The appendix is a small, worm-like structure that, in humans at least, serves no obvious purpose beyond becoming inflamed and ruining someone’s day. In fact, this murderous little organ is responsible for more than 40,000 deaths per year.1

Eytan Wine wears a collared shirt and smiles in front of a microscope.
Eytan Wine studies factors that contribute to intestinal inflammation and is exploring the potential role of the appendix.
Eytan Wine, University of Alberta

Charles Darwin hypothesized that the appendix was an evolutionary relic leftover from humanity’s distant ancestors shifting from leaf-based to fruit-based diets. “But I don’t think the answer is that simple,” said Eytan Wine, a gastroenterologist at the University of Alberta.

One hypothesis, said Wine, is that the appendix functions as a “safe house” for beneficial microbes. “The appendix is a [blind-ended] organ, where microbes could escape different insults to the gut physiology such as infection, or antibiotics, or toxins,” he said. If some of these beneficial species get wiped out, survivors in the appendix could replace them, re-balancing the gut microbiome. “[The safe house hypothesis] is not all that well studied,” said Wine. “It’s certainly plausible and somewhat supported.”

The appendix also contains a large amount of gut-associated lymphoid tissue, populated with various types of T and B cells as well as germinal centers.2 This has led researchers to hypothesize that it may function as an immune cell priming site.

A fluorescent microscopy image of periappendicular bowel shows a group of red-labeled bacteria cells embedded in a rough oval of green-labeled mucus tissue, encased in a ring of blue-labeled epithelial cells.
Researchers think bacteria from the appendix may migrate into other regions of the digestive tract; here, bacteria (in red) are embedded in the mucus layer (green) of a periappendicular section of bowel.
Nazanin Arjomand Fard

Yet people who have undergone appendectomies are often perfectly healthy. “To me, this [indicates that] maybe the importance is more in early life…immune development is a lifelong process, but the first few years of life—those are the critical times of immune education,” said Wine. Since most appendectomies are performed between ages 10 and 30, Wine speculates that by the time it is removed, the appendix may have already served its most important function.


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  1. Smith HF. Anat Rec. 2023;306(5):972-982.
  2. Mörbe UM, et al. Mucosal Immunol. 2021;14(4):793-802.