Dead Racists Society

Kenneth Miller recognizes that if we had a designer, it can't have been too intelligent:

If we can account for the evolution of complex structures by incremental advances, this might seem to leave us with no way to distinguish design from evolution. Evolution, then, might have produced such structures. But did it? In fact, there is a way to tell. Evolution, unlike design, works by the modification of pre-existing structures. Intelligent design, by definition, works fresh, on a clean sheet of paper, and should produce organisms that have been explicitly (and perfectly) designed for the tasks they perform.

Evolution, on the other hand, does not produce perfection. The fact that every intermediate stage in the development of an organ must confer a selective advantage means that the simplest and most elegant design for an organ cannot always be produced by evolution. In fact, the hallmark of evolution is the modification of pre-existing structures. An evolved organism, in short, should show the tell-tale signs of this modification. A designed organism should not. Which is it?

The eye, that supposed paragon of intelligent design, is a perfect place to start. We have already sung the virtues of this organ, and described some of its extraordinary capabilities. But one thing that we have not considered is the neural wiring of its light-sensing units, the photoreceptor cells in the retina. These cells pass impulses to a series of interconnecting cells that eventually pass information to the cells of the optic nerve, which leads to the brain. Given the basics of this wiring, how would you orient the retina with respect to the direction of light? Quite naturally, you (and any other designer) would choose the orientation that produces the highest degree of visual quality. No one, for example, would suggest that the neural wiring connections should be placed on the side that faces the light, rather than on the side away from it. Incredibly, this is exactly how the human retina is constructed.

What are the consequences of wiring the retina backwards? First, there is a degradation of visual quality due to the scattering of light as it passes through layers of cellular wiring. To be sure, this scattering has been minimized because the nerve cells are nearly transparent, but it cannot be eliminated, because of the basic flaw in design. This design flaw is compounded by the fact that the nerve cells require a rich blood supply, so that a network of blood vessels also sits directly in front of the light-sensitive layer, another feature that no engineer would stand for. Second, the nerve impulses produced by photoreceptor cells must be carried to the brain, and this means that at some point the neural wiring must pass directly through the wall of the retina. The result? A "blind spot" in the retina, a region where thousands of impulse-carrying cells have pushed the sensory cells aside, and consequently nothing can be seen. Each human retina has a blind spot roughly 1 mm in diameter, a blind spot that would not exist if only the eye were designed with its sensory wiring behind the photoreceptors instead of in front of them.

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 below the photoreceptor layer. The squid and the octopus, for example, have a lens-and-retina eye quite similar to the vertebrate one, but these mollusk eyes are wired right-side-out, with no light-scattering nerve cells or blood vessels above the photoreceptors and no blind spot.

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The living world is filled with examples of organs and structures that clearly have their roots in the opportunistic modification of a preexisting structure rather than the clean elegance of design. Steven Jay Gould, in his famous essay "The Panda's Thumb," makes exactly this point. The giant panda has a distinct and dexterous "thumb" which, like our own thumb, is opposable. These animals nimbly strip the leaves off bamboo shots by pulling the shoots between thumb and their five other fingers. Five? No, the panda doesn't have six fingers, because it's thumb isn't a true digit at all. In fact, it grips the shoot of bamboo between its palm and a bone in the wrist which, in giant pandas, has been enlarged to form a stubby protuberance.

A true designer would have been capable of remodeling a complete digit, like the thumb of a primate, to hold the panda's food. Evolution, on the other hand, settled for much less: a bamboo-gripping pseudo-digit that conferred just enough of an advantage to be favored by natural selection. As Gould himself notes, a single mutation increasing the rate of growth of this wristbone could explain the formation of the Panda's "thumb." Natural selection itself explains how this simple modification was advantageous. It is a clear case of the way in which evolution produces organisms that are well-adapted, but not necessarily well-designed.

A true designer could begin with a clean sheet of paper, and produce a design that did not depend, as evolution must, on re-using old mechanisms, old parts, and even old patterns of development. The use of old developmental patterns is particularly striking in human embryonic development. The early embryos of reptiles and birds, which produce eggs containing massive amounts of yolk, follow a particularly specialized pattern of development. This pattern enables them to produce the three vertebrate body layers in a disc of cells that sits astride a hugh sphere of nutritive yolk. They eventually surround that yolk with a "yolk sac," a layer of cells that supplies the embryo with nutrition from the stored yolk.

