by Carl Zimmer
The other major revolution that E. coli’s ancestors experienced was delivered by our own ancestors. Early eukaryotes, biologists suspect, were the predators of the early Earth. They were much like amoebas today, which prowl through soil and water in search of prey they can engulf. Bacteria that could defend themselves against these predators were favored by natural selection. Today bacteria have an impressive range of defenses against amoebas and other eukaryote predators. They can produce toxins that they can inject with microscopic needles into the amoebas. Their mucus-covered biofilms are difficult for predators to penetrate. Even when ingested, bacteria can avoid destruction.
In some cases, bacteria may have turned the tables on their predators. Amoebas today get sick with bacterial infections caused by species that have evolved the ability to infect and thrive inside hosts. Some bacteria are more polite lodgers, providing single-celled protozoans with life-giving biochemistry. Early eukaryotes acquired oxygen-breathing bacteria this way, and those bacteria are still part of our own cells today. Algae acquired photosynthesizing bacteria, and among their descendants are the plants that make the land green. Thanks to these bacterial partners, the continents could begin to support a massive ecosystem, with forests and grasslands and swamps becoming home to animals of all sorts, from insects to mammals.
These animals, the descendants of the predatory eukaryotes that harassed bacteria billions of years earlier, now became a new ecosystem for bacteria to invade. Thousands of species of microbes, including the ancestors of E. coli, adapted to the food-rich realm of the animal gut. They brought with them their abilities to break down organic carbon, communicate with one another, and cooperate. They had come a long way from the common ancestor of all living things. But as they took up residence inside humans and other animals, they had in their own way brought some branches of the tree of life together again.
E. COLI GOES TO COURT
The federal courthouse in Harrisburg, Pennsylvania, is a nondescript box of dark glass. Its judges deal mostly in humdrum conflicts over funeral-parlor regulations, liquor-store licenses, airport parking lots. But in 2005 a surge of people—reporters, photographers, and onlookers—hit the courthouse like a rogue wave. One case had drawn them all: Kitzmiller v. Dover Area School District. Eleven parents from the small town of Dover had taken their local board of education to court. They charged that the board was introducing religion into science classes. The world’s attention was fixed on the case because it represented the first time the courts would consider creationism in its latest incarnation, known as intelligent design. The trial opened on September 26, 2005. Projectors had been brought into the court, and the lawyers and expert witness used them to display images on a large screen. Again and again the same image appeared: the flagellum of E. coli.
Over the past twenty-five years E. coli’s flagellum has become an icon to creationists, a molecular weapon they try to wield against the evils of Darwin and his followers. For decades they have touted it in lectures and books as a clear-cut example of the handiwork of a divine designer. But it was not until the Dover case that they had the opportunity to present the flagellum to the world.
The strategy failed miserably. At the end of the trial, Judge John E. Jones ruled against the school board, in part because its case for the flagellum’s intelligent design was so weak. In fact, flagella are a fine example of how evolution works and a clear demonstration of why creationism fails as science.
Creationism—the belief that life’s diversity originated from specific acts of divine creation—first emerged in American history during the early years of the twentieth century. But it was never a single body of ideas. Some creationists argued that the world was a few thousand years old, while others accepted the geologic evidence of its great age. Some claimed evolution must be wrong because it did not accord with the Bible. Others tried to attack the evidence for evolution. They claimed that living species were so distinct from one another that they could not have evolved from a common ancestor. They pointed out the absence of transitional fossils, such as ones that might link whales to land mammals, and claimed that such gaps were proof that intermediate forms could not possibly have existed. When paleontologists discovered fossils of some of those transitional forms—such as whales with legs—the creationists simply retreated to another gap.
While creationists failed in the scientific arena, they had more luck in public high schools. In the 1920s, state legislatures began banning the teaching of evolution, and many of those laws stayed on the books for more than thirty years. It was not until 1968 that the U.S. Supreme Court ruled that banning the teaching of evolution amounted to imposing religion on students. If creationists could not keep evolution out of classrooms, they would try to get creationism in alongside it. They began to claim that creationism is sound science that deserves to be taught. These self-styled “creation scientists” founded organizations with august names, such as the Institute for Creation Research. They began working on a textbook about creation science that they wanted introduced into schools. And they looked around the natural world for things they could claim as scientific evidence of creation.
Biology had changed dramatically since the birth of creationism. Molecular biologists were plunging into the exquisite complexity of cells, discovering clusters of proteins working together like the parts of machines. Creation scientists mined the new research for structures they claimed were the result of creation, not evolution. One of the things they chose was E. coli’s flagellum.
In 1981, Richard Bliss, chairman of the Education Department of the Institute for Creation Research, came to West Arkansas Junior College to give a talk about creation science. He told his audience that in the creation model of life, “we would predict that we’d see a fantastic amount of orderliness, and there is, folks. There’s orderliness on a macro level and on a micro level. The further we get down into the molecular level the more we see this orderliness jump out and scream out at us.” As an example of this order, Bliss showed his audience a picture of E. coli.
