Function of the appendix found? A good bacteria safehouse.

A Boing Boing reader says: "Immunologists from Duke University believe they've found the function of the supposedly useless and often dangerous appendix: It's a reserve store of good germs to 'reboot' your digestive system in case another bug wipes out the germs necessary for human survival."
The function of the appendix seems related to the massive amount of bacteria populating the human digestive system, according to the study in the Journal of Theoretical Biology. There are more bacteria than human cells in the typical body. Most are good and help digest food.

But sometimes the flora of bacteria in the intestines die or are purged. Diseases such as cholera or amoebic dysentery would clear the gut of useful bacteria. The appendix's job is to reboot the digestive system in that case.



  1. It makes so much sense, it is really a surprise that no one has thought of it before. But I guess everything is obvious once it has already been said, right?

  2. Well I’m going to stay away from the sketchy river water then… They took my perfectly normal appendix out when I had abdominal surgery as an infant!

  3. I dunno. Bacteria have no trouble colonizing a newborn’s GI tract after birth (at which time it’s sterile) with no effort undertaken on our part. And I’m not sure I’m buying the “before we lived as densly as we do now, we’d have trouble getting bacteria from others” part either. Given ancient concepts of hygiene, how many other people would you have really needed around before you were sharing GI tract flora? Not to mention, it’s not like these bacteria have exclusively human hosts. Finally, other mammals can get cholera and other GI tract diseases too and lack an appendix.

  4. It’s always been something of an unverified urban legend that the appendix is useless and vestigial. I’ve read and known many experts and conspiracy theorists who’ve disagreed for years.

  5. I’m with ARI1413 on this. I do not buy it. And that “in olden times we had trouble picking up bacteria” crap is laughably incorrect. Seems like one of those situations where researchers are blowing something WAY out of proportion.


    Five scientists agreeing with your brand new and (seemingly) poorly researched theory does not a paradigm shift in biological thinking make.

    I guess I’ll have to read the actual article in Theoretical Biology though. But for now, I call bullshit.

  6. ARI1413: a newborn’s digestive system is more or less designed (well, evolved) to pick up and nourish a colony of digestive bacteria. A baby has plenty of close contact with its mother to get them from. The stomach isn’t in full swing yet, so it doesn’t indiscriminately destroy anything living. Conversely, an adult digestive system generally doesn’t allow bacteria to pass through the stomach alive. Research suggests little (if any) of the acidophilus you get in yoghurt or capsules survives to reach the intestines where it’s needed. So this theory makes sense in that regard. On the other hand, this also complicates the suggestion that in a modern society we re-build our good intestinal flora from other people; those shouldn’t really have much chance of getting to the gut either.

    And that comment at the end about tonsils – heh – tonsils have been known for some time to have a role in the immune system.

  7. “It makes so much sense, it is really a surprise that no one has thought of it before”

    A colleague of mine tells me that this is, in fact, a hypothesis that has been kicking around for a while. Says he: “i thought that the appendix in things that eat grasses was much larger and housed the bacteria that are needed to digest really fibrous material by fermentation”

    It is hard to assess news stories like this critically; the paper is not out yet & this appears to be a press release prior to publication that CNN has picked up on. The whole trend of pre-publication press releases is fairly annoying if you’re trying to track the science. It’s rarely a healthy thing (see e.g. the Fleischmann-Pons experiment)

  8. VIK: A lot of the acidophilus in commercial yoghurt doesn’t make it down to the gut, but brew your own and there are lots, lots more bugs in it.

    The commercial probiotic preparation VSL #3 has been shown to be as effective as steroids in fighting IBD (e.g. Crohn’s Disease) — we use it as a yoghurt starter. The resulting yoghurt is strong enough to blow your ears off, but it’s not only a tasty treat with honey (especially still warm from the yoghurt maker), it also keeps our daughter healthy (she’s got Crohn’s.)

  9. This theory does not explain the stories about finding fingernails or a penny in an excised appendix. But then again, maybe the little guy knows that such items are also hearty sources of delicious bacteria.

  10. I always thought that ages ago when our diet was more protein (meat, bugs, etc.) that it was extra large intestine that simply we did not need anymore with our move to carbohydrates as our main staple of food.

    Just a week ago, I learned that the Lower-GI (large intestine) is used primarily for water absorption, and not really the digestion of food. Not only that, you want to move meat out of the body as quick as possible–or else it rots, and is no good.

    But then I learn that carbs are no good either, as they turn right into fat quickly if you don’t use them up.

    So… No. I don’t really know. all I know is that it gets infected, and can kill you if it’s not removed. And somehow, that’s good enough for me.

  11. DragonPhyre>I always thought that ages ago when our diet was more protein (meat, bugs, etc.) that it was extra large intestine that simply we did not need anymore with our move to carbohydrates as our main staple of food.

    I’ve been on the Atkins diet, which reduces carbohydrate consumption to less than 20 grams per day. I take Atkins somewhat seriously, because the 1972 book was completely accurate about how much weight I would lose, how fast I would lose it, my increased energy level, et cetera.

    I believe very low carb diets are still somewhat controversial, but I’m still not convinced that they’ve been thoroughly tested. Dr. Atkins’ claim was that eating very low amounts of carbohydrates changed your metabolism to a kind of different ‘setting’, where you burn and store consumed calories differently than you do when eating large amounts of carbohydrates. It’s been suggested that this is a state similar to the conditions under which we evolved, but completely different from our current environment.

    The problem is that the vast majority of medical studies are and have been conducted on people eating the standard high-carb diet. If our bodies are really evolved to handle a completely different diet, then we should find out as much as we can about how we really react to that diet. Someone should fund an institute that would recruit and train people to be on low-carb diets over very long periods of time, maybe over generations, so we can gather data on this alternative, and perhaps natural, metabolic state.

  12. Darrell (9), have you ever considered reading the article in TB before you call bullshit? … That said, what did you find out?

  13. Dragonphyre, meat does not rot in the body anywhere other than when it’s stuck between your teeth. The HCL in the stomach dissolves meat and fat into a liquid in under an hour. This mixture is then quickly absorbed by the rest of the digestive system.

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