Placental mammals produce tiny eggs, so there would be no need to follow a developmental pattern that surrounds the non-existent mass of yolk. Nevertheless, as Scott F. Gilbert, the author of an influential book on developmental biology notes:

"What is surprising is that the gastrulation movements of reptilian and avian embryos, which evolved as an adaptation to yolky eggs, are retained even in the absence of large amounts of yolk in the mammalian embryo. The inner cell mass can be envisioned as sitting atop an imaginary ball of yolk, following instructions that seem more appropriate to its ancestors."

Indeed, human embryos even go so far as to form an empty yolk sac, surrounding that non-existent stored food. The human yolk sac develops from the same tissues as the yolk sacs of reptiles and birds, performs many of the same functions (except, of course, for using the non-existent yolk), and gives rise to the same adult tissues. That it why it has been known as a "yolk sac" for more than a century. The cells of the sac channel nutrients to the embryo (much as they do in birds and reptiles), and play a role in the formation of the circulatory, reproductive, and digestive systems. These functions do not explain, however, why the cells that perform them should take the form of a sac.

There is no reason, from the standpoint of intelligent design, for the human embryo to produce an empty yolk sac. Evolution, of course, can supply the answer. If placental mammals are descended from egg-laying animals, like reptiles, then the empty yolk sac can be understood as a evolutionary remnant. The yolk sac is produced by a process of development that could not be re-designed simply because mammalian eggs had lost their yolk. It suggests that mammals evolved from animals that once had eggs with large amounts of yolk. Does the historic fossil record support that contention? Absolutely. The very first recognizable mammals in the fossil history of life on Earth are known by a telling name: they are the "reptile-like mammals."

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The concept of intelligent design is particularly clear on one point: organisms have been designed to meet the distinct needs of their lifestyles and environments, not to reflect an evolutionary history. Is this distinction between evolution and design testable? I think it is, and the test is a simple one. Intelligent design dictates that the genetic system of a living organism should be constructed to suit its present needs, and should not contain superfluous genes or gene sequences that obviously correspond to structures or substances for which the organism has no need. In short, the master genetic plan should correspond precisely to the organism for which it codes.

No living bird has teeth, and that fact, of course, is behind the old saying that a rare object is "as scarce as hen's teeth." Why don't birds have teeth? A proponent of intelligent design must answer that they have not been designed to have teeth, quite probably because the designer equipped them with alternatives (hard beaks and food-grinding gizzards) that are superior for lightweight flying organisms.

Is this in fact the case? In 1980 Edward Kollar and his colleague C. Fisher decided to test whether or not chicken cells still have the capacity to become teeth. Intelligent design would predict that they cannot, because teeth were never designed into the organism.

Kollar & Fisher's experiment was simple. They took mouse tissue that normally lies just beneath the epithelial cells that develop into teeth, and put it in contact with chick epithelial cells. What happened? The chick cells, apparently influenced by the mouse tissue, dutifully began to develop into teeth. The produced impact-resistant enamel on their surfaces, and developed into clear, recognizable teeth (Figure 5). The experimenters took great care to exclude the possibility that mouse tissue had produced the teeth, first by making sure that no mouse epithelium was included in the experiments, and second by confirming that the cells in the tooth-producing tissue were indeed chick cells. Their experiments have since been confirmed by two independent groups of investigators.

No plan of intelligent design can account for the presence of tooth-producing genes in chicken cells. Indeed, it would be remarkably un-intelligent to endow birds with such useless capabilities. Evolution, on the other hand, has a perfectly good explanation for these capabilities. Birds are descended from organisms that once had teeth, and therefore they may retain these genes, even if other genetic changes normally turn their expression off. In short, birds have a genetic mark of their own history that no designed organism should ever possess. Designed organisms, after all, do not have evolutionary histories.

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In today's world, it is possible to test evolution and intelligent design as never before. Rather than depending upon the indirect evidence of structure and physiology, we can go right to the source to the genetic code itself. If the human organism is, indeed, the product of careful, intelligent design, a detailed analysis of human DNA should reveal that design. Remember the quotation from Of Pandas and People: "We cannot build a palace by tinkering with a tool shed and adding bits of marble piecemeal here and there. We have to begin by devising a plan for the palace that coordinates all the parts into an integrated whole." We can test intelligent design simply by examining the genome to see if it matches the prediction of a coordinated, integrated plan.

If, on the other hand, the human genome is the product of an evolutionary history, that DNA should be a patchwork riddled with duplicated and discarded genes, and loaded with hints and traces of our evolutionary past. This, too, can be tested by directly examining the coded sequences of human DNA.

