See Appendix

The vermiform appendix is a wormy-looking structure tacked on to the large intestine where it meets the small intestine. Doctor's still aren't sure what the appendix is for. Many people have had appendectomies without any noticeable health complications, and a few people are even born without an appendix. The appendix is likely a vestigial organ, which means that whatever species we evolved from needed an appendix for something, and humans just haven't evolved past having one yet. Our evidence for this is that Old World Monkeys have a more developed appendix than we do. Some think that our primate ancestors used the appendix as an extra intestinal structure for digesting leaves.

Some doctors believe that the appendix still has some uses for humans. Endocrine cells have been found in fetal appendices, suggesting that the appendix is useful for development of biological control mechanisms. Adult appendices are usually full of lymphatic cells, and the appendix may help the immune system in some way. Duke University researchers have found that the appendix can be a hideout for useful bacteria when illness strikes the intestines. At the very least, an appendix can be transplanted to reconstruct an unhealthy bladder or sphincter muscle.