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IN NOVEMBER of 1995, the Alabama Department of Education required all biology textbooks used in the state to display a disclaimer informing the young reader that this textbook discusses evolution, a controversial theory some scientists present as a scientific explanation for the origin of living things, such as plants, animals and humans. No one was present when life first appeared on earth, therefore, any statement about life's origins should be considered as theory, not fact.

The governor of Alabama in March of 1996 sent all biology teachers a copy of an antievolution book, Darwin on Trial, using his discretionary funds.

Shortly thereafter, another "evolution as theory rather than fact" law was considered in a nearby state. In March of 1996, the Tennessee legislature debated and ultimately rejected a requirement that no teacher or administrator in a local education agency shall teach the theory of evolution except as a scientific theory. Any teacher or administrator teaching such theory as fact commits insubordination.... (Tennessee HB 2972/SB 3229, 1996)

Also during the spring of 1996, Georgia voted down an amendment to an education bill that would "provide that local boards of education may establish optional courses in creationism;" and as part of any science curriculum wherein students are taught concerning the origins of life and living things, including the origins of humankind, teachers shall have the right to present and critique any and all scientific theories about such origins and all facets thereof, including without limitation scientific theories other than evolutionism.

"Critiques of evolution", or "arguments against evolution" are code-phrases for creation science, stimulated by Supreme Court Justice Antonin Scalia's dissent to Edwards v. Aguillard, the 1987 case that struck down "equal time for creationism and evolution" laws. Another "arguments against evolution" law was debated by the Senate Education Committee of the Ohio state legislature in May of 1996. It was ultimately rejected (by a vote of 12 - 8). The wording directed that whenever a theory of the origin of humans or other living things that might commonly be referred to as "evolution" is included in the instructional program provided by any school district or educational service center, both scientific evidence and related arguments supporting or consistent with the theory and scientific evidence and related arguments problematic for, inconsistent with, or not supporting the theory shall be included.

And, as this essay was being written, news arrived to the office of National Center for Science Education (NCSE) that the Cobb County, Georgia school district had requested MacMillan-McGraw Hill to delete a chapter on the Big Bang and earth's origin in an earth science booklet for fourth graders, after parents complained. Newspaper accounts reported that MacMillan would comply.

What's going on here? Clearly, pressure against the teaching of evolution has not abated, and (judged from the increasing number of calls for help that NCSE receives) even appears to be on the rise (Gillis, 1994; Scott, 1994; 1996.) What is it about evolution, more than any other scientific theory, that elicits this response? The Alabama disclaimer "no one was present" argument is especially puzzling, as many phenomena studied in modern science are not observed directly. In fact, no one has stood in space and observed the earth making its circuit around the sun through the course of a year, but we do not hear protestations that heliocentrism should be considered just a guess or hunch (the street definition of "theory.")

Heliocentrism, as Galileo discovered, was once considered a challenge to religion, because it was thought to conflict with the Bible. The Bible, read literally, assumes the ancient view of the cosmos that the earth is the center of the solar system and the sun revolves around it. Few Americans these days interpret the Bible as a geocentric document, but a healthy percentage still accept a literal reading of Genesis regarding the separate creation of plants and animals as independent "kinds". This belief contrasts starkly with the scientific concept that living species are descended with modification from ancestors that differed from then. Thus evolution, and not theologically-acceptable heliocentrism, is vigorously opposed by an active segment of modern American society.

Antievolutionism extends beyond mere Biblical literalism, however, as shown by comparing survey data on American religious opinions with survey data on attitudes towards evolution. Polls of adult Americans have consistently shown over the last fifteen years or so that a substantial proportion of us do not think humans evolved (whether other creatures evolved is usually not part of the standard query.) In May of 1996, the National Science Foundation released results from a telephone survey of 2,006 individuals who were asked questions about basic science literacy (Petit, 1996.) One question was, "Human beings as we know them today, developed from earlier species of animals." Only 44% of Americans answered "True". In 1994, the American Museum of Natural History asked "Human beings evolved from earlier species of animals, true or false" and only 45% agreed — results virtually identical to the NSF study.

Defining religious conservatism is tricky, as there is no uniform agreement on terms. One term for conservative Christians is "evangelical." Evangelicals are Christians who believe the Bible is inerrant, and that salvation is achieved only through Christ (Hunter, 1983.) According to Marsden (1987), about 20% of Americans are evangelicals, far fewer than the 44% of Americans who reject evolution.

