Can Evolution Produce an Eye? Not a Chance!
by David N. Menton, Ph.D.
The human brain consists of approximately 12 billion cells, forming 120 trillion interconnections. The light sensitive retina of the eye (which is really part of the brain) contains over 10 million photoreceptor cells. These cells capture the light pattern formed by the lens and convert it into complex electrical signals, which are then sent to a special area of the brain where they are transformed into the sensation we call vision.
In an article in Byte magazine (April 1985), John Stevens compares the signal processing ability of the cells in the retina with that of the most sophisticated computer designed by man, the Cray supercomputer:
“While today’s digital hardware is extremely impressive, it is clear that the human retina’s real-time performance goes unchallenged. Actually, to simulate 10 milliseconds (one hundredth of a second) of the complete processing of even a single nerve cell from the retina would require the solution of about 500 simultaneous nonlinear differential equations 100 times and would take at least several minutes of processing time on a Cray supercomputer. Keeping in mind that there are 10 million or more such cells interacting with each other in complex ways, it would take a minimum of 100 years of Cray time to simulate what takes place in your eye many times every second.”
If a supercomputer is obviously the product of intelligent design, how much more obviously is the eye a product of intelligent design? And yet, evolutionists are dead certain that the human eye (and everything else in nature) came into being by pure chance and the intrinsic properties of nature! Evolutionists occasionally admit that it is difficult for even them to believe such a thing. Ernst Mayr, for example, has conceded that:
“…it is a considerable strain on one’s credulity to assume that finely balanced systems such as certain sense organs (the eye of vertebrates, or the bird’s feather) could be improved by random mutations.” (Systematics and the Origin of Species, p. 296).
Evolutionists rarely attempt to calculate the probability of chance occurrence in their imagined evolutionary scenarios. While there is no way to measure the probability of chance occurrence of something as complex as the eye, there are ways to calculate the probability of the chance occurrence of individual protein molecules that are essential to life. Over a thousand different kinds of proteins have been identified in the human body, and each has a unique chemical composition necessary for its own particular function.
Proteins are polymers, whose chemical composition depends on the arrangement of many smaller subunits called amino acids. There are 20 different kinds of amino acids that are used to construct the proteins of all living organisms, including man. These amino acids are linked together end-to-end (like a string of beads) to form a single protein macromolecule. The average protein consists of a string of 500 amino acids. The total number of combinations of 20 different amino acids in such a string is, for all practical purposes, unlimited. Each protein in our body, however, must contain a specific sequence of amino acids if it is to function properly. It is the task of the genetic system in our cells to organize the assembly of the amino acids into precisely the right sequence for each protein.
Proteins have been called informational macromolecules because their amino acid sequence spells out information, in much the same way as the letters of the alphabet can be arranged to form a sentence or paragraph. We can appreciate the improbability of randomly assembling one of the essential proteins of life by considering the probability of randomly assembling the letters of the alphabet to form even a simple phrase in English.
Imagine if we were to try to spell out the 23 letters and spaces in the phrase “THE THEORY OF EVOLUTION” by using the evolutionary principle of chance. We might proceed by randomly drawing characters from a Scrabble set consisting of the 26 letters of the alphabet plus a space (for a total of 27). The probability of getting any particular letter or space in our phrase using this method would be one chance out of 27 (expressed as 1/27). The probability of getting all 23 letters and spaces in the order required for our phrase can be calculated by multiplying together the probability of getting each letter and space (1/27 x 1/27 x 1/27 — for a total of 23 times). This calculation reveals that we could expect to succeed in correctly spelling our phrase by chance, approximately once in eight hundred, million, trillion, trillion draws! If we were to hurry the process along and draw our letters at the rate of a billion per second, we could expect to spell our simple little phrase once in 26 thousand, trillion years! But even this is a “virtual certainty” compared to the probability of correctly assembling any one of the known biological proteins by chance!
