April 9th, 2009
I just read a really interesting book this week: Jerry Coyne’s new book for lay people, Why Evolution is True. I want to highly recommend it to anyone who is interested in finding out what exactly the evidence for evolution is, as well as a good explanation of the processes of evolution. I have read a number of books on this topic and of those, this is the best. It is pitched at the interested lay person, and you don’t need any special knowledge of biology or science or the scientific method – everything you need is in this tidy little book. It’s nice and short (abour 230 pages – you can read it in very short order). And it goes into a good level of detail: not too technical; a nice survey. Plus there are neat pictures and diagrams.
One thing I have noticed lately is that many of the spokesmen for evolution have started referring to “the fact of evolution” instead of “the theory of evolution.” I can only assume this is in response to the widespread misunderstanding of the term “theory.” How many times have I heard “But evoution is only a theory!” Yes… and no. The colloquial meaning of theory is different from the scientific meaning and when you are trying to educate the populace, which may get confused by the different meanings, I can see why it makes more sense to refer to the fact of evolution instead.
In common language, when people say “theory” they mean “guess,” as in, “It’s my theory that Bill is dressing so nicely because he is trying to get that promotion.” That’s a sort of if-then statement. In science, that would actually be a hypothesis. A hypothesis makes a statement about something that may be true, and it can be tested. If we asked Bill why he has taken to wearing a suit every day and he says it’s because his house recently burned down and the only clothes he has left are what was at the drycleaner… then we would consider our hypothesis disproven and we’d discard it.
Testing hypotheses can lead to a collection of facts. How do we explain the collection of facts? This is where theories come in. Theories organize and explain a collection of specific facts. A theory is an explanatory framework that does two things: it accounts for the facts we already know, and it guides the search for new knowledge. Theories therefore generate new hypotheses, like this: “If this theory is correct, then X should also be correct. Let’s test it!”
But science is conservative, and always open to the possibility that there may be a better model to explain the facts than the one we have. So the strength of a theory is based not only on the breadth of facts it encompasses and the predictions it confirms, but on showing that alternative theories do a less adequate job of accounting for the evidence. Theories will be modified or even discarded if the facts show it to be inadequate. This is the part of theory that is a process: every new finding is tested against the theory to see if it works. Can the theory account for this finding? If not, why? What part of the theory needs to be changed, or is this finding a fatal challenge to the theory? So the strength of a theory is something that emerges over time, as it survives more and more challenges and predicts more and more things that turn out to be true. 1
Evolution is an incredibly strong theory. It explains a vast, vast breadth of factual findings in science. It has, over and over, made predictions which have turned out to be correct. It has no rivals for adequacy of explanation. (Coyne’s book reviews these facts and predictions.) In this sense, it is indeed a fact. It is correct. The subtlety between an explanatory model which is overwhelmingly supported by all the facts and makes correct predictions on the one hand, and a fact on the other, is not easy to get across to the average joe. I just wrote up a very simple and abridged explanation and it took me several paragraphs! I support the use of the phrase “fact of evolution,” even though in a technical scientific sense it is not quite proper and I’m a bit of a pedant, because it is the best way to get across to people the reality of the situation.
Holy cow, I just meant to say I liked Coyne’s book and look what happened! Quick, ask me a personal question so we can get back to the fun stuff.
- Cozby, P. (2001). Methods in behavioural research. (8th ed.). New York: McGraw Hill. [↩]