In a nutshell, there is more antievolutionism than there are religious conservatives: antievolutionism appeals both to evangelicals as well as Americans who adhere to religiously-moderate faiths. There is an irony here: the "official" theologies of Catholic and mainstream Protestant Christianity are not literalist, and have accommodated evolution as the way God created (Scott, 1995.) NCSE's book, Voices for Evolution (Matsumura, 1995), includes a collection of statements from the Roman Catholic Pope, the Episcopalians, Methodists, United Church of Christ, Presbyterians, and the Lutheran World Federation (and several Jewish groups) all expressing respect for science and for evolution as part of science. Nonetheless, even if the ministers, priests and rabbis accept evolution, many people on the other side of the pulpit appear largely ignorant of their own theology!

It is important for those of us trying to teach evolution to recognize that many of our fellow citizens find evolution profoundly disturbing. They have been told or have somehow acquired the belief (sometimes from scientists, unfortunately) that evolution "proves" that there is no purpose to life, that life has no meaning, that they must give up their sense of the divine. According to a respected City College of New York poll, 90% of Americans describe themselves as religious (Goldman, 1991.) If evolution is presented as antithetical to religion (which is precisely how organizations such as the Institute for Creation Research present it), it is no wonder that a high percentage of Americans reject it. Actually, as suggested by the selections in Voices for Evolution, mainline Christianity can accommodate evolution, though it is doubtful that Biblical literalism can. As teachers and scientists, we need to leave an opportunity for the religious individual to work out the accommodation according to his or her beliefs, and not slam the door by inserting extra-scientific philosophical statements about purpose and meaning into our discussions of evolution. I will discuss this in greater detail below.
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Evolution is a necessary part of the science curriculum. A biology or earth science course taught without the inclusion of evolution is an inferior course. Students who take these courses without being told that evolution unifies the data and concepts of the field are being cruelly short-changed. They will leave the course having being misled that science largely consists of the tedious memorization of lists of facts, rather than a tool we can use to help us understand the world of nature. This episodic, atomistic view of science is particularly regrettable: it turns students away from studying science, and perhaps worse yet, defeats our efforts to produce a scientifically literate society.

Evolution needs to be taught, but some teachers will be doing so in a hostile environment. How can teachers present this topic and avoid the potential minefields? Or, since some of the land mines are unavoidable, how can a teacher defuse them?

Evolution Happened — First, teachers need to be confident that evolution is state of the art science. A common claim made by antievolutionists is that evolution is a "theory in crisis," in the words from the title of a popular antievolution book (Denton, 1985.) Many teachers have not studied evolution, feel unconfident about teaching it, and are susceptible to being swayed by "new" information that "evolution is not as well accepted as it used to be". Evolution is presented matter-of-factly at every decent college or university in this country, including Brigham Young, Notre Dame, and Baylor. It is simply untrue that evolution is being widely challenged by scientists themselves. Help your colleagues to understand that scientists do not debate whether evolution (change through time, descent with modification) took place, though they vigorously argue how it took place — the processes, mechanisms and details of evolution. The previously-mentioned Voices for Evolution contains 33 statements from scientific organizations, all of which reassure teachers that evolution is indeed the reigning paradigm explaining how the universe came to be in its present state. Some statements, such as that from the National Academy of Sciences' booklet Science and Creationism, clearly distinguish between evolution as something which should be taught in the science classroom, and creation science which should not:

...the Academy states unequivocally that the tenets of "creation science" are not supported by scientific evidence, that creationism has no place in a science curriculum at any level, that its proposed teaching would be impossible in any constructive sense for well-informed and conscientious science teachers, and that its teaching would be contrary to the nation's need for a scientifically literate citizenry and for a large well-informed pool of scientific and technical personnel. (Committee on Science and Creationism, 1984, p. 7-8.)

As scientists agree that evolution is a crucial part of science, so also do educators. The National Science Education Standards, released in February of 1996, present evolution as one of the "Unifying Concepts and Processes," as well as listing it prominently in the Content Standards for grades 9-12. Anticipating a tendency for states and districts to pick and choose among the standards rather than truly revise their curricula, the publication states firmly that, "No standards should be eliminated from a category." Perhaps presciently, the Standards chose evolution as a negative example. "For instance, 'biological evolution' cannot be eliminated from the life science standards." (National Research Council, 1996, p. 112.)

