While the rest of the world feted the 200th anniversary of Charles Darwin's birth, US scientists were forced to defend the theory of evolution from a skeptical public and a concerted attack campaign.
Top researchers gathered in Chicago presented papers showing how evolution can be witnessed in everything from the genetic similarities between humans and Neanderthals to the way planets form and crows use tools to catch bugs.
"Evolution is not an idea. It's a fact," James McCarthy, president of the American Association for the Advancement of Science said Thursday at the launch of a conference whose theme celebrated Darwin's work.
"It's impossible to deny evolution: the development of drug resistant microbes, pesticide resistant insects, there are abundant examples in ordinary life."
But the message has not gotten through to the US public.
Just 40 percent of Americans say they believe in the theory of evolution, according to a Gallup poll published Wednesday.
And previous polls taken over the past decade have consistently found that between 44 and 47 percent believe God created humans in their present form within the last 10,000 years or so.
"It's a uniquely American problem," McCarthy said.
Evolution is not well taught in US schools and many religious groups advocate a literal interpretation of the Bible.
One such group, which runs a 27 million dollar "Creation Museum" in Kentucky where animatronics dinosaurs frolic with Adam and Eve in the Garden of Eden, is hosting a free conference this weekend refuting evolution.
There are many more working behind the scenes to challenge or limit the teaching of evolution in the classroom, said Eugenie Scott, director of the National Center for Science Education.
"There has been a concerted effort by a pretty well funded movement to educate the public that evolution is weak science, and scientists are giving up on it and making the argument that you have to choose between evolution and religion," Scott told AFP.
The vast anti-evolution movement has developed over the decades, but has been sharply drawn in the courts since the famous 1925 case when a young biology teacher, John Scopes, was put on trial for teaching evolutionary theory in Dayton, Tennessee.
It was not until 1968 that the Supreme Court struck down an Arkansas law making it a crime to teach evolution and ruled that it was unconstitutional to ban the teaching of evolution under the powers of the separation of religion and state.
In 1987, the Supreme Court then ruled it was against the constitution to force creationism to be taught in schools, as that would be promoting religion in the state education system.
In the last decade, a number of attempts have been made to promote the teaching of "intelligent design" -- the contention that life is too complex to have originated without a creator -- as an alternative to evolution.
That theory has also been unable to pass the religious test in the courts, and so anti-evolutionists are instead trying to force teachers to allow for "criticism" of controversial science.
An "academic freedom" bill was passed in Louisiana last year and five other states are currently considering similar legislation, Scott said.
"The latest strategy is not to promote the frank teaching of intelligent design, but to sneak it in through the back door," she said in a telephone interview.
"In the biology business we'd call that adaptation - if nothing else evolves, the creationists do. They're always coming up with ways to subvert evolution."