Usually, the appendix gets attention only when it becomes inflamed or ruptures. It was long considered to be a useless, leftover organ that humans never evolved away from. But new research is moving the appendix up from the C-list, at last.
A team of scientists from Midwestern University have shone a spotlight on the appendix via a new study, which tracked 533 mammal species over a period of 11 million years. They specifically looked for any instances where the appendix had disappeared or reappeared. Reemergence would indicate an evolutionary need for the organ.
The researchers discovered that the appendix evolved between 29 and 41 times. That, coupled with the fact that the organ only disappeared 12 times from mammalian lineages, indicates that the appendix provides a service that modern medicine hasn't fully understood.
"Thus, we can confidently reject the hypothesis that the appendix is a vestigial structure with little adaptive value or function among mammals," the authors write in the study.
So, clearly the appendix does something. But what? The most likely job function is that it supports the immune system by harboring beneficial intestinal bacteria, which help keep the gut healthy and ward off infections. The scientists found that species with an appendix had higher concentrations of lymphoid tissue (important for immune response) in the cecum (a pouch at the connection of the large and small intestines). This type of tissue can also help stimulate growth of helpful gut bacteria.
Further, a 2012 study showed that only 11 percent of people with their appendix experienced a recurrence of a certain bacterial infection responsible for fever, abdominal pain, nausea and diarrhea. This compared with a 48 percent recurrence rate in people without an appendix.
All hope is not lost for those who require an appendectomy, however. Since the vast majority of these people continue with their lives, complication-free, it is believed that other immune-supporting tissues ramp up to compensate for the loss of the tiny organ.