One of the many fascinating things about evolution is that it generates disputes that can help us all better understand what science is and how it differs from religion or other areas of human endeavor.

Just such an enlightening dispute cropped up recently between two readers who were kind enough to let me share some of their correspondence. It all started when Elisa Winterstein wrote a letter to The Inquirer, stating that scientists rely on faith just as religious people do by accepting the idea of abiogenesis - the notion that life arose from non-living matter.

Her contention is mirrored in dozens of other reader comments I've seen, stating that science, like religion, requires faith.

Her letter goes on to say that, while scientists are considering various scenarios for the origin of life, none is currently backed by any evidence, and therefore, "to believe in abiogenesis does indeed require faith."

This struck me as odd, since life couldn't exist at the big bang, and it certainly exists now. What could be the alternative to life coming from nonliving matter? That cells popped into existence from nothing?

Another reader, Steve Mendelsohn, had the same reaction as I did. "According to current science, the universe began at the big bang without life. . . . Today there is life, ergo, biological life must have had to come from nonliving matter," he wrote. "Unless you have another explanation as to how we ended up with life here on Earth."

Winterstein, who identifies herself as a Christian with a Ph.D. in physical chemistry, responded: "Assuming that abiogenesis has occurred simply because 'we're here' is far from employing a rigorous scientific method. . . . That's where it is more like religious faith than scientific belief."

More probing from Mendelsohn - a patent lawyer - led her to clarify, saying that what requires faith is the assumption of a "naturalistic" explanation for the origin of life. In other words, the alternative is that life got here through supernatural forces.

Do Winterstein's views reflect the way scientists think?

Greg Petsko, a biologist from Brandeis University, said the concept of life originating from non-life is backed by copious evidence. "There are no components of any living organism that are not found in the Earth's crust or atmosphere. . . . And there's plenty of evidence that complex molecules can assemble spontaneously from simpler ones - so there's no faith required to believe life originated from non-life."

Some creationists argue that the origin of life from inanimate matter contradicts the work of Louis Pasteur, who showed that life can't be spontaneously generated from non-life. "Some like to think it is a trap" to discredit an evolutionary viewpoint for the origin of life, said University of Colorado geochemist Stephen Mojzsis, who studies the Earth's early history.

Pasteur showed that life doesn't routinely crop up under sterile conditions, but he didn't prove that it couldn't possibly happen, on a slower time scale under very different conditions.

There are several plausible scenarios out there in which relatives of DNA formed, became surrounded by bubbles of fat, and evolved into something like cells. It might have happened in layers of clay, or in underwater hydrothermal vents, or somewhere else.

But how exactly this took place is still an open question. Does that mean scientists are exercising a religious type of faith to seek out a natural explanation?

Not if you define faith as the Bible does, said University of Chicago biologist Jerry Coyne, author of the book Why Evolution Is True.

The definition is laid out in Hebrews 11:1: "Now faith is the assurance of things hoped for, the conviction of things not seen." Science is the opposite of faith - it relies on observation and evidence, Coyne said. "It's the conviction of things seen."

The fact that scientists studying the origin of life look for naturalistic answers can be seen as a pragmatic decision. They could seek supernatural explanations, but so far in the history of science, that's never paid off.

The only faith that scientists need is a faith in science, said Drexel University physicist Leonard Finegold, who teaches a science and religion course there. You have to believe in the scientific method, he said.

But this is very different from having a religious faith, because the scientific method leads to testable predictions, and religious faith does not. (Recall last spring's prediction of the Rapture, for example.)

Faith in science isn't blind - it's based on centuries of hindsight, in which scientific inquiries led to answers that could predict the future, whether it's eclipses or the effects of antibiotics or the way electrons move around computer chips.

Scientists don't automatically dismiss the supernatural. People have done a number of experiments on prayer, ESP and the like, Finegold said, and if any of this worked, they'd have to accept it.

But it never does in the long run.

Purdue University biologist David Sanders agrees that it's the predictive power of science that makes it fundamentally different from religion.

The fact that science can make predictions endows its insights with more meaning.

He agrees that scientists have faith that our senses give us information about the outside world. Scientists believe in reality, he said, but so does pretty much everybody else.

Chicago's Coyne, however, said even a belief in reality doesn't require blind faith. Experience and science compel us to accept it.

For one thing, evolution is unlikely to produce creatures that can't sense reality. "If you see a big cat coming at you, you'd better run," he said. It's a matter of survival.

If we were bad at detecting reality, we'd be extinct.

Contact staff writer Faye Flam at 215-854-4977 or fflam@phillynews.com. Read her "Planet of the Apes" blog at www.philly.com/evolution.