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An Old, Out of Context, Quotation

"To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree."

- Charles Darwin in The Origin of Species, J. M. Dent & Sons Ltd, London, 1971, p. 167. (p. 18 of The Revised Quote Book)

Darwin is not a "modern source." Furthermore, this quotation has been lifted out of context. According to the edition of The Origin of Species published by Encyclopedia Britannica, Inc., 1952 (in the Great Books series), here is the entire quotation in context:

"To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of Spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree. When it was first said that the sun stood still and the world turned round, the common sense of mankind declared the doctrine false; but the old saying of Vox populi, vox Dei ["the voice of the people = the voice of God "], as every philosopher knows, cannot be trusted in science. Reason tells me, that if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist, each grade being useful to its possessor, as is certain the case; if further, the eye ever varies and the variations be inherited, as is likewise certainly the case; and if such variations should be useful to any animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, should not be considered as subversive of the theory."

Darwin then went on to describe how some simple animals have only "aggregates of pigment-cells...without any nerves ... [which] serve only to distinguish light from darkness." Then, in animals a bit more complex, like "star-fish," there exist "small depressions in the layer of [light-sensitive cells] -- depressions which are "filled ... with transparent gelatinous matter and have a clear outer covering, "like the cornea in the higher animals." These eyes lack a lens, but the fact that the light sensitive pigment lies in a "depression" in the skin makes it possible for the animal to tell more precisely from what direction the light is coming. And the more cup-shaped the depression, the better it helps "focus" the image like a simple "box-camera" may do, even without a lens. Likewise in the human embryo, the eye is formed from a "sack-like fold in the skin."

George Gaylord Simpson in The Meaning of Evolution, points out that the different species of modern snail have every intermediate form of eye from a light-sensitive spot to a full lens-and-retina eye.

Neither would all the modifications necessary to improve clarity of vision need to be accomplished by a single method of change, nor by changes occurring simultaneously in the eye as a whole. For instance, Darwin continued: "If a lens has too short or too long a focus, it may be amended either by an alteration of curvature, or an alteration of density; if the curvature be irregular, and the rays do not converge to a point, then any increased regularity of curvature will be an improvement. So [also] the contraction of the iris and the muscular movements of the eye are neither of them essential to vision, but only improvements which might have been added and perfected at any stage of the construction of the instrument. Within the highest division of the animal kingdom, namely the Vertebrata [animals with backbones], we can start from an eye so simple, that it consists, as in the lancelet [small sea animals which evolutionists think resemble the earliest ancestors of fish], of a little sack of transparent skin, furnished with a nerve and lined with pigment, but destitute of any other apparatus. In fishes and reptiles ... the range of gradations of dioptric [optical] structures is very great ... In living bodies, variations will cause the slight modifications, generation will multiply them almost infinitely, and natural selection will pick out with unerring skill each improvement. Let this process go on for millions of years; and during each year on millions of individuals of many kinds; and may we not believe that a living optical instrument might thus be formed as superior to one of glass as the works of the Creator are to those of man?"

That is what Darwin wrote in context. Obviously, he was not admitting that the origin of the eye was an insuperable difficulty, as the editors of The Revised Quote Book wish to deceive their readers into thinking.

Coincidentally, the same week that I checked on the above quotation, the evolutionist, Stephen J. Gould, wrote an article on it! ("Common Pathways of Illumination," Natural History 12/94, p. 10) According to Gould, "Anti-evolutionists continually cite this passage as supposed evidence that Darwin himself threw in the towel when faced with truly difficult and inherently implausible cases. But if they would only read the very next sentence[s], they would grasp Darwin's real reason for speaking of absurdity 'in the highest possible degree.' (Either they have read these following lines and have consciously suppressed them, an indictment of dishonesty; or they have never read them and have merely copied the half quotation from another source, a proof of inexcusable sloppiness. Darwin set up the overt 'absurdity' to display the power of natural selection in resolving even the most difficult cases -- the ones that initially strike us as intractable in principle. The very next liner, give three reasons all supported by copious evidence for resolving the absurdity and accepting evolutionary development as the cause of optimally complex structures."

