What is Evolution?
Before Evolution
Thinking About Evolution
What is Natural Selection?
Isn't Evolution Just a Theory?
Evidence for Evolution
Evolution in the Fossil Record
"Doubts" About Evolution
Intelligent Design
Evolution and Faith
So is Everything Settled?
Resources

Biological evolution is change in the characteristics of living organisms over generations.

Despite your vastly superior tastes in music and fashion, you probably look vaguely like your parents, just as they look vaguely like their parents. For all of recorded history, people have looked more or less the same: two eyes, two ears, a nose, a mouth, a head sitting atop an oblong body with two arms and legs. Hairdos differed, but the basic body plan stayed the same for as far back as the history books go.

But if you were to go back further in time, a couple million years before anybody figured out how to write, your ancestors would still have two eyes, two ears, a nose, a mouth, a head sitting atop an oblong body with two arms and legs. But they would have more hair. And maybe not quite as much smarts. They would be much better at climbing trees, though. If you went further back in time, the arms would be front legs. Even further back in time, the fur would be scales. Really far back in time, there wouldn't be any legs at all, just fins for swimming.

Evolutionary theory argues that all the organisms alive on earth today share a common ancestor. As unlikely as it sounds, life forms from spiders to spider monkeys belong to the same family tree. Even fungus merits an invitation to the family reunion. A simple way to think of evolution is "descent with modification" — over many generations, organisms change into something different.

Johann Jakob Scheuchzer published Sacred Physics in the early 18th century. Showing scenes from Genesis, it illustrated the contemporary explanation for how life arose. Illustration from Scenes from Deep Time by Martin J.S. Rudwick

People took a long time to figure out that evolution happened, and before that, Western civilization relied largely on the Bible to understand how we got here. Starting in the Renaissance, however, some of society's keenest thinkers began to puzzle over just how the Bible could be literally true. Early on, the story that caused the most trouble was Noah's Flood.

One man who managed to stir some doubt was Niels Stensen (or Nicolaus Steno). A religious man, Steno wasn't out to disprove the Bible; he used it as the basis for his work in piecing together old landscapes. He figured out that rocks are deposited in layers with older rocks at the bottom, and in the landscape of Tuscany, he thought he saw the events described in Genesis. In the century following his death, however, people who searched rock layers for remains of earth's earliest inhabitants found something odd. According to Genesis, God made Adam, Eve, and all the animals first. Then Adam and Eve started a family and left plenty of descendents. Only later came Noah's Flood, which was held responsible for depositing all those weird remains, like shells, in rocks on top of mountains. If that actually happened, human remains should have appeared in the oldest rocks at the bottom of the heap, but they didn't. Human remains showed up only in the newest layers. The oldest layers of rocks held different creatures, and the further down in the heap one looked, the weirder the creatures got.

Steno wasn't alone in inadvertently causing Noah trouble. All the naturalists who traveled to the New World to draw, collect, measure and catalog what lived there threatened to sink Noah's Ark with too many passengers. After all, fitting two of everything living in Europe was enough of a challenge. Squeezing in all these newly discovered creatures from America looked impossible. Biblical scholars went back to calculating the length of a cubit.

One more problem for Noah was a shift in philosophy in the 17th and 18th centuries. Rather than simply relying on miracles, scholars and savants (there were few actual scientists just yet) adopted the view that God played by His own rules, so understanding nature could contribute to understanding God. And if God played by the rules, then a worldwide flood that covered the highest mountain peaks with water (and left seashells behind) would require the sudden creation and subsequent cleanup of a tremendous amount of liquid. That didn't look likely. Leonardo da Vinci himself poured scorn on such "just so" stories.

By the early 19th century, a different picture had emerged of the planet's history. Lead by scientists like Buffon, George Cuvier and James Hutton, the men (few women could participate then) who studied rocks and fossils accepted that the earth had been around for thousands, if not millions, of years before people came on the scene. Furthermore, many animals — giant ground sloths in South America, monstrous reptiles in England — had gone extinct long ago. So even if people continued to look to the Bible for spiritual guidance, they began to doubt it was a literal account of the history of life on earth.

Not everyone who accepted an ancient earth necessarily accepted biological evolution. By the early 19th century, the professional scientists and leisurely gentlemen who dabbled in geology or comparative anatomy entertained a variety of explanations for humanity's predecessors. Evolution was one explanation, but many savants believed a series of catastrophes had been followed by fresh creations.