The 500 amino acids that make up an average-sized protein can be arranged in over 1 x 10^600 different ways (that’s the number ONE followed by 600 zeros)! This number is vastly larger than the total number of atomic particles that could be packed into the known universe. If we had a computer that could rearrange the 500 amino acids of a particular protein at the rate of a billion combinations a second, we would stand essentially no chance of hitting the correct combination during the 14 billion years evolutionists claim for the age of the universe. Even if our high-speed computer were reduced to the size of an electron and we had enough of them to fill a room measuring 10 billion light years square (about 1 x 10^150 computers!), they would still be exceedingly unlikely to hit the right combination. Such a “room” full of computers could only rearrange about 1 x 10^180 combinations in 300 billion years. In fact, even if all the proteins that ever existed on earth were all different, our “room” full of computers would be exceedingly unlikely to chance upon the combination of any one of them in a mere 300 billion years!
Evolutionists counter that the whole probability argument is irrelevant since evolution is utterly purposeless, and thus never tries to make anything in particular! They insist, more over, that “natural selection” makes the impossible, possible. But evolutionists were vigorously challenged on this claim by mathematicians in a symposium held at Massachusetts Institute of Technology (the proceedings were published in the book, Mathematical Challenges to the Neo-Darwinian Interpretation of Evolution) Murray Eden, Professor of Engineering at M.I.T. said:
“The chance emergence of man is like the probability of typing at random a meaningful library of one thousand volumes using the following procedure: Begin with a meaningful phrase, retype it with a few mistakes, make it longer by adding letters; then examine the result to see if the new phrase is meaningful. Repeat this process until the library is complete.”
I will leave it to the reader to consider the probability that an intelligent Designer and Builder can intelligently design and build an eye.
Originally published in St. Louis MetroVoice, April 1994, Vol. 4, No. 4
Copyright © 1997 Missouri Association for Creation, Inc.
All Rights Reserved.
<tdleft” height=”13″ width=”121″>Kenneth Miller is a cell biologist and professor of biology at Brown University and coauthor of widely used high school and college biology textbooks. He has also written Finding Darwin’s God: A Scientist’s Search for Common Ground Between God and Evolution (1999). He served as an advisor to the PBS Evolution series and is featured in the first show, “Darwin’s Dangerous Idea.”
The human eye is
an organ of great
complexity, both in
structure and function.
|The case for evolution does not depend, even for a minute, upon a claim that living organisms are not complex or intricate. One case in point is a structure often cited as a perfect example of intelligent design: the human eye.||
|The eye, like a top-of-the-line modern camera, contains a self-adjusting aperture, an automatic focus system, and an inner surface that minimizes the scattering of stray light. But the sensitivity range of the eye, which gives us excellent vision in both sunlight and moonlight, far surpasses that of any film. Its neural circuitry enables the eye to automatically enhance contrast. And its color-analysis system enables it to quickly adjust to lighting conditions (incandescent, fluorescent, or sunlight) that would require a photographer to change filters and films.||
|The proponents of intelligent design assert that the combination of nerves, sensory cells, muscles, and lens tissue in the eye could only have been “designed” from scratch. After all, how could evolution, acting on one gene at a time, start with a sightless organism and produce an eye with so many independent parts, such as a retina, which would itself be useless without a lens, or a lens, which would be useless without a retina?||
Cross-section of a
|In a Darwinian world, the exquisite adaptations and specializations of living organisms are the products of natural selection, a process whereby the genetic variations — such as size, shape, and coloration — that give individuals the best chance to survive and reproduce are passed on to subsequent generations.|
|A tree frog’s eyes are adapted for night vision.||One improvement at a time|
|The pathway by which evolution can produce complex structures has been brilliantly explained in The Blind Watchmaker by Richard Dawkins, a biologist at Oxford University. The essence of Dawkins’s explanation is simple. Given enough time (thousands of years) and material (millions of individuals in a species), many genetic changes will occur that result in slight improvements in a system or structure such as the eye. However slight that improvement, as long as it is genuine, natural selection will favor its spread throughout the species over several generations.|
Birds have highly
|Little by little, one improvement at a time, the system becomes more and more complex, eventually resulting in the fully functioning, well-adapted organ that we call the eye. The retina and the lens did not have to evolve separately because they evolved together.|
|Evolution can be used as an explanation for complex structures if we can imagine a series of small, intermediate steps leading from the simple to the complex. Further, because natural selection will act on every one of those intermediate steps, no single one can be justified on the basis of the final structure toward which it may be leading. Each step must stand on its own as an improvement that confers an advantage on the organism that possesses it.|
From a simple patch
cells, a structure
like an eye can
|Building an eye|
|This step-by-step criterion can easily be applied to a complex organ like the eye. We begin with the simplest possible case: a small animal with a few light-sensitive cells. We could then ask, at each stage, whether natural selection would favor the incremental changes that are shown, knowing that if it would not, the final structure could not have evolved, no matter how beneficial. Starting with the simplest light-sensing device, a single photoreceptor cell, it is possible to draw a series of incremental changes that would lead directly to the lens-and-retina eye. None of the intermediate stages are unreasonable, since each requires nothing more than an incremental change in structure: an increase in cell number, a change in surface curvature, a slight increase in transparency.|
|This incremental process is the real reason why it is unfair to characterize evolution as mere chance. Chance plays a role in presenting random genetic variations. But natural selection, which is not random, determines which variations will become fixed in the species.
