Evolution, Creationism, and the Great Appendix Debate
One of the human body's most mysterious organs is fueling the anti-evolution fire.
Image: DEA PICTURE LIBRARY / Getty
William Parker—immunologist, chemist, and professor of surgery at Duke University—has a fondness for Gospel music.
That's why one morning in 2007, his car radio was tuned to K-LOVE, a Christian station, and he happened to catch their news segment between songs. "They said scientists had proven that Darwin was wrong," he remembers. "And then, I was surprised to find that they were referring to my own work."
Parker had recently co-authored a paper on the function of the appendix. To most, the appendix is known as the organ that doesn't do anything. It rarely crosses our radars, unless you get appendicitis and are one of almost 300,000 people per year in the US who has it removed.
But it was long suspected in the science community that the appendix did have some sort of immune function. Parker and his colleagues had found something definitive: a rich biofilm, or layer of bacteria, in the appendix. His paper proposed that the appendix was a "safe house" for good gut bacteria, and could help repopulate the microbiome after a nasty infection.
The appendix is not the focus of Parker's career, nor a puzzle he had been lusting after for a long time. Certainly, Parker was not thinking about Darwin when he published. But, he had incidentally refuted one of Darwin's theories of a vestigial, or leftover, organ, and a common example provided by textbooks and educators as evidence of natural selection.
"I was very naïve," Parker says now. "I had no idea that I was going to be on the Christian music station as the scientist who undermined Darwin."
Later, Parker googled his name and his appendix work. He found himself on creationism and intelligent design sites. His results, his data, and even quotes he gave in a press release were appropriated to say: Evolution was false.
"It was all over the web," he says. "Like a fungus."
For such a tiny organ, the appendix has been a source of big mystery for hundreds of years.
A quick anatomy lesson: The appendix is a worm-shaped projection off the cecum, which is a section of the large intestine. It doesn't attach to anything on its other side; it's like a mini cul-de-sac hanging off the intestine.
Jacopo Berengario da Carpi, an Italian physician, published the first description of the appendix in 1521 in his Commentaria, and he described it as just a small empty cavity. Leonardo Da Vinci had sketched the appendix in his anatomical drawings in the early 1500s, though they weren't published until much later.
Da Vinci was a remarkable dissector and anatomist, drawing musculature, nerves, vessels and the heart with amazing accuracy. His appendix is drawn almost doodle-like, in the corner of a page showing the intestines. Da Vinci had his own guess for its function.
His notation reads: "The auricle, of the colon, is a part of the monoculus and is capable of contracting and dilating so that excessive wind does not rupture the monoculus." That's to say, he thought it was a place to hold excess gas, to keep the intestines and colon from exploding.
Since Da Vinci, many famous anatomists wondered about the organ. Andreas Vesalius first used the word appendix in 1543 and compared it to a worm. Gabriele Fallopius (namesake of the fallopian tubes) also compared the appendix to a worm, in 1561. In 1579, Caspar Bauhin speculated that the appendix was a receptacle for a fetus's feces during gestation, a kind of mini-outhouse.
Other theories proposed that the appendix held chyle, a milky bodily fluid containing fats, and should thus be renamed the "torcular chyli." And there were various versions of Da Vinci's gas theory: that during bouts of constipation, or digestion, intestinal gas accumulated there.
Caspar Bauhin speculated that the appendix was a receptacle for a fetus's feces during gestation, a kind of mini-outhouse.
My personal favorite is from 1724, when Giovanni Domenico Santorini, an Italian anatomist, claimed the appendix was a natural habitat for intestinal worms, saying, "It is necessary for these animals to have a warm and quiet place in which to live and it is not at all improbable that the vermiform appendix provides such a refuge, for they could not live where there are powerful peristaltic movements or a large quantity of fecal matter. They breed in the appendix in much the same manner as fish lay their eggs in tranquil waters rather than in flowing streams."
By 1871, when Charles Darwin took a crack at it, there were many incorrect ideas floating around. Darwin was neither the first, nor probably the last, to have a theory about the appendix that turned out to be untrue. Darwin hypothesized in The Descent of Man, and Selection in Relation to Sex that the appendix actually had no function at all: It was a vestigial organ, he thought, leftover "in consequence of changed diet or habits."
Darwin knew that humans and other great apes had an appendix. Beyond that, he didn't know if other mammals had one too. So, he thought that in our ancestors, the cecum was bigger and lacked an appendix. When we started eating more fruit, and it shrank, he concluded that the appendix emerged due to this shrinkage.
In the years before and after Darwin debuted his theory, attention was paid less to the appendix's function, and more to how it could become inflamed, rupture, and cause death. Harvard pathologist Reginald Fitz came up with the term "appendicitis" in 1886, and promoted the surgical removal of the pesky organ.
When the appendix could be removed with little harm to its own owner, it seemed to prove Darwin right, and his idea that it was a vestige stuck.
In the 1960s and 70s, though, the notion that the appendix actually had a function reared its head again. With the development of tools to get a closer look at our organs, scientists found that the appendix contained a high concentration of lymphoid tissue, which stimulates the immune system when it encounters a bacteria or virus. It was unclear how important this was, because patients without appendixes still seemed to do fine.
