Since the advent of modern medical science, the purpose of the appendix has been debated at length, because the organ doesn’t do anything — except get infected, burst, and possibly kill its owner. Darwin thought it may have helped our evolutionary ancestors digest leaves, while others thought it helped our immune system, and still others thought it was a trashcan for bacteria. A team of immunologists at Duke University now have a new theory: it appears that our digestive system uses the appendix to store useful bacteria, for safekeeping. Our bodies need all kinds of intestinal bacteria in order to be healthy, but diseases like cholera can flush out the entire intestine, leaving behind a pristine environment devoid of any biotics — cholera as well as the good bacteria. This is where the appendix comes in: tucked away inside it are the good bacteria which, in the event of a digestive catastrophe, can repopulate the intestinal world.
In our modern civilization though, the appendix is still useless because we are in close contact with a lot of people and we easily replenish the good bacteria from them. However, in more sparsely populated scenarios — which were much more common some centuries ago — the appendix would re-start a lone survivor’s digestive system after a bout with a disease like cholera. So in the end, the appendix is still vestigial: yes, it has a function, but that function has been overcome by events and it is no longer used as intended. Kind of like wisdom teeth.