In a nation that wears its heart on its bumper, the war over Darwinism has evolved into a fish fight.

First, there was the Jesus fish, symbol of Christianity. Then there was the fish with feet, symbol of evolution. Then there was the truth fish, a big fish with the word "truth" eating the Darwin fish. Then there was the dinosaur eating the Jesus fish.

These plastic proclamations have spawned schools of other fish intended to annoy, amuse or simply befuddle. There is now a gefilte fish, with a Star of David and Hebrew-style letters. A horned sinner fish. A winged angel fish. A chubby Buddha fish. An " 'n' chips" fish.

The origin of the bumper fish is, like the origin of other species, disputed. But it appears that the first fish emerged from the pre-automotive mists of time as a symbol of Christianity. The Greek letters that form the word for "fish," transliterated as "icthus or "ixthys," can be used as an acronym for "Jesus Christ, Son of God, Savior." Legend has it that early Christians used a fish symbol to covertly identify themselves to one another.

These Christian fish, some unadorned, some with the Greek letters iota, chi, theta, upsilon and sigma, which look something like IXOYE, and some with the word "Jesus," began to appear on car bumpers in the 1980s during the Reagan presidency.

"It symbolizes that a person has a personal relationship with Jesus Christ," said Patty Ford, at Sonshine Christian Bookstore in Moorestown, Pa., where fish items are big sellers.

The reaction was swift. With the adaptation of feet, and the sometimes less-than-subtle addition of the word "Darwin," the fish was transformed into a symbol of evolutionists, liberals and wiseacres.

Why did Darwin-fish people put the symbol on their cars? Unsurprisingly, a college professor has studied the question.

Thomas L. Lessl, an associate professor of speech communication at the University of Georgia, trolled parking lots in several states for cars with Darwin fish. He left questionnaires for the owners, asking: Why did you put it on your car? What audience did you hope to reach? What does the Darwin fish mean to you?

The 51 responses ranged from hostile to whimsical.

"Mainly I did it to annoy the Christian right wing," wrote one respondent.

"It is a symbol of my belief in evolution and my irreverence for organized religion. . . . I have it on my car in good humor, not at all to offend anyone," another said.

"I bought the Darwin fish and put it on my car mainly because I thought it was good for a chuckle," another said. "My only problem with the Darwin-fish is that I don't want to give the impression that I equate Darwin with Christ, and I also believe that both men would be slightly annoyed to see how they've been idolized and [made] commodities."

Lessl said the responses showed that the Darwin fish was "subject to very different interpretations . . . but a substantial majority seemed to treat this as a worldview statement."

When battles over evolution are in the news, as with the current Dover, Pa., court case, sales of fish jump. That case, now being tried in federal court in Harrisburg, Pa., pits a school board that required students to be introduced to "intelligent design" as an alternative to evolution against parents who contend that it violates their religious freedoms.

"When something like that happens, a lot of people will see it as the last straw and call us and say, 'I want one of those things now,' " said Gary Betchan, co-owner of Evolvefish.com, a Colorado Springs company that has sold about 29,000 Darwin fish in the past three years. "If we had five years without the religious right, we'd be out of business."

Nona Williams, co-owner of Ring of Fire Enterprises of Ben Lomond, Calif., which sells more than 20,000 emblems a year, including about 3,000 Darwin fish, said the old standby Darwin has been eclipsed by the dinosaur-eating-the-fish emblem.

"A lot of people were really upset when the Christians came up with the truth fish and asked us to do a tit-for-tat. But we didn't want to do that," Williams said. Instead, she and partner Rob Watson created the dinosaur emblem, as well as what Williams calls "our naughty fish," a Darwin fish copulating with a Greek-lettered fish.

"They're just making a mockery of what Christians believe," said Ford, of the Sonshine bookstore.

The current bestseller in the evolution wars is the flying spaghetti monster, which isn't even a fish. It's a googly-eyed, tentacled ovoid that is a parody aimed at the "intelligent design" movement. Its promoters argue that the universe was created by a flying spaghetti monster.

Williams said she doesn't know what will come along next, but she is sure something will. It's the nature of evolution.