Why the appendix is ​​not as useless as it was thought for decades

It turns out that Charles Darwin was wrong… about the appendix.

For centuries, this cylinder-shaped organ with no outlet that measures about 10 centimeters and is connected to the cecum (the first portion of the large intestine) had been an enigma.

Jacopo Berengario da Carpi, an Italian physician, published the first description of the appendix in 1521 in his “Commentary“, and described it as a small empty cavity.

Leonardo da Vinci theorized that it was a place to retain excess gas and prevent the intestines and colon from bursting during bouts of constipation.

Andreas Vesalius first used the word ‘appendix’ in 1543 and compared it to a worm.

The Swiss botanist Caspar Bauhin speculated in 1579 that it was a receptacle for the feces of a fetus during gestation, a kind of mini latrine.

The 18th-century Italian anatomist Giovanni Dominico Santorini believed it to be the natural habitat for intestinal worms, which needed “a warm, quiet place to live.”

Without a very convincing theory, in his book on the theory of evolution “The Descent of Man” (1871), Darwin hypothesized that the appendix actually had no function: it was a vestigial organ that had lost its reason for be “as a result of changes in diet or habits”.

That was probably what they taught you in school.

But, already in the middle of the 20th century, with the development of tools to take a closer look at our organs, the idea that the appendix was only used to inflame and put lives at risk began to dissipate.

And, in the 21st century, scientists have been discovering that is far from being a bit leftover.

Sanctuary

In 2007, a team at Duke University Medical Center made a breakthrough when they discovered that the appendix had a rich biofilm.

It is a layer of beneficial bacteria that live in our intestines and help us extract nutrients and energy from food. Also, when they digest fiber, they produce short-chain fatty acids that can cross into your bloodstream and brain to protect you.

The mysterious and disdained organ was then like a reservoir of these bacteriaready to repopulate the intestine if we lose them, such as when we get diarrhea or take antibiotics.

That was something Darwin could never have guessed, since he lived long before scientists recognized the existence of the human microbiome.

And there was something else.

Decades earlier, the appendix had been discovered to have a high concentration of gut-associated lymphoid tissue, or GALT, but it was not known at the time that GALT helps stimulate the immune system in the event of an invading pathogen .

That is to say that, in addition to being a storage place for bacteria, it is involved in understanding when the intestine is threatened and how to respond.

Misunderstood

Six years later, another Duke University Medical Center study found that people without an appendix tended to be at increased risk of a very nasty and dangerous bacterial infection: Clostridium difficile, or C diff.

But scientists also discovered something that took them by surprise: the anti-evolutionists had used their research to their advantage.

They had inadvertently refuted something said by Darwin, but above all, perhaps the most common example cited in textbooks and by educators as evidence for natural selection.

Scientists, the creationists claimed, had shown that the theory of evolution was invalid.

“Darwin was wrong that the appendix was vestigial,” Heather Smith, professor of anatomy at Midwestern University in Arizona, conceded in conversation with the BBC. but vehemently clarified: “That doesn’t mean he was wrong about his theories of natural selection and our understanding of adaptation.”

In fact, his own research has shown that, far from undermining the theory of evolution, the appendix confirms it.

Millions of years

In 2017, Smith and a team of colleagues decided to compare the human appendix to that of 533 mammalian species.

Revealing a history of more than 80 million years, they built a consensus phylogeny of mammals, which is basically a great family tree.

With it you can collect data and map it, and that allows you to tell how many times a particular feature, in this case, the appendage, has evolved.

“We determined that the appendage has evolved around 30 different times throughout mammalian evolution, and that implies that it fulfills an important function, otherwise it would not continue to appear in evolution.”

In evolutionary terms, if an organ appears, remains and does not disappear, it is a good indicator that it is useful in some way. Even more so if it happens in several different mammalian lineages.

Ours burst onto the scene between 32 million and 20 million years ago, and it’s still there, so this study tells us that the appendix is ​​doing something important, even though we don’t yet know precisely what it is.

gut-brain axis

That one that was considered as an unnecessary organ has become the focus of several studies whose objective is to better understand its function.

One of them, published in July 2021 by researchers from Inserm and the French Museum of Natural History and inspired by that great family tree from Smith’s team, analyzed data on 258 species of mammals and found that the presence of the appendix correlates with a increased longevity

On the other hand, some cutting-edge research shows that there is a connection between the gut and the brain, known as the gut-brain axis.

“One of the most exciting areas in brain science and neurology at the moment is really the growing appreciation of the gut and gut microbiota in neurogenerative disease,” Professor John Cryan, from the University of New York, told the BBC. Cork, expert on the subject.

In this area, the expert on the gut-brain axis highlighted, although the research is still ambiguous, “one thing is clear: we cannot ignore the appendix in relation to intestinal brain signaling.”

What if it hurts?

Despite all this, there are cases where we really cannot live with the appendix.

Although a growing number of studies (including a meta-analysis of research that included 404 pediatric patients) have found that in cases of non-severe appendicitis, antibiotic treatment may be as effective as surgery, surgery is often not a safe option .

A ruptured appendix is ​​a serious medical emergency that can kill peopleand a severely damaged or cancerous appendix must be removed.

Not only is it proven that we can live a full and happy life without it, but none of this means that an appendectomy performed in a human to treat appendicitis has an effect on longevity.

Appendicitis at an early age is clearly beneficial as it strengthens the education of the immune system and allows it to fight any subsequent infection more effectively.

So the indicated treatment for appendicitis is still appendectomy.

What the recent history of this bit of our anatomy teaches us is that the human body is extremely complex and we still have a lot to understand.

* Part of this article is based on the episode”The Appendix” from the BBC series “Made of Stronger Stuff”.