Readers were busy this weekend, posting over fifty comments to my last post about HIV. Much of the discussion was sparked by the comments of a young-Earth creationist who claims that the evolutionary tree I presented was merely an example of microevolution, which–apparently–creationists have no trouble with. This claim, which has been around for a long time, holds that God created different "kinds" of plants and animals (and viruses, I guess), and since then these kinds have undergone minor changes, but have never become another "kind."

Some readers expressed frustration that the comments were getting side-tracked into arguments about creationism. I take a pretty relaxed attitutde to what goes on in the comment threads, though. Part of that attitude, I’ll admit,