This is where Parker entered the appendix narrative, and solved a centuries-old mystery. Parker and his colleague, Randall Bollinger, a surgeon at Duke who was performing multiple appendectomies per week, had their eureka moment when they found the biofilm.
The thick layer of good bacteria in the appendix, combined with previous immunological implications, left little question in their minds. This mysterious "worm" was a reservoir for good gut bacteria—something Darwin could have never guessed, since he lived long before scientists came to acknowledge the existence of the human microbiome, the communities of bugs that live on and in us.
It all made sense. The appendix was physically out of the way. If the gut was infected and its good bacteria flushed out or overpopulated by more virulent strains, it would be less affected. After the pathogen had been cleared, the bacteria hiding out in the appendix could repopulate the stomach.
The appendix is a reservoir for good gut bacteria—something Darwin could have never guessed, since he lived long before scientists came to acknowledge the existence of the human microbiome.
This was an important clinical finding, and Parker started to wonder about those who had their appendixes out: How did they recover from infections? Parker and collaborators found that patients without appendixes could be at a higher risk of not recovering. One group without appendixes had a two-fold increase in recurrent C. difficile-associated colitis. Parker thinks that other diseases associated with an altered microbiome would probably be similarly common among people missing their appendixes.
Parker doesn't think that appendectomies should stop completely. But he does think that their findings will provide important information to people who don't have their appendixes. They might recover more slowly, or be at greater risk following infections or heavy antibiotic use.
A growing number of recent studies have also found that in cases of non-severe appendicitis, antibiotic treatment could be just as effective as surgery. A meta-analysis of studies that included 404 pediatric patients, published on Monday in JAMA Pediatrics, suggested the same: for uncomplicated appendicitis, antibiotics is safe and effective. Together with Parker's work, these studies show there could be a motivation to hang on to our most wormlike appendages, and keep the microbial benefits they offer.
Parker's involvement in the appendix should have ended there, and it would have, if not for his childhood love of Gospel music.
"After hearing that radio show, I thought, We need to see what's going on here," he says. "What was really happening with the evolution of the appendix? Honestly, if it weren't for the creation scientists, I probably never would have looked at it further."
Parker is not an evolutionary biologist, and so he teamed up with Heather Smith, an associate professor of anatomy at Midwestern University (whose interest in anatomy stemmed from her own appendix removal at age 12), and Michel Laurin, a vertebrate paleontologist for France's National Center for Scientific Research. In a paper published last month, they took a deep dive into the evolution of the appendix, revealing a history of over 80 million years.
"Honestly," Parker says, "if it weren't for the creation scientists, I probably never would have looked at it further."
Discovering a function of the appendix—despite what the creationists said—didn't actually resolve the question of vestigiality. Was the appendix a leftover that was being put to another use? Or did it evolve specifically to perform the function it was serving? To find out for sure, Smith and Laurin and their colleagues built an evolutionary tree of 533 mammal species, using anatomical data published in previous literature.
Then, using computational and statistical techniques, they could ask the questions Darwin had been unable to: Which mammal species had appendixes? How many times had the appendix evolved, and was it more than would be expected due to chance alone? If a species did have an appendix, how big was it? What shape was it?"
What they found was that the appendix is not a vestige at all, but has popped up more than 30 times independently throughout mammalian evolution, usually together with a high concentration of lymphoid tissue in the cecum—the two probably evolved together as a protective set.
They estimated that overall there have been between 29 to 41 gains of the appendix among various mammalian species, and between 0 to12 losses. In evolutionary terms, if an organ shows up, sticks around, and doesn't disappear, that's a pretty good indicator that it's useful in some way. Even more so if it happens in several different mammal lineages. Our own appendix, which is the same the appendix of the chimpanzee, the gorilla, the orangutan, and the gibbon, hit the scene between 32 and 20 million years ago.
But perhaps more intriguing than the appendix's evolutionary pattern is a new problem the evolutionary tree presents: Why don't all mammals have an appendix? There are many animals that don't share common organs or body parts, but the reasons are usually apparent.
"You don't have any starfishes with wings, but it's obvious why," Laurin says. "Here's what's puzzling: In a large group [of appendix-free animals] that includes the bats, the cats, the dogs, the bears, horses, rhinoceroses, antelopes, cows, sheep, and whales—we have no idea why it's not occurring."
With such a diverse group, there are no commonalities in diet, body size, or group size that can explain the lack of an appendix. The appendix continues to hold some mystery, after all.
"This is very, very surprising," Laurin says. "And we don't yet have an explanation for it."
Still, Parker and his group were satisfied with the results. From a scientific perspective, the evolutionary pattern that they found was an even greater demonstration of natural selection.
"But a creationist looks at the same data, and reaches drastically different conclusions than us," Laurin says. Indeed, the scientists' most recent evolutionary work has been used as proof of an intelligent designer, who only doled out appendixes to those animals that needed one.
