Intelligent design, which holds that only an unspecified superior intellect can account for the complexity of life forms, is increasingly appearing in science forums and journals as an alternative to evolution theory.
Evolution has been widely accepted in scientific circles ever since Charles Darwin's Origin of Species revolutionised biological sciences 145 years ago.
But the new theory's support by a handful of biologists and non-scientists has put Darwinists on the defensive, while encouraging groups who consider evolution hostile to their religious beliefs.
Pro-evolutionists brand the new idea an unscientific melange of politics and religion.
"It is at its bottom a Christian religious movement," said Barbara Forrest, a professor of philosophy at Southeastern Louisiana University and a leading critic of the intelligent design movement.
But supporters argue that evolutionary theory cannot answer some large questions on how certain life forms developed.
"Science doesn't progress by ignoring something that is staring you in the face," counters Michael Behe, a Lehigh University professor of biochemistry and an intelligent design advocate.
Essentially, intelligent design holds that certain structures found in living things, such as the flagella of bacteria or extra wings on certain fruit flies, cannot be explained by Darwinian concepts of natural selection and random variation.
Behe argues that the complexity of the flagella and various "machines" inside cells could not have evolved from other life forms. Like a mousetrap or a wristwatch, he says, it is evident that these were designed, though by whom he is reticent to say.
God of gaps
Darwinists, who still comprise the large majority of scientists, say that Behe and others are simply appropriating what is yet unknown to conclude that it must be created by a higher intelligence.
The debate has become more rancorous in recent months.
In one incident, biologist Richard Sternberg filed a legal complaint against Washington's Smithsonian Museum of Natural History for branding him a religious fundamentalist and denying him access to facilities, due to his editorial role in the 2003 publication of a scientific paper by intelligent design advocate Stephen Meyer.
While he has neither endorsed nor denied the theory, intelligent design advocates have compared Sternberg to 16th century astronomer Galileo Galilei, branded a heretic for challenging Roman Catholic dogma with his scientific discoveries.
Spearheading the intelligent design movement is the Discovery Institute, a conservative thinktank in Seattle in the US northwest.
Scientific design support
Jonathan Wells, a senior Discovery fellow with doctorates in both cell biology and religious studies, said the debate is mainly about the "limits of Darwinism".
Scientists can conclude intelligent design exists through empirical evidence, he said. But defining the "intelligent designer" is "beyond the scope of science", he said.
Wells rejected critics' branding intelligent design as "new creationism", referring to a Bible-based explanation of life.
However, creationists in several states have cited intelligent design in trying to introduce their teachings into public schoolrooms.
In November, school officials in Dover, Pennsylvania ordered teachers to include intelligent design in ninth-grade biology courses.
Wells criticised the Dover action, saying: "We are not pushing intelligent design in high school classrooms."
Forrest points out, however, that a 1999 Discovery fund-raising document specifically endorses the conservative Christian agenda.
"Design theory promises to reverse the stifling dominance of the materialist worldview, and to replace it with a science consonant with Christian and theistic convictions," the document reads.
Intelligent design advocates have also been encouraged by a statement made in 1999 by then-Texas governor, now President George Bush, that he believed that "children ought to be exposed to different theories about how the world started".
Yet in February, Bush's science adviser John Marburger reportedly told a group of science journalists that "I don't regard intelligent design as a scientific topic".
Amid growing animosity, both sides agree that proving intelligent design in traditional scientific terms is next to impossible. "Can science show you whether God exists? No," said Wells.
"It is difficult to reconcile science with Christian philosophical questions," said Vittorio Maestro of Natural History magazine. "We aren't going to convince them and they aren't going to convince us."