Evolution is just a theory
Let’s start with a sensationalist claim: Evolution isn’t “just a theory” because it isn’t even a theory.
Why would I assert something so preposterous? For one, it’s a better rejoinder than many I’ve witnessed to some proponent of Creationism/Intelligent Design. Too many a stalwart guardian of The Scientific Method has educated any attackers of evolutionary theory, often with pained tones of one nobly suffering for a just cause, by misrepresenting what it is. Worse still, our noble warrior will often simultaneously bemoan the state of science education while explaining how The Scientific Method works in ways that no practicing scientist would recognize. Evolution is not a theory in this sense: there is no Scientific Method that exists which could make any “hypothesis” into a “theory”, because The Scientific Method (as it is still taught even at the university level) is a simplification of an outdated 19th century notion. It is a theory more in this sense: “evolutionary theory (ET) is not one theory but a system of theories” (p. 380 of Dagher, Z. R., & Boujaoude, S. (2005). Students’ perceptions of the nature of evolutionary theory. Science Education, 89(3), 378-391.)
Needless to say, a dialogue over any theory is unlikely to be of any value unless at least one side knows what a scientific theory actually is. Most people learn the wondrous fantasy of The Scientific Method in High School, but even university level textbooks rely on it to explain the very foundations of the sciences. By “The Scientific Method” I mean some variation of the following:
1) The scientist ponders over some phenomenon, such as what causes things to move (whether Aristotle’s spear or Galileo’s stone dropped from a ship’s mass), and formulates a hypothesis (possible explanation).
2) The scientist tests this hypothesis, trying to prove herself or himself wrong.
3) If the scientist cannot, they determine that the hypothesis is confirmed and it becomes a “theory”.
In reality, most experiments in the sciences are motivated by, interpreted using, and intended to extend or alter an existing theory. For example, evolutionary psychology requires the framework of evolutionary theory both to develop experiments and to interpret the results of these. No study in this field is possible without evolutionary theory being assumed from the start, and insofar as it extends evolutionary theory it does so by assuming its mechanisms and using them to explain how certain cognitive, emotional, or similar traits humans exhibit or possess are due to conditions tens of thousands of years ago. Most work in evolutionary theory, however, is more direct. Some involve species that die so fast we can test how they “evolve” in laboratory conditions in real time. Yet what we test in such experiments is not “evolutionary theory”.
This is true of theories in general. Most of the time, the things people associate with theories or laws in science, like the “law of gravity” or the “theory of relativity” are either things we know are wrong (like the “law of gravity”) or at least problematic (like relativity). Relativity is a theory in precisely the same way quantum physics is. In fact, these are two of the most successful theories of all time. Yet they remain problematic in part because they are currently incompatible (it’s a lot more complicated than that so physicists- please excuse the simplification).
Here’s the takeaway- theories are frameworks within which all scientific research is conducted. Quantum physics is “just a theory”. Most of the time peer-reviewed research doesn’t contain the word “theory” and there is never any description of a single hypothesis that was “confirmed” making it “theory” (hypothesis testing, both what it really is and why it is often an issue, will have to wait for another day). Don’t defend evolution by trying to equate theories with something akin to “proof”. Defend it by noting that for over a century entire fields of research from astrobiology & biophysics to computer science & evolutionary psychology are able to make successful predictions, develop real-world models, and explain observed phenomena all because of evolutionary theory.