If you want to know one reason why the debate over teaching evolution remains so contentious, consider the stickers some school boards have wanted to paste in high school biology textbooks. They label evolution a "theory, not a fact," suggesting that an alternative explanation is possible.
It's a clever strategy. Even people sympathetic to evolution often don't know how to respond to the assertion that evolution is "just a theory." And the opposite claim -- that evolution is a fact -- can generate skepticism among those who don't like to be told what to think.
The Origin of Intelligent Design|
It's an idea with a history as illustrious as its mere mention today can be contentious: that the order and complexity of the natural world are evidence of supernatural design. So-called natural theology is a doctrine that can be traced back to the Bible and that shaped the thinking of such early Christian philosophers as Thomas Aquinas.
One of the influential proponents of the notion that the existence of God could be understood by studying His creation was English philosopher John Ray (1628-1705). Ray's cataloguing of mammals, birds, fish, insects and plants inspired subsequent naturalists to collect and classify organisms as a reflection of the divine order of creation.
"There is for a free man no occupation more worthy and delightful," wrote Ray, "than to contemplate the beauteous works of nature and honour the infinite wisdom and goodness of God."
Ray's systems brought order to the chaotic study of nature. His insight that fossils were once living organisms overturned popular hypotheses of his time (that they were, for example, lusi naturae or mere games of nature). And, by encouraging naturalists to look at an organism's form in relation to its function, he paved the way for studies of adaptation.
A century later, English theologian William Paley (1743-1805) elaborated on these concepts in his "Evidences of the Existence and Attributes of the Deity, Collected from the Appearances of Nature." Using his famous analogy of a watchmaker, Paley inferred the existence of a creative god:
"In crossing a heath, suppose I pitched my foot against a stone, and were asked how the stone came to be there: I might possibly answer, that for any thing I know to the contrary, it had lain there for ever. . . But suppose I had found a watch upon the ground, and it should be inquired how the watch happened to be in that place; . . . . when we come to inspect the watch, we perceive (what we could not discover in the stone) that its several parts are framed and put together for a purpose . . . This mechanism being observed . . . the inference, we think, is inevitable, that the watch must have had a maker . . . who comprehended its construction, and designed its use."
Just as the watch's complexity provides evidence of a watchmaker, Paley reasoned, so the natural world's complexity provides evidence of a worldmaker.
This "argument from design" prevailed until Charles Darwin published his "Origin of Species" in 1859, shattering the existing paradigm.
Few scientists held out against the empirical evidence for natural selection that Darwin presented, but among them was one of the founders of the modern American scientific tradition, paleontologist Louis Agassiz (1807-1873).
Agassiz, whose vast private collection of fossils formed the nucleus for Harvard's Museum of Comparative Zoology, openly opposed Darwinism. He believed that the study of natural history was ultimately analogous to the analysis of God's thoughts.
"The combination in time and space of all these thoughtful conceptions exhibits not only thought," he wrote, "it shows also premeditation, power, wisdom, greatness, prescience, omniscience, providence. In one word, all these facts in their natural connection proclaim aloud the One God, whom man may know, adore, and love."
The arguments have evolved, but many of today's proponents of intelligent design echo the fundamental philosophy of the pre-Darwinian thinkers. In the words of one of the movement's leaders, William A. Dembski: "Undirected natural processes like the Darwinian mechanism are incapable of generating the specified complexity that exists in biological organisms . . . the natural sciences need to leave room for design." Evolutionary scientists, on the other hand, point to powerful evidence to demonstrate that the mechanisms described by Darwin are perfectly capable of explaining the complexity of life.
-- Frances Stead Sellers, for the Outlook staff
But these stickers use the words "theory" and "fact" in a very misleading way. The biggest problem is that "theory" has two separate meanings. In common usage, "theory" means an idea or a hunch: "I have a theory about why she left him." No one really knows what the reasons were, but we can guess.
That's not what "theory" means within science. When scientists speak of the theory of gravitation, cell theory or evolutionary theory, they are talking about scientific concepts that have been so thoroughly tested that they are very unlikely to change. Theories are the results of decades or centuries of scientific effort. They draw on many interconnected observations and ideas. They are the end products of science, not stages on the way to the truth.
In science, a hunch or conjecture is called a hypothesis, not a theory. When Copernicus proposed in the early 16th century that the Earth revolves around the sun rather than vice versa, his idea was a hypothesis. But four centuries of observation and thinking have convinced us that heliocentrism is a theory, not just an intriguing idea. It is compatible with everything we know about the solar system and explains observations that cannot be explained in other ways.
