Just a gut feeling

It’s been known for quite some time that the appendix is not simply a vestigial organ, as Darwin put it, but a useful organ. The bottom line is that it acts as an immune system primer in infancy, helping teach your body to distinguish between friendly microbes and dangerous pathogens. Throughout life, the appendix also acts as a bacterial backup drive for when you’ve had diarrhoea that allows your intestinal microbiome to repopulate.

Biologists Phil Starks and Lilia Goncharova have the full skinny on this tiny organ in an article in The Conversation.

Oh, and for those worried that having appendicitis can interfere with female reproductive health by leading to fallopian tube adhesions, apparently the pregnancy rate is slightly higher in females who have had appendicitis.

The pair point out that the appendix has evolved independently at least 32 times across different mammal species (including wombats and rabbits), which suggests it’s anything but a vestigial organ. In the world of biology, if a trait keeps popping up like that, it’s usually because it provides a major survival advantage.

Why do we get life-threatening appendicitis? Appendicitis is essentially a “plumbing failure” where a blockage in the organ’s narrow opening causes trapped bacteria to multiply rapidly, leading to dangerous swelling and infection. Quite the price to pay, as it can be lethal if untreated and the appendix becomes perforated or ruptures allowing the infection to enter the body cavity.

But, Starks and Goncharova point to a mismatch between our past and present: In high-pathogen environments with poor sanitation, the appendix was a lifesaver for recovering from chronic diarrhoea. In the developed world today, modern hygiene and antibiotics mean we don’t need that bacterial reboot function as often. Although many people do after long-term antibiotic use.

There are a few more bits of deceived wisdom surrounding the appendix:

The first is that eating seeds leads to appendicitis. While a blockage (fecalith) is the main cause, seeds are almost never the culprit. The “plug” is usually made of hardened stool or swollen immune tissue.

The second is that the appendix is on the left side of your abdomen. for most people it’s on the lower right side. Often the pain of appendicitis starts elsewhere in the abdomen as the brain struggles to locate the site of the problem in the early stages, and the pain then migrates very much to the core of the problem over hours or even days as the infection worsens.

The third myth is that you can’t live a full life without it. Well, we’ve already seen that is not a vestigial organ, but it is a non-essential bodily component and most people recover fully from an appendectomy. Indeed, other regions of the gastrointestinal tract can carry on some of the functions of the appendix.

One more myth is that the appendix is a ticking time bomb in everyone’s life. In fact, only one in ten of us will experience appendicitis, and most commonly, if it’s going to happen, it will happen in childhood. In older people the gallbladder is more likely to be problematic and cause a similar pain pattern.

A final thought. Darwin was right about most things when it comes to the fundamentals of evolution. However, he thought the appendix had been shrinking throughout human evolution because we stopped eating as many leaves as our primate ancestors. In reality, the human appendix is actually larger than the equivalent organ in many of our vegetarian primate cousins.