Bliss described its flagellum, detailing the many proteins that make it up and how they work together to make it spin. “I like to call it a Mazda engine,” Bliss said. He hoped that students could be taught the “creation model” of E. coli’s flagellum along with the “evolution model” and make up their own minds. “It’s just exciting science and exciting education,” he said.
This sort of argument swayed some state legislatures to pass laws requiring that creation science be taught alongside evolution. But the Supreme Court struck the laws down in the 1980s because they, in effect, endorsed religion. The Court declared creation science no science at all.
Creationists repackaged their old claims once more. They stripped away all mention of creationism, creation, and a creator. They argued instead that life shows signs of something they called intelligent design. DNA and proteins and molecular machines are simply too complex to have evolved by natural selection, they argued. These molecules were purposefully arranged, and that purpose reveals an intelligent designer at work. Just what or who that designer is they would not say, at least not publicly.
One of the most striking examples of this makeover was the transformation of a textbook originally called Creation Biology. A Texas publishing house had started work on the manuscript in the early 1980s, but in the wake of the Supreme Court’s rulings its editors began to replace the words creationism with intelligent design, creator with intelligent designer, and creationist with design adherent. Otherwise, they barely changed the language. In 1989, the textbook was published. Instead of Creation Biology, its publishers named it Of Pandas and People.
The evidence for creation—including the flagellum—now became the evidence of intelligent design. Richard Lumsden of the Institute for Creation Research waxed rhapsodic about it in a 1994 article published in the journal of the Creation Research Society, a “young-Earth creationism” organization: “In terms of biophysical complexity, the bacterial rotor-flagellum
is without precedent in the living world,” Lumsden wrote. “To the micromechanicians of industrial research and development operations, it has become an inspirational, albeit formidable challenge to the best efforts of current technology, but one ripe with potential for profitable application. To evolutionists, the system presents an enigma; to creationists, it offers clear and compelling evidence of purposeful intelligent design.”
While some proponents of intelligent design continued to call themselves creationists, others noisily rejected the name. They claimed that intelligent design is only the scientific search for evidence of design in nature. And for them E. coli’s flagellum was also a favorite example. William Dembski, a philosopher at Southwestern Baptist Theological Seminary, put it on the cover of his book No Free Lunch. He presented a calculation of the probability that E. coli’s flagellum had come together by chance. The number he came up with was spectacularly tiny, which Dembski took as evidence that it must have been produced by a designer. Biologists and mathematicians alike reject Dembski’s argument because it is supremely irrelevant. Mutations may be random—at least insofar as they don’t produce only variations an organism actually needs—but natural selection is not a matter of chance.
Dembski and other proponents of intelligent design claimed that the designer might be an alien or a time traveler. But personally they believed the designer to be God. Dembski wrote that intelligent design is essentially the theology of John’s Gospel in the Christian scriptures. And all the talk of aliens and time travelers did not scare off conservative religious organizations. Instead, they embraced intelligent design. Focus on the Family, for example, a large American evangelical organization, urged its members to demand that Of Pandas and People be used in schools whenever evolution was taught. In 2002, Focus on the Family’s magazine ran an article by Mark Hartwig extolling intelligent design. More than twenty years after Bliss’s lecture in Arkansas, creationists were still picking out E. coli as one of their prime exhibits.
“Darwinists dismiss the reasoning behind the intelligent-design movement, contending that living organisms were produced by the mindless processes of random mutation and natural selection,” Hartwig wrote. “But advances in molecular biology are shredding that claim. For example, consider the little outboard motor that bacteria such as E. coli use to navigate their environment. This water-cooled contraption, called a flagellum, comes equipped with a reversible engine, drive shaft, U-joint and long whip-like propeller. It hums along at 17,000 rpm.” Hartwig pointed out that it took fifty genes to create a working flagellum. If a single gene were disabled by a mutation, the flagellum would be crippled. There were therefore no intermediate steps by which a flagellum could have evolved. “Such systems simply defy Darwinist explanations,” Hartwig declared.
Focus on the Family was not the only organization trying to get Of Pandas and People into public schools. In 2000, a Christian legal organization called the Thomas More Law Center began sending lawyers to school boards around the country. They urged the boards to adopt the book and promised to defend them if they were sued. “We’ll be your shields against such attacks,” Robert Muise, one of the lawyers, told the Charleston, West Virginia, Board of Education. (The Thomas More Law Center calls itself “the sword and shield for people of faith.”) School boards in Michigan, Minnesota, West Virginia, and other states turned them down.
But in 2004 the Thomas More lawyers got a break when they visited the rural community of Dover, Pennsylvania. The Dover Board of Education decided to promote the teaching of intelligent design. One board member arranged for sixty copies of Of Pandas and People to be donated to the school library. The local school board added a new statement to the science curriculum. “Students,” it read in part, “will be made aware of gaps/problems in Darwin’s Theory and of other theories of evolution including, but not limited to, intelligent design.”
