Tautologies and Rhetoric

Today, I read PZ Myers's response to this argument against evolution. PZ does a fine job of taking it down, but there is one point I'd like to make, and this is something that shows up in many places. Egnor says that evolution is a tautology and is therefore false or fallacious. The problem is that a tautology is not a fallacy. In fact, by definition, a tautology is always true.

That's what a tautology is. Something that's always true, no matter what. For example, if x is true, then x is true. That statement is always true whether or not x is. It's just not interesting. There's no real claim or anything there. A tautology is only interesting when it gets combined with something else, which is what Darwin did with evolution by combining the tautology of "survivors survive" with variation and heritability.

And of course that doesn't mean that tautologies can't be used fallaciously. They're frequently used to sneak in a fallacy such as begging the question. But pointing out a tautology doesn't in and of itself show an argument to be fallacious.