The Test of Science

The creation science movement convinced the state of Arkansas to pass a statute requiring equal time for both creation science and evolution in science classes. But the courts have not been impressed with creationism’s new packaging. When Arkansas’s statute was challenged in district court in 1982, Judge William Overton threw it out on the grounds that it violated the First Amendment. Overton ruled that creation science was no science at all, but rather an attempt to promote religion in public schools.

Science is the search for natural explanations for what we observe in the world around us. Central to science is the construction of theories. In ordinary speech, theory may sometimes connote a rough guess or a hunch, but in science it has a specific meaning: a theory is an overarching set of proposals about some aspect of the universe. The germ theory claims that certain diseases are caused by living organisms. Newton’s theory of gravity holds that every object in the universe exerts an attractive force on every other object.

Theories cannot be directly proven right or wrong. Instead, they spawn hypotheses–testable predictions about specific applications of the theories. If the hypotheses tend to hold up, if they guide scientists to new discoveries about how the world works, and if different scientific approaches offer interlocking support, a theory is confirmed. Yet scientific knowledge is always subject to more testing and to uncovering deeper levels of reality. Newton’s theory of gravity works astonishingly well and can be used to send spacecraft to other planets. But it turns out to be embedded in an even broader theory, Einstein’s theory of relativity. Gravity, Einstein proposed, actually curves the fabric of space. One hypothesis that emerged from his theory was that light from distant stars would bend around the sun–a prediction that was confirmed during an eclipse in 1919. Physicists are now trying to establish an even broader theory of how the universe works, in which they can embed relativity and other theories, such as quantum physics.

The predictive power of science lets us perceive things in nature far beyond our senses. No one has seen the center of the Earth, but geologists know that it is an iron core by measuring the magnetic field it creates and the ways it alters seismic waves of earthquakes that pass through it. It is impossible to actually see a black hole, but the theory of relativity not only predicts that black holes will form from some collapsing stars, but that they will leave certain signatures–such as beams of x‑rays shot out by matter being sucked into them. And astronomers are now documenting the existence of those predicted beams.

Much of evolution’s work is likewise hidden from view, but it is not beyond our mental grasp. No one was alive 200 million years ago, but we can deduce from the geological record that the animals alive at the time inhabited a planet in many ways like Earth today. Living animals are subject to evolution, and so those ancient animals must have been as well. We don’t have a moment‑by‑moment record of life’s history, but we can get some understanding of what has actually happened over the past 4 billion years from the evidence that has been left behind.

As Judge Overton recognized in his 1982 decision, creationism cannot live up to science’s demands. Scientists come up with explanations for how nature works, and those explanations have consequences that they can test. It’s possible to test some of the consequences of creationist explanations, and they fail. Henry Morris, for example, has claimed that Homo sapiens must be only a few thousand years old, based on the current rate of population growth. He made this claim by extrapolating back from today’s population to a time when there were only two people on Earth (presumably Adam and Eve). “The most probable date for man’s origin, based on the known data from population statistics, is about 6,300 years ago,” Morris declared.

Morris’s claim has consequences. For one thing, it can be used to calculate the human population at any point in history. Historical records clearly show, for example, that the Egyptian pyramids were built around 4,500 years ago. If you use Morris’s own timetable to calculate how many people were on the planet at the time, you get a grand total of 600. Since there are historical records from people who lived outside of Egypt 4,500 years ago, those 600 people could not all have lived in Egypt. Given that Egypt constitutes only 1 percent of the Earth’s landmass, it might have contained only six people. In order to believe Morris’s claim that humanity is only 6,300 years old, we have to believe that a handful of people could have built the pyramids.

In order to make a case for creationism, its advocates try marshaling evidence from scientists, but they do so selectively, ignoring the full picture. For example, creationists sometimes point to the Cambrian explosion as proof of God’s work. “Significant from our standpoint is that at a certain time in the supposed geological calendar, popularly called the Cambrian era, are found a host of fossils which are virtually absent from older layers of rock,” write Wayne Frair and Percival Davis in A Case for Creation. “From a scientific standpoint alone it is evident that a spectacular event must have occurred at this time. It seems reasonable that the abrupt change at the period designated as Cambrian is a result of God’s creative activity.”