One early evolutionist, Lamarck, proposed a form of evolution in 1800. He suggested that organisms could acquire needed characteristics for changing environments, an idea that has been laughed off by history, but his views were actually more nuanced than modern accounts usually relate. Cuvier, regarded as the greatest comparative anatomist of his day, disdained Lamarckian "transmutation" but that didn't keep others from considering it, such as Erasmus Darwin, Charles Darwin's grandfather.

In 1831, Charles Darwin set sail on a sea voyage. Over the next several years, he examined living and fossil organisms that gave him an insight into the ancient past. Some time after he returned, he developed his theory of natural selection. He planned to publish his idea as early as the 1840s, but then Robert Chambers anonymously published Vestiges of the Natural History of Creation a quasi-scientific account of organisms changing over time. The reaction was fierce. Darwin held back — and gathered more evidence to support his case. In the late 1850s, a young naturalist, Alfred Russel Wallace, began to see organisms in the same light as Darwin. He wrote Darwin about his idea, and Darwin realized that, if he waited any longer, he would be scooped. Darwin's notes and correspondence, and Wallace's paper were all read aloud at the same scientific meeting in 1858. They spurred little reaction, but a year later, Darwin published The Origin of Species. Biology was forever changed.

United Kingdom Royal Mail Mint Stamps, issued February 12, 2009

Darwin has gotten more modern attention than Wallace, but they both deserve credit for the theory. They're famous today not because they proposed evolution. That had already been done. They're famous for proposing a viable explanation of how evolution occurs: natural selection.

In the wild, most parents produce more babies than can possibly survive. When sea turtles hatch, hundreds of them poke out of their shells and head for the ocean, desperately flopping their tiny legs as fast as they can. Many of them don't even reach the water; they're picked off by seagulls instead. Once in the water, many more baby turtles become snacks for their neighbors in their new watery neighborhood. Even if they avoid becoming a meal themselves, they have to find meals of their own, and food can be pretty limited in the wild.

Darwin cited artificial selection wrought by humans as evidence of the selective pressure environment can exert. Illustration from Evolution: The Triumph of an Idea by Carl Zimmer

Some life forms on earth — such as some bacteria, plants, even animals — reproduce by cloning — making exact replicas of themselves. In such populations, everybody is the same. For the rest of us, sex introduces variation into a population. Darwin pondered this variation, particularly the differences between the animals that survive and pass their characteristics on to their offspring, and those that instead get snatched up in the jaws of defeat. He (and Wallace) found that the key to surviving and producing offspring has to do with suitability to the environment. Birds that need to see their prey from afar, then swoop down and snatch up a meal, benefit from keen eyesight. Hunting birds with lousy eyesight often go hungry. Lizards scurrying around in forest floor litter benefit from good camouflage and swift legs. In a (literal) pinch, the ability to part with one's tail can keep a lizard alive. Ditto an octopus arm.

In other words, the life forms best suited to their environments are likely to live the longest and produce the most offspring.

But what if the environment changes? Lakes can dry up. Weather patterns can shift. A new species of vegetation can set up camp, favoring a new color of camouflage in lizards rustling around in the leaves. Any organism that happens to possess a characteristic well suited to the new environment will do better than its peers. Over time, the new characteristic may become so preferable to the old one that the population eventually looks different from how it used to look.

Darwin couldn't know about the discoveries of genetics that would follow in the 20th century. Genes — the inherited instructions that tell our cells what to do and tell our bodies what to look like — are passed from one generation to the next with remarkable accuracy. But every once in awhile, something goes wrong. The instructions get botched. These random mistakes are mutations. People often think of mutations as invariably harmful, but that's not always the case. Many (perhaps most) mutations have little or no effect, and some mutations are life savers. One example in human DNA is known as delta 32. When the plague, often referred to as the Black Death, struck Europe, it devastated the population, but a lucky few survived. They carried the delta 32 mutation that conferred resistance to the disease. The same mutation appears to confer a resistance to HIV, the virus that causes AIDS, today.

If your irritating little brother emptied a pail of sand over your school project, while you stood there thinking of ways to shorten his life, the little tyke might try to extricate himself with the argument that he had no idea the sand would actually fall down. After all, gravity's just a theory.

