The appendix — vestigial organ or vital part of evolution?


I remember a day in 1999 as if it was yesterday.

Some would remember that year for reasons like Y2K or the hoarding of cans of baked beans.

I was in my fifth year of medical school, attending a surgical lecture on the 10th floor of Tygerberg Hospital and for some strange reason, I recall the seats being the same bright orange as the old SAA aeroplanes’ tail.

I had felt a sudden onset of pain in my abdomen at a spot called McBurney’s point.

This is halfway between the navel and the right hip. From this and the severity of the pain, I self-diagnosed acute appendicitis and rushed off to the emergency department.

Later that evening, my appendix was removed and three days later I was attending lectures again.

The irony of developing a surgical condition during a surgical lecture was compounded when one of my classmates developed a testicular torsion during our urology rotation. We were getting concerned about our upcoming gynaecology rotation!

The appendix is a small,  pouch-like sac in the first part of the colon.

Its Latin name in “vermiform appendix”,  indicating its worm-like shape.

When it gets inflamed and subsequently infected it is called appendicitis. 

It usually develops after being blocked by a piece of stool called a fecolith but can also be obstructed by lymphatic hyperplasia, foreign bodies, cancer or parasites.

It is estimated that about 11-million people develop appendicitis each year, with 50,000 deaths due to complications, mostly in the developing world.

Appendectomies are one of the most common surgeries done worldwide and are often performed via laparoscopy in the modern era.

The first person to officially document the appendix was an Italian physician called De Carpi in 1521.

It had earlier, though, appeared in anatomical drawings by Leonardo da Vinci.

Since its identification, it has always been an organ shrouded in mystery and many theorised its function through the ages.

One of the interesting theories was postulated by another Italian, Santorini, in 1724.

He suggested that is was a good habitat for intestinal worms as it was  “a warm and quiet place”.

Then came Charles Darwin.

He thought the appendix was a vestigial structure just like the wisdom teeth in humans and wings in flightless birds.

Vestigial organs are organs retained during the process of evolution that have lost their ancestral function in a given species.

The theory was that as our diets changed from leaves to fruits, we lost the need for a large cecum (a pouch of large intestine next to the appendix) filled with high quantities of bacteria to help digest the leaves.

Thus the cecum and appendix got smaller over time.

The unanswered question was this: Why would we keep the appendix and not just lose  it completely?

Did it have some undiscovered function? It then came apparent that the evolutionary cost of losing it exceeded the value of keeping it.

A study published in 2013 looked at 533 mammals and their different evolutionary pathways over 11- million years.

In that time, the appendix had developed over 30 times in different mammals but was lost only 12 times.

Once the appendix had appeared it was more likely to remain then regress.

The newest theory about the function of the appendix is that it may be a safe haven for good bacteria in times of distress.

When a severe infection attacks the intestinal tract and overruns the immune system, the good bacteria could retreat into the appendix and repopulate the intestinal microbiome once the infection was under control.

It could thus be important in assisting our immune system in ensuring gut health.

It has been shown that patients who had a previous appendectomy have a higher risk of Clostridium infection recurrence.

This is a severe and life-threatening form of colitis.

The counter to this argument is that most cases of appendicitis, and thus appendectomy, happen in the young.

Research has not shown major long-term complication when groups of patients with and without an appendix were compared.

Interestingly, many of our domesticated animals, like cats, dogs and sheep, don’t have an appendix. This could be why Laika the Russian dog was sent to space before humans.

So if you want to become a Nasa astronaut your CV would be enhanced by adding the histology report of your appendectomy!

Having your wisdom teeth and gallbladder removed would be an added  bonus.

Dr T is a registered medical practitioner working in Nelson Mandela Bay

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