A New Article in <i>Salvo</i> Magazine Rebuts Objections that the Vertebrate Eye is Poorly Designed - Evolution News & Views

Evolution News and Views (ENV) provides original reporting and analysis about the debate over intelligent design and evolution, including breaking news about scientific research.

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A New Article in Salvo Magazine Rebuts Objections that the Vertebrate Eye is Poorly Designed

Salvo MagazineIf you're looking for a great Christmas gift for students, Generation Xers, or anyone born since, consider a subscription to Salvo Magazine. It provides credible and well-written commentary on social and scientific issues -- including a wealth of articles about intelligent design (ID). Speaking of design, it's also a very handsome-looking publication.

In the latest issue, ENV's Casey Luskin has an article dealing with biomimetics, but it also looks at rebuttals to the classical arguments that the vertebrate eye was "poorly designed." You can read the whole article, "Eyeballing Design," here. Excerpt:

Some materialists attack design arguments not by alleging that biological systems lack high levels of specified complexity, but by alleging that they are full of "flaws." Yet anyone who has used Microsoft Windows is painfully aware that flawed designs are still designed. But theistic evolutionist biologist Kenneth Miller argues that evolution would naturally lead us to expect the biological world to be full of "cobbled together" kluges that reflect the clumsy, undirected Darwinian process.5

For example, Miller maintains that the vertebrate eye was not intelligently designed because the optic nerve extends over the retina instead of going out the back of the eye -- an alleged design flaw. According to Miller, "visual quality is degraded because light scatters as it passes through several layers of cellular wiring before reaching the retina."

Similarly, Richard Dawkins contends that the retina is "wired in backwards" because light-sensitive cells face away from the incoming light, which is partly blocked by the optic nerve. In Dawkins's ever-humble opinion, the vertebrate eye is "the design of a complete idiot."6

A closer examination shows that the design of the vertebrate eye works far better than Dawkins and Miller lets on.

Dawkins concedes that the optic nerve's impact on vision is "probably not much," but the negative effect is even less than he admits. Only if you cover one eye and stare directly at a fixed point does a tiny "blind spot" appear in your peripheral vision as a result of the optic nerve covering the retina. When both eyes are functional, the brain compensates for the blind spot by meshing the visual fields of both eyes. Under normal circumstances, the nerves' wiring does nothing to hinder vision.

Nonetheless, Dawkins argues that even if the design works, it would "offend any tidy-minded engineer." But the overall design of the eye actually optimizes visual acuity.

To achieve the high-quality vision that vertebrates need, retinal cells require a large blood supply. By facing the photoreceptor cells toward the back of the retina, and extending the optic nerve out over them, the cells are able to plug directly into the blood vessels that feed the eye, maximizing access to blood.

Pro-ID biologist George Ayoub suggests a thought experiment where the optic nerve goes out the back of the retina, the way Miller and Dawkins claim it ought to be wired. Ayoub finds that this design would interfere with blood supply, as the nerve would crowd out blood vessels. In this case, the only means of restoring blood supply would be to place capillaries over the retina -- but this change would block even more light than the optic nerve does under the actual design.

Ayoub concludes: "In trying to eliminate the blind spot, we have generated a host of new and more severe functional problems to solve."7

In 2010, two eye specialists made a remarkable discovery that showed the elegant mechanism found in vertebrate eyes to solve the problem of any blockage of light due to the position of the optic nerve. Special "glial cells" sit over the retina and act like fiber-optic cables to channel light through the optic nerve wires directly onto the photoreceptor cells. According to New Scientist, these funnel-shaped cells prevent scattering of light and "act as light filters, keeping images clear." 8

Ken Miller acknowledges that an intelligent designer "would choose the orientation that produces the highest degree of visual quality." Yet that seems to be exactly what we find in the vertebrate eye. In fact, the team of scientists who determined the function of glial cells concluded that the "retina is revealed as an optimal structure designed for improving the sharpness of images."

ID-theorist William Dembski has observed that "no one has demonstrated how the eye's function might be improved without diminishing its visual speed, sensitivity, and resolution."9 It's therefore unsurprising that optics engineers study the eye to improve camera technology. According to another tech article:Borrowing one of nature's best designs, U.S. scientists have built an eye-shaped camera using standard sensor materials and say it could improve the performance of digital cameras and enhance imaging of the human body.The article reported that the "digital camera has the size, shape and layout of a human eye" because "the curved shape greatly improves the field of vision, bringing the whole picture into focus."10

It seems that human eyes are so poorly designed that engineers regularly mimic them.

References Cited:

5. Kenneth R. Miller, "Life's Grand Design," Technology Review (February/March 1994), pp. 25-32.
6. Richard Dawkins, The Greatest Show on Earth: The Evidence for Evolution (Free Press, 2009), p. 354.
7. George Ayoub, "On the Design of the Vertebrate Retina," Origins & Design, vol. 17:1 (Winter 1996).
8. Kate McAlpine, "Evolution gave flawed eye better vision," New Scientist (May 6, 2010).
9. William Dembski & Sean McDowell, Understanding Intelligent Design: Everything You Need to Know in Plain Language (Harvest House, 2008), p. 53.
10. Julie Steenhuysen, "Eye spy: U.S. scientists develop eye-shaped camera," Reuters (August 6, 2008).


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