Why don't bad design arguments work?

Continuing the discussion from Who is Right About Sinuses?:

Josh - That is precisely my point. I have resisted saying that my book is written as an argument against ID because it wasn’t written that way. I believe that strange quirks are best explained by common descendent and so, implicitly, they argue against design insofar as design is offered as contrary to common descent. So, much of the content of my book, I believe, challenges ID, but that doesn’t mean that it’s written as a direct challenge to ID. If that were my goal, just about every sentence of the book would be written differently and I would have chosen different examples. Many good books refuting ID have been written. My book was written for an audience that already accepts evolutionary theory. Although it wasn’t written to challenge ID, the content of the book does pose challenges because, as you note, these quirks are rather easily understood from the point of view of common descent. Without that perspective, they are conundrums. (Has an ID-based explanation for the crazy path of the recurrent laryngeal nerve been offered? What about GULO? What about other pseudogenes?)

So I am confused as to why you say that poor design arguments don’t work, while also acknowledging that biological quirks are best explained by common descent. I have never contended that poor design arguments, by themselves, are a slam dunk against ID. But in the context of everything else we know, I do think it’s a few more solid points that show that evolution is the best explanation and that ID comes up short at explaining the natural world.


I’m obviously not speaking for @swamidass here.

When talking of why design arguments don’t work, there’s the question of “don’t work for what?”

Discussions of apparently poor design, and how they evolved, are often interesting. So I suppose we could say that those work. What doesn’t work, is a “bad design” polemic as an attack on ID. And that doesn’t work because it doesn’t explain anything.

Gould and Lewontin came up with their “Spandrel” paper. But actually, their example of spandrels comes from the world of design. If you can have apparently bad design with evolution, then you can also have apparently bad design with design. And that’s why these arguments don’t work as arguments against ID.

If there were really a science of design, then the ID scientists should themselves be discussing bad designs that arose in the context of design.

“Bad design” arguments don’t work as arguments against ID. But the same sorts of discussions can be useful in explanations of why things are the way that they are.


Bad design arguments don’t disprove “Design”. They just disprove competent intelligent Design. If biological life was designed then the Designer was a bumbling incompetent klutz not capable of planning ahead. This is evidenced by the large number of kluged-together pieces often different from their original “design” function employed to get current biological systems to work.


So speaking of the “quirks” of the human nasal passages, how do they offer evidence of common descent?

Comparative anatomy with other primates? Nasal genetics?


That’s what I’m saying! So I guess you could say that suboptimal structure function and things like vestigial structures, anatomical homology, etc., are silent on the question of ID if it were being considered by itself. But these things fit so well within our understanding of common descent, that it’s strange to me to consider them neutral on the question of evolutionary theory. And since evolutionary theory and ID are in direct opposition, anything that fits well within evolutionary theory and is a conundrum for ID is weight on that side of the scale. (I agree that spandrels are not an argument FOR evolution, they are examples that remind us not to be too adaptationist WITHIN evolutionary thought.)


In the sinuses, it’s not the quirks that provide evidence of common descent. My point about the sinuses is that they demonstrate how evolution does not always generate elegant solutions, especially when many forces are applying selective pressures at the same time. The result is compromises, and evolutionary compromises are the explanation of most of our glitches and quirks. An intelligent designer would not be constrained the way evolution is, so I don’t see this as a neutral point, but that’s the nature of our disagreement.

But yes, comparative anatomy of the sinuses among primates - that’s the real support for the notion of common descendent and the rearrangement of the sinuses in our lineage helps to explain why they have the funny arrangement that they do. But if you don’t think in the evolutionary framework, you won’t see it that way. It’s like a Rorschach test.


That is what the “bad design” arguments are essentially about. Whatever function you can or can’t find for “bad designs”, the real evidence is how those features are distributed among species. You could argue about the down and upsides of an inverted retina, but the real evidence is that everything with a backbone has an inverted retina while certain invertebrate groups have a forward facing retina. The relationship between these seemingly independent features is beautifully explained by common descent.

“Bad design” arguments don’t work when we focus solely on our value judgments of the designs themselves outside the context of phylogeny, IMHO.

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Precisely. If Theory #1 predicts that we should see Observation A and Theory #2 predicts that we are just as likely to see Observation A as we are Observation B through Z, then Theory #1 wins out.

