Everyday Mysteries
WHY DO DOGS BARK? Dogs can be pretty good communicators. A yelp is easy to recognize as a sound of distress. Growls are obvious. A whine, coupled with a scratch at the door, may just keep the carpet clean and dry.
But what about barking? Is a dog sounding an alarm? Defining its territory? Just playing? The principles of evolution dictate that animals retain traits through natural selection. They hang on to functions that contribute to their survival, and that applies to making sounds no less than anything else. Scientists believe male birds sing, for example, to mark their territory, to attract mates, to maintain pair relationships, and to warn of impending predatory doom. But barking seems to defy all the rules of biological necessity. Biologists Raymond Coppinger and Mark Feinstein, who have studied this puzzle, say dogs often seem to bark extravagantly and for no apparent reason at all. The two Hampshire College scientists once spent the night in a Minnesota field listening to a guard dog bark continuously for seven hours. There were no other dogs around, no humans responding, no predators lurking. It just barked. Feinstein recently came upon two dogs in a hot car. "One was barking like crazy, the other staring out the window. They were under the same conditions," he says. "They've got this capacity which doesn't play any necessary function in their lives."
Those dogs, like all domestic dogs, are descended from the wolf, and wolves don't bark much. But their puppies do, and Coppinger and Feinstein believe that may help explain the mystery of barking. Early dogs (wolves really) were scavengers, hanging around human habitations--and their plentiful heaps of garbage. Humans, in turn, tended to tolerate the tamer ones; it was they that became the sires of what would become the domestic dog. Experiments in a number of animals have shown that breeding for tameness breeds animals that are, in effect, perpetual adolescents, displaying many youthful traits into adulthood. "You get an animal more like a juvenile wolf," says Feinstein.
So why do juveniles bark? Feinstein and Coppinger believe wolf pups are in a transition period; a bark is acoustically half-way between an infantile attention-seeking whine and an adult, hostile growl.
Adult dogs do find ways to use their barks to communicate; they might be asking to go in or out, defending territory, or just playing. But as Feinstein notes, precisely because barking has no biological necessity for dogs, "they can adapt it to use under almost any circumstance."
Ultimately, science's best answer may be the punch line of the old joke about why dogs chase their tails and lick themselves: because they can.
WHY DO PEOPLE LIKE HOT PEPPERS? Lovers of fiery cuisine and scientists alike agree that the hottest chili pepper is the habanero. Waxy and thumb-size, the habanero produces a punishing punch many times more intense than the better-known jalapeno. Chili pepper flavor is as complex as good wine, says Paul Bosland, a New Mexico State University professor. The habanero, he says, has a unique flavor and a "back-of-the-mouth, top-of-the-throat kind of heat. It's a persistent heat." Bosland, who is also director of the Chile Pepper Institute, says chili eaters work up to a "habituation level."
Like all chili peppers, habaneros get their heat from a tasteless, odorless chemical called capsaicin, which irritates certain nerves in the nose and mouth. Scientists rate hotness in Scoville units, a measure of capsaicin concentration. Plain old bell peppers rate a zero; jalapenos, 2,500 to 5,000 units; habaneros zoom as high as 300,000; pure capsaicin is a skin-blistering (literally) 15 million Scoville units.
But why would people willingly submit themselves to that kind of pain? Other mammals don't. Botanists believe plants use capsaicin as a defense to keep rabbits and other small mammals from eating them. Birds, which may not feel the heat of chili peppers, feed on them and disperse seeds through their droppings. Paul Rozin, a University of Pennsylvania psychology professor, observed a Mexican village where people ate plentiful quantities of chilies, but dogs and other animals that fed on human garbage ate peppers "out of necessity only," he says.
An old standby explanation is that people in hot climes eat spicy foods to perspire, in essence turning on nature's air conditioning. But it doesn't take a habanero to get a sweat going. Another theory is that the burn of chilies causes the brain to produce endorphins, the powerful chemicals that block pain and create a sense of well-being. Hot peppers, in other words, are a habit-forming drug.
Rozin, who discounts the endorphin theory, believes eating hot peppers is actually a form of "benign masochism." A pepper's burn, he says, is like riding a roller coaster. "Your body is responding as if in trouble, but you know you're really safe, getting a pleasure that comes from knowing better than your body."
