The study identified three key influences on Americans.
First, the researchers found that the effect of fundamentalist religious belief on opinions of evolution was almost twice as much in the U.S. as in Europe.
Miller says the U.S. has a tradition of Protestant fundamentalism not found in Europe that takes the Bible literally and sees the Book of Genesis as an accurate account of the creation of human life.
After European Protestants broke off from the Roman Catholic Church in the 16th century, they retained a hierarchy that remained part of the university system, Miller says.
"In the United States, partly because of our frontier history, most of the Protestant churches are congregationalthey don't belong to any hierarchy," he added.
"They're free to choose their own ministers and espouse their own beliefs."
That freedom also included the creation of their own Bible colleges for training ministers, Miller says.
"If you send them to a Bible college that teaches only the Bible, they'll come back preaching only the Bible," he added.
"There are very few European counterparts to that."
(Read a National Geographic magazine feature on the evolution of evolution theory in the United States, "Was Darwin Wrong?")
Second, the researchers tested whether an American's political views influenced his or her view of evolution theory.
The team found that individuals with anti-abortion, pro-life views associated with the conservative wing of the Republican Party were significantly more likely to reject evolution than people with pro-choice views.
The team adds that in Europe having pro-life or right-wing political views had little correlation with a person's attitude toward evolution.
The researchers say this reflects the politicization of the evolution issue in the U.S. "in a manner never seen in Europe or Japan."
"In the second half of the 20th century, the conservative wing of the Republican Party has adopted creationism as part of a platform designed to consolidate their support in Southern and Midwestern states," the study authors write.
Miller says that when Ronald Reagan was running for President of the U.S., for example, he gave speeches in these states where he would slip in the sentence, "I have no chimpanzees in my family," poking fun at the idea that apes could be the ancestors of humans.
When such a view comes from the U.S. President or other prominent political figures, Miller says, it "lends a degree of legitimacy to the dispute."
A Natural Selection?
Third, the study found that adults with some understanding of genetics are more likely to have a positive attitude toward evolution.
But, the authors say, studies in the U.S. suggest substantial numbers of American adults are confused about some core ideas related to 20th- and 21st-century biology.
The researchers cite a 2005 study finding that 78 percent of adults agreed that plants and animals had evolved from other organisms. In the same study, 62 percent also believed that God created humans without any evolutionary development.
Fewer than half of American adults can provide a minimal definition of DNA, the authors add.
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