In casual conversation, we talk about our "theories" all the time, i.e., "Men who are chauvinists at work are really henpecked at home, and they're just trying to vicariously get even with their wives." A scientific theory is different. Rather than being simple speculation, a scientific theory tries to make sense of a broad range of observations. The germ theory of disease is a good example. Before scientists understood the role that microscopic pathogens play in spreading sickness and infection, people used to blame cold weather, warm weather, "vapors," foreigners, even evil spirits. Today, the germ theory of disease is so well accepted that a doctor who refused to wash up before performing surgery would face a lawsuit, and probably lose his or her license to practice medicine.

A scientific theory starts out as a hypothesis, a proposed explanation for some phenomenon, and where possible, the hypothesis is subjected to testing. Scientists document such work and publish their papers in peer-reviewed science journals. Other scientists in the same discipline review and comment on the paper before it sees the light of day, and other researchers should be able to replicate the experimental results.

As evolutionary biologists have pointed out, any of the experiments designed to test Darwin and Wallace's theory of natural selection since it was first proposed could have proven the hypothesis wrong. None of those tests did. So evolution is "just a theory" the same way that the theory of plate tectonics and the germ theory of disease are just theories. And gravity.

One body of evidence Darwin turned to for his theory was artificial selection: the changes humans have caused in crops, livestock and pets. Humans have bred dogs, birds, cows and corn to their desires for hundreds, if not thousands, of years. If farmers and breeders could bring about such big changes in the short time span of recorded history, what could nature do?

Artificial selection shows the power of an outside selective force acting on a species, but that's not the only evidence for evolution. Other factors point to common origin for life forms. Bats, dolphins and people are all mammals, but bats fly, dolphins swim, and humans type, dine and doodle. If each species were carefully designed from scratch, there wouldn't be much need for overlap in skeletal structure. Yet all three types of animals share the same general limb design. Humans, dolphins and bats all have upper arm bones, lower arm bones, wrists, hand bones, and fingers. In dolphins, these bones are shortened to make a stiff flipper. Bats, meanwhile, spread their wings out over their finger bones.

Why would evolution do this? Because it works with whatever it's got handy (pardon the pun). Evolution can't see the future and it can't change the past. It can only cope with the present.

Another example of evolution working with what it's got appears in the difference between how whales and fish swim. Fish and their ancestors have always lived in the water. Whales moved back into the water after their ancestors wandered around on land. When fish swim, they wriggle their tails sideways, rather like a snake slithers. In contrast, whales move their tails up and down, because they inherited spines that were once attached to running legs.

Darwin pointed out the things he and his contemporaries could observe in the 19th century. In the 20th century, the neo darwinian synthesis combined Darwin's theory of natural selection with Gregor Mendel's discoveries related to genetics, and not long afterwards James Watson and Francis Crick uncovered the physical structure of DNA. This led to a whole new set of discoveries about common ancestry, such as some organisms carrying long-deactivated genes that were more useful to their ancestors. Dolphins and whales, for instance, carry hundreds of genes related to sensing smell in an air-based (not water-based) environment. But because these animals have returned to the water, those genes are no longer functional.

More striking than similarities among mammals are DNA similarities between a much wider range of animals. A gene that geneticists have dubbed BMP4 both strengthens the jaws of fish that eat a robust shellfish diet, and bulks up beaks of Galapagos ground finches. Another gene identified as FOXP2 helps young finches learn to sing, and young humans to speak. First found in fruit flies, hox genes regulate overall body plans for everything from bugs to birds. Arguably grisly experiments with these genes show that moving them around creates fairly disgusting mutants, like flies with legs sprouting from their heads.

Picking the Prettiest Male peacocks may very well consider their fancy tail feathers a pain in the butt. They're heavy, they get soaked in the rain, and they don't exactly improve the birds' lift. But peahens, like humans, apparently find those tail feathers pretty. Maybe a male's ability to sport big, lustrous feathers is a sign that he's robust enough to pass along desirable genes. In the long run, such big, heavy feathers just might reduce the peacock's chances of living to ripe old age, but ripe old age isn't necessarily evolution's aim; living long enough to breed is. In any case, organisms have been shaped as much by sexual selection — characteristics that wow the opposite sex — as the more mundane abilities to cope with environment. Image from Evolution: The Triumph of an Idea by Carl Zimmer

Even more basic than hox genes are the building blocks for all genes; DNA is the acronym for deoxyribonucleic acid. With the exception of some viruses that rely on just ribonucleic acid (RNA), all life on earth uses DNA. And in organisms with DNA, RNA helps transcribe genes into proteins. These building blocks of inheritance are common all living things on this planet.

