The Riddle of the Appendix

The New York Times, August 9, 2005

I recently spent a few days recovering from having my appendix removed. As I padded around my house in my pajamas, I pondered that dear departed bit of my gut.

I only became aware of my appendix when it flared with infection. Soon I was lying in an ambulance, with a paramedic poking at my abdomen. “Oh yeah,” he said, and went back to filling out paperwork.

The nurses and doctors at the hospital agreed, and a CT scan confirmed the diagnosis. Not long after, I was unconscious, and a surgeon was cutting open my side to get my appendix out before it ruptured. My life might be hanging in the balance, but the procedure had the routine efficiency of a teeth cleaning.

That’s what comes with practice. When I got back home, I began doing some research and found that each year, more than 250,000 Americans had appendectomies. The more I thought about that figure, the more absurd it seemed. Why should an organ fail in so many healthy people? What makes it more puzzling is that no one ever needs an appendix transplant. Appendix-free, I can expect a normal life.

I called Dr. Rebecca Fisher, a physical anthropologist at Midwestern University in Glendale, Ariz., who has given serious thought to the paradox of the appendix. “There are a lot of questions about this little thing that everybody takes for granted,” Dr. Fisher said.

The fact that I was alive without my appendix, she said, did not necessarily mean it had no function. The appendix buds off from a bulge at the front of the large intestine, called the cecum. It forms a narrow, finger-size pouch.

The appendix does not seem to be involved in digesting food, but it may help the gut to fight disease. The appendix is packed with immune-cell-producing tissues.

That fact has led some scientists to suggest that during childhood it teaches the gut’s immune system how to tell the difference between dangerous pathogens that should be attacked and harmless food that should be ignored.

But when people get their appendix removed, other immune-cell-producing tissues in the cecum and elsewhere can compensate for the loss.

Even if the appendix serves a function, it is hard to understand why it has such a peculiar shape. “There’s no real good explanation for why you’d have a blind end,” Dr. Fisher said. “The immune cells can still enter the cecum, but why make it harder? We really don’t know.”

The shape of the appendix is also the reason it is so dangerous. Its narrow channel can become sealed, either by a minor overgrowth of its own cells, or by a bit of half-digested food. Once the appendix is inflamed, the swelling cuts off blood vessels, making it vulnerable to bacteria.

You sometimes hear people who say they reject evolution claim that our bodies show clear signs of being “intelligently designed.” I wonder how many of them have had appendicitis.

To solve the paradox of the human appendix, Dr. Fisher wants to know how it evolved. “If only the appendix fossilized,” she said ruefully. Instead, she compared our guts to those of other species.

Chimpanzees and other apes are our closest living relatives, and they all have an appendix that looks a lot like ours. So it’s reasonable to infer that our common ancestor 30 million years ago also had one.

But when Dr. Fisher researched the guts of other primates, the picture got blurrier. “In some cases it’s absent, but in other cases it’s spot-on looking like a human appendix,” she said.

Some primate species fall somewhere in between these two extremes, with just a narrowed tip forming on the cecum. Dr. Fisher suspects that the appendix evolved several times in primates, but she cannot say what conditions favored its evolution. “Since the data is so poor, I think any trend would just be a lucky happenstance,” she said.

Still, I wondered how such a dangerous and disposable organ could survive over evolutionary time. “We consider it maladaptive because we want to live to a very old age,” Dr. Fisher said. “But from a strictly Darwinian view, it might not be.”

Imagine a trait that helps an animal survive to adulthood, but that also has side effects that can cause trouble later in life. If, on balance, animals produce more offspring with the trait than without it, natural selection will favor it.

Perhaps the appendix lifted the odds that our ancestors could resist childhood diseases and live to childbearing years. Even if it also caused deaths by appendicitis, the appendix might have been a net plus. (It’s also possible that appendicitis wasn’t such a big problem in the past. Some scientists have argued that modern Western life has made appendicitis more common, either as a result of a change in hygiene or in the foods we eat.)

Dr. Fisher’s “net-plus” hypothesis is one of several possible explanations. But they all remain speculation, she said, until scientists learn a lot more about the appendix. “It seems basic, but it’s also very hard,” she said.

As fascinating as the evolution of the appendix may be, my conversation with Dr. Fisher got me thinking about another part of the human body: the brain.

I was grateful that we have not only inherited a danger-prone appendix, but a brain that can invent surgery. Now I may live long enough to see the mystery of the appendix solved.