"Benchmarks for Science Literacy," the 1993 publication by the American Association for the Advancement of Science's Project 2061: Science for All Americans, cites evolution as an integral part of the science curriculum. Similarly, the California Science Framework and the curricula of most other states require evolution to be presented. (Some disguise it as "change through time," and confuse ontogeny with phylogeny by referring to evolution as "development.") Voices for Evolution includes statements from 30 science education organizations including the National Science Teachers Association, the National Association of Biology Teachers, and the National Science Supervisors Association — all exhorting science educators to teach evolution and not present creation science. If evolution is a "theory in crisis," somehow the entire science and education establishments are unaware of it.
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Now, appealing to authority may often be effective with students, but it is hardly something we wish to encourage! Opponents of evolution rely exceedingly heavily upon (out of context) quotations from authorities like Stephen Jay Gould in their attacks upon evolution. Because "famous scientist X" said something, it supposedly should be accepted. As it happens, when it comes to appeals to authority, the pro-evolution side wins hands down! We have the National Academy of Science, the Nobel laureates, and all the other heavy hitters of big science — but what is more important, we have the science itself. Teachers need to be familiar with the data and theory of evolution, and why this theory has such strong explanatory power. Evolution is accepted by scientists today because it explains more observations than any alternative. Any of a number of basic college level biology and especially evolution textbooks will provide teachers with plenty of evidence for evolution being the unifying theory explaining observations from biogeography, comparative anatomy, comparative biochemistry, the fossil record, developmental biology, and many other fields.

Define Evolution — A colleague in physical anthropology teaching a small college in the Southeast told me she was teaching a class of freshmen college students and found that none of them had ever studied evolution or even knew what evolution was. When they found out, they found the concept exciting and intellectually challenging, and they clamored for a special course on the topic. Their response, in her words, was "Of course species change through time! You mean that's evolution?!"

Sometimes finding out what evolution actually is (or more precisely, replacing erroneous ideas about evolution) in itself reduces students' reluctance to learn about it. A proper definition of evolution is important to helping students understand the concept.

It's been my experience (and perhaps yours too) that most non-scientists think evolution means "man evolved from monkeys," which is an exceedingly narrow definition. It is both scientifically accurate as well as strategically wise to embed evolution within the broadest scientific context possible. Evolution isn't just about humans, or even about living things. Astronomers do, after all, study cosmic evolution. Geologists and geophysicists study the evolution of the planet earth, and evolution is the organizing concept of earth science just as it is for the life sciences. Biologists and biochemists study the change through time of living things. Rejection of evolution doesn't mean merely rejection of "man evolved from monkeys," but rejection of principles relevant (and in some cases crucial) to modern science.

The word "evolution" is defined and used in many different ways, some more useful and accurate than others. Embedding evolution in a wide range of sciences requires a broad definition. What unites astronomical, geological, and biological evolution is the concept of change through time. But "change through time" can also refer to phenomena like the water cycle, or the rotation of the earth around the sun, or the passage of energy through a food chain, or the metamorphosis of insects. Not all change is evolution, so we must distinguish evolution as being cumulative change through time. The evolution of a star from white dwarf to supernova is one such cumulative change.

When we discuss organic evolution, we must be especially precise. Here I part company with many of my colleagues: I do not find the traditional "evolution is changes in gene frequencies through time" to be a useful definition, even if it were modified to be "cumulative changes in gene frequencies through time." Especially at the beginning of a course, who knows what a gene frequency is? The genetically-based definition of evolution is useful in understanding the major constituents of evolution (genetic variation, adaptation, reproductive isolation/speciation), but if a teacher waits until students understand all of the related concepts, it will be the end of the semester. If evolution is to be taught as the organizing principle of biology, we shouldn't wait until the end of the semester to let them in on the secret! I find that even college students lose track of the relationship of evolution to biology using this genetically-based definition, and I am sure high school students will also.

What do we want students to know about organic evolution? The "Big Idea" is that living things (species) are related to one another through common ancestry from earlier forms that differed from them. Darwin called this "descent with modification," and it is still the best definition of evolution we can use, especially with members of the general public and with young learners. Descent with modification makes biology make sense. We can study and understand the workings of evolution using genes, cells, fossils, ecology, taxonomy — you name the biological subfield, and evolution is there.

