Why Darwin Matters Page 9
Richard Dawkins cogently answers the information challenge by reconstructing the evolution of hemoglobin—the oxygen-carrying protein in blood. Human hemoglobin contains four protein chains called globins that are similar to each other but not identical. The alpha globins each contain a chain of 141 amino acids coded by seven genes on Chromosome 11—four are pseudogenes that do not produce proteins, two produce adult hemoglobin, and one produces embryo hemoglobin. Similarly, beta globins each contain a chain of 146 amino acids coded by six genes on Chromosome 16, some of which are disabled and one used only in embryos. Letter-by-letter analysis of the genes coding for hemoglobin reveals that the two sets of genes on Chromosomes 11 and 16 are distantly related and share a common globin gene from a common ancestor five hundred million years ago. That gene duplicated, after which both copies were passed down for half a billion years, one evolving into the alpha cluster on Chromosome 11 and the other evolving into the beta cluster on Chromosome 16. Gene duplications led to the increase in complexity of the gene clusters, leading to the existence today of nonfunctional pseudogenes. Since this alpha-beta split happened five hundred million years ago we can predict that we should find the same alpha-beta split in all animals that evolved within the last half billion years. Sure enough, that is precisely what we find. As a final test, the jawless lamprey fish, the only surviving vertebrate predating the alpha-beta split, should lack this genetic divide. And sure enough, it does. Blood hemoglobin is explained by evolution, not Intelligent Design. Q.E.D.43
In general, DNA has the elements of historical contingency and evolutionary history, not design. DNA is information, and if the Law of Conservation of Information requires the input of an Intelligent Designer in order to increase specified complexity of the genome, we have to wonder why the Intelligent Designer added to our genome junk DNA, repeated copies of useless DNA, orphan genes, gene fragments, tandem repeats, and pseudogenes, none of which are involved directly in the making of a human being. In fact, of the entire human genome, it appears that only a tiny percentage is actively involved in useful protein production. Rather than being intelligently designed, the human genome looks more and more like a mosaic of mutations, fragment copies, borrowed sequences, and discarded strings of DNA that were jerry-built over millions of years of evolution.44
We Cannot Observe Evolution: No laboratory experiments or field observations reveal evolution in action.
Another regular on the Intelligent Design circuit is the hunt for “evolution in action.” Scientists have not, and probably can never, provide examples of evolution at work that would satisfy an Intelligent Design creationist. It is one thing to infer in the fossil record the creation of a new anatomical structure, or the birth of a new species; it is quite another to witness it in the laboratory. And what examples we do have of evolution in action in the lab, creationists claim is not evolution.
But not only does science have an incredibly rich fossil record, the process of evolution can be seen at work at a number of different levels. Diseases are prime examples of natural selection and evolution at work, and on time scales we can witness, all too painfully. The AIDS virus, for example, continues to evolve in response to the drugs used to combat it—the few surviving strains of the virus continue to multiply, passing on their drug-resistant genes. Creationists respond that this is an example of microevolution, not macroevolution. Fair enough.
For an example of macroevolution, then, check out the research by the University of Michigan biologist James Bardwell, reported in the February 20, 2004, edition of Science, in which an E. coli bacterium that was forced to adapt or perish improvised a novel molecular tool. “The bacteria reached for a tool that they had, and made it do something it doesn’t normally do. We caught evolution in the act of making a big step.” The big step was a new way of making molecular bolts called disulfide bonds, which are stiffening struts in proteins that also help the proteins fold into their proper, functional, three-dimensional shapes. This new method restarted the bacterium’s motor and enabled it to move toward food before it starved to death.
It is a particularly important experiment because Bardwell developed a strain of mutant bacteria unable to make disulfide bonds, which are critical for the ability of a bacterium’s flagellum to work—the same flagellum that Intelligent Design theorists are so fond of presenting as an example of irreducible complexity. The researchers put these nonswimming bacteria to the test by placing them on a dish of food where, once they had exhausted the food they could reach, they either had to repair the broken motor or starve. The bacteria used in the experiment were forced to use a protein called thioredoxin, which normally destroys disulfide bonds, to make the bonds instead. In a process similar to natural selection, one researcher made random alterations in the DNA encoding thioredoxin and then subjected thousands of bacteria to the swim-or-starve test. He wanted to see if an altered version of thioredoxin could be coerced to make disulfides for other proteins in the bacteria. Remarkably, a mutant carrying only two amino acid changes—amounting to less than 2 percent of the total number of amino acids in thioredoxin—restored the ability of the bacteria to move. The altered thioredoxin was able to carry out disulfide bond formation in numerous other bacterial proteins all by itself, without relying on any of the components of the natural disulfide bond pathway. The mutant bacteria managed to solve the problem in time, swim away from starvation, and multiply.
