broke GULO isn’t neutral to our health and survival. It’s an error in the genetic material of all primates that has caused a great deal of death and suffering.

2.) I think also you are putting words into my mouth regarding what I think sub-optimal design… I’m not saying it’s kind of slam dunk, or “proof” of evolution on its own. I don’t think it’s neutral, though. I think it’s a much tougher thing for ID proponents to tussle with than those of us who accept evolution. These seams, as you call them, really do tell tales of our ancestral past and they line up with the other evidence of that past, so in that sense, it’s weight on the scales. For YEC or ID proponents, these seams are really incongruent. If we set aside all the examples that they dispute (sinuses, retina, etc.), we are left with plenty of examples that they don’t bother trying to explain (RLN, homologous anatomy) or do so very unconvincingly (vestigial structures, pseudogenes).

3.) You make a good point that we adopt their stance when we attempt to suggest what a designer could have or should have done, but that’s what “taking the fight to them” is about. A defense lawyer adopts the theory of the crime offered by the prosecution and then pokes holes in it. These things are challenges to ID precisely because ID’s central claim is “creation” is too elaborate to have come about through mutation and selection and must therefore have been designed by an intelligence. Okay, if you accept that view, then, the designer has a lot to answer for.


Speaking scientifically, there is no place for the term “bad design,” because there is no place for the word “design” altogether. We weren’t designed. We’re the product of mutation, selection, drift, luck (both good and bad) and four billion years of tinkering. That’s not design.

When I and others adopt the language of the design, it is to take on the position and language of the opposition in order to point out its weaknesses. I agree with you that it’s a departure from how scientists normally talk about their work. The point of my book is that these glitches, quirks, seams, errors (whatever you want to call them) are really interesting. They are head-scratchers, but more importantly, each tells us something about our past. And in so doing, affirms that we HAVE a past. In that sense, I do believe that the existence of these flaws is a strike against ID because they are not easily congruent with it, but are easily congruent, indeed expected, in evolutionary theory.


First let me say, as I have all along, that the human eye, like the cat’s eye, is remarkably good at its job. I’ll go further and say that the “best” of the camera-like eyes (I know little about the arthropod eye) are found in vertebrates, not cephalopods. The DI, and others, take my point to an extreme that I never have, by claiming that I say the vertebrate eye is terrible and far inferior to the cephalopod eye.

What I HAVE said, and I will say again, the apparently inverted arrangement of the vertebrate is a “seam” in the sense that this creates the need for additional adaptations to accommodate the suboptimal starting point in the tissue architecture. The DI has made a big deal of some of those adaptations, such as the matching of blood flow to demand (which evolution would predict as well, and also occurs in cephalopods) and the clever way in which photos are relayed through the thicker tissue layer to reach the photoreceptors. (I’m trying to avoid technical jargon, but I’m working on a scientific paper on this, so stay tuned for more precise details.) These accommodations show that evolution, given millions of years, comes up with solutions that overcome initial limitations. They don’t argue for design, or at least not any more so than they do evolution. However, there are three ways in which our arrangement could fairly be said to be inferior, at least as it began.

The first is the requirement of an optic disk, the place on the retina where the axons from the photoreceptor cells converge to form the optic nerve. This disk is only necessary because of the inverted arrangement and cephalopods don’t have it. The optic disk causes a blind spot. Of course, we have two eyes and our brains fill in the blind spot, but that’s not true of most vertebrates whose eyes do not have much overlap in their field of vision. Our eyes came forward to create our stereoscopic, 3-D vision, effectively compensating for the blind spot, but the same is not true of dolphins, horses… most vertebrate animals have their eyes on the side, so they have a wider fields of vision, but worse depth perception.

The second is that the thicker retinal layer of photoreceptor cells and the required vascular layer has led many scientists to suggest that retinal detachment is more common with the inverted arrangement. I understand that this is in dispute and, given how many other differences there are in the tissue architecture, it’s impossible to know for sure. But this seems likely to me.

