I get a bit worked up about evolution deniers. So much so that I spend much more time than I should engaging individuals in online discussions and forums, who, for whatever reason (okay, the reason is always religions) deny evolution. Without a doubt, they get most upset when I use the word “fact” to describe evolution by natural selection.
“Isn’t that very unscientific of you, to say evolution is a fact? It is just a theory after all.”
Well, yes and no. That last sentence betrays a fundamental misunderstanding of the what a scientific theory is, relative to other types of “theories”. A scientific theory is a very specific thing, it’s not the same thing as a theory about who killed Kennedy or a theory about who will win the Superbowl or even a theory about market behavior in economics. A scientific theory is an idea that has broad explanatory power, has been tested and verified by different objective observers, is consistent with other bodies of scientific knowledge, and explains particular facts. Facts, in turn, are just things that happen: e.g., apples fall when you drop them, humans evolved from apelike ancestors, the earth is an oblate spheroid. Scientific theories explain these facts – the theory of gravitation in the first (and last) instance, and Darwin’s theory of evolution in the second. It is possible these theories will be modified in the future, as Newton’s was by Einstein, but apples will still fall and humans will still have evolved from apelike ancestors – the facts don’t change.
A few individuals seem to be under the impression nothing can be proved or rightly called a “fact”. These people are playing a game with semantics. In any real sense, evolution is a fact, and descent with modification (Darwin’s preferred term) is the profoundly powerful theory that explains it.
If I could ask the American public to sit down and read one essay, it would be the late and inimitable Stephen Jay Gould’s “Evolution as Fact and Theory” – he says everything I just have with much more eloquence. Go read it, and consider offering it up the next time you’re spending too much time in a debate on YouTube.