Ideally, English would have a different word for these comprehensive organizing concepts in science. But for now, "theory" is doing double duty. So calling evolution a theory may seem to denigrate it in everyday terms, but in scientific terms that's high praise.
"Fact," on the other hand, is a word that makes many scientists uncomfortable. It implies that something is true beyond doubt. But the defining characteristic of a scientific statement is that its accuracy can be tested by comparing it to observations in the natural world; in other words, a scientific statement must be falsifiable. Accepting that something is true beyond doubt requires an act of faith. But that is a religious matter -- and science cannot aspire to the certainty of religion.
Many scientists are as loose with these terms as nonscientists are. They, too, speak blithely of theories when they mean hypotheses, despite the grief it causes evolutionary biologists. Partly, they are being careless. And maybe they lean toward the term because they know that theories are much more solidly established than are hypotheses. (Your idea may be a hypothesis, but mine is a theory.)
Evolution is not a hypothesis. It is a rich theory, built on hundreds of years of scientific research, that explains why the biological world is the way it is. It provides a mechanism for the continual change of biological organisms over time, beginning with the simplest replicating molecules. It accounts for the simultaneous diversity and unity of the living things we see around us.
No one can study biology for long without marveling at the rigor and creativity of the processes that produce biological change. The signature of evolution is apparent in every biological molecule, every organism, every ecosystem. The evidence for evolution is so overwhelming that biologists have trouble understanding how someone could not accept it. Researchers continue to investigate many interesting questions about evolution, such as how quickly or slowly it takes place. But studying whether evolution has occurred would be akin these days to studying whether the sun revolves around the Earth.
No empirical evidence supports the hypothesis put forth by creationism -- that God either created the world in its current form or directed the process of evolution. On the contrary, we would need the patience of Job to believe that God created the appearance of evolution as an illusion to test our faith.
If the proponents of creationism uncovered some facet of the biological world that contradicted the theory of evolution, some scientists -- though perhaps not all -- would be intensely interested. Coming across an anomaly in science is like winning the lottery. Unexplained findings can offer a shortcut to scientific fame, as when Alexander Fleming noticed that mold was preventing the growth of staph bacteria in culture. But creationists have not come up with a single scientific observation that undercuts evolution. Biologists have demolished the few arguments that creationists have proposed, such as the idea of "irreducible complexity." And at this point, creationist organizations such as the Discovery Institute in Seattle are spending most of their money on public relations rather than research.
Creationism is a religiously motivated idea, as U.S. courts, including the Supreme Court, have repeatedly affirmed. The same applies to creationism's most recent incarnation, intelligent design. Proponents of intelligent design argue that evolutionary theory is not yet sophisticated or complete enough to answer every question about the history of life, such as how life originated (though very interesting scientific work is being done on this question). Therefore a designer must be responsible for those features of the biological world where evolutionary processes remain unclear. But this God-of-the-gaps approach has repeatedly failed as science has progressed. And, again, it assigns to God a role in the material world that doesn't fit with what many religious people believe.
Despite the logical flaws in creationist arguments, scientists would be well served by finding more constructive ways to engage in the debate. When creationism is denied a hearing, those who are ambivalent have fewer opportunities to evaluate the evidence. Religion should not be taught in science classes, but suppressing discussion of creationism can create the mistaken impression that scientists have something to hide. And creationism is far from absent in many high school biology classes -- surveys reveal that many teachers already discuss it.
In Victorian England, scientists and creationists debated the merits of the case -- as in the famous confrontation between Darwinian scientist Thomas Huxley and cleric Samuel Wilberforce -- and science generally prevailed. At Cornell University, historian of biology William Provine organizes debates between creationists and biologists for his undergraduates and for a local school district, and he insists that students come away from these events with a much better understanding and appreciation of evolution.
For scientists, confronting creationism can be an endless and thankless task -- there are always more creationists who want to argue. And debates on the subject can be difficult for nonspecialists to follow, especially if creationists employ the arcane terminology of science. Still, scientists have an obligation to defend science against those who would undermine it.
This debate is not going to go away. Relatively few people in the United States believe that human beings evolved from nonhuman organisms without divine intervention. At the same time, most people are willing to acknowledge that evolution has occurred. Careful attention to how we speak and think about these ideas will not necessarily reduce the tension between them. But it might produce discussions that are a lot more enlightening.
Steve Olson, a writer who lives in Bethesda, is the author of "Evolution in Hawaii" (National Academies Press).