Although a complete sequence for all human DNA is at least a decade away, we already know more than enough of that sequence to begin to address the question of design. Let's take, as a representative example, a piece of chromosome # 11 known as the b -globin cluster. About 60,000 DNA "bases" are in the cluster, each base effectively representing 1 letter of a code that contains the instructions for assembling part of a protein. b -globin is an important part of hemoglobin, the oxygen-carrying protein that gives blood its red color. There are 5 different kinds of b -globin, and the cluster contains a gene for each one .

Why are there so many different forms of the b -globin gene? Here both evolution and intelligent design could supply an answer. Two of the genes are expressed in adults, and the other three are expressed during embryonic and fetal development. Evolution maintains that the multiple copies have arisen by gene duplication, a random process in which mistakes of DNA replication resulted in extra copies of a single ancestral gene. Once the original b -globin gene had been duplicated a number of times, so the explanation goes, slight variations within each sequence could produce the 5 different forms of the globin gene.

Why would different forms of b -globin be useful? The embryo, which is engaged in a tug-of-war for oxygen with its mother, must have hemoglobin that binds oxygen more tightly than the mother's adult hemoglobin. The 3 versions of the gene that are expressed during embryonic development enable hemoglobin to do exactly that. These slight variations enable embryonic blood to draw oxygen out of the maternal circulation across the placenta into its own circulation. Hence, gene duplication provided a chance for special forms of the b -globin gene to evolve that are expressed in fetal development.

Intelligent design proposes much the same mechanism, except that the production of extra copies and their modification to suit the embryo were a matter of intentional design, not chance and natural selection. Intelligent design maintains that the DNA sequences of each of the 5 genes of the cluster are matters of engineering, not random gene duplications fine-tuned by natural selection. So which is it? Are the 5 genes of this complex the elegant products of design, or a series of mistakes of which evolution took advantage?

The cluster itself, or more specifically a sixth b -globin gene, provides the answer. This gene is easy to recognize as part of the globin family because it has a DNA sequence nearly identical to that of the other five genes. Oddly, however, this gene is never expressed, it never produces a protein, and it plays no role in producing hemoglobin. Biologists call such regions "pseudogenes," reflecting the fact that however much they may resemble working genes, in fact they are not.

How can we be sure the sixth gene really is a pseudogene? Molecular biologists know that the expression of a gene like b -globin is a two-step process. First, the DNA sequence has to be copied into an intermediate known as RNA. That RNA sequence is then used to direct the assembly of a polypeptide, in this case, a b -globin. There is no evidence that the first step ever takes place for the pseudogene. No RNA matching its sequence has ever been found. Why? Because it lacks the DNA control sequences that precede the other 5 genes and signal the cell where to start producing RNA This means that the pseudogene is "silent." Furthermore, even if it were comehow copied into RNA, it still could not direct the assembly of a polypeptide. The pseudogene contains 6 distinct defects, any one of which would prevent it from producing a functional polypeptide. In short, this sixth gene is a mess, a nonfunctional stretch of useless DNA.

From a design point of view, pseudogenes are indeed mistakes. So why are they there? Intelligent design cannot explain the presence of a nonfunctional pseudogene, unless it is willing to allow that the designer made serious errors, wasting millions of bases of DNA on a blueprint full of junk and scribbles. Evolution, however, can explain them easily. Pseudogenes are nothing more than chance experiments in gene duplication that have failed, and they persist in the genome as evolutionary remnants of the past history of the b -globin genes.

The b -globin story is not an isolated one. Hundreds of pseudogenes have been discovered in the 1 or 2% of human DNA that has been explored to date, and more are added every month. In fact, the human genome is littered with pseudogenes, gene fragments, "orphaned" genes, "junk" DNA, and so many repeated copies of pointless DNA sequences that it cannot be attributed to anything that resembles intelligent design.

If the DNA of a human being or any other organism resembled a carefully constructed computer program, with neatly arranged and logically structured modules each written to fulfill a specific function, the evidence of intelligent design would be overwhelming. In fact, the genome resembles nothing so much as a hodgepodge of borrowed, copied, mutated, and discarded sequences and commands that has been cobbled together by millions of years of trial and error against the relentless test of survival. It works, and it works brilliantly; not because of intelligent design, but because of the great blind power of natural selection to innovate, to test, and to discard what fails in favor of what succeeds. The organisms that remain alive today, ourselves included, are evolution's great successes.