The appendix may be a safe house for gut bacteria, not useless leftovers
For generations the appendix was written off as useless, largely because removing it seemed to cause no harm. In 2007 researchers at Duke University proposed a job for it: sheltering helpful gut bacteria when illness or antibiotics flush the intestines, then restocking the gut afterwards. Later findings lent that idea some support.
The appendix is a narrow, finger-shaped tube closed at one end, hanging off the cecum, the pouch where the small intestine meets the large. Its formal name, vermiform, is Latin for worm-shaped. It usually sits in the lower right abdomen near the hip bone, though its tip wanders: behind the cecum is the most common position in Ghana and Sudan, while in Iran and Bosnia it most often dips into the pelvis. Some mirror-image identical twins carry it on the left side, and in very rare cases, about 1 in 100,000 in surgical records, it is missing altogether.
The case for a purpose has grown. William Parker, Randy Bollinger and colleagues argued in 2007 that its shape and position, tucked just below the main one-way traffic of food and germs, make it a good refuge for beneficial microbes. Research in 2012 found that people without an appendix were twice as likely to suffer a recurrence of Clostridioides difficile colitis, and a 2016 study linked having one to greater concentrations of immune tissue in the cecum. It is surrounded by gut-associated lymphoid tissue involved in B and T cell responses. Even so, it is still commonly classified as vestigial.
Charles Darwin suggested that earlier human ancestors used a larger version to break down fibrous leaves, much as horses, rodents and koalas rely on a big cecum full of cellulose-digesting bacteria. As diets shifted toward easier foods, mutations shrinking it stopped being costly, and over millions of years the cecum's tip dwindled into the appendix.
Inflammation, appendicitis, tends to start as vague pain around the navel, reflecting the organ's origin in the embryonic midgut, before settling in the lower right side at a spot known as McBurney's point. Surgeons have also found constructive uses for it: in the Mitrofanoff procedure the appendix is refashioned into a channel for draining the bladder.
Source: Appendix (anatomy)
