Appendix Evolved More Than 30 Times

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Multiple independent appearances of the cecal appendix in mammalian evolution and an investigation of related ecological and anatomical factors (2013)

Although the cecal appendix has been widely viewed as a vestige with no known function or a remnant of a formerly utilized digestive organ, the evolutionary history of this anatomical structure is currently unresolved.

Substantial evidence supports the view that the cecal appendix is an immune structure primarily functioning as a safe-house for beneficial bacteria, and comes from a range of disciplines, including medicine, epidemiology, immunology, and microbiology

Given all of the information available, a new working hypothesis might be developed in which the appendix has evolved as a microbial safe-house under selection pressure from gastrointestinal pathogens potentially transmitted via a range of mechanisms rather than via a single mechanism dominated by a particular dietary or social factor.

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The immunological functions of the Appendix: An example of redundancy?   (2018)

Biological redundancy ensures robustness in living organisms at several levels, from genes to organs.

In this review, we explore the concept of redundancy and robustness through an analysis of the caecal appendix, an organ that is often considered to be a redundant remnant of evolution. However, phylogenic data show that the Appendix was selected during evolution and is unlikely to disappear once it appeared. In humans, it is highly conserved and malformations are extremely rare, suggesting a role for that structure.

The Appendix could perform a dual role. 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. It is extremely rich in biofilms that continuously shed bacteria into the intestinal lumen.

The Appendix contains a microbiota as diverse as that found in the colon and could replenish the large intestine with healthy flora after a diarrhea episode. In conditions of modern medicine hygiene, and people live healthy without their appendix. However, several reports suggest that the effects of appendectomy could be subtler and associated with the development of inflammatory conditions such as inflammatory bowel disease (IBD), heart disease but also in less expected disorders such as Parkinson’s disease. Lack of an Appendix also predicts a worsen outcome for recurrent Clostridium difficile infection, which is the first nosocomial infection in hospitals.

Here, we review the literature and in combination with our own data, we suggest that the Appendix might be redundant in its immunological function but unique as a reservoir of microbiota.

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The Appendix in Parkinson’s Disease: From Vestigial Remnant to Vital Organ? (2019)

the appendix offers an appealing gateway to access the immune system, microbiome, and α-syn pathology within the intestine to benefit the development of a new generation of the therapies for PD that extend beyond the brain.

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The gut in Parkinson’s disease: Bottom‐up, top‐down, or neither? (2019)

in addition to gut‐brain pathways, the brain‐to‐gut communication may also be involved in Parkinson’s disease pathophysiology. In this mini‐review, we describe the strengths and limitations of the existing studies on the gut‐brain axis in experimental models of parkinsonism and discuss an alternative hypothesis in which the central and enteric nervous system would evolve separately during disease progression.

The term “appendix” does not seem to appear in this paper?   Hmm…

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