Is the appendix useless? Modern studies challenge long-standing belief

In our basic biology classes, we were taught about a small organ called the appendix and were told that it is vestigial, meaning it has no function in the body. However, recent studies have challenged this notion, revealing that the appendix is not as useless as once believed.

For many years, the human appendix was considered a vestigial organ—an evolutionary remnant with no real function. This belief stemmed from the idea that, as humans evolved and their diets changed, the appendix lost its original purpose and became redundant.

The appendix is a small, tube-like structure attached to the cecum, which is the beginning of the large intestine. It is typically around 2 to 4 inches (5 to 10 cm) long and is found in the lower right abdomen. The concept of vestigial organs was popularized by Charles Darwin and other evolutionary biologists who believed that certain structures in the body were remnants of ancestral traits that had lost their function due to evolutionary changes.

Early scientists hypothesized that it was once part of a larger digestive system adapted for processing a diet rich in cellulose, such as the diet of herbivorous ancestors. However, as humans transitioned to an omnivorous diet and developed more efficient digestion in the small intestine, the appendix was believed to have become functionally obsolete. This view was widely accepted for much of the 19th and 20th centuries, with many medical professionals regarding the appendix as a useless organ.

"Researchers believed the human appendix to be a vestigial organ based on evolutionary evidence of its anatomical and functional changes in different species, but recent studies have raised the possibility that the appendix may play a role in gut microbiome restoration and immunological functions," says Dr. Abhishek Goel , Additional Director - Department of General & Minimally Invasive Surgery, Max Super Speciality Hospital Noida.

The role of appendix

It harbors good bacteria
One of the most compelling modern theories is that the appendix acts as a "reservoir" for beneficial gut bacteria. The human digestive system is home to trillions of bacteria that help break down food and support overall health. However, infections, illnesses, or the use of antibiotics can sometimes wipe out these good bacteria, leading to digestive problems.

A 2013 study found that the appendix appears to harbor a large diversity of gut microbes, including significant amounts of “beneficial bacteria” or indicators of gut health, including the genera Bacteroides, Lactobacillus, and Bifidobacterium. "We conclude that the human appendix contains a robust and varied microbiota distinct from the microbiotas in other niches within the human microbiome. The microbial composition of the human appendix is subject to extreme variability and comprises a diversity of biota that may play an important, as-yet-unknown role in human health," the researchers have said.

It improves immunity
"The appendix was thought to be a vestigial organ, but recent research does not agree with this view. The appendix seems to play an important role in the immune system, especially at early stages in life, because it harbors beneficial gut bacteria and aids in the production of white blood cells. It also helps in repopulating the gut after infections such as diarrhea," says Dr. Mayank Madan, Director-Minimal Access and Bariatric Surgery, CK Birla hospital, Gurugram.

The appendix contains lymphoid tissue, which is known to play a role in immune responses. This tissue helps produce white blood cells, which defend the body against infections. Some studies suggest that the appendix may be particularly important in early life, helping to train the immune system to recognize harmful pathogens. The appendix has been found to produce immunoglobulin A (IgA), an antibody that helps protect the gut from infections. This suggests that, rather than being a useless structure, the appendix may contribute to the body's ability to fight off harmful bacteria and maintain a healthy immune balance.

It isn't just a mere leftover of evolution
If the appendix were truly vestigial, we might expect it to gradually disappear over time. However, recent studies have found that the appendix has independently evolved in multiple mammalian species, including primates, rodents, and marsupials. This suggests that the appendix provides some evolutionary advantage rather than being an obsolete organ.

A 2013 study by researchers at Midwestern University found that the appendix has been preserved in evolution for at least 80 million years, appearing in more than 30 different mammal species.

All about appendicitis and other complications
A major concern around appendix is when it becomes inflamed due to a disease known as appendicitis. "Symptoms of appendicitis include severe stomach pain, typically on the lower right side of the abdomen; nausea and vomiting; fever; and loss of appetite. Left untreated, the appendix can rupture, causing peritonitis - a potentially deadly infection. Such cases require removal of the appendix through surgery. In some instances, if the appendix forms an abscess, doctors may need to drain the abscess first before surgery, to avoid potential complications," explains Dr. Mayank Madan.

To this, Dr. Nitin Arora, Clinical Director - Robotic Surgery, Minimally Invasive, GI & Bariatric Surgery, Marengo Asia Hospitals Gurugram adds, "the most common indication of appendix removal is acute appendicitis ( inflammation of appendix) and its complications like rupture appendix, appendicular abscess etc. Other less common indications are recurrent appendicitis, mucocele of appendix, tumors of appendix."

What happens after the appendix is removed?
According to Dr. Abhishek Goel, after the appendix has been removed, the body operates normally with minimal changes. The appendix is found to play some role in regulating the gut microbiome and functions of the immune system; its absence, however, does not cause apparent health problems."

Dr Mayank Madan explains, "overall, adaptation happens without any major complication after appendix removal, because the immune system takes control and other bacteria in the gut maintain digestion. Mild digestive changes or a slightly higher risk of infections will occur in some individuals. The recovery period is fast and initially carries minor discomfort. Gradually, overall body function returns to normal without the appendix."

"Functionally, removal of the appendix doesn't have any significant effect on the body. However, patients may occasionally experience routine postoperative symptoms like pain at the surgery site, nausea, alteration of bowel movements etc.," adds Dr. Nitin Arora.