Evolution still happens today, and it's still driven by natural selection. As the glaciers retreated at the end of the Pleistocene 10,000 years ago, migratory marine fish moved into lakes and streams in North America and Eurasia. Adapting to new foods, new threats and new water conditions has diversified these stickleback fish (Gasterosteus aculeatus) so much that they show greater diversity in their body plans than different genera of fish. Variations include dramatic differences in the size or number of bony plates, body build and tooth structure. Some sticklebacks sport fins that other sticklebacks completely lack. And because sticklebacks often stick to their own size when it comes to mating, that promotes isolation of different reproductive groups. Off Florida's Gulf Coast, meanwhile, lies a young island archipelago, inhabited by pale-hued mice. The mice enjoy a genetic tweak that lightens their coats, making them mix better with pale beach sand than their darker mainland mice relatives. The beach mice's genetic mutation occurred after the islands formed some 6,000 years ago.

Some of the strongest evidence for evolution comes from our own species. Humans long believed ourselves to be the highest form of life on earth, made in the image of God. If so, our perfection needs a little work. Some of us have flat feet and some of us have cracked vertebrae and slipped discs — unfortunate results of upending a spine that had long been horizontal atop four-legged animals. Women got an especially raw deal: hips so wide they place extra strain on knees, yet not wide enough to make childbirth the least bit easy.

Ever suffered from the hiccups? Thank the convoluted path that nerves must follow between your brain stem and your diaphragm; in fish, those nerves enjoy a less troublesome route. We humans have appendices, perhaps useful to our ancestors, but in us useless leftovers that occasionally necrose and rupture. Before the invention of surgery and the adoption of surgical hygiene, your own appendix could easily kill you.

Again, why did evolution do these annoying things? Because evolution doesn't have to be perfect, it merely has to be effective. It only has to be good enough.

Today, benefited by sterile surgeries, antibiotics, vaccines, car ownership and convenience stores, we humans in the developed world must cope with new epidemics: diabetes and obesity. Our bodies — better adapted to a hunter-gatherer world where calories were scarce and exercise was abundant, where our bodies had to store fat to get us through long spells of little or no food — don't deal so well with the modern glut of cheeseburgers, bourbon and Twinkies.

Evolution of other organisms plays a role in human healthcare. Since humans learned about antibiotics, we've used them to fight infection, but we haven't always enjoyed the results we wanted. Staphylococcus (staph infection) evolved a resistance to Penicillin in 1946, to Methicillin in 1961, to Vancomycin in 1986, and to Zyvox in 1999. The HIV virus evolves so quickly that multiple species can thrive in a single patient. On these fronts, at least, evolution appears to be working against us.

When Darwin wrote The Origin of Species, he lamented the incompleteness of the fossil record. His friend T.H. Huxley disagreed, stating, "The primary and direct evidence in favor of evolution can be furnished only by paleontology. . . . if evolution has taken place, there will its mark be left; if it has not taken place, there will lie its refutation." In a way, both men were right.

Top: 1861 Archaeopteryx from Darwin and the Science of Evolution by Patrick Tort Bottom: 1877 Archaeopteryx from The Reign of the Dinosaurs by Jean-Guy Michard

To become a fossil, you have to be buried soon after you die — before weather or scavengers destroy your remains. The dirt and mud burying you then have to harden sufficiently to protect what's left of you over thousands or more likely millions of years. At some point, your remains have to find their way to the ground surface and erode out. And there's no guarantee that when your fossilized self sees the sun again that some human — let alone a human who knows or cares about fossils — will happen along at the right moment to find you. In other words, the odds of becoming a fossil are slim. The odds of being found as a fossil are slimmer still.

So the fossil record is spotty at best, but even with so many pieces missing, it tells us quite a bit about the history of life on earth, and more discoveries happen all the time.

One of the most important ways in which the rock record supports evolutionary theory is the succession of fossils in older versus newer rock layers. As far back as the 18th century, scholars realized that fossils in older layers differed more from modern life forms than fossils in newer layers. While many fossils from the Pleistocene Ice Age resemble organisms living today, far fewer fossils from the Age of Reptiles do. If you venture back in the rock record to the Precambrian (prior to roughly 550 million years ago), you'll find few fossils of multicellular organisms at all. So striking has this fossil succession been that when asked what would disprove evolution, 20th-century British scientist J.B.S. Haldane quipped, "Fossil rabbits in the Precambrian." No such bunnies have ever been found.

