Evangelical Christians, buoyed by the re-election of Republican President George W. Bush, are turning American schools into a battleground over whether evolution explains the origins of life or whether nature was designed by an all-powerful force.
   
In at least 18 states, campaigns have begun to make public schools teach "intelligent design" - a theory that nature is so complex it could only have been created by design - alongside Charles Darwin's theory of evolution.
   
"It's pretty clear that there is a religious movement behind intelligent design," said Steve Case, chairman of the Science Standards Committee, a group of educators that advises the Kansas Board of Education. The board will decide later this year whether to include intelligent design in biology classes.
   
Some scientists who espouse the theory say intelligent design does not question that evolution occurred but how it occurred: they believe more was at play than random mutation and natural selection. The theory, they insist, does not support the religious concept of a creator.
   
Those who advocate giving it equal treatment in schools have a different interpretation.
   
"Intelligent design promotes a rational basis for belief in God," said John Calvert, managing director of the Kansas-based advocacy group Intelligent Design Network Inc.
   
Americans' resistance to evolution is nothing new.
   
In 1925, Tennessee high school biology teacher John Scopes was prosecuted for teaching evolution in violation of a state law favouring creationism in one of the most celebrated trials in US history. Scopes was convicted and fined $US100 and the Tennessee Supreme Court overturned the verdict on a technicality.
   
Critics, civil liberties groups and many biology teachers, see intelligent design being used as a version of creationism - the theory that God created the world as described in Genesis. The US Supreme Court barred public school teaching of creationism in the 1980s for violating the separation of church and state. 
    
Push from Bush voters 
   
They say the push for intelligent design in America's schools comes from evangelical Christians, a group key to Bush winning a second term last November.
   
Supporters have proposed laws in state assemblies, campaigned for new policies at state and local school boards, and placed stickers in textbooks saying evolution is controversial and that students should consider alternatives.
   
The Dover Area School Board in Pennsylvania now requires that ninth-graders are told there are "gaps" in the theory of evolution, and that intelligent design is an alternative they should consider. The American Civil Liberties Union has challenged the policy in court as unconstitutional.
   
A bill in Missouri would require public school biology textbooks to contain a "critical analysis of origins" and highlight controversial topics "such as biological evolution."
   
According to the National Council for Science Education, a pro-evolution group in Oakland, California, other states considering legislation on the issue include Georgia, South Carolina, Mississippi, Montana, Oklahoma, Alabama, and Texas. Other state or local school boards debating the teaching of intelligent design include Ohio, Arkansas, Wisconsin, Kansas, Wisconsin, Maryland, Michigan, Tennessee and Alaska.
   
Most Americans believe in some form of creationism, according to a CBS poll conducted ahead of last November's election. 55% of Americans believed God created humans in their present form and a further 27% believed humans evolved, but God guided the process.
   
65% of all Americans favoured schools teaching creationism and evolution while 37% wanted creationism taught instead of evolution.
   
The poll found greater support for teaching creationism among Republican voters - 71% of Bush voters favoured teaching creationism alongside evolution.
   
One noted proponent of intelligent design complicates the debate by arguing it should not be taught in high school.
   
John West, a senior fellow at the Seattle-based Discovery Institute, which pioneered intelligent design research, said the theory was too complex to teach at high schools and was better suited to a college setting.
   
"There is a concern that intelligent design has been hijacked by people who don't really know what it says," he said. "We don't think it should be a political football."
   
Many biology teachers, such as those in Pennsylvania who refused to read the school board's statement on intelligent design to students, say the theory is not scientific.
   
"Intelligent design is a religious doctrine," said Wayne Carley, executive director of the National Association of Biology Teachers. "There is no research to support it, and it is clearly religious in that it posits a higher being."
   
Carley conceded the battle against the teaching of intelligent design is a hard one to win because proponents approach the issue as one of faith rather than rationality.
   
"We can argue that it's bad science but people don't want to hear that," he said. "They are coming from a much more basic gut level."