The human body has a few unneeded parts. We no longer rely on these organs or structures for any serious function, or they have atrophied or degenerated to the point that they don’t serve the function they used to.

Charles Darwin pointed to these vestiges of anatomy in humans and other animals as evidence for evolution. Eventually, by noting how the vestigial organs in one species were similar to functioning organs in other species, biologists concluded two otherwise dissimilar creatures must have shared a common ancestor. Here are five of the most notable vestigial organs in humans:

The Appendix: This small pouch attached to your large intestine, at the junction of the small intestine, no longer aids in digestion, and none of the 1 in 20 people who have one removed seems to miss it. In plant-eating vertebrates, it remains part of the digestive system. And a study in 2009 found that the human appendix might be useful, serving as an important storehouse for beneficial bacteria, which can’t wait for a chance a case of diarrhea so they can rush to the gut and save you.