Critics might ask what good that first tiny step, perhaps only five percent of an eye, might be. As the saying goes, in the land of the blind the one-eyed man is king. Likewise, in a population with limited ability to sense light, every improvement in vision, no matter how slight, would be favored — and favored dramatically — by natural selection.
vision and a
front of them.
|Another way to respond to the theory of intelligent design is to carefully examine complex biological systems for errors that no intelligent designer would have committed. Because intelligent design works from a clean sheet of paper, it should produce organisms that have been optimally designed for the tasks they perform. Conversely, because evolution is confined to modifying existing structures, it should not necessarily produce perfection. Which is it?|
|The eye, that supposed paragon of intelligent design, offers an answer. We have already sung the virtues of this extraordinary organ, but we have not considered specific aspects of its design, such as the neural wiring of its light-sensing units. These photoreceptor cells, located in the retina, pass impulses to a series of interconnecting cells that eventually pass information to the cells of the optic nerve, which leads to the brain.||
|An intelligent designer, working with the components of this wiring, would choose the orientation that produces the highest degree of visual quality. No one, for example, would suggest that the neural connections should be placed in front of the photoreceptor cells — thus blocking the light from reaching them — rather than behind the retina.|
seeing through a
network of blood
in front of the
|Incredibly, this is exactly how the human retina is constructed. Visual quality is degraded because light scatters as it passes through several layers of cellular wiring before reaching the retina. Granted, this scattering has been minimized because the nerve cells are nearly transparent, but it cannot be eliminated because of the basic design flaw. Moreover, the effects are compounded because a network of vessels, which is needed to supply the nerve cells with a rich supply of blood, also sits directly in front of the light-sensitive layer, another feature that no engineer would propose.|
|A more serious flaw occurs because the neural wiring must poke directly through the wall of the retina to carry the nerve impulses produced by photoreceptor cells to the brain. The result is a blind spot in the retina — a region where thousands of impulse-carrying cells have pushed the sensory cells aside. Each human retina has a blind spot roughly a millimeter in diameter — one that would not exist if only the eye were designed with its sensory wiring behind rather than in front of the photoreceptors.||
The optic nerve
|Do these design problems exist because it is impossible to construct an eye that is wired properly, so that the light-sensitive cells face the incoming image? Not at all. Many organisms have eyes in which the neural wiring is neatly tucked away behind the photoreceptor layer. The squid and the octopus, for example, have a lens-and-retina eye quite similar to our own, but their eyes are wired right-side out, with no light-scattering nerve cells or blood vessels in front of the photoreceptors, and no blind spot.|
In the human
bulges in the
pinch in to
|Evolution, which works by repeatedly modifying preexisting structures, can explain the inside-out nature of our eyes quite simply. The vertebrate retina evolved as a modification of the outer layer of the brain. Over time, evolution progressively modified this part of the brain for light sensitivity. Although the layer of light-sensitive cells gradually assumed a retina-like shape, it retained its original orientation, including a series of nerve connections on its surface. Conversely, mollusk eyes are wired optimally because rather than evolving from brain cells, which have wiring on the surface, they evolved from skin cells, which retained their original orientation with the wiring below the surface.||
|The living world is filled with examples of many other organs and structures that clearly have their roots in the opportunistic modification of a preexisting structure rather than the clean elegance of design. This does not, despite the fears of “intelligent design” advocates, amount to evidence against the existence of a Deity. Properly understood, as Darwin himself pointed out, it only deepens our respect for the power and subtlety of the Creator’s remarkable ways.||
SHOW ME THE SCIENCE [August 29, 2005]
by Daniel C. Dennett
[Editor’s Note: First published as an Op-Ed Page article in The New York Times on Sunday, August 28th.]