Third, several clades of vertebrate animals have evolved a structure called the tapetum lucidum in order to maximize sensitivity to low levels of light. This has evolved multiple times, as evidenced by the structural dissimilarity among distantly related clades. This structure is located behind the photoreceptors and bounces any light that slips past them (which happens more easily in the inverted arrangement) back toward them, so the photon has a second chance to hit the photoreceptor. This is what causes the “shine” in animals such as cats. This structure has evolved in nocturnal animals such as crocodilians and mammals (two very different TLs) and in several kinds of fish that are in deep and/or murky waters. It has not, however, ever evolved in cephalopods, who live in deep and murky waters because the “verted” retina can pack the photoreceptors into a cobble-stone-like layer so that no photons slip past.

As I said, the proof is in the pudding and vertebrate eyes may indeed be superior in function, but that’s only because they managed to overcome a less optimal starting point.


I will have to table this for another day. I have a stack of papers to grade that I promised the students I would have for them tomorrow. Good night all!

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I agree. Science does not consider divine design. So the “bad design” argument is a theological argument. If you are going to be making a theological argument, you should be making a competent well considered theological argument. This is where the bad design argument seems to fail.

Great, so look at the reasons you still want to make this argument.

An alternate view is to say that we are not designed to avoid eating fruit. It is not God’s purpose or intent for us to live this way. Eating in poorly rounded meal, without fruit, is deviating from how God designed us. It is not that we are designed poorly, but we deviate from the purposes for which we are designed.

This is an entirely reasonable alternate view, and there is no way to show it is wrong, which makes the argument you are making escapble.

We are on the same page here. I’ve never said you were claiming they were proofs. I’m just saying they are not helpful or strong arguments when framed as “bad design” arguments.

Your argument here, if I understand it, is that we have to make meet ID on these grounds because this where the conversation is waged. I agree, sort of.

ID advocates watching this will howl, but in my view ID is making a theological argument. You are arguing that we have to respond on the same ground with a theological argument. I, actually, entirely agree. However, to be effective it has to be a good theological argument, not a bad one. If, also, we are going to enter into this realm, we have to understand the rules of this game and be appropriately versed in it.

I agree with the high level strategy of bringing theology to bear in engaging ID, and I’m doing that here at Peaceful Science. However, the bad design argument is incoherent from a theological point of view. For example, theology does not claim that humans are perfect, but that we are good. We are not the best possible beings, but we are good for what God intended us. It is not clear at all that God has to answer for imperfections in how we are made. There is sufficient beauty and coherence in the human form for us to know certainly that we are are made “good.”

Another theological challenge to your reasoning here is that we expect God to design us in a manner very different than how humans design things. Common descent actually is a very theologically coherent example of a surprising way of creating/designing us that is very different than how humans design things. With that theology in mind, the argument you are making is substantially undermined.

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So in what sense are they poorly designed precisely? I"m not asking for a repetition of what you have written. I’m just wondering why you say this is poorly designed? It sounds like it might be optimally designed from a less than optimal starting point. That is not semantically equivalent to “bad design.”

Also, there may be some big advantages to having the retina wired this way. Let me offer a few alternate hypotheses.

  1. It is not clear that this “backward” configuration actually is less efficient at capturing light. What papers are their that demonstrate this? The lengths involved here are are tiny, and cells are transparent (except for the pigment). Do you have any references that can demonstrate that this is suboptimal for collecting light? How was that experimentally tested?

  2. One possible advantages of requiring light to go through cell bodies (the backwards wiring) before collection is that it enables evolution to tune the wavelengths of cells by putting different pigments in cellular vesicles. This is much more important for land vertebrates than water-bound octopi, who do not have as a wide a range of wavelengths to perceive. Given how important vision is to, for example, mammals. It is not clear that the octopi eye could reach the same level of tuning required for colored site as we see in mammals.

  3. I understand your hypothesis, that the “verted” retinal can pack tightly, but it is not clear to me why a mammal retinal couldn’t be packed tight. Can you show me the papers demonstrating that this is the case? Also, the tapetum lucidum is an another interesting case where the biophysics is really important to understand. It very well may be possible that this is an easy way of increasing the sensitivity of the “backwards” retina, but not the octopi retina, which would then explain why the more tight packing of vertebrate eyes is not common.

