by Lenny Flank
(c) copyright 2006
This argument is a longtime creationist favorite because, they say, it comes from Darwin himself:
"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" (Darwin, "Origin of Species, 1859)
The creationists, of course, neglect to finish the rest of Darwin's paragraph:
"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 certainly 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, though insuperable by our imagination, should not be considered as subversive of the theory." (Darwin, "Origin of Species", 1859)
Nevertheless, creationists soon took to applying the "what good is half a . . . . ?" argument and applying it to anything and everything they could think of. The argument, put simply, is that no complex structure can appear through step-by-step evolution, since it would all have to appear at once with all its parts, or it would not work at all and would not be able to be selected into the next generation. Therefore, the argument goes, these complex structures must have been created, all at once, intact:
The living cell is a marvellous, complex piece of machinery. It contains energy converters (mitochondria), production factories (golgi bodies), and the ability to repair or duplicate itself. It also contains an information storage library within a substance called DNA (deoxyribonucleic). This DNA contains the information which is passed on to future generations. . . . No known mechanism of mutation, either at the gene level or the chromosome level has been discovered which will produce evolutionary advancement. This is particularly so because all molecules involved in replication (DNA, RNA, protein) are interdependent with each other, and do not function in isolation. In other words the cell and its genetic contents, give the appearance of having been an initially created complex unit ready to work." (J.G. Leslie, AIG, "In Brief—D.N.A. mutation and design", Creation Magazine, May 1984)
"Snakes move the way they do, because they have a distinctive backbone. To make a lizard or alligator into a snake, you would need to add special backbones, (vertebrae) in special places. Without these additional bones, snake movement just isn’t possible. Then there’s that mouth. You would need to add an extra row of teeth to start with, then specially reshape them. At the same time you must change and redesign the jaw with a new suspension unit, to give it the special unlockable snake-wide swallow ability. The skull would then need re-inforcing to give more protection to the brain, and then you would have to change the shape of the throat so that it could breathe as well as swallow. All this before we even consider how to add special ducts and hollows for the snake’s venom or saliva, change the lungs, rebuild the eyes, and so it goes on. Well, how would you make a snake? One way you wouldn’t, is by slow small changes (or mutations) to a legged reptile. No observed mutation can do anything like produce the special equipment in a snake, even if you started with a ‘soundly functional lizard’. Snakes have not evolved either slowly or rapidly from any other creatures we call reptiles. Not only is there no trace of transitional forms in the fossil record, but no one has ever seen a mutated lizard or snake which would give a clue as to how it could have evolved to become so legless, and yet so perfectly adapted to being a snake. In fact, snakes look so deliberately designed that scientists who say otherwise, haven’t really got a leg to stand on!" (AIG, Creation Magazine, April 1983)
"For any person to believe that the human temperature control system which works so consistently and involves such complex engineering techniques is a product of an accidental process called evolution, means they are simply ignoring every discovery we have made to date about the science of engineering construction." (AIG, "Design—‘Man Computerised Thermostat’", Creation Magazine, Jan 1983)
"The tiny bombardier beetle could not possibly have evolved. His defence mechanism is amazingly complicated, and could only have been created with all the parts working together perfectly. . . . Common sense tells us that this amazing little insect cannon which can fire four or five ‘bombs’ in succession could not have evolved piece by piece. Explosive chemicals, inhibitor, enzymes, glands, combustion tubes, sensory communication, muscles to direct the combustion tubes and reflex nervous systems—all had to work perfectly the very first time—or all hopes for ‘Bomby’ and his children would have exploded!" (AIG, Creation Magazine, Dec 1989)
If the mammary glands, or breasts of animals that nurse their young, evolved slowly over millions of years, how did the young survive until these complex organs were perfected? Mammary glands are complex organs which will not produce milk until the whole complex system is complete. (Jerry Bergman, AIG Creation Magazine, March 1991)
How to obtain the various unique structures of the koala from the so-called ancestral types, each intermediate stage being fully functional and better adapted than its preceding ancestral form, stretches the imagination beyond limit. . . . The koala displays all the evidence of planned, purposeful design at the hand of a Master Designer. (Andrew Snelling, AIG Creation Magazine, Sept 1989)
Some have come to call this the "argument from personal incredulity" -- "I can't see how this could have happened, therefore it could not have happened". Others have pointed out that it's just another version of "god of the gaps". It is virtually impossible to deal with these creationist arguments since (1) the creationist can multiply them indefinitely simply by asking about each and every living organism on earth, and (2) no explanation will satisfy them unless it specifies every genetic change in every individual organism within every member of the evolutionary lineage -- an impossible task for anyone.
