Side Comments on Bad Design of the Eye

Continuing the discussion from Nathan Lents: Bad Design of the Eye?

The side conversation can begin now.

Outlier of a very small and recent group, Joshua! 1900 years of Christian witness are with you.

An atheist would use the bad design argument to show that God doesn’t exist. But I’m not sure about the Christian writer. Is the aim to show that “God creating through evolution” is a crappy way to do it? Or that evolution is autonomous of God (the dualistic demiurge argument)? Or is it just because Intelligent Design uses the word “design” and so anything that discredits that must be good, even if it louses up the doctrine of creation?

One simple conclusion is that, deliberately or not, it directly contradicts the biblical witness. Psalm 94 says:" Does he who formed the eye not see?" The “senseless ones among the people” turn out to be able to demolish the psalmist’s argument, because he who formed the eye was, in fact, a blind watchmaker doing a bad job. The psalmist has not demonstrated God’s ability to see and judge, because his major premise was overturned by “bad design”. Good result, guys!


Maybe but scientists are my tribe. I am an outlier among them.

I agree with you, Josh. I don’t like calling them bad designs. I like biological quirks or oddities. I think Elliot Sober and Greg Dawes thoroughly rebuted the bad design argument. I think it’s only evidence against design if design is understood as special creation and separate ancestry. Common ancestry is the best explanation for these quirks. What we see as a bad design may be the best way of doing things given the constraints of biology. Common ancestry can’t escape these contraints where design could. So i think these “bad designs” are more evidence for common ancestry than against design


In which case, we get the question why God would choose to use a faulty tool such as common descent.
I am impressed that science can detect bad design . While it fails to detect design.
Quite a feat.

There were arguments that preceded Darwin and these fall along the lines of “would God necessarily create the best of all possible worlds?” and “do we live in the ‘best of all possible worlds?’” So, philosophically, one could at least go back to Leibnitz, circa 1710. And the response in “Candide” by Voltaire (1760’s). It’s generally related to the problem of evil.

I’ve got artificial parts sewn and/or affixed into my body that would suggest some degree of sub-optimality or trade-offs if we assume that humans were specifically designed by a divine agent.

Side note: What’s interesting in the ‘bad design’ sphere is that ENV folks felt the need to defend the optimality of various imperfect biological systems and components. Why?

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The non theist certainly doesn’t have to answer that question. But it does raise interesting questions for theist. And I think they have reasonsble and plausible answers that are consistent with God’s character.

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Even this atheist agrees with much of what you have said on the subject. “Bad design” requires a lot of subjective and arbitrary judgments. I think we could say that the vertebrate retina is suboptimal and could have been different. We could certainly say that humans wouldn’t design such an eye if we were using a top-down approach to the design. Even in our own designed cameras we don’t have the wires running in front of the CCD, and we would never design a camera in such a way.

Here is a crude diagram of the cephalopod and vertebrate eyes:


In the vertebrate eye, the nerves running from the photoreceptors are in the light path, and then have to punch through the retina in order to get the nerve impulses to the brain. Having the nerves (and blood vessels) in front of the photoreceptors decreases resolution and sensitivity. The cephalopod eye has the photorecpetors right out front and the nerves exit out the back of the retina. The cephalopod eye is more optimal for resolution and sensitivity.

If these eyes were produced through a bottom-up approach (i.e. each step is contingent on the step before it) then it makes a lot more sense. The early vertebrate photoreceptors had nerves running in front of them. Sensing light was more advantageous than not sensing light, so this adaptation was kept. Everything else was built on this foundation which is why there are suboptimal features. A bottom-up approach can only tinker with what it starts with.


This seems highly doubtful to me. For several reasons I’ll explain later. Perhaps most obviously, the nerves are transparent.

The glass in this window is transparent:

Not a valid analogy. There is no evidence the distortion is bad for the eye. To the contrary, some of the distortion improves the human eye relative to cephalopods.

So it is the cephalopod eye that is suboptimal?

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I’ll explain next week with lents. Most likely though is neutral. In fact it is neutral till proven otherwise.

A better term than “bad design” is “historically constrained”, i.e. dependent on previous versions of the system and therefore almost certain to be globally suboptimal.


That is a much better term. That is the key point. There is a historical record there, which is strongest evidence for common descent when it is demonstrably neutral.

I’d say it’s pretty good when it’s demonstrably advantageous (exact convergence being rare), and better when it’s demonstrably neutral, but even when a trait is advantageous, if it’s suboptimal that’s extra evidence for common descent unless you postulate a problematic sort of creator: one who’s malicious, incompetent, crazy, or is himself forced to work with some kind of historical constraints.

Now of course creationists commonly invoke the Fall to account for any suboptimality, but even that can’t explain suboptimality that’s Historically Constrained ™.


I’m not sure constrained is quite right…but I get your point and largely agree. The big point though is bad design is not quite right. It would be better to say that it looks like shared history.


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And more susceptible to detachment from the retina due to fluid leakage. I call it a bad design that is fixable by modern science and technology.