One argument raised about the fossil record is that it has no transitional forms. Yet two of the earliest, most famous fossils ever found were stunning examples of transitional fossils. In 1860, the limestone quarry in Solnhofen, Germany, yielded a fossil feather. A year later, the same quarry gave up a better prize: a partial skeleton of Archaeopteryx lithographica. Sir Richard Owen, in all fairness a brilliant comparative anatomist, described the fossil as "unequivocally a bird" and suggested that, if the whole creature were found, it would look like a modern bird. It certainly wouldn't have any teeth. In 1877, a complete specimen was found at Solnhofen, and this fossil sported a toothy grin to refute Owen's prediction. It was a reptile on its way to being a bird.

Ichthyostega, Acanthostega and Tiktaalik are all examples of transitional fossils left by fish slowly transmogrifying into landlubbing tetrapods. Transitional forms also document the mammalian return to water. Paleontologist Phil Gingerich was overjoyed to find a whale ancestor, Rodhocetus, in Pakistan. Years earlier, he had been disappointed to find a fairly pedestrian fossil whale ancestor, Basilosaurus, in the same region. Yet he perked up considerably when he found the creature's diminutive legs. Why hadn't anybody found its legs before? Because nobody had looked. Why had nobody looked? "Because whales don't have legs!" Years later, Gingerich found fossils of the whale species Maiacetus inuus, including a pregnant mother. The whales' teeth were well-suited to a diet of fish, but the fetus was positioned head-down, characteristic of life on land. Together, the fossils indicated another transitional form — a whale that lived most of its life in the sea, but had to return to land to give birth.

Some of the most compelling — and to some, the most upsetting — evidence for evolution comes from our own human lineage. The first recognized fossil human, a Neanderthal fossil, appeared in Germany in 1856. Eugène Dubois who was born shortly afterwards, found a more ancient ancestor in Java, the first Homo erectus fossil. In the 20th century, Raymond Dart, and Louis and Mary Leakey found even more ancient Australopithecus fossils in Africa. In 1974, Donald Johanson and his team discovered Lucy, later classified as Australopithecus afarensis. Lucy overturned long-held assumptions that humans sprouted bigger brains before they started walking upright. In the fall of 2004, Peter Brown, Mike Morwood and their colleagues made probably the most astonishing announcement to date. They had found an 18,000-year-old, 1-meter-tall "hobbit," Homo floresiensis. Controversy raged around the hobbits, with some alleging the hominids were malformed, little-brained midgets, but braincase scans suggested otherwise. Although certainly not an ancestor of modern humans, Flores Man appeared to be a different species of human that had coexisted with anatomically modern humans for thousands of years.

In 1925, Tennessee schoolteacher John Thomas Scopes was tried for teaching evolution, in violation of the recently enacted Butler Act. The act outlawed the teaching of "any theory that denies the story of the Divine Creation of man as taught in the Bible." The American Civil Liberties Union offered to defend anyone who defied the act, in hopes of overturning the law. Instead, Scopes's conviction was thrown out on a technicality, and the law remained on the books until the late 1960s.

In the decades following the Scopes Monkey Trial, quite a lot changed, yet some things remained very much the same. Teaching evolution is no longer illegal in the United States, but millions Americans still oppose the teaching of evolution in public school science classrooms. (Of the world's industrialized nations, only Turkey's population shows greater opposition to evolutionary theory than the U.S.) The U.S. also enjoys the rather unique distinction of politicizing evolution. During the 1990s, Republican Party platforms called for the teaching of "creation science" in Alaska, Iowa, Kansas, Oklahoma, Oregon, Missouri and Texas. In a New York Times editorial in 2005, moderate Republican, Episcopal minister and former senator John C. Danforth described the U.S. as the only country where a political party adopted a position on evolution. In June 2008, Governor Bobby Jindal signed into law the Louisiana Science Education Act singling out evolution (and global warming and human cloning) for what the act described as critical analysis.

In extreme cases, some Americans endorse the teaching of biblical literalism in public schools. Others push for the instruction of Intelligent Design. Still others want teachers to "teach the controversy."

What controversy?