Besides Gould's article there have appeared several others on the topic of the evolution of the eye, demonstrating that such an evolution is far from "absurd," but rather is entirely plausible.

See professor Kenneth R. Miller's excellent article on eye evolution, "Life's Grand Design" (Technology Review, v. 97, no. 2, Feb./Mar. 1994, pp. 24-32).

See also D. E. Nilsson and S. Pelger's article, "A pessimistic estimate of the time required for an eye to evolve" (Proceedings of the Royal Society B, 1994, v.. 256, pp. 53-58).

In his recent book, River Out of Eden (Basic Books, 1995), Richard Dawkins points out how Nilsson and Pelger set up a computer model of evolving eyes to determine if a smooth gradient of change exists from a pigmented eye spot to the camera eye with a lens and cornea, and how long it would take such a transformation to occur. They employed pessimistic figures for the amounts of change possible per generation -- giving their model only 50% "heritability" (many human traits are over 50% inheritable), and chose pessimistic values for the coefficient of variation (how much variation there typically is in a population). And they determined that Darwinian evolution could produce a good camera eye in less than a half a million years! That's a mere "blink of the eye" in geologic time!

Since an eye's efficiency can be easily measured using elementary optics, their computer simulation had more validity than, say, trying to measure how subtle anatomical changes increased the efficiency of a cheetah's speed and agility.

"Nilsson and Pelger began with a flat retina atop a flat pigment layer and surmounted by a flat, protective transparent layer. The transparent layer was allowed to undergo localized random mutations of its refractive index. They then let the model deform itself at random, constrained only by the requirement that any change must be small and must be an improvement on what went before. The results were swift and decisive ... leading unhesitatingly from the flat beginning through a shallow indentation to a steadily deepening cup. The transparent layer thickened to fill the cup and smoothly bulged its outer surface in a curve [the cornea]. And then, almost like a conjuring trick, a portion of this transparent filling condensed into a local, spherical subregion of higher refractive index [a lens]." -- Dawkins, pp. 80-81

And the lens that formed was not of a uniform refractive index, but was "graded," just like real eyes, with the highest refractive index near the center of the lens! And it was graded according to the optimum ratio for vision, known as "Mattiessen's ratio."

I should add that Nilsson and Pelger's computer simulation never produced an eye that combined the focus of two lenses -- one placed directly behind the other -- lenses that could slide toward and away from each other to produce added magnification and "close-ups" of small objects and far away objects, as in a "zoom camera." Instead, the best "zoom" available to us humans is to bring the newsprint closer to our eyes! I guess the "Biblical Creator" in his infinite wisdom could not design eyes any better than natural selection could. However, robots of the future will undoubtedly have such "extra" design features added by their human creators.

Other recent articles, like Gould's, mentioned above, have pointed out how a common genetic key triggers the development of eyes of vastly different construction in animals as varied as flies and mice (in vertebrates and invertebrates). So, all eyes may originate from a common ancestor that evolved this genetic trigger. See for instance, Peter Monagham's article, "Revelations from Fruit Flies" (Chronicle of Higher Education A8-A9, May 26, 1995). And also see Carol Yaesuk Yoon's article, "The Wizard of Eyes: Evolution Creates Novelties by Varying the Same Old Tricks" (New York Times, Nov- 1, pp. C1, C11).

Also see the articles on eye evolution in Science, v. 265, no. 5173, Aug. 5, 1994, pp. 742 & 785; and in Nature, v. 368, Apr. 21, 1994, p. 690.

As an aside, I must mention a recent article in Discover magazine (Jan. 1996), titled, "From Fin to Hand," that discussed how merely extending the length of time a particular gene remained activated during embryological development, had a lot to do with turning a fin into a hand! So, minor mutations of embryologic growth patterns might produce larger effects than expected, even perhaps in the story of eye evolution from an eyespot to a skin dimple to an eye cup, etc.

E.T. BABINSKI

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