A new study suggests that the human appendix, long considered a useless “evolutionary leftover,” may actually play an important role in the body, according to The Conversation.

Researchers found that an appendix-like structure independently evolved at least 32 times across 361 mammal species.

This recurring pattern is an example of convergent evolution, where similar traits emerge independently in different groups of animals. Such traits often provide a survival advantage.

The appendix is a narrow projection at the junction of the small and large intestines. For decades, biology textbooks described it as a rudiment—a leftover from distant ancestors that lost its function. Even Charles Darwin suggested that the appendix was a remnant of a larger intestinal section used by ancient primates to digest plant material. Modern evidence increasingly challenges this view.

One explanation for the appendix’s persistence is its role in the immune system. The walls of the organ contain large amounts of lymphoid tissue, clusters of immune cells that help protect the body and regulate the gut microbial environment. This system is particularly active in childhood and adolescence, when immunity is still developing.

Another hypothesis involves the gut microbiome. Some scientists believe the appendix may serve as a “safe house” for beneficial intestinal bacteria. During severe gut infections, when much of the microbiome is depleted, bacteria preserved in the appendix may help restore microbial balance more quickly.

The fact that similar organs have repeatedly appeared in different mammalian groups—from primates to rodents and marsupials—suggests that the appendix likely provides evolutionary advantages. Researchers therefore consider it increasingly unlikely that the appendix is a random or useless anatomical feature. Instead, it appears to be a small but functionally significant component of the complex interaction between immune system and the intestinal microbiome.