Evolution: Theories and Fact

This article originally appeared on the AJS.COM Wiki, and then was moved to the old essays blog, but this issue continues to come up over and over, so it seems this is still relevant, sadly.

Theories and facts are often misunderstood and the terms misused in the debate over the validity of scientific knowledge in our society. Probably the best known example of this was in the debate over Intelligent Design that spilled over into the Federal Court System in the United States in the form of Kitzmiller v. Dover Area School District, a case that pitted eleven parents of Dover, Pennsylvania students against the Dover Area School District and many organizations including the American Civil Liberties Union. In this case, the parents wanted the school board to require this phrase to be read aloud in biology classes:

Because Darwin's Theory is a theory, it is still being tested as new evidence is discovered. The Theory is not a fact.

Now, at first glance, this repetition seems to make sense. A "theory is a theory"... certainly that seems reasonable. Then we say that it's "still being tested as new evidence is discovered," and certainly we can turn on the Discovery Channel to observe the truth of this. "The Theory is not a fact," is where the train comes off the tracks, as it were. It sounds reasonable at first glance, but it's not. It's a subtly incorrect usage of the word "fact" that leads the incautious reader to a false conclusion.

What's a fact?
At the core of the confusion is the word "fact." A fact is an observable piece of information which is not readily contradicted. As an example, I'd like to choose a particularly interesting fact: the sky is blue.
Look out your window on a clear day, and you can easily confirm this fact. The sky is actually a lovely shade of "sky blue" that has been praised in painting and poetry alike for thousands of years. It's also misleading and arguably wrong, but that doesn't mean that it's not a fact.
Wait... the sky isn't blue? Well, no. The sky is made up of essentially colorless gases which only look blue because of the way light refracts through it and reflects off of sub-micron particles suspended in it. This can be explained by the electromagnetic wave theory's model of the propagation of light, and the special cases of that theory that comprise what we call "optics". This tells us how light that is comprised of the full spectrum (such as sunlight) can appear to come from all directions and have a blue color when passing through an atmosphere such as ours which is composed of certain types of gasses with certain particles suspended in it.
So the fact that the sky is blue is actually less useful to us than the theory of optics which builds on and explains many facts.

What's a Theory?
When I say, "I've got a theory," in casual conversation, what I mean is that I have guessed at something.
In science, the word theory means something very different. In order to understand that, we have to explore the scientific method:

• Observe a phenomenon
• Produce a hypothesis that both explains the phenomenon and makes testable predictions
• Test the predictions of the hypothesis
• If the test failed to match the predictions, revise the hypothesis and continue

This is a fairly basic summary of the scientific method, and you can see that we call our initial guess a "hypothesis." That is because our explanation does not become a theory in science until it has passed through this process many times and has been confirmed each time. Any failure to confirm a theory is a drastic blow against that theory's credibility, and typically results in the revision or discarding of the theory. For larger, more encompassing theories, you might test each prediction seperately, and what confirmation or failure means for each, individual test is hard to generalize about.
For example, relativity is Albert Einstein's theory that suggests that we can understand the nature of the universe more accurately than physics was able to previous to 1905 by assuming that a great many (perhaps all) interactions in the universe are bounded by their relative frames of reference, rather than by some absolute frame of reference. What most lay people today do not understand about relativity is just how shocking and controversial it was at the time. It explained a great deal of the confusing observations that had been made, but most scientists didn't accept relativity until literally dozens of experiments had been conducted that confirmed many of its predictions about the way the universe behaves. Even today, people devise new experiments to test the limits of its predictions, and it's known to be wrong under certain special cases where quantum mechanics takes over (specifically, when you're dealing with the very, very small).
However, when we say "relativity is a theory" and that it's "still being tested," that couldn't mean anything further from the idea that it's not a very, very well established element of our body of scientific knowledge. At the very least, we know that it accurately describes elements of how everything of the universe that we can see and interact with behaves. That's no small accomplishment.

