What use is an appendix?

| 18 Comments

Here's an excellent and useful summary of the appendix from a surgeon's perspective. Creationists dislike the idea that we bear useless organs, remnants of past function that are non-functional or even hazardous to our health; they make up stories about the importance of these vestiges. Sid Schwab has cut out a lot of appendices, and backs up its non-utility with evidence.

The study I cited most often to my patients when asked about adverse consequences of appendectomy is one done by the Mayo Clinic: they studied records of thousands of patients who'd had appendectomy, and compared them with equal thousands who hadn't. (Back in the day, it was very common during any abdominal operation to remove the appendix. Like flicking a bug off your shoulder. No extra charge: just did it to prevent further problems: took an extra couple of minutes, is all.) The groups were statistically similar in every way other than presence of the worm. There were no differences in incidence of any disease. It's as convincing as it gets, given the impossibility of doing a prospective double-blind study.

I have a personal interest in this: I was nearly killed by my appendix at the age of 9, and had it removed. I haven't missed it since.

18 Comments

I had mine taken out in 1972, at the age of 7. It had burst and I had to spend a week in Soviet hospital (ugghh!). In any case, I haven’t missed it and my life hasn’t changed. However: I seem to remember seeing something about the appendix’s utility in our immune system. I don’t remember where; or even the general tone of the article (at least it wasn’t phrased as a direct piece of creationist hogwash, but they are quite good at concealment, as we all know). Are you familiar with those claims?

No difference in the incidence of ANY disease?? What about appendicitis?

Dr. Loren G. Martin, Oklahoma State University (physiology), SciAm Oct. 21, 1999:

http://www.sciam.com/askexpert_ques[…]809EC588F2D7

FL

No difference in the incidence of ANY disease?? What about appendicitis?

True, I haven’t had appendicitis since my appendix was removed when I was 17…

I’m glad, too, that was one heck of a tummyache.

Dr. Loren G. Martin, Oklahoma State University (physiology), SciAm Oct. 21, 1999:

http://www.sciam.com/askexpert_ques[…]809EC588F2D7

FL

Yes, “the appendix helps with the immune system” thing is now conventional wisdom with creationists. But if you read what Martin says, basically all he’s got is (a) it has immune system cells, and (b) surgeons can use it as a spare part in a particular surgery.

(b) is rare and only useful in the last decade or so. (a), on the other hand – how do we know the immune system cells aren’t there simply to forestall the fatal infections which still occur anyway at a significant rate – according to this article:

A life table model suggests that the lifetime risk of appendicitis is 8.6% for males and 6.7% for females

There darn well better be immune cells in the appendix with this sort of thing being a regular occurence in the population. But this is a long ways from showing the appendix has a function; rather, we might just be seeing evolution try to make the best of a bad situation.

I remember coming across this a while back that says something similar to the link FL posted:

http://www.livescience.com/humanbio[…]ppendix.html

I’m certainly not in FL’s camp and don’t really understand why creationists would even try to use that as evidence against evolution.

I actually haven’t had my appendix out and I have to say, you guys aren’t making me feel better about the possiblilty of needing it out in the future.

:(

As a child I suffered from what might be descriptively called “periodic recurring appendicitis.” Finally, the scarred, distended thing was taken out when I was 14 after jaundice had started to set in. When I was told it served no purpose I was certainly happy, but it has left me with a lingering question.

The problem with calling the appendix a vestigial organ is precisely that it tends to kill us. I am puzzled as to why we would still have one if there were a net selection pressure to remove it. Other vestigial organs are notable mainly for their complete lack of impact on our lives one way or the other, but the appendix is extremely dangerous. What maintains its existence?

Assuming the appendix is truly vestigial, I can think of a few reasons we might still have it. 1) It was used very recently and has not had time to disappear. 2) It is not controlled by a single gene, the mutation of which would cause the appendix to vanish.

I think the first explanation can be demolished easily. There have been enough studies to show that as an adult organ the appendix literally does nothing. It has rudimentary lymphatic tissues but seems to go out of its way not to use them. This characteristic is clear and must have taken some time to be fixed in the population. It would have been a lot simpler for the appendix to simply disappear—assuming that were genetically possible.

The next explanation is harder to dismiss. It may very well be that there is no simple genetic description of the appendix. Perhaps there simply is no single and exclusive on/off gene to control expression of appendix tissues. Whatever the case, eventually we will discover it, I am sure.