"The creationists have misinterpreted, either mistakenly or deliberately, our work," Laurin says. "I was horrified when I found out what they wrote about my paper. And since I'm the author, I can tell you it's a very severe misinterpretation when they stated that our results indicated that the appendix had no evolutionary pattern."
In many ways, the appendix is not a unique story. Websites like DarwinismRefuted.com, Creation.com, and AnswersinGenesis.com often cite scientific work that refines key evolutionary examples as proof that the entire idea of evolution is incorrect. (While conveniently omitting new fossil and genetic examples of evolution.)
It's worth noting that these sites rarely misquote or inaccurately present the science or scientists. In many cases, it's impressive how well communicated the findings of certain papers are. It's merely the conclusions drawn from the findings that are misrepresented.
After referencing Parker, Smith and Laurin, AnswersInGenesis.com says that the group still "ties the appendix back to evolution, saying the appendix is 'likely to be a derived feature, selected for a purpose, the enigma is that we didn't know what that purpose might be.'" But then the site provides its own resolution: "How's this for an answer: the appendix is yet another clever design of a loving God."
"The creationists have misinterpreted, either mistakenly or deliberately, our work," Laurin says. "I was horrified when I found out what they wrote about my paper."
I reached out to several of the creation sites for a response to the allegations that they misinterpreted Parker and his colleague's work. Joel Tay from Creation.com wrote back to me: "Our article simply noted that Parker's work overturned previously held evolutionary assumptions which had been confidently asserted as a refutation of creationist ideas." Tay says that since they acknowledged the scientists believed their findings had an evolutionary explanation, "we would dispute the idea that we misused Parker's research."
A Creation.com article on Parker's work is titled "Appendix shrieks creation."
Glenn Branch, the Deputy Director of the National Center for Science Education, says that the appendix and all similar scenarios "play into a creationist narrative in which the evidence for evolution presented in textbooks is shaky or conjectural at best, or the product of hoax and conspiracy at worst."
Any instance of revision is an occasion to tear down the whole theory, while ignoring something important: Science should itself evolve with greater technological and statistical tools, the kinds that Laurin, Smith, and Parker used that did not exist in the 19 th century.
The evolution of our understanding of the appendix is an example of evidence-based science at its best. As the evidence changed, so did our hypothesis. The appendix reminds us: New understandings are not grounds for dismissal.
Another question the case of the appendix raises: Why was it still being used as an example for evolution at all? It had been known for decades that it probably served some function, however ambiguous, and yet that knowledge had never broken into the mainstream.
In biologist Stephen Jay Gould's essay, The Case of the Creeping Fox Terrier Clone, he investigated the source of another outdated evolutionary comparison given in textbooks: of an early horse ancestor, the Eohippus, which for years got described as being the size of a fox terrier. In fact it was likely about twice the size of a fox terrier.
It turned out that the Eohippus-fox terrier link was made by a paleontologist working at the American Museum of Natural History in the 1900s, who was interested in fox hunting. Textbook writers kept using the comparison without considering if it was accurate (or useful, given that most people don't know what or how big a fox terrier even is).
"Science education is a freight train, not a Ferrari," Branch says. "The fact that there's this lag time between discovery and acceptance within science, and incorporation in curricula and textbooks, is understandable and there's nothing very sinister about it."
It's not proof that science is wrong, or a hoax, if it uses an outdated example to prove a point, like the appendix. It happens all the time. But most areas of science (like the question of the size of the Eohippus) don't face ideological opposition, he says. So the perfectly understandable lags in implementing changes won't be misrepresented, or used in campaigns to alter science education in schools.
Also, Branch says, it can be hard to let go of a counter-argument that has served the science community for so long. "Creationists point to 'well-designed' organs that perform their job admirably, like the vertebrate eye, and say, it works by design, so there must be a designer," Branch says. "It's very tempting to say in return, here's an organ that doesn't do anything. Bad designer? Incompetent designer? No designer at all? There's that particular way of arguing for evolution against creationism."
The most disturbing part of the whole appendix debacle, for Parker, was not his name on creationist sites, news, or radio, but quieter feedback he says he received from other scientists: The appendix's important role as a creationist counter-argument hindered the dissemination of his 2007 findings. "This pushback was never very public and mostly exists in the form of a persistent effort to pretend my work doesn't exist," he says. "The 'vestigial appendix' is still being touted as evidence for natural selection."
"This is still the most frustrating thing to me, even to this day," he says. "This latest paper is one more in a series that clearly disproves Darwin's views on the appendix, but I fear that knowledge about this body part in our gut is just not getting out to the public."
In the end, Parker feels their work on the appendix added to the body of knowledge of how evolution works. And the new questions it raised about the presence or absence of the appendix, and appendicitis treatment options, will provoke interesting research.
Parker has since moved on to other areas of research. Laurin and Smith will carry the appendix torch from here. "Parker should feel good about advancing scientific knowledge," Branch says. "That should be enough. If he failed to convince people who have gotten themselves into a situation where they're incapable of appreciating his contribution—I don't think he can blame himself for that."