Sadly, it's not because most Americans understand the science behind it. Evolution ain't controversial at the local level BECAUSE IT JUST ISN'T TAUGHT.
Yep, teachers all over the country simply avoid the topic. The NYT details how it's impossible to determine how widespread the practice, but anecdotally it's very common. Even if evolution is in the textbooks and there is no goofy disclaimer that it's "just a theory" (which in scientific terms of course means an idea that is widely accepted with oodles and oodles of evidence to back it up), teachers may assign it for reading but they won't touch the topic in class with a ten foot pole.
Among the sad/funny anecdotes -- one survey shows that one-third of high school biology teachers believe in creationism or at least think it should be taught.
Another good comment:
"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."" says the New York Times.
"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."
God help us.
