Also, the worm-shaped organ outgrowth acts like a bacteria factory, cultivating the good germs, Parker said.

That use is not needed in a modern industrialised society, Parker said. If a person’s gut flora dies, they can usually repopulate it easily with germs they pick up from other people, he said. But before dense populations in modern times and during epidemics of cholera that affected a whole region, it wasn’t as easy to grow back that bacteria and the appendix came in handy.

In less developed countries, where the appendix may be still useful, the rate of appendicitis is lower than in the US, other studies have shown, Parker said.

He said the appendix may be another case of an overly hygienic society triggering an overreaction by the body’s immune system.

Even though the appendix seems to have a function, people should still have them removed when they are inflamed because it could turn deadly, Parker said. About 300 to 400 Americans die of appendicitis each year, according to the CDC.

Five scientists not connected with the research said that the Duke theory makes sense and raises interesting questions.

The idea “seems by far the most likely” explanation for the function of the appendix, said Brandeis University biochemistry professor Douglas Theobald. “It makes evolutionary sense.”

The theory led Gary Huffnagle, a University of Michigan internal medicine and microbiology professor, to wonder about the value of another body part that is often yanked: “I’ll bet eventually we’ll find the same sort of thing with the tonsils.”