Is Evolution “just a theory”, a scientific theory, or a fact?
There is a lot of misunderstanding when it comes to determining the status of evolution. We are all familiar with the lay, and often religion-motivated, misinterpretation of evolution being “just a theory”. This misrepresentation of the status of evolution is based on a confusion—a confusion which in many cases is deliberate—between the meaning of theory in the lay discourse versus scientific discourse. Another common area of misunderstanding is in addressing whether evolution is a scientific theory or a fact. Here’s the short answer: evolution is both a scientific theory and a fact.
I’m quickly going to comment on the irony of the “just a theory” argument. This argument gets its strength from the fact that many people do not know the difference between theory in lay discourse versus scientific discourse. Its power is based entirely on ignorance. As most of the people reading this blog probably already know, here’s the difference. A lay theory can be something that someone has just thought up; it can be deeply thought out or just pulled out of thin air. A scientific theory, on the other hand, is a carefully tested and evidentially supported means of explaining data. A theory is based on rigorous scientific testing of a hypothesis (which is the closest thing in science to a lay theory; though these hypotheses are generally more thoughtfully developed and evidentially-justified than most lay theories), intense peer review, and the constant possibility of disconfirmation.
The “just a theory” versus scientific theory is not the only area of misunderstanding. People, including many scientifically-oriented skeptics, frequently misappraise the status of evolution. Is it a theory or a fact? The answer is both. It is both because there are two dimensions to evolution: historicity and mechanism. Historically, evolution is a fact. The evidence for the idea that species evolved by way of gradual changes in population gene pools over time is so overwhelming that to not grant it the status of fact would simply be ludicrous. While it is true that we can’t truly know anything aside from each own personal existence, to the extent that we can we can know that other things we can know that evolution is a historic fact. The evidence from genetics, archaeology, comparative anatomy, embryology, and so forth preclude the possibility that a person can be knowledgeable of the relevant information, honest, rational and not believe in the factuality of evolution. These 4 factors simply cannot coincide. At least one of them has to be false.
The late eminent paleontologist Stephen J. Gould explains the issue as follows:
Evolution is a theory. It is also a fact. And facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world’s data. Theories are structures of ideas that explain and interpret facts. Facts do not go away when scientists debate rival theories to explain them. Einstein’s theory of gravitation replaced Newton’s, but apples did not suspend themselves in mid-air, pending the outcome. And humans evolved from ape-like ancestors whether they did so by Darwin’s proposed mechanism or by some other yet to be discovered.
The theoretical area of evolution is with regard to the mechanisms by which the historically factual process of evolution occurred. While we know for certain that evolution did occur because we have the data—the data are the facts, we use scientific theory to explain the data. That’s what scientific theories do: explain data. When it comes to explaining the data, not only is evolutionary theory a theory, it cannot become a fact. Theories explain data. Facts are data. So it’s not like we call natural selection a theory of evolution because we simply do not have enough evidence to call it a fact yet. We call it a theory because it explains the data. It will never be a fact. Indeed, if fact was a latter rung on the ladder (hypothesis–> theory –> fact) we would have been calling natural selection a fact for a long time by now. Natural selection is not the only scientific theory of evolution. There are others such as genetic drift and punctuated equilibrium theory. Natural selection, however, is the only process by which complex functionality can evolve.