For decades, the appendix was taught to be a vestigial organ, an antique reminder of a lost evolutionary purpose. However, new research suggests that the appendix may not be useless — it could play a very important role in the immune system.

According to the research, the appendix may actually serve as a reservoir for beneficial gut bacteria to ensure that not all this healthy bacteria is lost in the unfortunate case of diarrhea, The Independent reported. As a result, it may take individuals without an appendix longer to recover from intestinal illness.

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For the study, now published online in the journal Comptes Rendus Palevol, researchers looked at 533 different mammal species, noting both the presence and absence of the appendix, and what came as a result of both. This presented a clear evolutionary timeline for the organ, and showed that once it was introduced into mammalian bodies, it stayed. As taught by the theory of evolution, the organ’s persistence throughout time would suggest it did, and still does, serve an important purpose.

The research revealed that animals who had an appendix also had higher concentrations of something known as lymphoid tissue in the pouch of skin that connects the small and large intestines, Time reported. This tissue is associated with our immune system and the growth of good bacteria, thus suggesting the appendix’s true role in our health.

While we’ve come to view bacteria in a bad light, scientists recently have been emphasizing the importance of healthy bacteria in the digestive system. For example, according to, these bacteria help to break down foods, stimulate the immune system, and produce vital vitamins and hormones.

Although the new research suggests the appendix is not as useless as once thought, we still don't know why this organ is so prone to an inflammation known as appendicitis, though some scientists think it may be due to a blockage, The Independent reported.

Source: Smith HF, Parker W, Kotze SH, Laurin M. Morphological evolution of the mammalian cecum and cecal appendix. Comptes Rendus Palevol. 2017

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