The human appendix, which is thought to be of little use to the body, may actually serve as a reservoir for beneficial gut bacteria, a new study has found.
The appendix, a narrow pouch that projects off the caecum in the digestive system, has a notorious reputation for its tendency to become inflamed (appendicitis), often needing surgical removal.
Researchers from the Midwestern University Arizona College of Osteopathic Medicine in the US gathered data on the presence or absence of the appendix and other gastrointestinal and environmental traits for 533 mammal species.
They mapped the data onto a phylogeny (genetic tree) to track how the appendix has evolved through evolution, and to try to determine why some species have an appendix while others do not.
They discovered that the appendix has evolved independently in several mammal lineages, and almost never disappears from a lineage once it has appeared. This suggests that the appendix likely serves an adaptive purpose.
They found out that species with an appendix have higher average concentrations of lymphoid (immune) tissue in the caecum. Lymphatic tissue can stimulate growth of some types of beneficial gut bacteria.