What the appendix does and why it persists
Mar 9th 2026
Once written off as useless, the appendix actually evolved repeatedly and supports immune and microbial roles, but modern sanitation and the risk of appendicitis have reduced its evolutionary advantage.
- The appendix evolved independently many times in mammals, appearing in at least 32 instances across 361 species.
- It contains gut associated lymphoid tissue and lymphoid follicles that help train the immune system and produce antibodies such as immunoglobulin A.
- Researchers propose the appendix can serve as a microbial refuge where biofilms shelter beneficial bacteria that help repopulate the gut after severe infections.
- Appendicitis is a common and potentially life threatening condition that is usually treated by removing the appendix.
- Large studies find no decrease in fertility after appendectomy and in some cases report a small increase in pregnancy rates.
- Ancestral benefits from the appendix in unsanitary environments have declined with modern sanitation and antibiotics, making the organ more of a medical liability today.