Blue Hill, Me.
PRESIDENT BUSH, announcing this month that he was in favor of teaching about “intelligent design” in the schools, said, “I think that part of education is to expose people to different schools of thought.” A couple of weeks later, Senator Bill Frist of Tennessee, the Republican leader, made the same point. Teaching both intelligent design and evolution “doesn’t force any particular theory on anyone,” Mr. Frist said. “I think in a pluralistic society that is the fairest way to go about education and training people for the future.”
Is “intelligent design” a legitimate school of scientific thought? Is there something to it, or have these people been taken in by one of the most ingenious hoaxes in the history of science? Wouldn’t such a hoax be impossible? No. Here’s how it has been done.
First, imagine how easy it would be for a determined band of naysayers to shake the world’s confidence in quantum physics — how weird it is! — or Einsteinian relativity. In spite of a century of instruction and popularization by physicists, few people ever really get their heads around the concepts involved. Most people eventually cobble together a justification for accepting the assurances of the experts: “Well, they pretty much agree with one another, and they claim that it is their understanding of these strange topics that allows them to harness atomic energy, and to make transistors and lasers, which certainly do work…”
Fortunately for physicists, there is no powerful motivation for such a band of mischief-makers to form. They don’t have to spend much time persuading people that quantum physics and Einsteinian relativity really have been established beyond all reasonable doubt.
With evolution, however, it is different. The fundamental scientific idea of evolution by natural selection is not just mind-boggling; natural selection, by executing God’s traditional task of designing and creating all creatures great and small, also seems to deny one of the best reasons we have for believing in God. So there is plenty of motivation for resisting the assurances of the biologists. Nobody is immune to wishful thinking. It takes scientific discipline to protect ourselves from our own credulity, but we’ve also found ingenious ways to fool ourselves and others. Some of the methods used to exploit these urges are easy to analyze; others take a little more unpacking.
A creationist pamphlet sent to me some years ago had an amusing page in it, purporting to be part of a simple questionnaire:
Do you know of any building that didn’t have a builder? [YES] [NO]
Do you know of any painting that didn’t have a painter? [YES] [NO]
Do you know of any car that didn’t have a maker? [YES] [NO]
If you answered YES for any of the above, give details:
Take that, you Darwinians! The presumed embarrassment of the test-taker when faced with this task perfectly expresses the incredulity many people feel when they confront Darwin’s great idea. It seems obvious, doesn’t it, that there couldn’t be any designs without designers, any such creations without a creator.
Well, yes — until you look at what contemporary biology has demonstrated beyond all reasonable doubt: that natural selection — the process in which reproducing entities must compete for finite resources and thereby engage in a tournament of blind trial and error from which improvements automatically emerge — has the power to generate breathtakingly ingenious designs.
Take the development of the eye, which has been one of the favorite challenges of creationists. How on earth, they ask, could that engineering marvel be produced by a series of small, unplanned steps? Only an intelligent designer could have created such a brilliant arrangement of a shape-shifting lens, an aperture-adjusting iris, a light-sensitive image surface of exquisite sensitivity, all housed in a sphere that can shift its aim in a hundredth of a second and send megabytes of information to the visual cortex every second for years on end.
But as we learn more and more about the history of the genes involved, and how they work — all the way back to their predecessor genes in the sightless bacteria from which multicelled animals evolved more than a half-billion years ago — we can begin to tell the story of how photosensitive spots gradually turned into light-sensitive craters that could detect the rough direction from which light came, and then gradually acquired their lenses, improving their information-gathering capacities all the while.
