A stomachache was not how Smith wanted to start vacation. “I was hoping I would get better,” she says, “So I could go ski.”

As the day progressed, things worsened. A sharp pain developed in her lower right side. She couldn’t swallow the soup her sister warmed up for her at lunchtime. By the time she saw a doctor later that afternoon, she was hunched over in pain.

When she learned that her appendix was infected, she didn’t have much time to be afraid. She was rushed into surgery. The next morning, her appendix was gone.

“It was a little scary because it happened so quickly,” says Smith, now an evolutionary biologist at the Arizona College of Osteopathic Medicine at Midwestern University in Glendale, Ariz. But she has never missed her long-lost organ. In fact, the emergency left her with a lifelong fascination for a body part she no longer has.

“I have always been interested in the appendix and trying to figure out why we have one,” Smith says. “There’s been this idea for so long that it didn’t do anything.”

Appendices have long been considered “vestigial structures.” That means we don’t actually need them. The brain, heart, skin and most other organs are essential for survival. But you can live a long life without an appendix. The same goes for tonsils, wisdom teeth, body hair and other vestigial structures.

At best, according to traditional thinking, vestigial structures just take up space. At worst, they can get infected and cause all sorts of trouble. So why do we have these unnecessary body parts in the first place?

Growing evidence suggests that we have them because they aren’t actually unnecessary at all. Their function probably depends on where you live (and perhaps when you lived). In some parts of the world, people still need vestigial body parts. Studying where and when these features are or were useful is helping scientists make new advances in modern medicine. The work is also providing insight into the history of humankind — telling scientists things about our ancestors that we didn’t know before.

“It may be the case with a lot of unnecessary body parts that they may have had a function in the past but we don’t necessarily need that function anymore,” says Smith, who ended up studying the appendix sort of by accident. “That can give us insights.”

The hidden point

The appendix is a small organ that looks like a little worm (lower left of image). It doesn’t lead anywhere, but may serve as a haven for good bacteria.

3drenderings/iStockphoto

Consider your body, and you’ll notice a hodgepodge of random features that might seem silly when you stop to think about them. What’s the point of fingernails, for example? Why is there hair on your toes? And what’s the deal with muscles in your ears? Do we really need muscles in our ears?

Throughout history, scientists, too, have wondered about structures that don’t seem to do anything useful. The appendix is a popular example. This little, worm-like pouch is about four inches long and less than half an inch wide.

The organ grows near where the long intestine meets the short intestine. The intestines are essential for digestion, but the appendix appears to just sit there.

“It’s a dead-end sack,” says William Parker, an immunologist at Duke University in Durham, N.C. “It doesn’t go anywhere.”

Parker didn’t start out intending to study the appendix. His specialty is the immune system — a collection of organs, cells and molecules that our bodies use to stay healthy. But his research led him to the appendix anyway.

Parker knew that the human body is full of tiny organisms called bacteria, which can overwhelm the immune system, cause infections and make a person sick. He also knew that some bacteria are good for human health. Among other benefits, these “good” bacteria help people digest food and fight off “bad” bacteria that cause disease.

The immune system doesn’t just benefit from good bacteria, though. In the 1990s, Parker and colleagues began to figure out that the immune system also helps good bacteria flourish. These bacteria appear in thin layers called biofilms, which grow on the side of the gut near and inside the appendix. These biofilms, the researchers learned, provide a barrier that keep out bad bacteria.

“Once we figured that out, it should have been obvious to us what the appendix did,” says Parker, whose team also found that the appendix has a particularly robust biofilm. “It’s in the perfect spot to harbor bacteria — out of the flow and with a thin, narrow opening. And there’s a large amount of immune tissue associated with it.”

After stumbling on a possible link between the immune system and the appendix, though, the scientists still had some clues to compile before being sure of the organ’s purpose.

Hangout for good bacteria

In 2007, Parker’s team put together all the evidence they had gathered and came up with a conclusion: The appendix serves as a “safe house,” Parker says, a storage bin for good bacteria. If bad bacteria attack, good bacteria emerge from the appendix and come to the rescue.

Having a safe space for good bacteria should be especially useful in parts of the world that are poor and undeveloped — places where people are starving, medicine is hard to come by, clean water is scarce and diarrhea can kill. In those places, Parker says, the appendix probably helps keep people alive, especially young children.

