Darwinist Francisco Ayala writes, “The imperfection of structures is evidence for evolution and contrary to the arguments for intelligent design.” He writes,
Consider the human jaw. Because we have too many teeth for the jaw’s size, wisdom teeth need to be removed, and orthodontists make a decent living straightening the others. Would we want to blame God for this blunder? A human engineer would have done better.
One difficulty with attributing the design of organisms to the Creator is that imperfections and defects pervade the living world. In the human eye, for example, the visual nerve fibers in the eye converge on an area of the retina to form the optic nerve and thus create a blind spot; squids and octopuses do not have this defect. Defective design would seem incompatible with an omnipotent intelligent designer.
Skeptic Michael Shermer asks, “Why would an intelligent designer have built an eye upside down and backwards?” Do flaws in design preclude a designer?
RESPONSE: Several responses can be made:
First, the argument from design doesn’t give evidence for the goodness of God –but the greatness of God. Our perception of a moral law gives evidence for a moral God (e.g. Moral Argument). However, this subject is not being discussed under the argument for design. It would be similar to a skeptic asking, “How does the argument from design demonstrate that Jesus rose from the dead?” That’s just it. It doesn’t. Most Christian apologists use a cumulative case for Christianity, utilizing several arguments, rather than just one overwhelmingly sufficient proof.
Second, even bad design proves design. For instance, a junker car might be poorly designed, but it is still designed. Consider looking at a picture of a medieval torture rack. While we would certainly consider the designer evil, we would still have to consider the object designed. For this reason, this objection confuses morality with design.
Third, some designs turn out to be good after all. For instance, consider so-called “junk DNA.” Junk DNA is the extra DNA that does not code for proteins in the cell. Naturalists formerly claimed that junk DNA had no purpose at all. And, if it had no purpose, then a designer wouldn’t have included it in the genetic code. However, recently, microbiologists have discovered that junk DNA actually does have a function in the cell. More and more of its function is being discovered, as microbiology investigates this.
Fourth, some trade-offs in design cannot be avoided. For instance, when we engineer a car, should we design it for speed or for size? Favoring one will necessarily decrease the other. Similarly, in nature, strengthening a predator would necessarily weaken the prey. Dembski writes, “Our view of design is shaped too much by sports competitions. We always want to go faster, higher, longer and stronger. But do we really want to go faster, higher, longer and stronger without limit? Of course not. It is precisely the limits on functionalities that make the game of life interesting.”
Fifth, some biological systems are not designed, but have mutated. We cannot ascribe every design flaw to the original design, because mutation and natural selection has certainly played a role in our current adaptability. Dembski explains, “The first question that needs to be answered… about any biological structure, is whether it displays clear marks of intelligence. The design theorist is not committed to every biological structure being designed. Naturalistic mechanisms like mutation and selection do operate in natural history.” Finally, Dembski notes the irony of criticizing the design flaws of the human eye: “There’s also an irony here worth noting: the very visual system that is supposed to be so poorly designed and that no self-respecting designer would have constructed is nonetheless good enough to tell us that the eye is inferior.”
 Ayala, Francisco José. Darwin and Intelligent Design. Minneapolis: Fortress, 2006. 34.
 Ayala, Francisco José. Darwin and Intelligent Design. Minneapolis: Fortress, 2006. 86.
 Ayala, Francisco José. Darwin and Intelligent Design. Minneapolis: Fortress, 2006. 85.
 Shermer, Michael. Why Darwin Matters: The Case against Intelligent Design. New York: Times, 2006. 17.
 Dembski, William A. The Design Revolution: Answering the Toughest Questions about Intelligent Design. Downers Grove, IL: InterVarsity, 2004. 61.
 Dembski, William A. The Design Revolution: Answering the Toughest Questions about Intelligent Design. Downers Grove, IL: InterVarsity, 2004. 63.
 Dembski, William A. The Design Revolution: Answering the Toughest Questions about Intelligent Design. Downers Grove, IL: InterVarsity, 2004. 60.