The Human Appendix: What Is It Good For?

The Human Appendix: What Is It Good For?

Absolutely nothing! That’s the answer soul singer Edwin Starr gave in 1970 to the question, “War, what is it good for?” It’s also the same response evolutionary biologists give when asked about the human vermiform appendix.

The human appendix is one of the prototypical examples for “bad” biological designs.1 According to skeptics, this structure is suboptimally designed. About 7 percent of people in developed countries suffer from appendicitis. And the inflamed appendix can be removed without any consequence. In fact, appendectomies help prevent ulcerative colitis.

Additionally, the human appendix is interpreted as vestigial by evolutionary biologists. Accordingly, this structure was once functional in evolutionary ancestors, but was no longer needed by its descendents and experienced decay, losing function.

Why would a Creator produce a poorly designed structure with minimal function that appears to have an evolutionary etiology (origin)? In response to this challenge, intelligent design advocates point out that, because of the lymphatic tissue associated with it, the appendix appears to serve a role in the immune system. Still, the exact nature of this putative function has never been fully established.

Researchers from Duke University Medical Center now think that they have figured out what the appendix is good for: as a storehouse for beneficial microbes.2 These scientists note that the human colon is coated with a biofilm that consists of helpful bacteria. This microbial coating may aid in digestion and participate in other biological activities. Perhaps most importantly, it excludes pathogenic bacteria from the surface of the colon. Occasionally the microbial content of the colon becomes imbalanced and pathogens gain a foothold and take over the biofilm. The body responds by flushing the colon. Bacteria from the appendix then repopulate the colon, reestablishing a healthy biofilm.

The Duke University scientists maintain that the human appendix is well designed to operate as a bacterial storage unit. Its thin, worm-like architecture and constricted opening prevent pathogenic bacteria from entering it. And its out-of-the-way location, attached to the caecum (the bulbous structure at the beginning of the colon that forms a cul-de-sac where the small intestine joins up with the colon), isolates it from the flow of fecal material through the digestive tract.

The association of lymphatic tissue with the appendix is also important. This tissue produces compounds that promote the growth of microbes within the appendix.

Interestingly, a comparative anatomy study published in 1980 (conducted from an evolutionary vantage point) demonstrated that the distribution of appendixes among primates and other mammals doesn’t match the expected pattern if it was a vestigial structure.3 Instead, its occurrence suggests that it is a structure that has utility.

It looks like the appendix is really good for something after all. Perhaps it’s just as well that Edwin Starr passed away. I doubt he would ever want to record a song about the vermiform appendix.

  1. Douglas Theobald, “The Vestigiality of the Human Vermiform Appendix: A Modern Reappraisal,” Talk Origins website,, accessed June 24, 2008.
  2. R. Randal Bollinger et al., “Biofilms in the Large Bowel Suggest an Apparent Function of the Human Vermiform Appendix,” Journal of Theoretical Biology 249 (2007): 826–31.
  3. G. B. D. Scott, “The Primate Caecum and Appendix Vermiformis: A Comparative Study,” Journal of Anatomy 131 (1980): 549–63.