Evolution
So now, we come to evolution. Is it "just a theory"? Is it a fact? That's a bit hard to answer only because evolution is such a broad category. It's a bit like saying "particle physics is a theory." In reality, evolution is the culmination of many theories and areas of discipline. Let's break it down from the parts that are very well established to those that are broader speculations about the history of species:

Natural Selection
This is the idea that when a species is poorly adapted to its environment, it dies off while more adapted species live and continue to reproduce. This process produces, for example, antibiotic-resistant strains of bacterial disease, as can be observed in modern news. There's no real doubt that natural selection happens, as it's been observed in the fossil record and in the modern world. It's really more of a mechanism than a theory, but it's a good point to start.

Common Descent
Here is where we come into direct conflict with the doctrines of many religions, but interestingly, this is also one of the least controversial ideas. Essentially common descent is a theory of the origin of all of the species in our world and suggests that they all have a common ancestor. This seems counter-intuitive at first because the idea that a duck and a human have a common ancestor has no basis in our experience. My father and his father and his father's father were all humans. To imagine that there's a point in that chain where one of those anscestors is something other than human is quite hard to picture. After all, how could a duck give birth to a human?
In fact, when seen over the long-term the idea that the huge variety of species on our world would have common ancestors is not terribly hard to believe, just because there's so much time involved. There's also tremendous evidence for this that Darwin couldn't forsee, but which his theories predicted. For example, he didn't even know what the mechanism of the passing on of traits was, but when genetic material was discovered, it immediately confirmed everything that Darwin had predicted! All species, no matter how different looking, had similar genetic structure and their genetics clearly implied a process of descent from one species to the next. In fact, now we can measure the distance in time between two modern species and their nearest ancestor fairly accurately, and when we do we find that the fossil record agrees with such measures.

Speciation
Speciation is the process by which new species appear and is the underpinning of common descent. It can happen in a number of ways. What's interesting here, is that there's still significant debate over how speciation occurs in nature. Does it happen slowly and incrementally, or is it mostly a static process with sudden change happening over a small number of thousand or even hundred years? We don't know for sure, since all we have at our disposal are fossils, and those only tell us what was around at a fixed point in time, not how that species changed over the course of a few hundred thousand years.
So speciation as a process is well documented, but the mechanics are still being worked out in detail.

Summary
So, just from these few examples of the elements of modern evolutionary science, you can see that there's no easy way to describe the field in a short "true or false," "theory or fact" way. Instead, we must look at each part and determine how the weight of over a century of evidence has refined our concepts of evolution and what that means about the stability of our scientific understanding.

In conclusion: Evolution is not a fact
So the statement was, "the theory is not a fact." I think that now the astute reader will have grasped why this is both true and fundamentally misleading. No scientific theory is a fact. They are scientific theories and that implies that they are both not obviously true like a fact and also very rigorously tested and refined from their starting points as simple speculations that predict testable results to established parts of our scientific body of knowledge.
Many people become frustrated when they try to propose an alternative to a scientific theory and no one wants to listen or take them seriously. Though there is certainly elitism in the scientific community, as with any community, it's important to realize that this isn't what's going on here. What's really happening is that the new idea is bouncing up against the weight of dozens and often hundreds of the smartest skeptics on the planet who tried and failed to tear down this theory before it became well established. There's going to be some resistance to new attempts to do the same on a large scale. Sometimes it happens. Sometimes you'll see an Einstein turn a field on its ear, but it's very rare and always meets with rigorous debate and experimentation before it's accepted.
Now, I'm not going to go into the politics. I don't really think that either the religious zealots or the anti-religious zealots are right, here. I think that there's value in having the discussion, and that's what's important, so the politics be damned; I just hope that there's a kid in high school who's being made curious by the debate and decides to look into the details on his or her own. To them I say: congratulations, you've learned what education is really all about.

Links to look into:

• Water bugs that have adapted to underground life in only a couple hundred years
• Evolution Is a Fact and a Theory on talk.origins
• "production of isolated individual facts is unimportant unless you can tie all those facts together in an explanatory framework" testimony by Kenneth R. Miller, P.D. in the Kitzmiller, et al. v. Dover Area School District federal court case
• The evolution article on Wikipedia (which has many excellent references that you should follow, rather than just reading the article alone).