In fact, people in the developing world rarely get infected appendixes, like Smith’s. Most cases of appendicitis, in fact, occur in the United States and other developed countries, where water is purified, hospitals are sterilized and medical care is easier to get.

Those trends suggest that the appendix evolved in our ancestors to maintain health in a bacteria-filled world. Today, places such as the United States might be too sterile for the appendix. When the organ has nothing do, the immune system can turn on itself, sending people to the emergency room, Parker says. Other problems, such as allergies and immune diseases, might have similar roots.

Even in ultra-clean societies, then, the appendix and other vestigial organs might be unrecognized heroes.

“Just because body parts don’t seem to have any usefulness here doesn’t mean you wouldn’t need them if you were suddenly thrown in the middle of the woods somewhere and had to drink from whatever mud hole you could find nearby and you had to run away from predators,” Parker says. “Problems we are having today with allergies and autoimmune diseases are a result of the body not really fitting in with our culture.”

Figuring out the true purpose of the appendix and other overlooked organs, Parker adds, is an important step toward solving medical mysteries.

“We want to understand how the body functions so we can work towards getting it to function normally,” he says.

To do that, it can help to take an historical view. By considering what was normal a long time ago and comparing the old normal to the new normal, researchers can see how evolution has shaped our bodies over hundreds of thousands of years. That process of change over time is called evolution.

“The best way to figure out how the body was designed to work,” Parker says, “is to look at how it was meant to work over hundreds of millions of years of evolution.”

Wise beyond our years

The appendix isn’t the only example of a body part with hidden powers. Wisdom teeth are another. This final set of molars usually grows in at around age 20. Today, most people get their wisdom teeth removed before the bulky molars can squeeze other teeth out of place or get infected.

Millions of years ago, though, human faces weren’t as flat as they are today and mouths had more room for wisdom teeth. After 20 years of life without dental care, our ancestors would have benefited from a fresh set of strong teeth that could chew and grind raw food.

Our ancestors may have found wisdom teeth more useful than we do.

Lakhesis/iStockphoto

As for other structures long thought to be pointless, a recent study found that the spleen stores a whole lot of immune cells. Among other roles, those cells help to repair hearts that are damaged. Tonsils, which are also removed routinely in many developed countries, probably help boost the immune system, as well, Parker says.

As they continue to find purposes for seemingly purposeless body parts, scientists are connecting our present with the past. They are also connecting the human animal with other animals on Earth.

Last year, Smith teamed up with Parker and other colleagues to look at a whole bunch of mammal species, some that lived tens of millions of years ago. The researchers found that the appendix has existed in a wide range of animals, from rodents to primates to Australian marsupials. The study also revealed that the appendix evolved more than once throughout history. Both findings suggest that the appendix has had an important purpose throughout time.

By looking closely at our body’s “pointless” parts, we can begin to imagine what our bodies used to be able to do. Recognizing the body’s lingering power could also open up a whole new future of possibilities.

“Our evolution gives our bodies a lot of resilience and strength we really don’t need very much in our society,” says Parker. “I sit around in my office and have all the food I want. My body can do so many things I never ask it to do.”

This story and other Science News for Kids features describing research in medicine and biology are supported with funding from The Lasker Foundation. The foundation and its programs are dedicated to the support of biomedical research toward conquering disease, improving human health and extending life.

Instead of eating reasonable portions of fruit, vegetables, whole grains, and other healthy foods, lots of people eat too many cookies and chips. Many people just eat too much food in general.

One result is an epidemic of obesity that has swelled the waistlines of millions of adults and kids. This increase in obesity has led to increases in the occurrence of diabetes, heart disease, cancer, and other illnesses (see “Packing Fat“).

Some people have trouble controlling how much they eat. Others are so worried about getting fat that they strictly limit how much they eat and may end up starving themselves.

But for other people, food becomes the enemy. They worry so much about getting fat that they either severely limit what they eat or make themselves throw up right after eating. Doctors say that these people have eating disorders.

Eating disorders among teens are much less common than obesity is. Yet the health consequences of eating disorders can be just as severe.

Not eating enough can lead to heart attacks, weak bones, organ damage, and fainting spells. Repeatedly throwing up causes chemical imbalances in the body, erodes teeth, and destroys the stomach lining.

Researchers are zeroing in on what causes certain people to develop eating disorders, why some people are more at risk than others, and what kinds of education programs work best to keep people from taking drastic measures to lose weight or stay slim.

