“Yeah, well, evolution is only a theory”

“Yeah, well, so is gravity”

I’m sure many people have heard an exchange similar to this one at some point in the past. It is one of the most common, and most misleading exchanges possible in debates about scientific ideas.

Now, I’ll be the first to admit, I don’t have a dog in this fight. There are conservative Christians I agree with on many things who also support some form of evolutionary theory, and Christians who I agree with on many other issues who are opposed to any form of evolutionary theory. To be honest, my background is not in the biological sciences, so I simply do not have enough understanding of the raw data.

My problem with the above exchange is that it is at best misleading, and at worst betrays a fundamental misunderstanding about the role of theories.

Both statements are, however, true (as far as they go).

A theory (at least as I understand it), is a useful (often predictive) reasoned explanation for the factual data which can be observed in the world. That is to say, the theory is a method of interpretation of experience. While such things ARE open to debate, the way to disabuse a theory is to provide a competing theory that deals with observable data (facts) in a better way.

An example is the copernican model of the universe. Some said that the earth was the centre of the universe, Copernicus said the sun was. Copernicus had a simpler theoretical model to deal with the data, and so his theory was seen to be closer to the truth. Unfortunately, neither theory is true, as thanks to further observation, we now believe that our entire solar system (including both sun and earth) to be on the outer edge of a galaxy speeding away from a central point that was “the big bang”. The facts that were observed at the time, though, led to the conclusions Copernicus made.

The problem with the statement “well, it’s only a theory” is that it is often used to say that it’s okay to attack the theory in its entirety simply because it’s a theory. It’s as if the speaker believes that a theory is nothing more than an opinion, rather like the preference for classical music over jazz. That is not what any scientific theory is, and so the statement that it is “just a theory” is misleading.

One would think that the main question is to get to truth. We want to know if the theory accords to reality; we want to know if the theory is true.

So the best response would be something akin to “yeah, it is. So what? Is it true?”

However, misunderstanding in the popular imagination is often compounded by the response, “yeah, so is gravity.” The intended implication here being that disagreeing with evolutionary theory is somehow akin to denying that things fall down.  In case I miss the point, one person I was speaking to added the phrase “things still fall down”.

We would all say, “of course”. The problem is that the fact that things fall down is not technically the theory of gravity. Stuff falling down(or rather, bodies of mass tending towards one another) is a FACT . Gravity is the theory used to explain that fact.

When applied to evolution, we see how this parallel is misleading. Evolutionary theory is a theory designed to deal with the fact that we presently have many species of life that to greater or lesser extents, resemble one another. Given that that resemblance is aided by similar evidences in the fossil record of species of apparently increasing complexity over time, and that extinctions seem to follow a pattern, the theory (or theories) of evolution get proposed to account for the facts we have. Evolution is, I am told, a very good theory that has a mass of predictive power. That said, the theory of common descent of species diversified mainly through the engine of natural selection is a theory, it is not a fact. It is an interpretation of the observed data, not the observation itself.

Again the question is one of truth, not of fact. Does the theory resemble reality? Does the theory make sense of the facts?

The person who advocates for evolution is not necessarily claiming a simple opinion, nor is the person questioning evolution necessarily questioning facts.