Of course, Intelligent Design theorists will respond that the researcher acted as an intelligent designer would have in nature, and thus this supports their case; but, in fact, the researcher was acting as the force of natural selection, and thus this is evidence for evolution in action. Bardwell concluded that “the naturally occurring enzymes involved in disulfide bond formation are a biological pathway whose main features are the same from bacteria to man. People often speak of Computer Assisted Design (CAD), where you try things out on a computer screen before you manufacture them. We put the bacteria we were working on under a strong genetic selection, like what can happen in evolution, and the bacteria came up with a completely new answer to the problem of how to form disulfide bonds. I think we can now talk about Genetic Assisted Design (GAD).”
Perhaps we should now talk about GAD instead of GOD.
Microevolution and Macroevolution: Life shows signs of intermittent intelligent design intervention that accounts for large-scale changes.
Ever since Darwin, creationists have argued that natural selection can account for minor changes within a species, but cannot produce new species, new body forms, or new lineages. The argument presented today is a more sophisticated version in which, according to some (but not all) theorists, several billion years ago an Intelligent Designer created the first cell with the necessary genetic information to produce all of the irreducibly complex systems we see today. Then the laws of nature and evolution took over to create diversity within each species. When totally new and more complex species, body forms, and lineages appear in the fossil record, these are signs of the Intelligent Designer stepping in, intervening with a new design element. Microevolution proceeds by natural selection, but macroevolution is in the hands of the Designer.
First, how does one distinguish the processes of microevolution (evolution within and below the species level) from those of macro-evolution (evolution above the species level)? Within evolutionary biology there has been considerable debate about whether the microevolutionary process of natural selection operating on individuals within populations can by itself account for the diverse macroevolutionary forms of life. Today, the new science of evolutionary developmental biology, “evo-devo” for short, reveals that the wide diversity of forms evolved through an interaction of the embryological development of forms and the subsequent pruning of these forms by natural selection.
For example, it turns out that the bodily architecture of vertebrates is the product of blueprint Hox genes that direct the construction of repeating parts, such as ribs and vertebrae. In embryological develo
pment, various structures form or do not form depending on whether the Hox genes are expressed or not. Natural selection operates on expressed forms only, since these result in organisms that survive long enough to pass on their genes for the future expression of those forms. Similarly, the wide variety of eyes found throughout the animal kingdom—from the compound eyes of flies to the camera eyes of vertebrates—evolved under the control of the commonly shared Pax-6 gene, which directs the production of photoreceptor cells and light-sensing proteins. Each type of complex eye we find today evolved from simpler photoreceptive structures in a distant common ancestor of arthropods, cephalo-pods, and vertebrates. Evo-devo biologist Sean Carroll explains that
the ancestor possessed two kinds of light-sensitive organs, each one endowed with a distinct type of photoreceptor, as well as with light-sensitive proteins called R-opsin and C-opsin, respectively. One organ was a simple two-celled prototype eye; the other, called the brain photoclock, was a part of the animal’s brain and played a role in running the animal’s daily clock. The arthropod and squid retinas incorporated the photoreceptor from the simple prototype eye, whereas the vertebrate eye incorporated both kinds of photoreceptor into its retina.45
Instead of eyes evolving forty or more different times in evolutionary history, it appears that this simple genetic complex led to the embryological development and evolutionary refinement of a two-part system; in some species one part is incorporated, and in others both are.
More generally, instead of an extensive genetic tool kit with genes for constructing each and every bodily structure, evo-devo shows that a small set of gene complexes such as the Hox genes and the Pax-6 genes are expressed in novel ways that can generate large-scale changes in a nonincremental fashion. This explains why the human genome is not especially different from the mouse genome. It is not the number of genes that counts so much as how genes are turned on or off. Evolution involves old genes developing new tricks.
Second, a species is a group of actually or potentially interbreeding natural populations reproductively isolated from other such populations. We see evolution at work in nature today, isolating populations and creating new species, that is, new populations reproductively isolated from other such populations. As the new isolated populations drift genetically away from the parent populations, they eventually can no longer interbreed, making new species.46 If evolution can do this, why can’t it also create higher-order categories of organisms?
Third, some speciation may be precipitated by characteristics adapted to distinct environments that then drive populations into reproductive isolation, which leads to the creation of a new species. Similarly, sexual selection—female mate selection of males—may drive populations to diverge into different species. If females prefer certain traits in males, such as coloration, within one population, the males can change so dramatically that they are no longer appealing to females of another population, thereby making the two populations reproductively isolated: thus a new species. Research shows that speciation occurs more often in polygamous species than in monogamous species, further evidence linking sexual selection to the origin of new species.47
Fourth, to turn the tables on Intelligent Design theorists, how does Intelligent Design explain micro and macro forms? Did the Intelligent Designer personally tinker with the DNA of every single organism in a population? Or did the ID simply tweak the DNA of just one organism and then isolate that organism to start a new population? When and where did the ID intervene in the history of life? Did the ID create each genus and evolution then create each species? Or did the ID create each species and evolution create each subspecies? Most Intelligent Design theorists accept natural selection as a viable explanation for microevolution—the beak of the finch, the neck of the giraffe, the varieties of subspecies found on earth. If natural selection can create subspecies, why not species, genera, families, and on up the classification scale to kingdoms?