It’s important to learn how to recognize signs of disordered eating in yourself and your friends, doctors say, because research shows that getting treatment early on is the key to a quick recovery.

Starving yourself

In the United States, eating disorders affect as many as 10 million girls and women and 1 million boys and men.

One type of eating disorder is called anorexia (or anorexia nervosa). People with anorexia eat only tiny amounts of food. They’re often obsessed with measuring food portions or counting calories. They may exercise for hours every day to burn off the few calories that they do consume. Someone who weighs 100 pounds can drop to an unhealthy weight of just 80 pounds, or even less, if they develop anorexia.

People with anorexia may be obsessed with measuring food portions, counting calories, and checking their weight.

PhotoDisc

Instead of starving themselves, people with an eating disorder called bulimia (or bulimia nervosa) eat a huge amount—like a quart of ice cream, a giant bag of chips, or a package of cookies—in a short time. Then, they try to get rid of the food by forcing themselves to vomit.

Both disorders often begin around puberty, when kids’ bodies change in important ways. These changes can be stressful, especially for girls.

People have long blamed eating disorders on a culture that idolizes skinny women and muscular men. The idea is that pictures in movies and magazines become unrealistic goals for people, who then take dangerous measures to change the way they look.

One of the most surprising findings in recent years, however, is that genetics and biology may also play a role. Anorexia and bulimia run in families, says Kelly Klump, a psychologist at Michigan State University in East Lansing.

Genes and hormones

Klump and her coworkers have found that the family connection starts to emerge after puberty, usually in the early teen years. That’s when levels of certain hormones start to change in kids’ bodies.

Hormones are chemical compounds that help keep our bodies working properly. Hormones control how quickly cells make and digest proteins. They play roles in how fast we grow, how hungry we are, and how we feel.

Klump suspects that each person’s genes determine his or her particular hormone levels. That’s what makes some people more likely to develop unhealthy eating behaviors. Hormone differences may also explain why eating disorders are more common among girls and women than among boys and men.

In one eating disorder, a person may be tempted to eat everything in sight, then try to get rid of the food by throwing up.

Finding a genetic link, however, doesn’t mean that fate determines who will end up with an eating disorder. “You’re not doomed,” Klump says. It only means that some people are at greater risk.

Media images

Whatever your risk for an eating disorder, one thing is certain: Media images have a big impact on how people feel about themselves.

Some studies have shown that girls who try to look like movie stars and fashion models are more likely to make themselves vomit than other girls are, says Alison Field. She’s an eating disorder expert at Children’s Hospital Boston.

And studies by Harvard psychiatrist Ann Becker showed that the occurrence of bulimia skyrocketed in Fiji after television was introduced to that South Pacific island in 1995. After just 3 years of watching commercials for exercise equipment and TV shows full of good-looking, superthin actors, the number of Fijian girls who said they vomited to lose weight jumped from 3 percent to 15 percent.

Media and advertising images can be misleading. Photos of models and actors are often touched up to make them look better.

Learning to resist the allure of media images may be the most important way for kids to protect themselves from eating disorders, Field says. After all, pictures can be deceiving.

The images that we see have usually been altered in various ways to make models and actors look even better than they do in person. “There’s manipulation behind all ads,” Field says. Ads are supposed to make you feel bad about yourself so that you buy stuff.

Dieting risks

Many schools today teach students about the hazards of obesity and the importance of staying lean. However, some studies have shown that kids who diet end up gaining more weight than those who don’t. The more people try to restrict their food intake, the more likely they are to think about food. And the more they think about food, the more likely they are to head for the kitchen.

The best strategy, Field says, might be to teach kids about obesity and eating disorders. After all, the underlying message is the same. If you eat well and get enough exercise, your weight and health should fall into place.

School-based educational programs can be quite powerful. In one recent study, 500 middle-school girls participated in a program called Planet Health. The program taught the girls about nutrition and fitness within the context of other school subjects. After 2 years, the number of girls who were using diet pills or vomiting to lose weight dropped from 6.2 percent to 2.8 percent. It might be worth encouraging your school to adopt a similar program.

In the meantime, if you or any of your friends are showing signs of eating disorders, it’s important to get help right away. Talk to a parent, a teacher, a doctor, or some other adult you trust.

