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[♪ INTRO]

The appendix gets a bad rap.

You probably never think about it unless it's the reason you're doubled over in abdominal pain.

And for the most part, it gets written off as a useless organ left over from our evolutionary past.

But even though you can usually ignore it, you've got to give your appendix some credit,

because it might not be as useless as you thought.

The appendix has evolved in mammals at least twenty-nine times,

which is a pretty good sign that it does something.

And back in 2016, an international team of researchers set out to understand

why it appears so many times.

They started by looking at what kinds of things animals with appendixes have in common.

But first, they had to define what an appendix even is,

since the thing we call an appendix comes in all shapes and sizes across mammals.

As a starting point, the researchers defined it as a section of tissue extending from the cecum,

the beginning of the large intestine.

Then they used computer models to analyze data on hundreds of mammals.

They gathered information about their habitats and social behavior

and, of course, whether or not they had an appendix.

They concluded two things.

The first was that the appendix has evolved more times than it's been lost,

so it must have some kind of evolutionary advantage.

And second, after finding high concentrations of lymph tissue, which protects the body against foreign invaders,

they concluded that the appendix is involved in immunity across mammals.

And that seems to be the case for humans as well.

Within the inner layers of the appendix, we find all kinds of densely packed immune cells,

including T and B cells and natural killer cells,

which are all important parts of your body's immune response.

But we also find a reservoir of good gut bacteria hanging out in there.

It's the same type of bacteria that line the insides of the intestine, creating a protective barrier against invaders.

Given its prime position just off the colon,

researchers think the appendix might dish out emergency rations of gut bacteria in times of crisis,

like during cases of extreme diarrhea.

Diarrhea can flush out your intestines,

but the appendix may be able to provide a fresh population of the gut bacteria

that keeps your digestion on track.

They say you don't know what you have until it's gone and it's true.

One way to appreciate the immune function of the appendix is to see what happens when it comes out.

A study published in 2015 found that patients who contracted a particular bacterial infection,

called Clostridium difficile, were twice as likely to develop a severe infection

if they didn't have an appendix.

That study alone doesn't prove that the appendix prevents infection,

but it does raise questions about whether or not surgeons should remove the appendix

when they don't need to,

since that might actually cause trouble rather than prevent it.

That said, appendicitis can be deadly, so if your appendix needs to come out,

it's coming out.

But otherwise, maybe we shouldn't be so quick to dismiss this organ

that's usually just trying to be a pal.

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