A recent Harris poll asked Americans “Do you believe in Darwin’s theory of evolution?” Others more eminent have commented on the answers; I would like to comment on the question.
Darwin, of course, never used the word “evolution,” but let that pass. As for the rest, it would be difficult to cram a larger number of serious errors into so small a space. Errors of presentation, of logic, and of scientific and historical fact, all of which play into the hands of our Creationist opponents.
Start with the obvious, the word “theory.” In common language a theory always involves speculation. In academic discourse, it means a coherent set of ideas that explain the facts. Calling something a theory in this sense tells you nothing at all about how certain it is. A theory can be wrong (phlogiston theory), known to be approximate from the outset (ideal gas theory), very close to the truth but since improved on (Newton’s theory of planetary motions), or as certain as human knowledge ever can be (number theory in mathematics). Of course you can explain all this, but you should not put yourself in such a vulnerable position in the first place. It wastes time in debate, or in the classroom. It puts you on the defensive, and thus, paradoxically, confers legitimacy on the attack. It allows the focus to shift from what we know about the world to the words we use to talk about it. This takes us away from science to the domain of the philosophers, lawyers, and expositors of Scripture who are fighting on behalf of Creationism.
And so it distracts from what you should be talking about, namely the facts. Evolution, whether we mean changes in the genetic make-up of populations over time, or the common descent of living things on earth, is a fact. It is supported by, and explains, innumerable more specific facts concerning the fossil record, molecular phylogeny (the same kind of evidence that is used every day in DNA paternity tests), the frozen-in historical accidents of organs that have lost or changed their function, the distribution of species throughout space and time, and much more besides. Creationism cannot explain these facts, except by appeal to the whims of the Creator.
Next “Darwin’s.” Darwin did indeed have a theory, as independently had Wallace, which was that different species had arisen gradually by natural selection operating on variation. This he supported by meticulous observation, but the range of evidence available to him was far more limited than what we have today. He lamented the poverty of the then known fossil record, laments that Creationists echo to this day as if nothing had changed. He knew nothing about mutations or even about the existence of specific genes, and so he had no idea how new variants could arise and spread. His assumption of gradualism is in contrast to later ideas such as punctuated equilibrium, and we now know that much if not indeed most variation arises through neutral drift. Thus not only do we know far more facts about evolution than Darwin could have dreamt of, but our theories, too, incorporate numerous additional concepts.
Finally, worst of all, “believe in.” Believing always carries with it the feeling that disbelief is an option. Some members of the jury believe the witness, others don’t. Some people believe that Hillary Clinton will be the next President of the United States, but no one would say they “believe” that Barak Obama is the current incumbent, because no sane person doubts it. I don’t “believe in” atoms, or gravity, or quantum mechanics, because I regard them as established beyond dispute, although our notions about them will no doubt continue to change as we learn more. And exactly the same is true of evolution.
Does it matter? Yes, it matters enormously. Creationists often maintain that evolution and Creation are both beliefs, whose respective advocates differ, not about observable facts, but about how those facts are to be interpreted. They obsess about Darwin, referring to evolution as “Darwinism,” and to those who accept this reality as “Darwinists.” The aim here is to bypass 150 years of experimental and intellectual discoveries, to bog us down in the day disputes of the late 19th century, or even (“Darwin’s doubt,” see here and here) to enlist Darwin himself as an unwitting ally. And they contrast evolution, as “only” a theory, with facts or even with scientific laws, in order to claim that it is far from certain and that different views deserve a hearing.
Most people have not thought long and hard about evolution. And in the US at least, much of what they have heard about it will have come from its theologically motivated opponents. These opponents, whether through “statements of faith” that make obscurantism a virtue, or through “academic freedom bills” that disguise telling lies to children as open intellectual debate, use carefully crafted words to stake spurious claims to the moral high ground.
We should not, ourselves, be using words that help them do this.