The appendix is probably the most famous of humanity's vestigial organs, but it might not actually deserve the "vestigial" part of that title. The appendix may actually save vital bacteria for the body's later use.
The current scientific consensus is that the appendix was once useful when humans ate a lot of high-cellulose plants, but in recent years an alternative view has emerged. The appendix might actually serve as a vital reserve for bacteria usually found in our gut. If a disease like cholera ravages our body, the gut's supply of beneficial bacteria can be wiped out. In this view, the appendix then releases additional bacteria to make up for the shortfall.
It's an intriguing idea, but there are two major issues with it. First, we're talking about a hypothesis that completely reimagines the function (or lack thereof) of one of our body's organs. That falls into the category of an extraordinary claim that needs some truly extraordinary evidence to back it up. Second, it's almost impossible to find any good, solid evidence of this, let alone extraordinary evidence.
It's easy enough to come up with a testable hypothesis: people who still have their appendixes should be able to recover from severe gut infections better than those who have had the organ removed. The problem is how to test that prediction in a way that doesn't violate every single ethical guideline.
It's a topic that science writer Rob Dunn has explored in a post over at Scientific America:
To test this prediction, one could compare the fate of individuals with and without their appendixes after being experimentally infected with a gut pathogen. Easier said than done. Not even college students will voluntarily sign up for a dose of cholera, and lab rats, those time honored guinea pigs who never object to being poked, do not have an appendix.
There was one way forward...Scientists could compare the fates of individuals who suffer gut infections and have an appendix to those of individuals who suffer the same gut infections and do not have an appendix. They could, in other words, take advantage of the natural, albeit terrible, experiment created by the spread of human disease. The trouble was such a study would be easiest in developing countries where Cholera and other similar diseases are prevalent, but those are the same regions where medical records (of appendectomies, for example) tend to be the worst.
For the complete story of how researchers navigated this logistical nightmare, you can check out Dunn's article. But the upshot is this: the initial evidence does seem to suggest that the appendix has some role to play in restoring depleted gut bacteria, although further tests are needed. If that result holds up, however, it will place medical science in a quandary — if the benefits of keeping the appendix are big enough, does it then make sense to perform appendectomies, or to try instead to save the inflamed organ with antibiotics? That's an unexpected question that doctors may have to grapple with in the relatively near future.