A widespread public perception in the United States (and to a lesser degree in some other nations) is that scientists disagree about whether evolution is real. In October and November of 2001, Seattle-based think tank the Discovery Institute placed advertisements in The New York Review of Books, The New Republic, and The Weekly Standard. These ads featured a list of 100 PhDs (!) who "dissented from Darwinism." Members of the American public were understandably persuaded that a genuine controversy existed.

In February 2003, theoretical physicist Lawrence Krauss, a keynote speaker at the annual meeting of the American Association for the Advancement of Science, unveiled a response to the list of 100 PhDs. The National Center for Science Education (NCSE) had collected a list of 200 PhDs who agreed with the following statement:

Evolution is a vital, well-supported, unifying principle of the biological sciences, and the scientific evidence is overwhelmingly in favor of the idea that all living things share a common ancestry. Although there are legitimate debates about the patterns and processes of evolution, there is no serious scientific doubt that evolution occurred or that natural selection is a major mechanism in its occurrence. It is scientifically inappropriate and pedagogically irresponsible for creationist pseudoscience, including but not limited to "intelligent design," to be introduced into the science curricula of our nation's public schools.

Besides finding twice as many scientists as the Discovery Institute, NCSE added a further twist: In order to support the pro-evolution statement, evolutionists not only had to hold a PhD in science. They also had to be named Steve (or Steven, Stephen, Esteban, Stephanie, or some derivative). "Steve" was chosen for two reasons: in honor of the late Stephen Jay Gould, and because people named Steve or some variation comprise roughly 1 percent of the American population. So the Steve list could be multiplied by 100 to get a ballpark figure of how many scientists think evolution is real. Steves armed with PhDs have continued to sign up since February 2003. Steve number 300 was Stephen Hawking. On September 5, 2008, the Steve-o-Meter reached 900. On February 13, 2009, Steven P. Darwin — professor of ecology and evolutionary biology at Tulane University in New Orleans, although no relation to the most famous evolutionist — became Steve number 1,000.

So in comparing scientists with doubts about Darwin to scientists who accept evolution, the score isn't 100 to 200, or even 100 to 1,000. It's more like 100 to about 100,000. Project those percentages onto an election, and evolution wins by a landslide.

That's not to say there is no debate about evolution. Clearly there is. But it's a cultural debate, a religious debate and — given recent religious influence in American government — a political debate. But it's not a scientific debate.

In 2004, William Dembski wrote in The Design Revolution:

Intelligent design is not an evangelic Christian thing, or a generally Christian thing or even a generically theistic thing. . . . Intelligent design is an emerging scientific research program. Design theorists attempt to demonstrate its merits fair and square in the scientific world — without appealing to religious authority.

But in 1999, the very same guy had written in Intelligent Design: The Bridge Between Science and Theology:

[A]ny view of the sciences that leaves Christ out of the picture must be seen as fundamentally deficient. . . . [T]he conceptual soundness of a scientific theory cannot be maintained apart from Christ.

Intelligent design (ID) argues that many features found in living organisms are so complex, they must have been planned by an intelligent designer. A cornerstone of the argument is "irreducible complexity": some multi-faceted features simply could not have evolved by chance, and the removal of one part would collapse the whole system. Yet in a paper critiquing intelligent design, Elliot Sober observed that a horse with one, two or even three legs couldn't run very well, but horses didn't likely evolve one extra leg at a time. Appendages like four legs aren't controlled by four sets of genes, but by a single gene set that governs the development of appendages.

The leading think tank behind the intelligent design movement is the Discovery Institute in Seattle, Washington. In 2001, the institute's "Wedge Strategy" was leaked on the Internet. In part, it stated:

Design theory promises to reverse the stifling dominance of the materialist worldview, and to replace it with a science consonant with Christian and theistic convictions.

In 2005, intelligent design was put on trial in Dover, Pennsylvania, in 400 F.Supp.2d 707 (M.D. Pa. 2005). In the trial, as before, ID supporters insisted that they were promoting science, not religion. But one of the more interesting pieces of evidence offered by the plaintiffs was the straightforward substitution of "design proponents" for "creationists" in a textbook recommended to introduce intelligent design. Philosophy professor and long-time ID tracker Barbara Forrest examined successive versions of the book, Of Pandas and People, and found one substitution that went horribly awry: "cdesign proponentsists." Evolutionists described this sloppy substitution as the missing link between creationism and ID. On December 20, 2005, the presiding judge, John E. Jones III (a lifelong church-going Republican appointed by George W. Bush, it is worth noting) reached this conclusion about intelligent design:

Teaching intelligent design in public school biology classes violates the Establishment Clause of the First Amendment to the Constitution of the United States (and Article I, Section 3 of the Pennsylvania State Constitution) because intelligent design is not science and "cannot uncouple itself from its creationist, and thus religious, antecedents."

