Immune function of the appendix: chicken or egg?

I was reading around AiG (as you do), and I came across this article called (Your appendix...it's there for a reason).Now, everyone agrees there is a reason for the human veriform appendix, the question revolves around what that reason is.It is known that there is a larger collection of lymphoid tissue in the appendix than many other areas of the gastro-intestinal tract. The creationists argue that this is because the Creator gave us the appendix because of that function.However, I argue (and I'm sure others have, but I can't find anything on it at the moment) that it is the other way around: the function evolved because of the structure.The human veriform appendix is very susceptible to infection. Appendicitis has a very high mortality rate when untreated. Therefore, there would be a great selection pressure acting to keep people from dying from appendicitis.So, what do you need to combat an infection? Lymphocytes. Where do they come from? Lymphoid tissue. So, it makes sense that the appendix will have lymphoid tissue, given its susceptability to infection.The lymphoid tissue, present within the entire of the GIT, especially Peyer's patches of the ileum, could probably have evolved to increase in number in certain locations with relative ease (compared to other evolutionary developments). With such a concentration of lymphoid tissue, it is then easy for it to take on a role in the immune system.Therefore, I conclude that it is precisely because the appendix is vestigial (thus small and easily infected), that it needs to have this immune function to protect itself.

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In fact, there is plenty of lymphatic tissue all over the gut region. At any rate, what is it about lymphatic tissue that it can only be embedded in a small, blind sac? If we needed extra lymphatic tissue, surely it could be embedded in a more solid, pancreas-like organ.Also, there has been no indication that people who have had their appendices removed are any more prone to health problems, and there are individuals who are born without appendices -- they, likewise, have no more health problems than those with healthy appendices.

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So what you're saying then, is that the little bugger is entirely useless? Fancy that, AiG was wrong. I'd make a note of it, but I just filled the last of my 500 notebooks full of their errors

I think that is a neat answer Doddy. The only reason there is a concentration of lymphatic tissue in the appendix, from which creationists infer it to be important to the immune system, is that it is important to the immune system as a likely area of infection.This is just one more example of the creationist canard that for a feature to be vestigial it must have absolutely no functionality.TTFN,WK

You can remove or kill all of your current Lymphocytes and still be healthy: they are about to do this to me. New lymphocytes are generated constantly and only "live" for about 30 days and they are constantly being replaced. The replacement cells do not come from the lymph nodes or the veriform appendix but from bone stem cells. Lymph nodes are there to provide places for the lymph nodes to be organized, ready to fight infection - and these are located throughout the body. You can also remove lymph nodes without impacting your ability to fight infection: this is common to biopsy lymphoma, and I have had several whole nodes removed for that purpose.Lymphatic system - Wikipedia

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The lymphatic system has three interrelated functions: (1) removal of excess fluids from body tissues, (2) absorption of fatty acids and subsequent transport of fat, chyle, to the circulatory system and, (3) production of immune cells (such as lymphocytes, monocytes, and antibody producing cells called plasma cells).

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Those first two functions are part of the digestive system function and thus would be expected in an organ that was originally for digestion. Thus the vestigial use of the appendix is as a continued use of the lymph system because that part is still beneficial while the rest of the function is no longer served by the appendix.

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The thymus, spleen, lymph nodes, peyer's patches, tonsils, vermiform appendix, and red bone marrow are accessory lymphoid tissues that comprise the lymphoid organs. These organs contain a scaffolding that support circulating B- and T-lymphocytes and other immune cells like macrophages and dendritic cells.

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And because the lymph system was already there in the appendix when all other functions became obsolete it allowed the opportunity for this organ to evolve to assist the lymph system because that was beneficial (selected for).This can of course also be compared to the lymph function in other animals that do have functional appendixes to see what the difference is.

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