Researchers at Midwestern University Arizona College of Osteopathic Medicine have suggested that the human appendix, although widely viewed as a vestigial organ with little known function, may serve as a reservoir for beneficial gut bacteria and as a secondary immune organ that catalyzes immune cell response. According to the paper published in the journal Comptes Rendus Palevol, the organ evolved independently in several mammal lineages, over 30 separate times, and it almost never disappears once it has appeared. This led researchers to believe that it likely serves an adaptive purpose.
The study also reveals that the species with an appendix have higher average concentrations of lymphoid (immune) tissue in the cecum – a pouch connected to the junction of the small and large intestines or from which the appendix develops, suggesting that the organ may play an important role as a secondary immune organ. Moreover, lymphatic tissue can also stimulate growth of some types of beneficial gut bacteria, which provides further evidence that the appendix may serve as a “safe house” for helpful gut bacteria.
Animals with certain shaped ceca (tapering or spiral-shaped) were more likely to have an appendix than animals with a round or cylindrical cecum. Therefore, the appendix isn’t evolving independently, but as part of a larger “cecoappendicular complex” including both the appendix and cecum, researchers explain.
Reference: Morphological evolution of the mammalian cecum and cecal appendix – Comptes Rendus Palevol, ScienceDirect.