Much of the anxiety about evolution stems from the fear that, in accepting the theory, one denies the existence of God. In fact, evolutionary theory makes no demands about religious faith (or lack of it). People who accept evolution are free to draw their own conclusions about a higher power in the universe.

Although some evolutionists such as Richard Dawkins are atheists, other evolutionists, such as Kenneth Miller (biology professor at Brown University, and author of Finding Darwin's God) and Francis Collins (head of the National Human Genome Research Institute) see no conflict between evolutionary theory and religious belief. Mainstream Protestantism, Roman Catholicism, branches of Judaism and Islam all accept evolution.

Michael Zimmerman, evolutionary biologist and dean of the College of Letters and Science at the University of Wisconsin at Oshkosh, recently initiated a letter stating:

We the undersigned, Christian clergy from many different traditions, believe that the timeless truths of the Bible and the discoveries of modern science may comfortably coexist. We believe that the theory of evolution is a foundational scientific truth, one that has stood up to rigorous scrutiny and upon which much of human knowledge and achievement rests. To reject this truth or to treat it as "one theory among others" is to deliberately embrace scientific ignorance and transmit such ignorance to our children. We believe that among God's good gifts are human minds capable of critical thought and that the failure to fully employ this gift is a rejection of the will of our Creator.

Scientists acknowledge that there are some questions science simply cannot answer. Whether Genesis as recorded in the King James Bible describes a literal truth about the physical universe is a testable hypothesis, and it turns out to be false. We know this from dating of rocks and fossils, for one thing. But whether or not there is a God is not a testable hypothesis. That's a matter of personal belief. As Stephen Jay Gould put it, science and religion are "nonoverlapping magisteria." While evolution doesn't require a supreme being, it doesn't preclude the existence or involvement of such a being, either.

In a word: no. Although there's virtually no debate among scientists about whether evolution happens, they continue to debate how it happens. The story gets more intriguing every day.

Niles Eldredge co-founded the theory of punctuated equilibria (rapid bursts of evolution separated by long periods of little or no change) with Stephen Jay Gould in the early 1970s. He has since articulated a more comprehensive "sloshing bucket" theory of evolution, arguing that most evolution occurs in regional turnovers of species. A migrating sandbar on the ocean floor will decimate the bottom-feeders in its way, but the same kinds of animals will populate the sea floor in the sandbar's wake. But an asteroid hitting the earth is a complete game-changer. How hard the bucket of life gets kicked determines slosh size.

The more scientists examine life on earth, the more they unravel complex webs of interaction. For example, leafcutter ants feed on a certain type of fungus, and scientists long thought that leafcutter ants kept their fungal gardens pest-free with careful weeding. Then a graduate student discovered that the gardens were under continual threat from a different kind of fungus, a parasitic fungus. He also discovered that the worker ants' abdomens were covered with a substance commonly used in antibiotics. What had long looked like a simple partnership between two species (ants and the fungus they ate) was a more complicated relationship between four species (ants, their fungal food, an annoying fungal pest, and the built-in antibiotic).

Closer examination of genetics reveals more flexibility than once thought, too. In August 2003, researchers at Duke University reported that the diet of a pregnant mouse mother could affect the functioning of her offspring's genes. Part of the field of epigenetics, this study showed that outside factors like nutrition and stress could affect how genes operate without modifying the actual DNA sequence. Epigenetic markers instead work by activating or deactivating stretches of DNA, and in some cases, modified epigenetic patterns can be inherited. Likewise, the relatively new field nicknamed evo-devo, that relates evolution to biological development, promises to tweak how we view the process of evolution.

In January 2007, Nigel Goldenfeld and Carl Woese predicted that coming discoveries in how microbes swap genes — a process known as horizontal gene transfer, or HGT — would force a redefinition of organisms and "evolution itself." They wrote:

[M]icroorganisms have a remarkable ability to reconstruct their genomes in the face of dire environmental stresses, that in some cases, their collective interactions with viruses may be crucial to this. In such a situation, how valid is the very concept of an organism in isolation?

Will textbooks be rewritten soon? Stay tuned.

