But the war is far from over.

Utah has become the latest state where the teaching of evolution in public schools has turned into a political and religious battle. The Utah Senate may vote this week on a bill that would require teachers to tell students the state does not endorse any of the competing theories about the origins of humans.

The problem for scientists is there are no legitimate contenders squaring off against Charles Darwin's theory of evolution.

"There's lots of debate over the details," said University of Utah biologist Don Feener. "There's no debate that it's the best explanation."

Part of the confusion boils down to definitions. To the general public, any idea is a theory.

Scientists reserve the word theory for a hypothesis, or idea, that has withstood rigorous examination to explain something that can be observed.

Evolution, a theory that is still developing, provides a robust explanation about the diversity of life on Earth, from humans to squid to bacteria, he said.

"It's very difficult to be a biologist and not recognize the importance of evolution," U. biologist Denise Dearing said.

The theory of evolution explains how changes can emerge in an individual species as well as how new species can come into existence. Part of the extensive theory details that humans, chimpanzees and apes all evolved from a common ancestor.

The current diversity of life developed over millions of years, with gradual changes, or mutations, happening across generations. Series of such changes can eventually lead to new species.

Natural selection is a key concept in evolution. It dictates that useful changes, or mutations, will survive, while unhelpful changes probably will disappear.

Anti-evolutionists and intelligent design advocates argue that evolution could not possibly explain the diversity of life or the creation of complex organs, such as eyes. Their suggestions rely on faith that a higher being - either a god or something with a similar résumé - is the only explanation.

They say evolution cannot be valid because they see little evidence of transitional, or intermediate species, which are creatures that bridge the gaps moving from reptile to birds, for example.

"That's just false, there are thousands of intermediate species," said biologist Dale Clayton, who co-teaches the U. biology department's ecology and evolution course with Feener. "The fossil record is chockablock full of them."

Among the most notable intermediate species is Archaeopteryx, a dinosaurlike reptile that lived 150 million years ago. It shows bird features like feathers on the tail while retaining reptile characteristics like teeth. The fossil is believed to capture a creature evolving into a new species.

Feener explained that no matter how many missing links are found, anti-evolutionists demand more. Critics want to know where are the transition animals before and after the new missing links, creating a never-ending search. Feener said these are not arguments that will dislodge evolution.

For decades, scientists have tested ideas to discredit evolution, but the theory has survived.

When intelligent design and anti-evolutionists try to point out flaws, they offer no testable ideas to replace evolution, Feener said. These ideas instead demand faith that a higher power is responsible for life.

"Scientists purposely exclude supernatural causes," said Feener. "We cannot test them."

Clayton said many scientists believe in religion as well as science, but that the two realms must be kept separate. Science demands testable explanations for observable occurrences.

Attacks on evolution in the public schools - which have also happened in Pennsylvania and Kansas - are examples of extremists trying to bring religion into the schools, he said.

"It is impossible to debate these guys who are pushing a religious agenda within the science arena," Clayton said.

Scientists do not have to settle for believing in the theory of evolution. There is a body of work that lays out how various hypotheses interact with one another to explain the diversity of life.

"It's not about belief," Feener said. "It's about what the data tell us."

U. biologist Jon Seger said one of the most convincing new bodies of evidence supporting evolution has come about thanks to the growing number of genome maps for various species. While each of these genetic blueprints reveals differences between species, the most striking aspect is how genetically similar all living creatures are to one another. Humans and chimpanzees share about 96 percent of the same DNA.

"It's absolutely, completely, totally convincing," Seger said. "It is proof."

Anyone who has examined the evidence can see that the similarities point toward an ancient common ancestor that links all species, he said.

"It's not a little anecdote here and there," Seger said of the ever-growing body of evidence for evolution. "There is no room to wiggle out."

glavine@sltrib.com