I've got two stories in tomorrow's New York Times about getting sick.
One is about malaria. I've always been fascinated by how parasites can manipulate their hosts for their own ends, and much of my book Parasite Rex is dedicated to explaining how this creepy remote control works. I've come across many new examples from time to time. Now a new study shows that the parasite that causes malaria can alter us humans to turn us into good mosquito bait. As with most stories about life, this one is ultimately about evolutionin this case, how parasites repeatedly have evolved ways to boost their own reproductive success by manipulating hosts like us.
I've never gotten malaria (knock on wood), but I have just experienced the subject of my second piece: appendicitis. Three weeks ago I got appendicitis, and if I lived 150 years ago my appendix would have probably ruptured and I'd have died. Fortunately, I got to the hospital without a hitch and had a straightforward operation to get the appendix out. Once the anesthesia cleared from my head, I began mulling how odd it was that I was born with an organ so exquisitely suited to failure and so useless to me. The manipulations of the malaria parasite are remarkable adaptations, but the appendix is, to a great extent, an maladaptation.
In the article, I offer some of the ideas scientists have had about how we all ended up with an appendix, but there was one interesting take on the appendix that I didn't have room to include in my story. Evolutionary biologists Randolph Nesse and George Williams wrote an article a few years back in Scientific American, in which they argued that all things being equal, natural selection should favor mutations that made the appendix dwindle away to nothing. So why isn't it gone? Perhaps if the appendix got even smaller than it is now, it would become even more prone to appendicitis and cause more deaths. Natural selection, in other words, has reached a dead end.
It's an interesting idea, but it would take a study of thousands of peoplemeasuring their appendix and seeing who does or doesn't get appendicitisto test it. Perhaps some philanthropist will get appendicitis some day and decide to drop a few million bucks to figure out how exactly we all got stuck with this peculiar little time bomb.
Since the creationist response will be predictable:
I can't find some my other comments of last days. Did you try to remove them like mosquito and appendix?. People are terrorized by different ones, also from differnt kind of languages of mistakes. Do yo like only you kind of mistakes and lamguage?
John,
No offense, but is English your 2nd language? If not, you need to take more time in writing comments. You sound, well,.. sorry, but kind of nutty in the two above.
As far as I can tell, John is italian, and a nutty one too. He's frequently around NG and blog all over the places here. Don't try to understand him, we (italians) can't.
Marco
P. S. And yes, english is my nth language, if you ask...
ah, could anyone tell me what John was talking about? I'm wondering whether John really knows what "appendix" is...
and...Carl, take care of yourself.
The appendix has a significant amount of lymphatic tissue in it, so it may have some immune function as well as being a vestige of the caecum.
I'd be interested to see if there's been any work to see whether appendectomised patients are slightly more susceptible to gut illnesses. It may not be evolutionarily relevant now, but historically an extra 1% protection against typhoid or cholera might make all the difference.
In response to Peter--actually, those of us without an appendix are slightly less likely to suffer colitis, an immune disorder of the bowels. No other affect has been documented.
Is the average size of the appendix changing (or any other differences in the appendix) between those who can take advantage of modern medicine and those who can not? Realize the time frame is not that large just curious if anyone is looking into that.
The NYT seems have made a mistake with the photograph used to illustrate your mosquito piece. That's a wasp, not a mosquito.
I was thinking that maybe the appendix is just too small (in evolution term, not fisically) to be "perceived" by natural selection. It is flying under to radar, so to speak, and so it cannot be selected against. Maybe it is a kind of neutral organ, without any pros and cons on individual fitness. The explanation of Williams and Nesse appears to me just a little too panselectionist. Why not look at appendix as a kind of invisible spandrel?
Marco
I'm not buying the argument that evolution has reached a dead end here. It seems quite reasonable to me that certain people WOULD have a mutation that leaves them appendix-less. The question is, with modern medicine such as you just experienced, is the lack of an appendix any longer an advantageous mutation? Seems to me that either the presence or lack of one has become irrelevant, or that its presence confers some advantage at least some of the time, as a couple of people noted above.
Looks like the caption for the picture in the malaria article got messed up. The caption says that it is a picture of a mosquito, when it is actually a picture of a wasp.
