Is the human appendix getting smaller?

[saddlestone-man]

TL;DR Summary

Is there any evidence that the human appendix is getting smaller?

Hello All

It seems to be accepted wisdom that the human appendix is gradually getting smaller, and eventually it will disappear altogether. Is there any evidence that this is true?

For the organ to get smaller generation by generation, wouldn't there have to be a selective advantage for smaller appendices versus bigger ones?

This might have been true once but in these times, modern medicine simply removes a troublesome organ so there is very little mortality due to larger appendices.

best regards ... Stef

 

[Vanadium 50]

It seems to be accepted wisdom

Reference, please?

 

[Laroxe]

Summary:: Is there any evidence that the human appendix is getting smaller?

Hello All

It seems to be accepted wisdom that the human appendix is gradually getting smaller, and eventually it will disappear altogether. Is there any evidence that this is true?

For the organ to get smaller generation by generation, wouldn't there have to be a selective advantage for smaller appendices versus bigger ones?

This might have been true once but in these times, modern medicine simply removes a troublesome organ so there is very little mortality due to larger appendices.

best regards ... Stef

To be honest I don't think anyone knows. I suspect the fact that the appendix was seen as a vestigial structure of no real use would lead people to think it would be lost through evolutionary processes, but that would be slow and we have no comparative data. However it appears that the appendix is being rehabilitated, and is now considered a functional structure important in maintaining a healthy biome. If that's the case then the answer would be no.

 

[jim mcnamara]

Short answer: No. We need it.

Appendix is generally necessary, not something that can always harmlessly be removed.
A hypothesis for the function of the appendix (red)- safe haven for necessary for gut microbiota
Plus known functions - Short version:

First, it is a concentrate of lymphoid tissue resembling Peyer's patches and is the primary site for immunoglobulin A production which is crucial to regulate the density and quality of the intestinal flora. Second, given its shape and position, the Appendix could be a unique niche for commensal bacteria in the body

-- see this review paper:

Semin Immunol . 2018 Apr;36:31-44.
doi: 10.1016/j.smim.2018.02.005 Epub 2018 Mar 2.
"The immunological functions of the Appendix: An example of redundancy? "
Girard-Midou MJH, et al.
Edit - link that works (for me anyway)
DOI: 10.1016/j.smim.2018.02.005

 

[hutchphd]

I think it is just that our bellies are getting bigger
Actually the appendix as a repository to re-inoculate us with the appropriate microbiome after an intestinal event is compelling

 

[256bits]

Summary:: Is there any evidence that the human appendix is getting smaller?

For the organ to get smaller generation by generation, wouldn't there have to be a selective advantage for smaller appendices versus bigger ones?

Is there a set of genes that control the size of particularly the appendix?
You would have to investigate that arena.
Or a set that would shut off/ turn on its formation during embryonic development.

Anyways, if you are relying upon Darwin's interpretation, he was wrong in that it is a vestigial organ, an idea which permeated textbooks incorrectly. It's removal may not be an actual life threatening event, but neither is removal of wisdom teeth, spleen, an appendage, an eye, or many more organs that can be added to the list.

Not just humans have an appendix. And there are many animals that do not.
Question would be why would it evolve for some and not other animals.
Is diet a criteria. Sanitation. Preditor/prey.

Darwin theorized that the appendix in humans and other primates was the evolutionary remains of a larger structure, called a cecum, which was used by now- extinct ancestors for digesting food. The latest study demonstrates two major problems with that idea. First, several living species, including certain lemurs, several rodents and a type of flying squirrel, still have an appendix attached to a large cecum which is used in digestion. Second, Parker says the appendix is actually quite widespread in nature. "For example, when species are divided into groups called 'families', we find that more than 70 percent of all primate and rodent groups contain species with an appendix." Darwin had thought that appendices appeared in only a small handful of animals.

https://www.sciencedaily.com/releases/2009/08/090820175901.htm

A repository for bacteria was known for quite some time, and only recent research has led to 'confirmation' that this is beneficial for humans.

