The appendix is not a useless organ. For over a century it was seen as an evolutionary leftover, but recent studies challenge that idea.
Evolution: it appeared independently between 16 and about 30 times in mammals over 80 million years, suggesting survival value. Why some animals (cats, dogs, horses, whales) lack it remains a mystery.
Likely functions:
- A refuge for beneficial gut bacteria, helping repopulate the intestines after severe diarrhea.
- Lymphoid tissue (immune cells) that helps defend the body against pathogens.
Evidence (French team):
- 2021 study: across 258 mammal species, those with an appendix live longer, probably due to lower mortality from infections.
- 2023 study: across 1,251 primates, those with an appendix had less frequent and less severe diarrhea.
- Caveat: the animals lived in a park, not in the wild.
Appendicitis: it is caused by a blockage and can lead to peritonitis, but it is much less common than the illnesses the appendix helps prevent. Surgery remains the treatment.
Conclusion: the appendix has a protective function and may contribute to longer lifespan.