These creationists leave out a few key facts. The fossil record runs back well over 3 billion years before the Cambrian explosion, and paleontologists have found fossils of multicellular animals as old as 575 million years, some of which are clearly relatives of the groups that appeared during the Cambrian explosion 40 million years later. The Cambrian explosion certainly happened quickly, as geological history goes, but it still took around 10 million years. And judging from the way different animal embryos are built, a few relatively small genetic changes may have triggered many of the dramatic transformations to animal bodies seen during that time.

Most arguments for creationism aren’t really arguments for it at all, but are just quibbles with evolutionary biology. Many creationists, for example, will grant that evolution can happen on a small scale within a species: bacteria can evolve resistance and the length of beaks on Darwin’s finches can change size. But this sort of microevolution, creationists say, cannot produce macroevolution, such as the creation of totally new body plans. For evidence, they claim that no one has ever seen such transformations happen, and that there are no fossils of the intermediates involved.

Darwin addressed this issue in Origin of Species when he pointed out how rarely fossils form and how sparse their record must be. Despite the scarcity of fossils, paleontologists have found many intermediate forms that creationists have claimed could not exist. Creationists used to get enormous pleasure out of the lack of walking whales, for example. That was before paleontologists starting digging up whale feet.

The many whales with legs that paleontologists have now uncovered are probably ancient cousins of today’s whales rather than direct ancestors. Nevertheless, their position on the evolutionary tree shows how early whales moved from land to the sea. A whale may look radically different from its closest living relatives such as cows and hippos–in fact it may be hard to imagine how one could evolve into the other–but the transitional fossils of whales show how the transformation could have occurred in small steps. Ambulocetus, for example, is an alligator‑like whale that could have swum like an otter by kicking its short legs. Protocetus, on the other hand, had smaller hind legs and looser hips, which allowed it to get more power out of its tail.

Like other transformations documented in the fossil record, the origin of swimming whales seems to have taken place over millions of years a rate of evolution far slower than the sort that has been documented in wild animals, such as the guppies of Trinidad. It’s not possible to predict macroevolutionary patterns from such short‑term change, but the fact remains that if you accept microevolution, you get macroevolution for free.

Paley Rides Again

In the wake of Judge Overton’s 1982 rejection of “creation science,” creationists headed back to the drawing board. They searched for new ways to get their ideas back into the public schools. Today their preferred tactic is simply to strip their claims free of all mention of God and the Bible.

This new strain of creationism goes by the name of Intelligent Design. Life, the argument goes, is so complex that it could not have evolved. Instead, it must have been created by a designer. Exactly who was this designer, you may ask. Arguments for Intelligent Design coyly leave that question open. But traditional creationists see Intelligent Design as a sharp wedge they may be able to use to crack the public school shell. Of Pandas and People, a 1989 book about Intelligent Design intended for children, got this rave review from Answers in Genesis, a Flood Geology organization: “Intended for textbook use in public schools, this superbly written book has no Biblical content, yet contains creationists’ interpretations for classic evidences usually found in standard textbooks supporting evolution.”

Advocates of Intelligent Design claim that they’re at the scientific forefront. Instead of challenging evolution with the old attacks on missing links or the age of the planet, they draw on biochemistry and genetics. They claim that there is an irreducible complexity to the molecular working of life. In order to clot a wound, for instance, a long cascade of chemical reactions creates the clotting molecules. Take out one of the elements in the cascade, and a person bleeds to death. How, then, could evolution have built up this system from simpler parts?

Intelligent Design should sound familiar. It is a new spin on William Paley’s watch lying on the heath over 200 years ago. Paley declared that if you encounter something that is complex, made of parts that each are essential for the whole thing to work, you have found something that must have been designed. The trouble with Paley is that a complex design does not necessarily require a designer.

