Don: I used to think that the appendix is useless, but now I'm hearing that the appendix actually does serve a purpose. So, which is it? Y: Great question. It's true that for a long time scientists thought that the appendix didn't really serve a purpose. But a few years ago a study showed that the appendix in fact plays an important role. It's a sort of hangout for useful bacteria needed to help us digest food. After a bad case of diarrhea, when most of the bacteria in our guts is washed out, the appendix sends a fresh batch in to take over. D: Right. And not only that, but a more recent study has found that the appendix has a long and storied history. It's been around in animals including kangaroos, rodents and apes for at least eighty million years. In other words, it's fairly common in nature. Y: Now, it's true that in developed countries with modern sanitation, the human appendix has less to do than it once did. In those places, where diarrhea isn't a major problem, the appendix isn't called upon all the time to do its thing. That's why when people in the United States and other developed countries have their appendix removed, they don't seem to miss it. D: But in places where drinking water and sanitation aren't as safe, the appendix plays a larger role in keeping people healthy.