WHAT MAKES A GREAT VIOLIN The historic violins most sought after by today's players and collectors were crafted hundreds of years ago in Cremona, Italy, by three famous makers: Andrea Amati, Giuseppe Guarneri, and Antonio Stradivari. Performers like Marylou Speaker Churchill of the Boston Symphony Orchestra say the best Cremona violins have "a tone quality that grabs you and you can't put it down."
For centuries, the secrets of their magnificent tone have been a sort of Holy Grail for makers, scientists, and cranks. Just what mixture of four-centuries-old alchemy, art, and skill produced the Stradivarius and its kin? Some believe Cremonese violin makers used very dense wood from old trees, floated down river from the Alps to Venice's saltwater lagoons, where mold attacked the wood and opened microscopic holes. That may have made the wood less dense and more resonant. Some modern makers have tried various methods of reproducing this special property; they have baked wood to reduce its density, buried it in the sand, and even simulated salt exposure by saturating wood in a solution made by boiling shrimp shells in potassium hydroxide.
Then there's the centuries-old hunt for the "lost Cremona varnish." Joseph Nagyvary, a Texas A&M University biochemistry professor and violin maker, has removed minute samples of varnish from several Cremona instruments and studied them under a scanning electron microscope. The varnish, he claims, contains minerals, such as quartz, calcite, and gypsum, which may account for the surface luster of Strads--and, more important, may have penetrated the wood's surface, enhancing and amplifying sound.
Devotees see the best Cremona violins as an unattainable standard. Yet some players, makers, and scientists insist that the mystique of ancient violins is mostly in our heads. Carleen Hutchins, who has been making and researching violins for 50 years, believes time will prove some of today's instruments are as good as any Stradivarius. "We can do everything except [give them] 100 years of playing," she says. The skeptics say even trained listeners can't reliably tell an old violin from a new one on the concert stage.
There is no doubt that the Cremona makers were highly skilled craftsmen. But the debunkers say that searching for lost secrets is nonsense. Your local True Value Hardware store has better varnish than Stradivari used, for one thing. "No one can tell the sound of a varnished from an unvarnished instrument," adds James Beament, author of The Violin Explained, "for varnish, like beauty, is only skin deep."
Hutchins, who says "old-time violin makers hate my guts," says the best modern makers have not only the skill but also the science to help them accomplish what Stradivari had to do by ear--and trial and error. One key, she believes, is carefully adjusting the wooden top and back plates of the instrument so that they vibrate in patterns that reinforce certain tones. Unlike the simple, regular vibration patterns of string, plates vibrate in a series of complex and difficult-to-predict modes. And shaving off a fraction of a millimeter of wood from one spot can dramatically alter the relative loudness of a note's overtones, or harmonics, which are what determine the timbre of a sound. Different patterns of overtones are why a violin and a flute--or a good and a not-so-good violin--can sound so different, even when playing the same note.
Hutchins analyzes the vibration modes of a violin plate by covering it with a powder of aluminum flakes, then placing the plate atop a loudspeaker emitting a single tone. She then progressively raises the tone's pitch until the wood begins to vibrate. The glitter jumps into a pattern revealing how different areas of the plate vibrate up and down. Hutchins believes there are three modes in a plate that are most important to violin tone.
One reason comparisons between old and new violins are so difficult--and potentially misleading--is that the sound ultimately depends on the skilled hands of a player. Expectations on the part of both performers and listeners color a performance and how it is perceived, notes Gary Sturm of the Smithsonian Institution's musical instrument collection.
Violinists, says the Boston Symphony's Churchill, who owns a 1691 Stradivarius, have a unique bond to their old instruments. "We are in awe of its age, we are in awe of its price, but we're also in awe of the potential of such an instrument in our hands," she says. Perhaps that's what most makes a Strad a Strad.
NOISE: GOOD OR EVIL? Electrical engineers have been fighting hums and hisses ever since they discovered how to capture a signal on a wax cylinder or in a radio beam. Low-level noise takes many other forms that erode the quality of transmitted signals, from static and snow that bedevil television pictures to random electronic pulses that disrupt online communications. So it probably seems quite odd that some researchers are asking whether there are situations where noise is good.
