What if humans didn't have an appendix?

The series "Imaginary Earths" speculates what the world might be like if one key aspect of life changed, whether related to the planet or humanity.

The appendix is often thought of as a useless artifact of evolution, much like the remnants of hind leg bones seen in whales. In fact, about 1 in 100,000 people are born without an appendix, according to a report in the journal Case Reports in Surgery. What might life be like then if everyone lacked an appendix?

The appendix is a small worm-shaped dead-end sac that juts out from the cecum, the beginning of the large intestine. Slightly more than 1 in 20 people get appendicitis, the potentially deadly inflammation of the appendix, according to the National Institutes of Health.

Charles Darwin suggested the appendix was a vestigial organ from ancestors that ate leaves, potentially helping them digest food. As these ancestors evolved to rely on a fruit-based diet that was easier to digest, Darwin speculated the appendix no longer served a function, much like the small triangular coccyx bone at the base of the human spine, a remnant of tail bones found in our distant ancestors.

However, "if Darwin knew then what scientists know now about the appendix, he would have never suggested it was a worthless vestige of evolution," William Parker, an associate professor of surgery at Duke University School of Medicine in Durham, North Carolina, told Live Science.

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In 2007, Parker and his colleagues found the appendix may serve as a reservoir of useful gut bacteria, the kind that help the body to digest food, they reported in the Journal of Theoretical Biology. When diseases flush both good and bad microbes from the gut, good bacteria can emerge from the safe harbor of the appendix to help restore the gut to a healthy state.

In addition, the appendix possesses a high concentration of lymphoid tissue. This tissue generates white blood cells known as lymphocytes that help mount immune system responses to invading germs, suggesting the appendix may help make, direct and train these immune cells, evolutionary biologist Heather F. Smith at Midwestern University in Glendale, Arizona, told Live Science. 

When Smith, Parker and their colleagues investigated when the appendix evolved in the animal kingdom, they found the appendix has been around in mammalian evolution for at least 80 million years, much longer than expected if the appendix really was a vestige, they reported in 2009 in the Journal of Evolutionary Biology. Moreover, they also discovered the appendix evolved independently at least 32 times among mammals, in species as diverse as orangutans, wombats, platypuses, beavers, koalas, porcupines and manatees, they wrote in 2013 in the journal Comptes Rendus Palevol.

"When we looked in species that have an appendix, we didn't find any commonalities in diet or how social they are or where they lived, but species that did have an appendix had a concentration of immune tissue there, so given this common theme, one might presume a common function," Smith said.

So what might happen "if you waved a magic wand and the appendix suddenly vanished?" Parker said. "That might depend on when in history it happened."

If the appendix disappeared in a hunter-gatherer society "and a scientist from a spaceship or something watched what happened, you'd see a lot more people dying of infectious diseases than they would otherwise," Parker said. "Then, over a long time, over millions of years, I think something would slowly evolve that worked the same as an appendix so that people wouldn't die so much."

If the appendix vanished in a society with agriculture after people started living in settlements, "I think more people would die," Parker said. "People would have started living in crowded areas, and with poor sanitation, disease would spread more." 

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If the appendix disappeared in a modern society after the Industrial Revolution, people would have antibiotics to help them survive, Parker said. However, without an appendix, people would not have the appendix's reservoir of helpful bacteria to help them recover from harmful infections. "When that happens, we may need to give people fecal transplants," Parker said.

Yes, that's right, fecal transplants. These increasingly common procedures transfer feces from healthy people into the guts of patients with intestinal problems, via a tube or capsule placed down one's throat or up one's bottom. The idea is that the transplant will bring healthy bacteria into guts overrun by harmful microbes. Bodies overrun with harmful microbes may become more common as antibiotics get overused and germs evolve resistance against these drugs. "Fecal transplants don't encourage antibiotic resistance," Parker said.

One potential upside of a world without appendixes is the disappearance of appendicitis. Globally, "there are more than 10 million cases of appendicitis every year, and up to 50,000 people a year die from it," Smith said. Appendectomies, or surgical removal of the appendix, "is one of the most frequently performed abdominal surgeries. If we didn't have the appendix in the first place, you wouldn't have people dying from appendicitis, and not costs from surgery and hospitalization."

However, prior work has suggested that appendicitis may be due to cultural shifts linked with industrialized society and improved sanitation, Parker said. The idea goes that these shifts left our immune systems with too little work, opening up the possibility that they could go haywire without the appendix.

All in all, a world without an appendix might leave humanity struggling with germs more often. The idea that the appendix is an organ whose time has passed may have itself become a notion whose time is over.

Originally published on Live Science.