Another possibility is that the appendix is not vestigial, but serves some as-yet-unidentified role, perhaps prenatally or prior to weaning. Perhaps, the existence of the appendix is important for the proper development of the GI tract. These are just brain-stormed hypotheses but you could probably add your own. The point should be clear; we do not know for a fact that the appendix is completely vestigial.

Of course the adult appendix actually is vestigial, in fact. This has already been discussed ad nauseum. While this implies much about the nature of any alleged creator who would curse us with such an organ, it also, through the mechanism of natural selection, implies that the appendix serves some important purpose, still hidden from us. Eventually we will discover it, I am sure.

It might be worth pointing out that at least in mammals, the entire GI tract contains immune cells. Lots of ‘em, all througout the mucosal layer. In fact, the GI tract is your largest immune organ. The real question is whether the appendix has any special immune function that is not already done by the rest of the tract.

Isn’t this accepting the way creationists have “framed” the issue?

The main point about the appendix isn’t that it’s no longer functional, it’s that it’s no longer serving the original function it had. (whether it’s now functionless or serving another function)

Either way it’s slam dunk evidence for evolution. (and non-vegetarianism)

John Vreeland said: “Assuming the appendix is truly vestigial, I can think of a few reasons we might still have it. 1) It was used very recently and has not had time to disappear. 2) It is not controlled by a single gene, the mutation of which would cause the appendix to vanish.”

I can think of another possibility: perhaps the appendix genes serve other, valuable functions which outweigh the risk of appendicitis.

The immune cells in the appendix are found throughout our gut, so there is nothing special about them in the appendix.

Also selection against the appendix is constrained by the fact that if the appendix got smaller the risk of infection would increase.

John Vreeland Wrote:

I think the first explanation can be demolished easily. There have been enough studies to show that as an adult organ the appendix literally does nothing. It has rudimentary lymphatic tissues but seems to go out of its way not to use them. This characteristic is clear and must have taken some time to be fixed in the population. It would have been a lot simpler for the appendix to simply disappear—assuming that were genetically possible.

Nesse and Williams disagree there, as Carl Zimmer mentions; they suggest that evolving the appendix away is very difficult because small appendices are more prone to infection. It would be better if it were gone entirely, but evolutionary pathways to that condition have to get around the fitness valley of a small-but-not-yet-completely-absent appendix.

I haven’t missed it since.

As far as you know.

I’ve never particularly missed my foreskin… I don’t think.

Do creationists have a function for that?

Is there a connection between appendicitis and diet?

Creationists have nothing to gain from the appendix.

The fact that it appears to be mainly vestigial or to have changed in function strongly supports the theory of evolution.

Of course, if it had a function, that wouldn’t argue against the theory of evolution at all! Creationists’ almost childishly desperate claims that the appendix is not vestigial are entirely defensive. They lose if it’s vestigial (as it appears to be), but they don’t win if it has a function.

Incidentally, the spleen has a number of functions, but humans can survive indefinitely without a spleen, albeit at higher risk of bacterial pneumonia and possibly with some other issues. Makes perfect sense from an evolutionary standpoint. Makes no sense at all under creationism.

harold — That’ll make them vent their spleen!

This was interesting, I had no idea creationists were trying to highjack the science itself. The old Martin (SciAm) and the newer Wanjek (LiveScience) texts are unreferenced and suspicially alike in data. The Wikipedia article ( http://en.wikipedia.org/wiki/Vermiform_appendix ) is referencing creationist texts.

As many times before, the Talk Origin text is superior in scope and references. ( http://www.talkorigins.org/faqs/ves[…]ppendix.html ) That the appendix can’t be vital seems obvious since “many people have been found who completely lack an appendix from birth” without visible effects.

I’ve never particularly missed my foreskin… I don’t think.

Do creationists have a function for that?

No, but scientists may have. The foreskin seems to present objects to the immune system. (Langerhans cells in the foreskin.) Apparently it also makes for different sexual mechanics with and without.

The former possibility seems to be akin to the appendix function. Sometimes the total result seems bad (higher risk for HIV infection with foreskin), sometimes it can be good (lowered risk for syphilis and virtually nil risk for chlamydia with foreskin).

But why should the foreskin be seen as vestigial? Almost all mammals have foreskins. It is also a protective sheath, which could be the main function.

My appendix was very useful to me in that when it went bad and was removed, the surgeon took a carcinoid tumor with it. I would not have known about the tumor until it started to give me problems, by which time it would have been much worse to deal with.

That said, I’m not superstitious, just lucky.

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This page contains a single entry by PZ Myers published on February 18, 2007 1:46 PM.

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