I think Marco may be closest to the truth on this appendix question. Look, evolution simply is survivable genes being passed on. Some add to survivablity at a given place in space and time. Obviously then, these genes are held by those most likely to bring forth the next generation. Some genes have little or no effect on survivability. If those genes are carried by "survivors" (those who pass on their genes) then those genes will continue to be passed on even though they are, basically, neither negative or positive. While it is true that the appendix does, on the surface, seem to be a negative in terms of survivabiltiy, it is not so much so that it would necessarily evolve out of existance. For instance, how many people do you know who had to have an emergency appendectomy to save their lives? (Not to belittle YOUR experience, Carl, but I don't know anyone)! Not saying their aren't plenty of you out there, just saying that it isn't something that MOST people suffer through during their life span. And even for those who DO, how many of them successfully passed on their own genes prior to appendicitis? Probably most. I certainly haven't heard of many children suffering from it. It's easy to see how we would not have evolved away from it. Just like our male nipples. Useless, but no harm, so they stay. Now if my nipples start blowing up, I'm going to be pissed, but I HAVE already passed on my genes so I'm guessing there will be a lot of male nipples in future generations even if mine explode.
"It's an interesting idea, but it would take a study of thousands of peoplemeasuring their appendix and seeing who does or doesn't get appendicitisto test it."
Is there a reason why you couldn't measure the size of appendices that are cut out versus size in people dying of unrelated causes? Presumably this would be considerably cheaper. Is there some reason why any such methodology is inherently flawed or the statistics can't be made to work?
Carl, in your appendix article you wrote,
"The appendix does not seem to be involved in digesting food, but it may help the gut to fight disease. The appendix is packed with immune-cell-producing tissues."
How do we know that this isn't mere some kind of preemptive step the body takes to reduce the chance of *appendicitis*? Perhaps there is some fundamental developmental pathway that prevents the easy removal of the appendix, so the next best thing evolution could do was pack it with immune cells, in order to minimize the damage.
In support:
Quoth the talkorigins.org FAQ, "Deadly infection of the appendix at a young age is common, and the lifetime risk of acute appendicitis is 7%."
So lots of immune cells might be particularly important at a young age.
I was surprised that Rebecca Fisher didn't talk about the caecum in other nonprimate placentals and marsupials. A well-developed caecum is evidently a fundamental trait basal to any primate derivatives:
http://www.talkorigins.org/faqs/vestiges/appendix.html#caecum
PS: I got malaria when I was 7 years old, when my family was on sabbatical in Zambia. I was a good little boy and took the awful-tasting chloroquine every week, but I *still* got it because the malaria was resistant. Friggin' evolution. Fortunately, back in the 1980's, the cure of "lots more chloroquine" still worked.
I am an anthropologist and mother of a 12 year old son who suffered a ruptured appendix several weeks ago (and is happily fine now). I am intrigued by the remark that appeared in parentheses in the article -- about supposed cross-cultural differences in the incidence of appendicitis. I read this on several websites at the time of my son's illness, and it was repeated -- unprompted, I might add -- by the surgeon, but I've found it hard to track the relevant research down. I would imagine it would be very tricky to get good cross-cultural data on something like this; how precisely -- if at all --are deaths following abdominal distress recorded in more remote areas of the world, for example? But solid research in this direction would, I feel, be a source of answers on the broader evolutionary questions about the appendix in humans.
Rates of appendix rupture as a function of race and ethnicity in the U.S. show that minorities are ca. 30% more likely to exhibit rupture, due not to biological factors but to differences in the timeliness of obtaining healthcare.
Link for above study -
http://www.pophealthmetrics.com/content/3/1/4
People in hunter-gatherer societies and Central Africa don't get appendicitis. It's a somewhat new problem. Something has changed in our environment. For all I know it's western diets that cause appendicitis.
Jeez, I wondered why you weren't posting much. Get well soon, Mr. Zimmer. Hope you're back on your feet (keyboard!) in no time!
BCH
About 50 years ago when surgeons used a major incision to access the abdominal cavity, when they got ready to close, the looked to see if the patient had an appendix. If one was there, it was taken out.