The useless parts of human bodies

Have you ever had your wisdom teeth removed? I have – all 4 of them. I was 18, and my dentist was concerned that my jaw was too small to handle these extra teeth butting their way in, so – bam! – out they came. It was not a pleasant experience. I’m glad that I had them all out at the same time, so that I don’t ever have to go through it again! Of course, the reason I could have them pulled out like that is that wisdom teeth don’t seem to have a purpose. For modern humans, all indications are that they are totally useless. Of course, they may have been a useful part of our jaws thousands of years ago, but that usefulness is (apparently) long gone.

Interestingly enough, wisdom teeth are not the only seemingly useless parts of our bodies. There are 2 other well-known pieces of anatomy that fall into this category of uselessness – the tonsils and the appendix. In fact, not only are all 3 of these body parts apparently pointless, they can be a lot of trouble. Tonsils are often infected and inflamed. When wisdom teeth become impacted, they can damage other teeth or cause gum infection or bone damage. And appendices can become inflamed, requiring rapid removal by surgery to reduce the risk of the infection turning lethal. So surgeons remove these things routinely. And people live just fine without them. So, they’re useless, right?

Maybe not. It turns out the appendix may have a purpose after all. In October, scientists at Duke University’s medical school announced a theory about the possible job of the appendix. They suggest that the appendix is a back-up storage system for intestinal bacteria.

It turns out that our intestines are chocked full of bacteria – in fact, your body contains more bacteria cells than your own body cells! Most of these bacteria (which are also referred to as “bugs”) are helpful, and in fact are essential for you to digest your food. However, there are certain diseases that can wipe out the flora from your digestive system – diseases such as cholera and amoebic dysentery. These diseases are characterized by severe diarrhea, which quickly flushes out the friendly bugs residing in your gut. If that happens, your digestive tract needs a way to rapidly recover those helpful bacteria. Enter the appendix. The authors of the report argue that the appendix serves as a safe-house for intestinal bugs, allowing them to survive in an offshoot of the intestines that would be protected from the intestinal ravages of severe diarrheal diseases. (The location of the appendix is consistent with this hypothesis. It is a small, finger-shaped structure located near the beginning of the large intestine.)

In the western world characterized by dense populations, we don’t have much of a need for this function of the appendix. Cholera and amoebic dysentery are rarely (if ever) encountered in western society anymore. But even if we were to contract some disease that wiped out our intestinal flora, we could rapidly pick them up again from the people we encounter every day. (Yes, the bugs can be shared.) However, in areas of the world where cholera could devastate entire regions of people, this job of the appendix could be very relevant. In fact, here is a curious fact – in less developed societies in the world, the rate of appendicitis is much lower than in first-world countries. That would be consistent with the fact that people in regions exposed to severe diarrheal diseases must rely more on their appendix than do those who live elsewhere.

On a related note, I found some interesting facts about appendices in other animals. It turns out that appendices are large and very functional in animals whose diets consist mainly of vegetative matter. This includes koala bears (who have perhaps the longest appendix of any animal in the world), opposums, kangaroos, rabbits and zebra. The diet of these animals is very dense in cellulose. Cellulose is the main component of the cell walls of plants, and it is very difficult to digest. Our digestive systems cannot make the enzyme needed to break cellulose apart, so we are actually unable to digest cellulose at all. (It simply goes through our systems.) The appendices of animals that eat a lot of plant matter house a specialized set of bacteria that secrete the enzyme to digest the cellulose that they eat. Without this bacteria, these animals would simply be unable to digest most of what they've taken in.

I guess that means it would be pretty serious for a koala bear to get a case of appendicitis!