We can’t yet say what all the details of this process were, but real eyes representative of all the intermediate stages can be found, dotted around the animal kingdom, and we have detailed computer models to demonstrate that the creative process works just as the theory says.
All it takes is a rare accident that gives one lucky animal a mutation that improves its vision over that of its siblings; if this helps it have more offspring than its rivals, this gives evolution an opportunity to raise the bar and ratchet up the design of the eye by one mindless step. And since these lucky improvements accumulate — this was Darwin’s insight — eyes can automatically get better and better and better, without any intelligent designer.
Brilliant as the design of the eye is, it betrays its origin with a tell-tale flaw: the retina is inside out. The nerve fibers that carry the signals from the eye’s rods and cones (which sense light and color) lie on top of them, and have to plunge through a large hole in the retina to get to the brain, creating the blind spot. No intelligent designer would put such a clumsy arrangement in a camcorder, and this is just one of hundreds of accidents frozen in evolutionary history that confirm the mindlessness of the historical process.
If you still find Test Two compelling, a sort of cognitive illusion that you can feel even as you discount it, you are like just about everybody else in the world; the idea that natural selection has the power to generate such sophisticated designs is deeply counterintuitive. Francis Crick, one of the discoverers of DNA, once jokingly credited his colleague Leslie Orgel with “Orgel’s Second Rule”: Evolution is cleverer than you are. Evolutionary biologists are often startled by the power of natural selection to “discover” an “ingenious” solution to a design problem posed in the lab.
This observation lets us address a slightly more sophisticated version of the cognitive illusion presented by Test Two. When evolutionists like Crick marvel at the cleverness of the process of natural selection they are not acknowledging intelligent design. The designs found in nature are nothing short of brilliant, but the process of design that generates them is utterly lacking in intelligence of its own.
Intelligent design advocates, however, exploit the ambiguity between process and product that is built into the word “design.” For them, the presence of a finished product (a fully evolved eye, for instance) is evidence of an intelligent design process. But this tempting conclusion is just what evolutionary biology has shown to be mistaken.
Yes, eyes are for seeing, but these and all the other purposes in the natural world can be generated by processes that are themselves without purposes and without intelligence. This is hard to understand, but so is the idea that colored objects in the world are composed of atoms that are not themselves colored, and that heat is not made of tiny hot things.
The focus on intelligent design has, paradoxically, obscured something else: genuine scientific controversies about evolution that abound. In just about every field there are challenges to one established theory or another. The legitimate way to stir up such a storm is to come up with an alternative theory that makes a prediction that is crisply denied by the reigning theory — but that turns out to be true, or that explains something that has been baffling defenders of the status quo, or that unifies two distant theories at the cost of some element of the currently accepted view.
To date, the proponents of intelligent design have not produced anything like that. No experiments with results that challenge any mainstream biological understanding. No observations from the fossil record or genomics or biogeography or comparative anatomy that undermine standard evolutionary thinking.
Instead, the proponents of intelligent design use a ploy that works something like this. First you misuse or misdescribe some scientist’s work. Then you get an angry rebuttal. Then, instead of dealing forthrightly with the charges leveled, you cite the rebuttal as evidence that there is a “controversy” to teach.
Note that the trick is content-free. You can use it on any topic. “Smith’s work in geology supports my argument that the earth is flat,” you say, misrepresenting Smith’s work. When Smith responds with a denunciation of your misuse of her work, you respond, saying something like: “See what a controversy we have here? Professor Smith and I are locked in a titanic scientific debate. We should teach the controversy in the classrooms.” And here is the delicious part: you can often exploit the very technicality of the issues to your own advantage, counting on most of us to miss the point in all the difficult details.
William Dembski, one of the most vocal supporters of intelligent design, notes that he provoked Thomas Schneider, a biologist, into a response that Dr. Dembski characterizes as “some hair-splitting that could only look ridiculous to outsider observers.” What looks to scientists — and is — a knockout objection by Dr. Schneider is portrayed to most everyone else as ridiculous hair-splitting.