Audio recording is one place where it's becoming increasingly difficult to say whether noise is a force for good or evil. The vinyl phonograph record is noisy. Ticks, pops, scratches, and hiss all intrude. However, a very soft musical passage can still be discerned, even when its sound is quieter than all of that unwanted noise. Compact disks, on the other hand, are silent. Most CDs are recorded digitally; music becomes binary digits, long strings of zeros and ones. In the quietest sections, the sound level fades until there is no more digital information, and it cuts off. For just that reason--the arbitrary cutoff of sound--stereo snobs have for years argued that the CD is harsh and unrealistic.
Now, engineers are finding that by adding noise, they can improve CD sound. It's called dither, a low-level noise, about the volume of one digital bit (the smallest significant amount of recordable digital information), which is mixed into the sound being recorded. The addition of dither noise pushes low-level sound signals above the one-bit threshold, allowing a CD to capture what before would have been distorted or lost altogether. Ken Pohlmann, a digital expert at the University of Miami School of Music, says a CD recorded without dither captures a 95-decibel range from loudest to softest. With dithering, the range becomes 120 decibels.
Noise may play a similar, paradoxically useful role in visual perception. Enrico Simonotto of the University of Genoa shows research subjects a video on a computer monitor; the image is contrastless and contains very little apparent detail. To most people, it looks like a nearly blank screen. But when he introduces random "noise"--minute grains of color, almost like adding snow to a TV picture--viewers recognize what the image is, a human face. As the noise increases and the image begins to resemble a pointillist painting, features such as a beard and eyeglasses become apparent. Scientists studying this phenomenon of "stochastic resonance" believe the noise may help the brain's neurons detect weak signals.
Clearly, no one suggests rubbing a record with sand or watching TV without an antenna. But as science learns more about how we see and hear, noise seems to be a lot more than just, well, noise.
WHY DO WE HICCUP? The medical literature lists more than 300 causes of hiccups. So-called everyday hiccups can result from inhaling too much air, eating spicy foods, or drinking too rapidly. Excessive smoking, laughter, and fatigue all make the list.
But those in search of an explanation for why the body reacts to food, drink, air, or the Three Stooges that way will take little comfort from the fact that No. 1 on the list of causes is "no known cause." Particularly odd is that hiccups seem to be almost unique to humans as a species. "It's pretty rare to see hiccuping animals," says Dr. Charles Welford, a clinical assistant professor at the University of Illinois College of Medicine at Rockford. Welford has studied every article on hiccups published in three languages since 1860 in a so-far-unsuccessful quest for an explanation of the phenomenon.
We know what hiccups are: rhythmic, uncontrollable contractions of the diaphragm, the large muscle that separates the chest from the abdominal cavity.
Chronic hiccups, lasting from days to years, can actually be a debilitating condition--even (rarely) fatal. Doctors treat them with tranquilizers and muscle relaxants, numbing of the throat, hypnosis, and, occasionally, surgery to sever one or both of the phrenic nerves, which carry motor impulses to the diaphragm. For less serious cases, there are, of course, hundreds of home remedies of varying utility. Some scientific evidence backs up bag breathing, sipping water without pausing for a breath, and other approaches that have the effect of elevating carbon dioxide in the blood. That appears to decrease the sensitivity of nerves in the brain that trigger the diaphragm.
The best explanation for why people hiccup at all is that hiccups seem to be just a vestige of fetal growth. The hiccup serves a useful purpose before we're born, as part of our prenatal exercise regimen. In the womb's liquid environment, the diaphragm flexes, in order to grow stronger. Meanwhile, the epiglottis closes, to prevent water from getting into the lungs.
Once we start breathing air, however, there is no apparent benefit to hiccups. We simply don't grow out of them. There is no question that the hiccup's more socially unacceptable cousin, the burp, aids in digestion. We hang on to it for good reason. But the hiccup, science seems to think, just is.
The acoustics of quality No musical instrument produces a pure tone. Accompanying each note is a series of overtones--which are what make a violin sound like a violin and a flute like a flute. Overtones are multiples of the basic pitch frequency; the number of overtones and their relative loudness determine a sound's quality.
Involuntary contractions How a hiccup happens 1. To keep food from entering the lungs, the epiglottis normally shuts when you swallow 2. In a hiccup, first the diaphragm suddenly contracts as if to draw air into the lungs, then the epiglottis shuts, interrupting the breath. [Illustration labels]: Epiglottis; Esophagus; Windpipe; Lungs; Diaphragm
This story appears in the August 18, 1997 print edition of U.S. News & World Report.