The appendix is a little branch at the base of the large intestine. It resembles a little, closed tube, and it produces mucus and contains lymphatic tissue, which is part of the immune system. It also contains bacteria. Sometimes the appendix can become inflamed and painful, a condition called appendicitis. It is thought that this condition usually begins when the opening of the appendix becomes blocked, allowing the bacteria inside the appendix to spread and infect the appendix wall. Once the appendix is infected the body mounts an immune response to fight off the infection, resulting in inflammation. If the appendicitis becomes severe, the appendix may rupture, spilling the infection into other areas of the body. This is a very serious condition that can result in death.

It doesn't appear that the appendix serves any clear purpose, so you are right to ask: why would the body have a little organ that doesn't help but that could really hurt? Why possess an organ that is nothing more than a liability? Indeed, many scientists have asked this same question!

One popular theory is that the appendix is a vestigial organ-- that is, an organ that used to serve an important function, even though it doesn't any more. According to this theory the appendix used to be important, either because our bodies worked a little differently or because the environment was different. For example, maybe in the past the appendix produced a lot of mucus that was important for helping digestion and preventing infection in the intestines somehow, but now we don't need it anymore because we have better, cleaner food or because our stomachs work better in the first stages of digestion than they used to. Of course, this example seems far-fetched, but it is possible that our appendix used to do something important that we don't need it to do anymore, because something is different today.

It is also possible that the appendix does perform a function, but we just don't know what it is yet. There was a time when people didn't know what any of the organs were for, but over time we have learned the function of most of them. For example, in the early to mid-1900s it was believed that the thymus served no useful function, and that it was simply a vestigial organ that could even pose problems. Today we know, however, that the thymus is incredibly important to proper immune system function. The appendix does not have a clear function that we know about, but that doesn't necessarily mean it doesn't do anything! It is clear, though, that the appendix is not incredibly important, as thousands of people have it removed with no bad consequences. At the same time, however, there is some evidence suggesting that there is a slight increase in the occurrence of some diseases (such as Crohn's disease, which affects the bowels) in people who have had their appendix removed. This may be because the appendix does perform some function in fighting these diseases-- or it may just be a side-effect of the surgery!

It is difficult to say for sure, but we can certainly say that whatever function the appendix might or might not have, it is not really a very important organ today.