Nevertheless, evidence does exist illustrating how many of these supposedly "unevolvable structures" could have evolved. So, how can an eye evolve step by step? Well, we start with an eyespot, a small spot on the skin of a small invertebrate that contains pigments (and nearly ALL organisms have pigments in their skin). Some pigments (such as rhodopsin) are light-sensitive and produce chemical changes in the presence of light. Hence, an organism with a crude "eyespot" like this would have the selective advantage of telling light from dark -- all with nothing but a patch of pigmented skin. This is the sort of eye that many unicellular organisms and some very simple multicellular organisms like worms have.
Let's make a small improvement, and add a mutation which allows a layer of transparent skin to cover the eyespot (two or three genes at most -- largely a change in the growth pattern of the skin). This will protect it from damage and give a selective advantage to the worms that have it.
Now let's make a minor change in how the pigmented spot grows, and change one regulatory gene to make the central portion of the spot grow faster than the outer portions. This has the effect of pulling the center of the spot in to make a shallow dish or bowl shaped area, lined with light-sensitive pigment. A simple change, but a very large advantage -- it allows differing areas of pigment to react according to the way in which light is falling on it -- allowing the organism to detect the direction of the light. It is the type of eye found in some worms and in some mollusks (clams and scallops).
Another small change in regulatory genes deepens the cup, making it more and more direction-sensitive (and thus gives more and more selective advantage). The result is a hollow ball, lined with light-sensitive cells, with a small pinhole in front, and a fiber at the back that is connected to the nervous system. This is nothing but a pinhole camera. It gives maximum direction sensitivity, and also allows a crude image to be focused on the back of the eyeball, where each individual light-sensitive cell is impinged upon by differing intensities of light, thus providing the nervous system with the information necessary to form an image. This is the type of eyeball found in the nautilus.
Next, another minor change in regulatory genes causes the transparent skin covering the front of the eye to thicken. This changes the refraction of the light entering the eyeball. Mutations which allow the center of this transparent layer to grow more quickly than the edges, form a semi-spherical transparent layer in the front of the eyeball -- a lens. This is the type of eye that many fish have.
Now, a mutation which doubles the transparent layer, allowing the inner one to grow and form the spherical lens, while the outer layer remains thin. Now we have a cornea. Just as in many fish today.
Now, we add a change in regulatory genes which alters the growth pattern of some of the muscles and connective tissue just inside the cornea, one which allows them to form a flat circular sheet in front of the lens, which can be pulled in or out against the sides of the eyeball. Now we have an iris. The same sort of eye found in many fish today.
Now, mutations which change the rate at which different portions of the lends grow will change its focusing length and thus the sharpness of the image it is able to form. Since sharper images will be selected for, these will tend to transform the spherical lens into a lenticular one, fastened to the side of the eyeball by the same connective tissue and muscles which held the original transparent layer in place (and from which the iris developed). As yet, these muscles are incapable of changing the focal length of the eye by pulling the lens into different shapes. At best, they can pull the lens a short distance to and fro to change the focal length. This is the same sort of eye that modern snakes and frogs have.
Mutations which produce stronger and more controlled muscles will allow the eye to be focused by pulling on the lens to alter its shape, rather than by moving the whole lens back and forth. And this is the type of eye found in birds and mammals.
And there we have an eye, produced step by step, each with just small changes, each change being fully functional and a selective advantage for the organism that has it.
And how do we know that each of these steps is not only possible, but actually works? Because all of them still exist today in various organisms.