In short, no science. Indeed, no intelligent design hypothesis has even been ventured as a rival explanation of any biological phenomenon. This might seem surprising to people who think that intelligent design competes directly with the hypothesis of non-intelligent design by natural selection. But saying, as intelligent design proponents do, “You haven’t explained everything yet,” is not a competing hypothesis. Evolutionary biology certainly hasn’t explained everything that perplexes biologists. But intelligent design hasn’t yet tried to explain anything.
To formulate a competing hypothesis, you have to get down in the trenches and offer details that have testable implications. So far, intelligent design proponents have conveniently sidestepped that requirement, claiming that they have no specifics in mind about who or what the intelligent designer might be.
To see this shortcoming in relief, consider an imaginary hypothesis of intelligent design that could explain the emergence of human beings on this planet:
About six million years ago, intelligent genetic engineers from another galaxy visited Earth and decided that it would be a more interesting planet if there was a language-using, religion-forming species on it, so they sequestered some primates and genetically re-engineered them to give them the language instinct, and enlarged frontal lobes for planning and reflection. It worked.
If some version of this hypothesis were true, it could explain how and why human beings differ from their nearest relatives, and it would disconfirm the competing evolutionary hypotheses that are being pursued.
We’d still have the problem of how these intelligent genetic engineers came to exist on their home planet, but we can safely ignore that complication for the time being, since there is not the slightest shred of evidence in favor of this hypothesis.
But here is something the intelligent design community is reluctant to discuss: no other intelligent-design hypothesis has anything more going for it. In fact, my farfetched hypothesis has the advantage of being testable in principle: we could compare the human and chimpanzee genomes, looking for unmistakable signs of tampering by these genetic engineers from another galaxy. Finding some sort of user’s manual neatly embedded in the apparently functionless “junk DNA” that makes up most of the human genome would be a Nobel Prize-winning coup for the intelligent design gang, but if they are looking at all, they haven’t come up with anything to report.
It’s worth pointing out that there are plenty of substantive scientific controversies in biology that are not yet in the textbooks or the classrooms. The scientific participants in these arguments vie for acceptance among the relevant expert communities in peer-reviewed journals, and the writers and editors of textbooks grapple with judgments about which findings have risen to the level of acceptance — not yet truth — to make them worth serious consideration by undergraduates and high school students.
SO get in line, intelligent designers. Get in line behind the hypothesis that life started on Mars and was blown here by a cosmic impact. Get in line behind the aquatic ape hypothesis, the gestural origin of language hypothesis and the theory that singing came before language, to mention just a few of the enticing hypotheses that are actively defended but still insufficiently supported by hard facts.
The Discovery Institute, the conservative organization that has helped to put intelligent design on the map, complains that its members face hostility from the established scientific journals. But establishment hostility is not the real hurdle to intelligent design. If intelligent design were a scientific idea whose time had come, young scientists would be dashing around their labs, vying to win the Nobel Prizes that surely are in store for anybody who can overturn any significant proposition of contemporary evolutionary biology.
Remember cold fusion? The establishment was incredibly hostile to that hypothesis, but scientists around the world rushed to their labs in the effort to explore the idea, in hopes of sharing in the glory if it turned out to be true.
Instead of spending more than $1 million a year on publishing books and articles for non-scientists and on other public relations efforts, the Discovery Institute should finance its own peer-reviewed electronic journal. This way, the organization could live up to its self-professed image: the doughty defenders of brave iconoclasts bucking the establishment.
For now, though, the theory they are promoting is exactly what George Gilder, a long-time affiliate of the Discovery Institute, has said it is: “Intelligent design itself does not have any content.”
Since there is no content, there is no “controversy” to teach about in biology class. But here is a good topic for a high school course on current events and politics: Is intelligent design a hoax? And if so, how was it perpetrated?
DANIEL C. DENNETT is University Professor, Professor of Philosophy, and Director of the Center for Cognitive Studies at Tufts University. Among his books are Consciousness Explained; Darwin’s Dangerous Idea; and Freedom Evolves.