Dr. John Frandsen, a retired zoologist, was at a dinner for teachers in Birmingham, Ala., recently when he met a young woman who had just begun work as a biology teacher in a small school district in the state. Their conversation turned to evolution.
"She confided that she simply ignored evolution because she knew she'd get in trouble with the principal if word got about that she was teaching it," he recalled. "She told me other teachers were doing the same thing."
Though the teaching of evolution makes the news when officials propose, as they did in Georgia, that evolution disclaimers be affixed to science textbooks, or that creationism be taught along with evolution in biology classes, stories like the one Dr. Frandsen tells are more common.
In districts around the country, even when evolution is in the curriculum it may not be in the classroom, according to researchers who follow the issue.
Teaching guides and textbooks may meet the approval of biologists, but superintendents or principals discourage teachers from discussing it. Or teachers themselves avoid the topic, fearing protests from fundamentalists in their communities.
"The most common remark I've heard from teachers was that the chapter on evolution was assigned as reading but that virtually no discussion in class was taken," said Dr. John R. Christy, a climatologist at the University of Alabama at Huntsville, an evangelical Christian and a member of Alabama's curriculum review board who advocates the teaching of evolution. Teachers are afraid to raise the issue, he said in an e-mail message, and they are afraid to discuss the issue in public.
Dr. Frandsen, former chairman of the committee on science and public policy of the Alabama Academy of Science, said in an interview that this fear made it impossible to say precisely how many teachers avoid the topic.
"You're not going to hear about it," he said. "And for political reasons nobody will do a survey among randomly selected public school children and parents to ask just what is being taught in science classes."
But he said he believed the practice of avoiding the topic was widespread, particularly in districts where many people adhere to fundamentalist faiths.
"You can imagine how difficult it would be to teach evolution as the standards prescribe in ever so many little towns, not only in Alabama but in the rest of the South, the Midwest - all over," Dr. Frandsen said.
Dr. Eugenie Scott, executive director of the National Center for Science Education, said she heard "all the time" from teachers who did not teach evolution "because it's just too much trouble."
"Or their principals tell them, 'We just don't have time to teach everything so let's leave out the things that will cause us problems,' " she said.
Sometimes, Dr. Scott said, parents will ask that their children be allowed to "opt out" of any discussion of evolution and principals lean on teachers to agree.
Even where evolution is taught, teachers may be hesitant to give it full weight. Ron Bier, a biology teacher at Oberlin High School in Oberlin, Ohio, said that evolution underlies many of the central ideas of biology and that it is crucial for students to understand it. But he avoids controversy, he said, by teaching it not as "a unit," but by introducing the concept here and there throughout the year. "I put out my little bits and pieces wherever I can," he said.
He noted that his high school, in a college town, has many students whose parents are professors who have no problem with the teaching of evolution. But many other students come from families that may not accept the idea, he said, "and that holds me back to some extent."
"I don't force things," Mr. Bier added. "I don't argue with students about it."
In this, he is typical of many science teachers, according to a report by the Fordham Foundation, which studies educational issues and backs programs like charter schools and vouchers.
Some teachers avoid the subject altogether, Dr. Lawrence S. Lerner, a physicist and historian of science, wrote in the report. Others give it very short shrift or discuss it without using "the E word," relying instead on what Dr. Lerner characterized as incorrect or misleading phrases, like "change over time."
Dr. Gerald Wheeler, a physicist who heads the National Science Teachers Association, said many members of his organization "fly under the radar" of fundamentalists by introducing evolution as controversial, which scientifically it is not, or by noting that many people do not accept it, caveats not normally offered for other parts of the science curriculum.
Dr. Wheeler said the science teachers' organization hears "constantly" from science teachers who want the organization's backing. "What they are asking for is 'Can you support me?' " he said, and the help they seek "is more political; it's not pedagogical."
There is no credible scientific challenge to the idea that all living things evolved from common ancestors, that evolution on earth has been going on for billions of years and that evolution can be and has been tested and confirmed by the methods of science. But in a 2001 survey, the National Science Foundation found that only 53 percent of Americans agreed with the statement "human beings, as we know them, developed from earlier species of animals."
And this was good news to the foundation. It was the first time one of its regular surveys showed a majority of Americans had accepted the idea. According to the foundation report, polls consistently show that a plurality of Americans believe that God created humans in their present form about 10,000 years ago, and about two-thirds believe that this belief should be taught along with evolution in public schools.
These findings set the United States apart from all other industrialized nations, said Dr. Jon Miller, director of the Center for Biomedical Communications at Northwestern University, who has studied public attitudes toward science. Americans, he said, have been evenly divided for years on the question of evolution, with about 45 percent accepting it, 45 percent rejecting it and the rest undecided.
In other industrialized countries, Dr. Miller said, 80 percent or more typically accept evolution, most of the others say they are not sure and very few people reject the idea outright.
"In Japan, something like 96 percent accept evolution," he said. Even in socially conservative, predominantly Catholic countries like Poland, perhaps 75 percent of people surveyed accept evolution, he said. "It has not been a Catholic issue or an Asian issue," he said.
Indeed, two popes, Pius XII in 1950 and John Paul II in 1996, have endorsed the idea that evolution and religion can coexist. "I have yet to meet a Catholic school teacher who skips evolution," Dr. Scott said.
Dr. Gerald D. Skoog, a former dean of the College of Education at Texas Tech University and a former president of the science teachers' organization, said that in some classrooms, the teaching of evolution was hampered by the beliefs of the teachers themselves, who are creationists or supporters of the teaching of creationism.
"Data from various studies in various states over an extended period of time indicate that about one-third of biology teachers support the teaching of creationism or 'intelligent design,' " Dr. Skoog said.
Advocates for the teaching of evolution provide teachers or school officials who are challenged on it with information to help them make the case that evolution is completely accepted as a bedrock idea of science. Organizations like the science teachers' association, the National Academy of Sciences and the American Association for the Advancement of Science provide position papers and other information on the subject. The National Association of Biology Teachers devoted a two-day meeting to the subject last summer, Dr. Skoog said.
Other advocates of teaching evolution are making the case that a person can believe both in God and the scientific method. "People have been told by some evangelical Christians and by some scientists, that you have to choose." Dr. Scott said. "That is just wrong."
While plenty of scientists reject religion - the eminent evolutionary theorist Richard Dawkins famously likens it to a disease - many others do not. In fact, when a researcher from the University of Georgia surveyed scientists' attitudes toward religion several years ago, he found their positions virtually unchanged from an identical survey in the early years of the 20th century. About 40 percent of scientists said not just that they believed in God, but in a God who communicates with people and to whom one may pray "in expectation of receiving an answer."
Luis Lugo, director of the Pew Forum on Religion and Public Life, said he thought the great variety of religious groups in the United States led to competition for congregants. This marketplace environment, he said, contributes to the politicization of issues like evolution among religious groups.
He said the teaching of evolution was portrayed not as scientific instruction but as "an assault of the secular elite on the values of God-fearing people." As a result, he said, politicians don't want to touch it. "Everybody discovers the wisdom of federalism here very quickly," he said. "Leave it at the state or the local level."
But several experts say scientists are feeling increasing pressure to make their case, in part, Dr. Miller said, because scriptural literalists are moving beyond evolution to challenge the teaching of geology and physics on issues like the age of the earth and the origin of the universe.
"They have now decided the Big Bang has to be wrong," he said. "There are now a lot of people who are insisting that that be called only a theory without evidence and so on, and now the physicists are getting mad about this."