healthHealth and Medicine

The Appendix Might Not Be So Useless After All


Tom Hale

Senior Journalist

clockJan 10 2017, 17:54 UTC

decade3d - anatomy online/Shutterstock

The appendix has long been a bit of a mystery. At its worse, it's considered a useless evolutionary throwback whose sole purpose is to give you a nasty case of appendicitis. However, one research team of medical doctors have a theory of what purpose this little organ could serve.

Researchers from the Midwestern University Arizona College of Osteopathic Medicine have worked on a study that suggests it could serve as “a reservoir” for beneficial gut bacteria.


The appendix is a worm-like strip that projects off at the crossroads of the small and large intestines, called the cecum. In the past, it has been widely viewed as a "vestigial organ" with no known present-day function for humans. None other than Charles Darwin first theorized it could be a vestigial organ from an evolutionary ancestor used to digest leaves. However, peculiarly, only a handful of mammals have the organ.

In this study, associate professor of anatomy Heather Smith and her team tracked the evolutionary history of the appendix by studying the cecum of 533 different mammals, from beavers and rabbits to common wombats and brushtail possums. Their research found it has evolved independently at least 30 separate times in several mammal lineages. Rather interestingly, once the appendix appears, it almost never disappears. This led them to the idea that it could serve some advantageous function.

Their study set out to see if ecological factors – such as diet, climate, and where an animal lives – correlated with which species have an appendix. Instead, they found that species with an appendix have higher average concentrations of lymphoid tissue, which is key in creating an immune response, in the cecum in the lower abdomen.

Research over the past few years has shown that lymphatic tissue can also foster the growth of beneficial gut bacteria. This led the team to conclude that the organ plays some role in the immune system, particularly acting as a “safe house” for helpful gut bacteria. That also means it isn't evolving on its own as, but as part of a larger "cecoappendicular complex".


The theory might not be set in stone, but at least they might have finally found the appendix some purpose in life.

healthHealth and Medicine
  • tag
  • immune system,

  • anatomy,

  • biology,

  • intestine,

  • gut bacteria,

  • mammal,

  • organ,

  • immune response,

  • appendix,

  • vestigial organ