I"m not trying to be difficult here. I think some of what you have written are reasonable hypotheses. However, that is far from certain. I’m not sure if they have been demonstrate correct over alternate hypothesis yet. Do you know if they have been? What citations do you have?

I want to be clear that I am NOT calling you out @NLENTS, so please don’t take this personally. I’m just not sure that the string of facts here are actually known to be true scientifically. There are alternate hypotheses, and it is not clear which hypothesis is correct. In each case, it might be:

  1. You actually are correct, and this is actually demonstrated in the literature.

  2. You may or may not be correct, but it is not demonstrated in the literature.

  3. You are just not correct, and the opposite is demonstrated in the literature.

The challenging problem, for me, as a scientist, is that this ends up being a very complicated morass to sort out. the argument ends up raising far more questions than it answers, almost like a Gish Gallop. For the argument to work, we have to be dismissive of these questions. However, science doesn’t work that way. We care about those questions, and we know our intuitions on how they will be answered are often wrong.

That is why calling them “Mysteries” is, in my view, far more accurate and true to science.

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I’m reminded here that I am neither a theologian or philosopher. What do some of those of relevant expertise think of the theology of the “bad design” argument? @jongarvey @deuteroKJ @Philosurfer

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This is can be effective sometimes, assuming their theory and following it to the necessary consequences. It’s great for defense lawyers because the prosecution is required to make its case. But this is not always the situation for the ID advocate/Creationist, who can just ignore those consequences and move on to another claim. To use this effectively requires specific claims from ID, and “too complex to evolve” is not specific about what is complex or what was designed.

This is interesting, because countering (for example) a YEC argument with a theological argument is often effective because it reframes their argument to what it is (theology). If I do the same versus an ID argument then I get accused of not being scientific. So either I’m not being sneaky enough in disguising my theological arguments against ID, or maybe it is just a bad argument.

I like @NLENTS comments about GULO. Why should a designer assemble parts well enough to work, but allow harmful flaws to remain? It the eye is designed, then why leave GULO broken, bad knees, bad back, and a host of other design flaws?

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Remember how I answered this? I suggested occurs because God designed by a process of common descent. Though the GLUO is not used for making Vitamin C any more, in the past it did have a purpose. You cannot presume God did not design us by an evolutionary process. An argument for common descent is not an argument against design.

ID is more difficult because…shall we say “doublespeak?”

Though, in recent years it has become easier. I think they have given up on the original plan of using “Intelligent Designer” as an end run around methodological naturalism. Now, it seems many prefer to just get rid of methodological naturalism.

What has been most helpful for continuing the conversation is to ask them for a mathematical model of design. They are in a difficult bind if we make the legitimate request to produce a mathematical model of design that explains features currently explained by common descent, with at least as much mathematical rigor. As it is, the vast majority of patterns we see in biology are explained by common descent. Until we have a mathematical alternative, common descent is the conclusion of science, regardless of methodological naturalism.

For the longest time, there was nothing coming out of ID on this. There is, now, an example of one model from @Winston_Ewert. That is a good step for them, though it is preliminary results at best. It is hard to imagine it extending to all the patterns.

With ID, engaging the theology has been just as important as laying down what they need to do to make their case. To their credit, this seems to be taken seriously by the best of them (@Winston_Ewert and @Agauger). To their detriment, others in their camp tend to oversell and puff at every turn. This is not helping their scientific case. I am hopeful this fact is going to sink in sometime in the future.

I do. I was grasping for a theological argument that was not overtly scientific. A better argument is that science does not deal with the supernatural, and conversely it should not be possible to know God by means of science. Until ID explicitly rules out supernatural cause, it is making a claim that is “bad theology”. (according to the theologians I have discussed this with.)

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2 posts were merged into an existing topic: Side Comments on Bad Design of the Eye