Last, just because Intelligent Design theorists cannot think of how nature could have created something through evolution, that does not mean that scientists will not be able to do so either. Intelligent Design is a remarkably uncreative theory that abandons the search for understanding at the very point where it is most needed. If Intelligent Design is really a science, then the burden is on its scientists to discover the mechanisms used by the Intelligent Designer. And if those mechanisms turn out to be natural forces, then no supernatural force is necessary, and they can simply change their name to evolutionary scientists and get to work.
The Second Law of Thermodynamics makes evolution impossible.
According to the laws of physics, entropy increases—systems change from hot to cold, from ordered to disordered, and from complex to simple. Yet evolutionists state that the universe and life move from chaos to order and from simple to complex, the exact opposite of the entropy predicted by the Second Law of Thermodynamics. Creationist Henry Morris stated the argument thus: “Evolutionists have fostered the strange belief that everything is involved in a process of progress, from chaotic particles billions of years ago all the way up to complex people today. The fact is, the most certain laws of science state that the real processes of nature do not make things go uphill, but downhill. Evolution is impossible.”48
Yet on any scale other than the grandest of all—the three-billion-year history of life on earth—species do not evolve from simple to complex, and nature does not simply move from chaos to order. The history of life is checkered with false starts, failed experiments, small and mass extinctions, and chaotic restarts. It is anything but the textbook foldout of linear progress from single cells to humans.
Further, the Second Law of Thermodynamics applies to closed, isolated systems. Since the earth receives a constant input of energy from the sun, it is an open-dissipative system, and entropy may decrease and order increase (though the sun itself is running down in the process). The earth is not strictly a closed system, and life can evolve without violating natural law. As long as the sun is burning, life may continue thriving and evolving, just as automobiles may be prevented from rusting, burgers can be heated in ovens, and all manner of things in apparent violation of Second Law entropy may continue. As soon as the sun burns out, entropy will take its course—and life on earth will cease.49
In addition, an open-dissipative system such as we find on the earth slips in and out of thermodynamic equilibrium. The sciences of nonlinear dynamics and of chaos and complexity theory show that systems can spontaneously self-organize into more complex systems when they are in states of thermodynamic nonequilibrium. When a system is out of balance, energy flowing in and out of the system triggers the parts of the system to interact with one another locally, and these coupled interactions reverberate throughout the system to sustain it. Autocatalysis, or feedback loops within the system, can cause it to grow in complexity. From these self-organized autocatalytic interactions emerge complexity and order.50 All of this happens without any top-down input. Evolution no more breaks the Second Law of Thermodynamics than one breaks the law of gravity by leaping into the air.
Evolution is random, and randomness cannot produce complex specified design.
It seems obvious that even the simplest of life forms are too complex to have come together by random chance. Take a simple organism consisting of merely 100 (102) parts. Mathematically there are 10158 possible ways for the parts to link up. There are not enough molecules in the universe, or time since the Big Bang, to account for these possible ways to come together in even this simple life form, let alone to produce human beings. It is the equivalent of a monkey randomly typing Hamlet, or even just the sentence “To be or not to be.” It cannot happen by chance.
An understanding of evolutionary theory, however, makes clear that natural selection is not “random,” nor does it operate by “chance.” Natural selection preserves the gains and eradicates the mistakes. The eye evolved from a single light-sensitive cell into the modern complex eye through thousands of intermediate steps
, many of which still exist in nature. Yes, in order for the monkey to type the first thirteen letters of Hamlet’s soliloquy by chance, it would take 2613 trials (approximately 1018 times 2) to guarantee success—a number sixteen times as great as the total number of seconds that have elapsed in the lifetime of the solar system. But if each correct letter is preserved and each incorrect letter eradicated, as happens in natural selection, the process operates much faster. How much faster? My friend and colleague Richard Hardison constructed a computer program in which letters were “selected” for or against, and it took an average of only 335.2 trials to produce the sequence of letters TOBEORNOTTOBE, which on his computer took less than ninety seconds. The entire play can be generated in about four and a half days!51
The icons of evolution are fallacies, fakes, or frauds.
Creationists of yore used to bleat about how the history of evolutionary science is nothing more than a catalogue of mistaken theories and overthrown ideas. Nebraska Man, Piltdown Man, Calaveras Man, and Hesperopithecus—all once claimed by scientists to be proof of human evolution—have all been shown to be mistakes or frauds. Clearly science cannot be trusted.
Intelligent Design theorists have modernized this argument through Jonathan Wells’s book Icons of Evolution: Science or Myth? Why Much of What We Teach About Evolution Is Wrong.52 Wells identifies ten “icons” of evolution, presented regularly in textbooks, that he says are mistakes, myths, or frauds: