Originally Posted by segovius
I think you'll find it is actually a theory - or group of theories, some of them conflicting.
Semantics. In science, a theory means something quite different than in colloquial language. A scientific theory is nothing more than an explanatory framework that makes sense of known observations and makes predictions
about future observations.
There are differing levels of theories: theories like Gravity, Relativity, and Evolution are credible, well-tested and verified by facts. They can still turn out to be wrong -- like any scientific theory -- and they are refined every time new observations are made, but at this point, the evidence so overwhelmingly supports these theorems, that they might as well be taken as "facts". This is similar to how you drive across a bridge, knowing (though perhaps ignoring) that it could
collapse, but understanding that the likelihood of this happening is so remote that you ought to simply go about your life as if it will not happen; trusting that city engineers are constantly testing the structural integrity of the bridge to see that it is still sound.
Other theories are discredited or discarded, but these, too, are scientific theories as they make predictions that can be tested through experimentation. One example of a discarded theory is the Ether. 100 or so years ago, when light was first discovered to be a wave, it was postulated that if light was a wave, then it would need a medium to propagate through: sound had air, and water waves had water, so light needed the ether. This particular theory never quite panned out, and was discarded on the heap of failed ideas (though I hear that it's making a come-back of sorts).
Yet other theories are untested. String Theory is the obvious example at the moment. Athough it looks like a promising mathematical model, no one has really devised a way to test it adequately. Until then, it's just a pretty mathematical model.
There may be other ways of classifying scientific theories, but you get the point.
I would, however, challenge you to produce real conflict in evolution. At this point there is much debate about the forces that drive evolution: how much role did natural selection play? what role did sexual selection have in the process? Does evolution act slowly? or is it punctuated? or some combination? are there other forces at work? how can we observe these? But the basic "fact" of evolution hasn't been debated for decades (other than religious people who bring up the same tired arguments over and over -- irreducible complexity, anyone?), perhaps even since Darwin.
The last word that I'll leave is a little anecdote from last Thanksgiving. As is proper for all holidays when families get together, I got in a debate with my brother about evolution. He is a Christian and thinks, like many people, that there must be some conspiracy among scientists to prop up what he sees as a demonstrably false "theory." What made me the angriest about the exchange was that my brother completed his undergraduate degree in Biology. His university failed him that he came out of his degree with no appreciation for what evolution actually is.
I shared my dismay with my girlfriend, who is a PhD candidate in Cell Biology at UNC Chapel Hill. She snorted at my brother's belief and said, "well, I guess I should just quit my program right now, because if evolution is not true then none of my experiments will work."
That is how working biological scientists see this whole debate. Those, whose business it is to understand and even exploit evolutionary theory for in their daily work, see evolution as completely self-evident. The consensus of the scientific (biological) community is almost completely united in acceptance of evolutionary theory. It is absurd to think that there is some conspiracy among these working scientists to trick the public. It is as absurd as believing that the Jewish Holocaust didn't happen, that Castro killed JFK or that Bush orchestrated 9/11. Evolution is tested and re-confirmed every single day. It is among the most tested theory that humans have ever devised. It is a "fact."
*"fact" is of course in quotations as, in science, there are no facts in the absolute sense of the word.