With medical advances and lifestyle that we have nowadays ( repopulate the gut bacteria with a suppository ) we may not actually need it.
If we revert back to caveman living, then it may be necessary, or at the very least beneficial.

 

[Rive]

With medical advances and lifestyle that we have nowadays ( repopulate the gut bacteria with a suppository ) we may not actually need it.

Well. Regarding those medical advances: before the introduction of really safe food it definitely had that function.
After the introduction of some really nasty (yet: life-saving!) antibiotics, it has that function again

 

[russ_watters]

With medical advances and lifestyle that we have nowadays ( repopulate the gut bacteria with a suppository ) we may not actually need it.
If we revert back to caveman living, then it may be necessary, or at the very least beneficial.

I don't subscribe to that first definition of "need". In my opinion, we should indeed be referring to the un-augmented capability. Saying that you could replace the function by artificial means if it is lost is reflective of the function being needed.

Why does this matter? There is still evolutionary pressure involved, even if we can reduce that pressure via artificial means.

 

[jim mcnamara]

To assert what @russ_watters is presenting:
Evolution does not care if you are first world or not. If you remove the effects of immunoglobulin A, regardless of your background, you are more likely to develop Crohn's disease or a lot of other GI-related conditions. So, for example, thinking you have a "fix" with yogurt [pills] for the possible sequelae of appendectomy is problematic. Unfortunately, the fixes are often short term, when prescribed after a long run of antibiotics and patients get diarrhea or other worse issues. Like Clostridium difficile.

Actual human feces pills are used to combat Clostridium difficile induced very serious problems. Big problem for elderly patients. Poop pills is what they call them...

Poop pills for C. difficile white paper for non-medical types:
https://www.nih.gov/news-events/nih...plants-restore-gut-microbes-after-antibiotics

Confused?
BTW if you actually had read the first link you would be aware of this issue. Admittedly, that paper does have "medicalese" terms so if you are a pure Physics type it may be a harder read. ... this is how I get even for my having to wade through some wall-o-math QM posts with little understanding ...and reduce link readership in Bio links all at the same time

 

[256bits]

There is still evolutionary pressure involved,

Evolution does not care if you are first world or not

Is there any indication that there is evolutionary pressure, which is the premise of the OP?
I would say not.

 

[russ_watters]

Is there any indication that there is evolutionary pressure, which is the premise of the OP?
I would say not.

I think @jim mcnamara described it in pretty compelling detail. Could you comment on why you don't think what he described constitutes evolutionary pressure?

 

[256bits]

I think @jim mcnamara described it in pretty compelling detail. Could you comment on why you don't think what he described constitutes evolutionary pressure?

As far as is known, any species that has acquired an appendix, has not ever lost it.
So where is the pressure to loose the appendix?

 

[Rive]

So where is the pressure to loose the appendix?

I don't think that's the right angle for this. Even the eyes (most of it) can be lost if there is no pressure to maintain it.

I think the actual size of the appendix is more or less proportional to its usefulness.

 

[russ_watters]

As far as is known, any species that has acquired an appendix, has not ever lost it.
So where is the pressure to loose the appendix?

I feel like you switched sides in the discussion. The pressure is to keep the appendix because we "need" it. If you now agree with that great.

 

[256bits]

I don't think that's the right angle for this. Even the eyes (most of it) can be lost if there is no pressure to maintain it.

I think the actual size of the appendix is more or less proportional to its usefulness.

That is understandable, from both the individual and the species perspective.
We lost our tails as a species for some reason, and acquired thumbs for another reason.

But, the appendix stays around within a species that has acquired it.
From a sexual selection point of view, does the absence/presence of an appendix have any effect upon the ability of an individual to acquire a partner and procreate, and care for the young.
The organ does not seem to be energy extensive, so maintenance is of minimal concern.

 

[russ_watters]

But, the appendix stays around within a species that has acquired it.
From a sexual selection point of view, does the absence/presence of an appendix have any effect upon the ability of an individual to acquire a partner and procreate, and care for the young.

Well, it does kill people. And it also aids in recovery from GI conditions that also kill people. So it exerts both positive and negative evolutionary pressures.