The appendix was not useless

For a long time we were taught that the appendix was a useless leftover of evolution, a little pouch with no function that only caused trouble when it got infected.

In 2007, some researchers put forward another idea: the appendix might work as a safe refuge for the gut's beneficial bacteria. When an infection or a severe bout of diarrhoea empties and wipes out the intestinal flora, that small reservoir would help to repopulate it afterwards with good bacteria kept out of harm's way.

It is not an essential function: anyone who loses their appendix lives perfectly normally. But the idea changes the story: perhaps the organ we called useless had been quietly doing a job all along.

Source: Duke University