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Human Appendix Not a Useless Organ


Darwin was wrong, say researchers at Duke University Medical Center, Arizona State University, and the University of Arizona: the human appendix is not a useless, evolutionary remnant of a larger structure. The appendix has a function, and the newfound understanding of its purpose may help researchers someday find a way to prevent appendicitis.

The first-ever study of the evolution of the appendix and information on its critical function has just been released in the Journal of Evolutionary Biology. This is a follow-up to a report from about two years ago, when investigators at Duke University Medical Center proposed that the human appendix serves as a storage area for beneficial bacteria that can be used to repopulate the intestinal tract (gut) when good bacteria levels have been depleted by diarrhea or other gastrointestinal conditions. The gut needs various microorganisms, including beneficial bacteria, for digestion to occur.

The appendix is a two- to four-inch long pouch that is located near where the large and small intestines meet. Scientists have long speculated about the function of the appendix, especially since it is populated with immune system tissue. William Parker, PhD, assistant professor of surgical sciences at Duke and the senior author of the current study, and his colleagues now believe that the immune system cells protect the beneficial bacteria in the pouch until they are needed by the intestinal tract.

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Parker and the other researchers propose that in countries without modern sanitation practices and endemic diarrhea-causing diseases, the beneficial bacteria harbored in the appendix can emerge and enter the intestinal tract after diarrheal symptoms have emptied the bowels. In industrialized societies that have good hygiene practices, however, the stored beneficial bacteria may not be needed or needed rarely. This idea supports the fact that removing the appendix today has no apparent negative impact on the body.

Appendicitis, or inflammation of the appendix, may be the result of too much sanitation, commonly referred to as the “hygiene hypothesis.” This hypothesis suggests that people who live in sanitary societies suffer with high rates of allergies and other immune system disorders because their immune systems are not challenged enough. In other words, we are so clean that when something does attack the system, it can overreact, resulting in inflammatory conditions, such as appendicitis.

In a Science Daily report, Parker said that our new understanding of the appendix may help us prevent appendicitis if we can challenge the immune system today much like it was back in the Stone Age. If we can do that, he said, “we would see far fewer cases of allergies, autoimmune disease, and appendicitis.”

Duke University Medical Center, “Inside Duke Medicine”
Randal Bollinger R et al. Journal of Theoretical Biology 2007 Dec 21; 249(4): 826-31
Science Daily, August 21, 2009
Smith HF et al. Journal of Evolutionary Biology 2009 Aug 12.