Lungs, for example, appear to have evolved in fish long before any air‑breathing land vertebrate existed. There are still some primitive, air‑breathing fish alive today, such as the bichir of Africa. Lungs are helpful to the bichir, but not absolutely essential, because it can get oxygen through its gills. But by breathing through its lungs from time to time, a bichir can boost its swimming stamina with an extra supply of oxygen to the heart. Around 360 million years ago, one lineage of air‑breathing fish began spending some time on dry land. As they increased their time out of the water, they adapted their limblike fins to support their weight as they walked. Eventually their gills disappeared altogether. Over the course of millions of years, these early tetrapods became completely dependent on their lungs–a process documented with fossils.

Here we have a complex system (the tetrapod body) that collapses if you take away one part (the lungs). And yet a study of the fossil record and living animals shows that this system is not irreducibly complex. Evolution can add something like a lung because it is advantageous; in time, that added piece of anatomy may become essential, and thus impossible to remove.

Evolution can produce complex biochemistry from simpler precursors in much the same way as it can produce complex anatomy. In recent years, scientists have been able to put together strong hypotheses about two cases: how Antarctic fish keep from freezing to death and how our blood clots.

First the unfrozen fish: a family of species called the notothenioids survive in subfreezing waters thanks to a natural antifreeze in their bloodstream. Their liver creates a sugar‑studded protein that bonds to the surface of microscopic ice crystals and stops them from growing. Antifreeze has allowed notothenioids to thrive in the Antarctic Ocean: 94 species are known so far, with new ones discovered every year.

Making antifreeze is a complex process, and without it the notothenioids would die. But just because it is complex doesn’t mean that evolution could not have produced it. The biochemist Chi‑Hing C. Cheng and her fellow researchers at the University of Illinois have discovered clues as to how the antifreeze gene evolved. They found that it has some remarkable resemblances to another gene expressed not in the liver but in the pancreas, where it produces a digestive enzyme that is injected into the intestines. Cheng found that the instructions for making an antifreeze molecule are contained in a nine‑base sequence that is repeated dozens of times in a single gene. (The repetition allows a single gene to produce a lot of antifreeze.) Cheng discovered that the same nine‑base sequence is embedded in the digestive‑enzyme gene. The only reason that the enzyme gene doesn’t make antifreeze is that the sequence is located in a section of “junk DNA” that gets edited out of the gene before its sequence is used to build a protein.

Cheng discovered other similarities between the antifreeze gene and the digestive‑enzyme gene. At the front of each gene is a sequence that acts like a shipping label, telling cells to secrete their proteins rather than keep them within the cell, and the labels match almost perfectly. And at the end of each gene is a command that tells a cell to stop translating it into RNA; the sequences of the two commands are almost identical.

With these discoveries in hand, Cheng proposed how the antifreeze gene came into being. At some point in the distant past, the digestive‑enzyme gene was accidentally duplicated. The original version continued making its enzyme, while the extra copy went through a series of mutations. The nine‑base sequence was moved to a new part of the gene where it was no longer edited out as junk DNA, but produced a protein: antifreeze. Later, mutations duplicated the nine bases many times over so that the gene could make even more antifreeze. And as the antifreeze portion of the gene grew, the original part that made the digestive enzyme was eliminated. Eventually all that remained of the old gene was the shipping label at the front and the translation‑stopping signal at the end.

Because the original digestive enzyme is made in the pancreas, Cheng suggests that the earliest versions of the antifreeze protein were made there as well. The pancreas produces digestive enzymes that it injects into the intestines to help break down food. Because the fish swallows cold water, the intestines are a prime place for ice to form. As a result, a primitive antifreeze protein in its gut would have allowed a fish to survive in cold waters where it would otherwise freeze to death.

Eventually the signals that control when and where the antifreeze genes become active evolved as well. Instead of switching on in the cells of the pancreas, the antifreeze genes started becoming active in the liver. While the pancreas sends its enzymes to the intestines, the liver can inject enzymes into the bloodstream. By filling the fish’s blood with antifreeze, it could protect the fish’s entire body against ice and let it withstand even colder temperatures.

In 1999 Cheng’s group found a remarkable confirmation of their hypothesis: a chimera gene. In the DNA of an Antarctic fish they discovered a gene that contained the instructions both for making antifreeze and for making the digestive enzyme. This was exactly the sort of intermediate on the path from a digestive gene to a true antifreeze gene that the scientists had predicted.