Rebutting Karl Giberson and Francis Collins' Argument for Eye Evolution
Over time mutations in DNA can produce novel features, as we noted earlier, like feathers from scales or eyes from light-sensitive pigment. (p. 35)
There's no citation for their sentence, and Giberson and Collins do not provide us with any documentation to back it their claim. In fact, they give no further discussion of this point, as if they want the reader to simply take their assertion on faith.
In the previous post we showed that the evidence has refuted the hypothesis that feathers evolved from scales. Let's now test their claim that mutations over time produced eyes from light-sensitive pigments.
Light-Sensitive Pigments Aren't the Only Starting Point
Classical explanations for the evolution of the eye assume that the eye can be built via such small, step-by-step changes. Darwin believed the eye could evolve under a scheme of "fine gradations," but standard evolutionary accounts for the origin of the eye fall far short of that mark: they lack details, ignore biochemical complexity, and in fact invoke sudden and abrupt appearance of key components of eye morphology.
For example, all accounts of eye evolution start with a fully functional eyespot, not mere "light-sensitive pigments." As Mark Ridley's textbook Evolution explains, the commonly-cited model of eye evolution
began with a crude light-sensitive organ consisting of a layer of light-sensitive cells sandwiched between a darkened layer of cells and a transparent protective layer above. The simulation, therefore, does not cover the complete evolution of an eye. To begin with, it takes light sensitive cells as given ... and at the other end it ignores the evolution of advanced perceptual skills (which are more a problem in the evolution of the brain than the eye).
(Matt Ridley, Evolution, p. 261 (3rd Ed., Blackwell, 2004).)
Ridley calls it "not absurd" (p. 261) to assume simple light sensitive cells as a starting point, but evolutionary biologist Sean B. Carroll cautions to "not be fooled by these eyes' simple construction and appearance. They are built with and use many of the ingredients used in fancier eyes." (Sean B. Carroll, The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution, p. 197 (W. W. Norton, 2006).)
Likewise, after reviewing some of the basic biochemistry underlying the processes that allow vision, Michael Behe (responding to Richard Dawkins) observes: "Remember that the 'light-sensitive spot' that Dawkins takes as his starting point requires a cascade of factors including 11-cis retinal and rhodopsin, to function. Dawkins doesn't mention them." (Michael J. Behe, Darwin's Black Box: The Biochemical Challenge to Evolution, p. 38 (Free Press, 1996).)
In fact, no accounts for the evolution of the eye provide an account for this always-assumed starting point, which is far more complex than a few "light-sensitive pigments."
Other Eye Parts Appear Abruptly
In addition to assuming the abrupt appearance of a fully-functional eyespot, standard accounts of eye-evolution invoke the abrupt appearance of key features of advanced eyes such as the lens, cornea, and iris. Of course the emplacement of each of these features--fully formed and intact--would undoubtedly increase visual acuity. But where did these parts suddenly come from in the first place? As Scott Gilbert put it, such evolutionary accounts are "good at modelling the survival of the fittest, but not the arrival of the fittest." (John Whitfield, "Biological Theory: Postmodern evolution?," Nature, Vol. 455:281-284 (2008).)
As an example of these hyper-simplistic accounts of eye evolution, Francisco Ayala's book Darwin's Gift asserts that, "Further steps--the deposition of pigment around the spot, configuration of cells into a cuplike shape, thickening of the epidermis leading to the development of a lens, development of muscles to move the eyes and nerves to transmit optical signals to the brain--gradually led to the highly developed eyes of vertebrates and celphalopod (octopuses and squids) and to the compound eyes of insects." (Francisco J. Ayala, Darwin's Gift to Science and Religion, p. 146 (Joseph Henry Press, 2007).)
Ayala's explanation is vague and shows no appreciation for the biochemical complexity of these visual organs. Thus, regarding the configuration of cells into a cuplike shape, Michael Behe asks (while responding to Richard Dawkins on the same point):
And where did the "little cup" come from? A ball of cells--from which the cup must be made--will tend to be rounded unless held in the correct shape by molecular supports. In fact, there are dozens of complex proteins involved in maintaining cell shape, and dozens more that control extracellular structure; in their absence, cells take on the shape of so many soap bubbles. Do these structures represent single-step mutations? Dawkins did not tell us how the apparently simple "cup" shape came to be.
(Michael J. Behe, Darwin's Black Box: The Biochemical Challenge to Evolution, pg. 15 (Free Press, 1996).)
Likewise, mathematician and philosopher David Berlinski has assessed the alleged "intermediates" for the evolution of the eye and observes that the transmission of data signals from the eye to a central nervous system for data processing, which can then output some behavioral response, comprises an integrated system that is not amenable to stepwise evolution:
Light strikes the eye in the form of photons, but the optic nerve conveys electrical impulses to the brain. Acting as a sophisticated transducer, the eye must mediate between two different physical signals. The retinal cells that figure in Dawkins' account are connected to horizontal cells; these shuttle information laterally between photoreceptors in order to smooth the visual signal. Amacrine cells act to filter the signal. Bipolar cells convey visual information further to ganglion cells, which in turn conduct information to the optic nerve. The system gives every indication of being tightly integrated, its parts mutually dependent.
The very problem that Darwin's theory was designed to evade now reappears. Like vibrations passing through a spider's web, changes to any part of the eye, if they are to improve vision, must bring about changes throughout the optical system. Without a correlative increase in the size and complexity of the optic nerve, an increase in the number of photoreceptive membranes can have no effect. A change in the optic nerve must in turn induce corresponding neurological changes in the brain. If these changes come about simultaneously, it makes no sense to talk of a gradual ascent of Mount Improbable. If they do not come about simultaneously, it is not clear why they should come about at all.
The same problem reappears at the level of biochemistry. Dawkins has framed his discussion in terms of gross anatomy. Each anatomical change that he describes requires a number of coordinate biochemical steps. "[T]he anatomical steps and structures that Darwin thought were so simple," the biochemist Mike Behe remarks in a provocative new book (Darwin's Black Box), "actually involve staggeringly complicated biochemical processes." A number of separate biochemical events are required simply to begin the process of curving a layer of proteins to form a lens. What initiates the sequence? How is it coordinated? And how controlled? On these absolutely fundamental matters, Dawkins has nothing whatsoever to say.
(David Berlinski, "Keeping an Eye on Evolution: Richard Dawkins, a relentless Darwinian spear carrier, trips over Mount Improbable," Review of Climbing Mount Improbable by Richard Dawkins (W. H. Norton & Company, Inc. 1996)," in The Globe & Mail (November 2, 1996).))
In sum, standard accounts of eye evolution fail to explain the evolution of key eye features like:
The biochemical evolution of the fundamental ability to sense light The origin of the first "light sensitive spot" The origin of neurological pathways to transmit the optical signal to a brain The origin of a behavioral response to allow the sensing of light to give some behavioral advantage to the organism The origin of the lens, cornea and iris in vertebrates The origin of the compound eye in arthropods
At most, accounts of the evolution of the eye provide a stepwise explanation of "fine gradations" for the origin of more or less one single feature: the increased concavity of eye shape. But that does not explain the origin of the eye.
Giberson and Collins claim that "[o]ver time mutations in DNA can produce novel features ... like ... eyes from light-sensitive pigment." But their vague argument provides us with no citations or discussion of the evidence to back up that claim. In fact, much evidence not cited in their book can be found which challenges their assertion. It seems that they simply want us to take their evolutionary claims about the power of mutation on faith.