You need to realize that you’re not alone, Field says. You can really benefit from the help that other people can give.

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“My nickname is ‘Spit Queen,’” says Navazesh, who teaches at the University of Southern California School of Dentistry in Los Angeles. She can joke about her work, but she also wants you to know that spit, or saliva, is much more than the slimy stuff that you might use to wet a spitball.

“Most people take saliva for granted,” she says. “It’s one of the least-respected body fluids.”

Saliva protects your teeth and helps you digest food.

Teethwise (http://www.teethwise.org/ )

Saliva actually deserves a lot of respect. To start with, it protects your teeth and allows you to talk and eat. Police investigators use the results of saliva tests to solve crimes and nab drunk drivers. Doctors are starting to use spit instead of blood to diagnose diseases and to test for pregnancy.

Analyzing saliva can be a lot like looking into a crystal ball. Navazesh, for example, is working on a project that uses saliva to determine a kid’s chances of developing dental cavities.

“Scientists are investing hours and hours of their lives to discover more about saliva,” she says. “It’s a fountain of opportunity.”

Like water

Most people treat saliva as if it were like water. It’s easy to understand why. Saliva is made up of more than 99 percent water.

But saliva also contains a variety of substances called proteins that give it unusual powers. Some of the proteins clean your teeth and gums by preventing bacteria from sticking to the surfaces. Others kill bacteria, viruses, and fungi.

Cats take advantage of the antiseptic properties of saliva when they clean themselves with their tongues.

It’s these cleansing and antiseptic properties of saliva proteins that explain why dogs lick their wounds and cats clean themselves with their tongues. Spit also contains special proteins known as enzymes, which help digest your food as you chew.

Scarce spit

In healthy people, three pairs of major salivary glands and many small ones produce a constant supply of spit. The average healthy mouth produces about 600 milliliters of saliva each day. That’s enough to fill a 12-ounce soda bottle.

Salivary glands can stop doing their jobs, however, when people have certain diseases, take some kinds of medicines, or go through treatment for cancer.

The most dramatic demonstrations of saliva’s importance come from people who don’t have enough. In an exhibit room at the National Museum of Dentistry in Baltimore, Md., a video screen shows people describing how hard life can be when spit is scarce.

“It seems to take over your whole being,” one woman says. “Your mind stays with your mouth. You can’t get satisfied.”

Another patient says that she sometimes wakes up in the middle of the night with her tongue stuck to the roof of her mouth because there’s no saliva to keep things moistened.

Imagine what it would be like to have a wad of peanut butter in your mouth all the time. That’s how it can feel if you don’t have enough saliva.

These patients have a hard time chewing and swallowing, Navazesh explains. They don’t enjoy the taste of food. They choke easily on crunchy items.

For patients such as these, scientists have developed medicines that push the salivary glands to work harder and produce more moisture.

Liquid information

Recent saliva research has revealed how rich in information the liquid is.

Easy to collect and store, saliva contains a lot of information about a person’s health.

NIH

For example, one promising role for saliva is in diagnosing disease. Doctors today draw blood to look for signs of disease based on the presence of various substances in the blood. It now turns out that saliva holds the same information.

Your spit also contains samples of the genetic material DNA. Everyone’s DNA is different. Analyzing DNA in a glob of spit can tell doctors whether you are susceptible to certain diseases. Such an analysis can also tell investigators whether you were the one who stopped to drink a glass of water or licked an envelope to seal it at the scene of a crime.

For doctors, the nice thing about spit is that it’s easy to get. No needles are necessary.

Predictive power

Navazesh and her coworkers are studying how proteins in saliva affect teeth. Their goal is to use information about what’s in spit to predict a person’s chance of getting cavities.

Information about what’s in spit may predict a person’s chance of getting dental cavities.

The project involves kids between 7 and 14 years old. All are checked once a year for new cavities. Using statistics to account for differences in diet and lifestyle, the researchers are trying to link a kid’s saliva proteins to the development of cavities.

The researchers hope to develop a test that will identify patients whose teeth need special care, such as sealing. Down the line, such treatments could prevent a lifetime of extra visits to the dentist and unpleasant dates with the drill.

As scientists unveil how helpful saliva can be, it might be time for you to think differently about your own.

“Look at your saliva as a friend rather than an enemy,” Navazesh says. “Love your saliva. Have respect for it. And take care of your teeth.”

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