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Scientists at a large gathering in St. Louis didn't just defend evolution — they rallied in support of it.

Many at the American Association for the Advancement of Science, the nation's largest gathering of scientists, spoke out over the weekend against what they called religious pressure in public schools. And they enlisted the help of about 300 teachers from across the Midwest who attended the conference to discuss the national debate over evolution.

"We are not rolling over on this," Alan Leshner, chief executive of AAAS and executive publisher of the journal Science, told the St. Louis Post-Dispatch. "It's too important to the nation and to the nation's children."

Some teachers told of parents who insist they abandon high school biology texts in favor of biblical creationism or intelligent design — the theory that life is so complex that it must be the work of a supernatural designer. They told of school board pressure in the science classroom.

On Sunday morning, scientists announced the formation of the Alliance for Science, a new organization of scientists, scientific groups and supporters. The goal is to fight what they see as an assault on science from religious conservatives.

The new organization will seek to create graduate fellowships, increase funding for research, train math and science teachers, and build tax incentives for research and development, said co-chairman Paul Forbes.

Earlier last week, a panel outlined tactics that public school teachers and scientists can take, including using the media, educating voters and going to court, if needed.

Critics saw the gathering as a sign of insecurity.

"I don't understand how you can have a discussion of intelligent design if you only invite critics," said John West, a senior fellow at the Discovery Institute, a Seattle think tank that supports scholars researching intelligent design. "That sounds like a monologue, not a discussion. I thought this was supposed to be science, not a pep rally."

The Cleveland, Mo.-based Creation Science Association for Mid America believes in a literal interpretation of the Bible as a basis for much of science. President Tom Willis called the scientists "desperate."

"Most would be out of a job if they couldn't sell evolution to children," Willis said.

But at the conference, middle school teacher Liz Petersen of Ladue said that every year a parent steps close, puts a finger to her nose and says she doesn't want her child to learn evolution. Petersen shrugs it off.

The debate has hit public schools across the country. In December, a judge in Dover, Pa., ruled that intelligent design "is not science."

Last year, a federal judge ordered a school system in Georgia to remove from biology textbooks some stickers that called evolution into question.

Dozens of states are debating the issue. Missouri legislators have tried three times since 2003 to change how science is taught in public schools. Each ultimately failed, but another bill has been introduced this year.