The board of education also demanded that teachers read a second statement aloud to all Dover biology classes. They were required to say that evolution was a theory, not a fact (confusing the nature of both facts and theories). “Intelligent Design is an explanation of the origin of life that differs from Darwin’s view,” the statement continued. “The reference book Of Pandas and People is available for students to see if they would like to explore this view in an effort to gain an understanding of what Intelligent Design actually involves. As is true with any theory, students are encouraged to keep an open mind.”
Dover’s science teachers refused to read the statement. They declared that to do so would violate the oath they took not to give their students false information. The superintendent came to the classrooms to read the statement instead. When curious students asked what sort of designer was behind intelligent design, he told them to ask their parents and walked out.
Two months later, eleven parents filed a lawsuit. Their lawyers argued that the statement violated the First Amendment because it represented the impermissible establishment of religion. And on an autumn day the trial began.
The plaintiffs called parents and teachers to testify how the board of education had pressured teachers not to teach “monkey to man evolution” and promised to bring God back into the classroom. The defense responded by bringing in two biologists as expert witnesses, Scott Minnich of the University of Idaho and Michael Behe of Lehigh University. Like Dembski, Minnich and Behe are fellows at the Discovery Institute in Seattle, the leading organization for the promotion of intelligent design.
Behe has never managed to publish a paper in a peer-reviewed biology journal arguing for intelligent design based on original research. Instead, he has presented his case mainly in op-ed columns, speeches, and books. Behe claims that some biological systems could not have evolved by natural selection because they are what he calls “irreducibly complex.” He asserts that something could be called irreducibly complex if it is “a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning.” It would be impossible, in his view, for natural selection to gradually produce an irreducibly complex system, because it would have to start with something that didn’t work. “If a biological system cannot be produced gradually it would have to arise as an integrated unit, in one fell swoop,” he concludes.
Behe uses a few examples to illustrate irreducible complexity. The flagellum is one of his favorites. He claims it is obviously too complex to have evolved from a simpler precursor. Faced with the wonder of the flagellum, Behe writes, “Darwin looks forlorn.”
At the Dover trial, Behe had a textbook illustration of E. coli’s flagellum projected on the courtroom screen, and he proceeded to marvel at it all over again. “We could probably call this the Bacterial Flagellum Trial,” a lawyer for the school board said.
Behe inventoried the flagellum’s many parts and told Judge Jones that Darwinian evolution could not have produced its irreducible complexity. “When you see a purposeful arrangement of parts, that bespeaks design,” he said. The flagellum, Behe explained, was built for a purpose—to propel bacteria—and it was built from many interacting parts, just like the outboard motor of a boat. “This is a machine that looks like something that a human might have designed,” he said.
The plaintiffs’ witnesses were eager to talk about the flagellum as well, in order to demolish Behe’s claims about irreducible complexity. Kenneth Miller, a biologist at Brown University, pointed out that Behe’s claims about irreducible complexity could be tested. Behe, Miller reminded the court, had defined an irreducibly complex system as one that would be nonfunctional if it were missing a part. Miller then showed the court a computer animation of the flagellum. He began to dismantle it, removing not just one part but dozens. The filament disappeared. The universal joint vanished. The motor slipped away. All that was left when Miller was done was the needle that injects new parts of the filament into the shaft.
Miller had removed a great deal of
an irreducibly complex system. By Behe’s definition, what remained should no longer be functional. But it is. The ten proteins that make up the needle are nearly identical in both their sequence and their arrangement to a molecular machine known as the type III secretion system. This is the needle used by E. coli O157:H7 and other disease-causing strains to inject toxins into host cells.
“We do break it apart, and lo and behold, we find—actually we find a variety of useful functions, one of which I have just pointed out, which is type III secretion,” Miller testified. “What that means, in ordinary scientific terms, is that the argument that Dr. Behe has made is falsified, it’s wrong, it’s time to go back to the drawing board.”
Behe tried to play down Miller’s testimony. When Behe said that a system became nonfunctional when it lost a part, he now claimed, he had meant that it lost its particular function. By removing part of the flagellum, Behe argued, Miller was left with something that could not propel a microbe. “If you take away those parts, it does not act as a rotary motor,” Behe said.
He then claimed that most people would assume Miller was implying that a type III secretion system evolved into a flagellum, something evolutionary biologists were not agreed on. Some had raised the possibility that the flagellum had evolved into a type III secretion system or that both structures evolved from a common ancestor. Yet Miller had not said anything of the sort. He had simply tested Behe’s claims, carefully hewing to Behe’s own words. And Behe’s claims had not held up to the evidence.
Over the course of the trial it became clear that Behe had some strange demands for scientists who would explain how the flagellum—or any other supposedly irreducibly complex systems—evolved. “Not only would I need a step-by-step, mutation-by-mutation analysis,” he said, “I would also want to see relevant information such as what is the population size of the organism in which these mutations are occurring, what is the selective value for the mutation, are there any detrimental effects of the mutation, and many other such questions.”
