I was thinking recently about the common attempts to explain what a scientific theory is by pointing out that gravity is “just” a theory. This is, of course, usually in defense of people who say that evolution is “not a fact, just a theory.” I was thinking about how the concept of evolution, in general and abstracted from a biological context, is a very logical idea that doesn’t actually need evidence in order to make sense. This differs greatly from the theory of gravity, which only makes sense in light of observations. Thus, evolution makes more sense than gravity. Let me explain.
Both concepts were developed in light of observation. For gravity, people recognized that things always fall when dropped. Eventually it was found that all objects fall at the same rate, and then realized that there was a force between all objects, dependent on mass, that pulls them toward one another from very great distances. The simple equation describing the gravitational force between two objects can then be used to predict what the interactions between those objects will be like. Gravity is a beautiful example of the scientific method, where we start from observation, come up with rules, and then test those rules against more observations. On top of that, the theory has been fine-tuned over a few centuries to be able to describe more and more observations. The important point I want to make here is that, in the absence of observations of falling objects, gravitational theory makes no sense at all. The equations are useless unless you observe and take measurements of moving objects. The theory only applies to observation.
So how does this contrast with evolution? Like gravity, evolution was a theory developed by many people over many years. Darwin was not the first to come up with it, he was just the first to pile up so much evidence for its occurrence in nature. My claim is, however, that the evidence isn’t necessary. Why is this? I’ll first state that evolution is not specifically a biological concept. It has to do with pieces of information that copy themselves and are prone to some amount of error. Any self-replicating information can and will evolve.