For example, everyone teaches some taxonomy in high school and junior high. But how many explicitly teach how the concept of descent with modification makes it possible to group organisms into taxa? Horses and donkeys are similar because they shared a common ancestor quite recently, geologically speaking (in fact, they can still interbreed, though the hybrid is sterile.) The horse/donkey group can be grouped with zebras because it shared a common ancestor with zebras, and so on up through genera, families, orders, classes, and phyla. Most of the time taxonomy is taught backwards: organisms are classed together because they are similar. Wrong. They are classed together and they are similar because they shared a common ancestor.

A good example of a confused understanding of evolution is even found in some textbooks. How many times have you seen the peppered moth or other cases of industrial melanism used as an example of evolution? It is an example of change, but fluctuating change. Remember that the frequencies of melanic genes shifted back to their pre-industrial lows after scrubbers were placed on smokestacks and air pollution was reduced. Industrial melanism is an example of natural selection, not of evolution. A good exercise would be to have the students figure out whether industrial melanism could be an example of evolution (as in our definition of "descent with modification.") (Hint: add reproductive isolation and speciation!)

Define Theory — Not incidentally, teachers also need to be clear in their minds about what a "theory" is, because (as illustrated in the examples with which I opened this essay) evolution is under attack for being "just" a theory. The problem is that "theory" is used outside of science in a deprecating way as a synonym for guess or hunch. What is a "fact" and what is a "theory?"

A fact is a confirmed observation. For example, it is a confirmed observation that every tetrapod known has at some stage of its life, a humerus, a radius and ulna, and a distal cluster of bones corresponding to carpals, metacarpals and phalanges. The general public (and even some scientists) use the word "fact" to imply capitol T "Truth": unchanging agreement. In science, facts, like theories, may change: it was once a fact (for about 10 years) that Homo sapiens had 48 chromosomes. But other observations were confirmed and explanations found for the erroneous observations, and now we know that there are 46. In general, though, in science we treat facts as statements we don't need to test and question anymore, but rather can use as givens to build more complex understandings.

A theory, in science, is a logical construct of facts and hypotheses that attemptsto explain a natural phenomenon. It is an explanation, not a guess or hunch that one can casually disregard. Theory formation — explanation — is the goal of science, and nothing we do is more important. A scientist joked that we should applaud the Tennessee law punishing teachers for teaching evolution as a "fact rather than a theory" because "everyone knows that theories are more important than facts!" Theories explain facts, but the general public doesn't know that.

Concerning evolution, then, what's a fact and what's a theory? One hears from many scientists, "Evolution is FACT!!!" The meaning here is that evolution, the "what happened," is so well supported that we don't argue about it, anymore than we argue about heliocentrism versus geocentrism. We accept that change through time happened, and go on to try to explain how. What we mean and what is heard is often different, however. What the public often hears when scientists say "Evolution is FACT!" is that we treat evolution as unchallengeable dogma, which it isn't.

We must learn to present evolution not as "a fact" in this dogmatic sense, but "matter of factly," as we would present heliocentrism and gravitation. Most people consider heliocentrism and gravitation as "facts", but they are not "facts" in my definition of "confirmed observations." Instead, they are powerful inferences from many observations, which are not in themselves questioned, but used to build more detailed understandings.

From the standpoint of philosophy of science, the "facts of evolution" are things like the anatomical structural homologies such as the tetrapod forelimb, or the biochemical homologies of cross species protein and DNA comparisons, or the biogeographical distribution of plants and animals. The "facts of evolution" are observations, confirmed over and over, such as the presence and/or absence of particular fossils in particular strata of the geological column (one never finds mammals in the Devonian, for example.) From these confirmed observations we develop an explanation, an inference, that what explains all of these facts is that species have had histories, and that descent with modification has taken place. Evolution is thus a theory, and one of the most powerful ones in science.

We may also speak of "theories" (plural) of evolution, in the sense of the explanations for how descent with modification has taken place. It is conceptually sound to separate evolution as something that did or did not happen from explanations about how, or how fast, or which species are related to which. I'll return to this idea below.

Indeed, teachers have to be sure that students know what theories are and why they are important. Students also must — this is crucial — learn as part of their science instruction that our explanations change with new data or better ways of looking at things. Antievolutionists make the statement that "evolution isn't science because you guys are always changing your minds about stuff." This is not a criticism. That's the way a vigorous science works.

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