Two centuries after Charles Darwin's birth on Feb. 12, 1809, people still argue passionately about his theory of evolution.
Was Darwin right? Should schoolchildren be exposed to contrary views in science class? These two controversies continue to rage, partly because both sides are evenly matched.
Most scientists and courts that have ruled on the matter say that overwhelming evidence backs Darwin's explanation of the origin and evolution of species, including humans, by natural selection.
Many people, especially religious and social conservatives, strongly disagree.
Among them are "creationists," who take literally the Genesis story that God created the world and mankind in six days no more than 10,000 years ago. Others support "intelligent design," the idea that life is too complex to have arisen without a supernatural "designer," presumably God.
Public opinion surveys consistently have shown that Americans are deeply divided over evolution. The most recent Gallup poll on the issue, in June 2007, found that 49 percent of those surveyed said they believed in evolution and 48 percent said they didn't. Those percentages have stayed almost even for at least 25 years.
Gallup found a political angle to the split. Two-thirds of Republicans rejected Darwin's theory, while majorities of Democrats and political independents accepted it.
A Harris poll published last December found that more people believe in a devil, hell and angels than in evolution.
The controversy is most acute in the public schools, where conservatives want evolution banished from science classes or at least described as "a theory, not a fact."
Darwin's supporters counter that to scientists a theory isn't just a guess or a hypothesis but a widely accepted explanation of natural events supported by the best available evidence.
At a recent hearing before Texas' State Board of Education, scientists and social conservatives exchanged fiery arguments over a rule that requires science textbooks to cover "the strengths and weaknesses" of evolutionary theory.
Darwin critics control seven of the 15 seats on the board and have the support of Republican Gov. Rick Perry. The chairman of the board, Don McLeroy, a dentist, is a creationist who believes that the Earth is only thousands of years old, not billions as most scientists think. The board will decide the issue in March.
Louisiana's State Board of Elementary and Secondary Education adopted guidelines Jan. 15 that allow teachers to use "supplemental materials" that aren't in regular textbooks about "controversial" subjects such as evolution and global warming.
Louisiana's new rules "ensure the state's teachers their right to teach the scientific evidence both for and against Darwinian evolution," according to the Seattle-based Discovery Institute, the headquarters of the intelligent design movement.
"We fully expect to see the Discovery Institute's book, 'Explore Evolution,' popping up in school districts across the state," Barbara Forrest, a Darwin supporter in Hammond, La., told Science magazine.
The Louisiana school board also eliminated language that had banned the teaching of creationism or intelligent design, saying that the ban is unnecessary.
"The creationists got what they wanted," said Patsye Peebles, a retired Louisiana science teacher.
The opposition to the Discovery Institute is led by the National Center for Science Education, a pro-Darwin research center based in Oakland, Calif.
The center contends that intelligent design is a subtle way to introduce religion into science education, which the courts consistently have declared unconstitutional.
"The phrase 'strengths and weaknesses' has been spread nationally as a slogan to bring creationism in through the back door," center executive director Eugenie Scott told the Texas school board.
Similar proposals are pending or expected in Alabama, Arkansas, Florida, Georgia, Michigan, Missouri, Oklahoma and South Carolina, according to Glenn Branch, the deputy director of the National Center for Science Education.
"In a typical year, NCSE will be monitoring about 80 episodes of creationist activity in the United States and abroad," Branch said.
"This issue isn't going away," John West, a senior fellow at the Discovery Institute, wrote in an e-mail to his allies last May. "Although Darwinists are doing their best to shut down and intimidate anyone who raises questions about neo-Darwinism, we still have free speech, and they can't prevent people from hearing about the debate in the public arena, no matter how hard they try."
The theory of evolution itself is evolving. Since Darwin's day, researchers have acquired powerful tools that revealed DNA's role in passing inheritance from generation to generation, something Darwin knew nothing about.
Around the middle of the 20th century, this led to the "Modern Synthesis," a major updating of evolutionary theory to accommodate new information. Many biologists are suggesting still another revision, which some call "Modern Synthesis 2.0."
For example, Darwin described evolution as the growth of a tree, the "Tree of Life." The tree began with a single, original organism at the root, with myriad species branching off from the trunk.
Biologists increasingly say that evolution resembles a web or a bush rather than a tree. Microbes constantly swap DNA. Hybrid plants and animals cross species lines, blurring sharp lines between species.
"We understand evolution pretty well," said W. Ford Doolittle, a Darwin supporter and biologist at Dalhousie University in Halifax, Nova Scotia. "It's just that it's more complex than Darwin imagined."
ON THE WEB
Discovery Institute: discovery.org/csc
National Center for Science Education: www.ncseweb.org
(c) 2009, McClatchy-Tribune Information Services.
Visit the McClatchy Washington Bureau on the World Wide Web at www.mcclatchydc.com>
Explore further: All about the fossilized bones of (maybe) Homo naledi