Recommended resources:
Understanding Evolution from the University of California, Berkeley
Project Steve from the National Center for Science Education
Talk Origins Archive
Ken Miller on The Colbert Report

For more information:
Evolution: The Triumph of an Idea by Carl Zimmer
PBS Evolution Teacher's Guide
Evolution by Linda Gamlin
Your Inner Fish by Neil Shubin
Intelligent Thought edited by John Brockman
Darwin and the Science of Evolution by Patrick Tort
The Seashell on the Mountaintop by Alan Cutler
The Meaning of Fossils by Martin J.S. Rudwick
Scenes from Deep Time by Martin J.S. Rudwick
The Canon by Natalie Angier
Song of the Dodo by David Quammen
The Reign of the Dinosaurs by Jean-Guy Michard
Taking Wing by Pat Shipman
"From Atoms to Traits" by David M. Kingsley in Scientific American Magazine, January 2009 issue
"Modern Darwins" by Matt Ridley in National Geographic Magazine, February 2009 issue
"The Latest Face of Creationism" by Glenn Branch and Eugenie C. Scott in Scientific American Magazine, January 2009 issue
"15 Evolutionary Gems" by Henry Gee, Rory Howlett and Philip Campbell in Nature Magazine, January 2009 (http://www.nature.com/evolutiongems)
"Biology's Next Revolution" by Goldenfeld and Woese in Nature Magazine, January 25, 2007 issue
"Confessions of a Darwinist" by Niles Eldredge in Virginia Quarterly Review, Spring 2006 issue
"Hierarchies and the Sloshing Bucket: Toward the Unification of Evolutionary Biology" in Evolution Education and Outreach, January 2008 issue
"Humans as the World's Greatest Evolutionary Force" by Stephen R. Palumbi in Science Magazine, September 7, 2001 issue
"Public Acceptance of Evolution" by Miller, Scott and Okamoto in Science Magazine, August 11, 2006 issue
"What is Wrong with Intelligent Design?" by Elliott Sober in The Quarterly Review of Biology March 2007 issue
"Scientific Illiteracy and the Partisan Takeover of Biology" by Liza Gross in PLoS Biology, May 2006
"New Protocetid Whale from the Middle Eocene of Pakistan: Birth on Land, Precocial Development, and Sexual Dimorphism" by Gingerich, ul-Haq, von Koenigswald, Sanders, Smith and Zalmout in PLoS One, February 2009
Early Whales Gave Birth on Land (http://www.nsf.gov/news/news_summ.jsp?cntn_id=114086&org=NSF&from=news)
Project Steve (http://www.ncseweb.org/resources/articles/3541_project_steve_2_16_2003.asp)
Steve Darwin is Steve #1000 (http://ncseweb.org/news/2009/02/steve-darwin-is-steve-1000-004308)
The Wedge Strategy (http://antievolution.org/features/wedge.html)
Wikipedia: Dover Trial (http://en.wikipedia.org/wiki/Kitzmiller_v._Dover_Area_School_District)
NOVA: Judgment Day: Intelligent Design on Trial Program Transcript (http://www-c.pbs.org/wgbh/nova/transcripts/3416_id.html)
Secrets of the Dead: Black Death (http://www.pbs.org/wnet/secrets/case_plague/clues.html)
Who's Afraid of Darwin? (http://www.wiretapmag.org/education/33038/)
Clergy Letter Project Background (http://www.butler.edu/clergyproject/clergy_project.htm)
A Pregnant Mother's Diet May Turn the Genes Around (http://query.nytimes.com/gst/fullpage.html?sec=health&res=9A0DE4DD103CF934A35753C1A9659C8B63)
Now: The Rest of the Genome (http://www.nytimes.com/2008/11/11/science/11gene.html)
From a Few Genes, Life's Myriad Shapes (http://www.nytimes.com/2007/06/26/science/26devo.html)
Darwin Still Rules, but Some Biologists Dream of a Paradigm Shift (http://www.nytimes.com/2007/06/26/science/26essay.html)

Illustrations in title graphic from:
Evolution: The Triumph of an Idea by Carl Zimmer
Human Origins: The Search for Our Beginnings by Herbert Thomas
The Reign of the Dinosaurs by Jean-Guy Michard
The Dragon Seekers by Christopher McGowan
Wonderful Life by Stephen Jay Gould
See References for more information.

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Narrative text and graphic design © 2007-2009 by Michon Scott - Updated April 25, 2009