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@NLENTS thanks for picking up the conversation. Unfortunately, I am a bit swamped today. I’ll try and answer a bit if we can. When I have a moment, I will give brief overview of why I think it doesn’t work so well, and then reopen our thread on the design of the eye (Nathan Lents: Bad Design of the Eye?). I think this will be instructive as to why I think the argument ends up having some problems, in my view.

I also continue to reiterate that your angle on this is not idiosyncratic to you, and is probably the dominant view amoung biologists (not all the agreement you are getting on this thread). No one, especially not observers, should interpret this as a referendum on @NLENTS specifically. I am the outlier here, but I think I can also make my case coherently enough that you will at least understand where I am coming from.

I am sure of that, also. I’m not afraid of ideas different than mine. :slight_smile:


Agreed. I guess that helps explain my confusion. I am thinking of design arguments ONLY in the context of phylogeny. Without phylogeny as context, most commentary on design/optimal function is really just guess work (whether you’re down with evolution or not) and also you leave yourself open to the possibility that we just don’t know enough to really say whether its suboptimal. But when you bring in phylogeny and do some comparison, I think you’re on more solid ground. No one doubts that many vertebrates have excellent eyes, some better than any cephalopods. If you don’t accept common descent, that’s the end of the story. Within an evolutionary context, there’s so much more we can ask.

@NLENTS I just finished your book. (I am a slow reader) I found it to be an excellent summary on how humans came to be humans. The material on nutrition (including GULO) was excellent and explains a lot. While I agree that the book’s intent wasn’t to go after DI and their intelligent design nonsense, the book clearly refutes all their claims. We can call a lot of things about our bodies that we feel are bad design but the facts are that evolution isn’t about good or bad design. It is about survival of the genes, so given that we survived, well then our design is good enough. Certainly not perfect but certainly good enough to enjoy life while we are healthy. Thanks again for your contributions here.

I’m really trying to understand this. The nasal arrangement in humans does or does not provide evidence of common descent. They are or are not best explained by common descent.

Now I will admit that i do not have your book and i have not read it. But if it would help the conversation I would gladly purchase it. This is strictly a guess.

I would surmise that you do not argue for common descent when discussing the human sinuses but rather argue for evolution by means of an argument that what we see would not be expected of an intelligent designer but is what we would expect from a process like evolution. The issue of common descent probably doesn’t even come up. I could be totally wrong.

If I am correct then it is a “bad design” argument for evolution. This is not to say that there are no “strange quirks” that are best explained by common descent. If humans and mice share the exact same “strange quirk” for example. Any experts in the nasal anatomy of mice here?


This isn’t directed at Nathan, but I don’t believe I ever did receive a satisfactory answer to my question about what it is exactly that prevents evolution from achieving optimal designs. So why should we not expect optimal designs from evolution?

And then, of course, if it’s not an optimal design, that would be evidence against evolution, not evidence for evolution. Right?

The feedback from selection in evolutionary processes moves a species’ morphology towards local fitness maxima in the fitness landscape i.e. a place “good enough”. There is no pressure or requirement for evolution to move a species to an optimal absolute fitness maximum. So the answer is nothing prevents it but it’s not necessary and usual not obtained.

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Now if “evolution” does not predict optimal design and “evolution” does not predict sub-optimal design, then why should “sub-optimal” design be evidence for evolution any more than optimal design is evidence for evolution? Otoh, if it predicts both optimal and sub-optimal design, then the conclusion would always be, therefore evolution.

In case people have not caught on yet, these are the same sorts of objections to ID. What’s good for the goose is good for the gander.

Design predicts both optimal and sub-optimal design. Therefore any instance of either one is evidence for ID.

The point here being that the case for evolution ought to rest on something different than bad design.

5 posts were merged into an existing topic: Nathan Lents: Bad Design of the Eye?

Evolution predicts sub-optimal design will be much more common than optimal because there are many more ways to be “good enough” (especially when forced to reuse existing parts) than there are to be perfect. And that’s exactly what we find. Kludged together systems with repurposed parts whose function is just “good enough”.

Design doesn’t predict either because Design pushers won’t commit to hypothesizing about the abilities and available mechanisms of the Designer. Except maybe those who claim the Designer is their Omnipotent God in which case sub-optimal design needs explaining. “He works in mysterious ways” doesn’t cut the muster.

It does, in spades.

Yes. As pointed out before if biological life was Designed then the Designer was an incompetent klutz with no ability to plan in advance and who had to kludge together solutions on the fly. Not Very impressive for a Designer who supposedly created the whole universe just for us.

Sounds like a probability argument to me.