The Universal Sense (4 page)

We don’t know much about the first vocal animals aside from the fact that it is unlikely they were vertebrates. Invertebrates have always outnumbered vertebrates in both biomass and diversity, and they were here billions of years before we were. But there is little fossil or genetic data on the emergence of vocal behavior. Both ways of tracing elements of biological history require a common ground, a presumptive chain of commonality, or at least a limited number of adaptations to check out. There are hundreds if not thousands of adaptations that allow animals to make sounds. Modern snapping shrimp create deafening 100 dB underwater choruses by snapping an oversized claw so quickly that it pulls gas bubbles from the water; these bubbles then explode in a pressure wave so intense they make pulses of light. Spiny lobsters make a ratchety violin sound by rubbing an extension of their antenna across a raspy area on their shell near their eyes. But even vertebrates have evolved extraordinarily diverse ways of making sounds, many not needing complex vocal apparatus. Once animals started developing hearing, almost any generated sound could carry meaning.

The earliest vocal animals probably didn’t use dedicated sound-generating structures, as almost any controllable sounds can be used to communicate, as shown by the winner of the
award for most unusual vertebrate communication structure, the herring’s fast repetitive tick (FRT). Herring have excellent hearing, although no one ever quite understood why, since they didn’t seem to have any vocal apparatus and were never heard to make sounds. But a study in 2003 showed that large groups of herrings would release bubbles from their anuses that made ultrasonic noises that fit nicely into their hearing range, thus demonstrating communication and social coordination by herring FRTs (and guaranteeing Ben Wilson, lead author on the study, a place in the history books of acronym generation). But this somewhat scatological example makes an important point: most totally aquatic sound-making animals do not use what we think of as typical vocal mechanisms. Terrestrial vertebrates usually use modifications to their respiratory tracts to drive air over some tissue that can vibrate in a controllable fashion, whether it be an opera singer driving air from her lungs over her vocal folds and through her mouth or a leaf-nosed bat driving it through the incredibly baroque folds overlying its nose, forming the beam for its echolocation signals. But underwater vertebrates rarely use such systems, as the greater density of water means that pushing water through small openings to make vibrations takes a great more energy than does pushing air through the same structures. So many underwater animals, such as sea trout, will use stridulation, rubbing stiff fin-like structures against each other, similar to how terrestrial crickets sing. Others, like the toad-fish, will rub sonic muscles against their air bladders, sort of like rubbing your hand across a balloon to make it squeak or hum.

And even though the earliest noisemakers were not contemporary sea trout, toadfish, or even farting herring, they probably used these and other mechanisms to make sounds. The more sounds they made, the more complex their behaviors could become
and the farther their social and survival webs could reach, traveling on the backs of the waves of sound. And as more and more living things joined the chorus, something very interesting happened to the Earth: its sounds changed. From a place of percussive impacts and landslides, rasping sands, and the white noise of wind-driven storms, living things began to make purposeful,
harmonic
sounds of their own, more tonal, controlled, and packed with meaning. The math underlying the sounds became more integer-like, less random. The Earth’s acoustics expanded from incidental noise to songs. And as the biosphere grew more complex, Earth developed an
acoustic ecology
, a measurable change in the vibrational energy of our land, sea, and air, driven by the emergence of life on our planet.

Even though the rain of iron and ice from the sky has diminished to the occasional fireball over Canada or piece of falling space junk, Earth is still a noisy place, but at least now there are listeners around to appreciate the sounds of a living planet. And we should. Every impact that has rung the Earth like a giant bell, every grinding earthquake formed by one tectonic plate sliding under another, every tidal wave, and every soft wind has contributed to the formation of life, shaking up the primordial ooze and adding energy to prebiotic chemicals, forcing them to collide, interact, and begin replicating. And to this day, the beat goes on.

What does sound do to us today? The Earth still surrounds us with its intrinsic sounds—earthquakes, wind, rockfalls, blowing rain and snow—but now a great deal of the sounds that fill the thin skin of our planet between the deepest oceans and the atmosphere come from living things. Life, as any new parent knows, is a very noisy thing. And sound and noise continue to drive the evolution and development of life, from shaping our
environment down to forming our very synapses. By listening, we hear not only the sounds of individual animals but the songs of a healthy biosphere.

I was recently reading an article on attempts to clone a thylacine—a Tasmanian tiger (which is not a tiger but a dog-sized marsupial hunted to extinction in Australia in the last century). In search of what they must have sounded like, I found a few short films of wild thylacines, but they were all silent. Then something occurred to me: I will never hear the sound of the thylacine. With every species extinction, we lose something from the acoustic ecology. No more sounds of the wings of a flock of passenger pigeons a million strong. No awkward squawks of dodos. And despite Hollywood’s best efforts, we will never hear the roars or songs of dinosaurs. But going into the field and just recording the surroundings (a common technique in bioacoustics, the study of biologically based sounds) often gives surprising results that lend hope for species that haven’t been seen for decades and are feared extinct. The great Ivory-billed Woodpecker, North America’s largest woodpecker, has been presumed extinct since 1944 due to habitat destruction. But based on recordings made in 1935 by Arthur Allen, scientists as recently as 2005 have claimed that they have heard if not seen this bird, leading to hope that a small population has survived in the southern United States. (And of course there are the innumerable recordings of Bigfoot stomping and growling in the Pacific Northwest, despite the fact that subsequent audio analyses have shown that these sounds easily could have been made by anything from bears to humans.)

As humans spread into undeveloped nature, we fill the spaces with human sounds, human voices, traffic, music, advertising
jingles, street-corner preachers, and bands. Humans bring the noise. And our ability to consider increasingly loud and noisy environments as “normal” and “home” makes it worse. It takes a radical shifting of attention or a change of place to realize the value of quiet. Rather than enriching our space with the sounds of life, we are crowding out the calls of other species.

But on the other hand, human technology and innovation are letting us hear things we’ve never heard before. Whether it’s ultrasonic microphones that let us hear the bar-brawl loudness of a swarm of bats screeching at 120 dB above our heads on an otherwise quiet summer night or interplanetary probes letting us listen in on the sounds of the thunder on Venus or the winds on Saturn’s moon Titan, our technology allows us to hear more and further than any other species on this planet. But to appreciate the sensory richness in which we are embedded, we need to be quiet once in a while when we are in a new place, and just listen.

Chapter 2
Spaces and Places: A Walk in the Park

When I was a kid, my mother used to listen to a radio personality named Jean Shepherd. He was mostly known as a storyteller and a humorist (and is primarily remembered today for the film version of his tale “A Christmas Story”). But I remember him because he used to tell stories about how things sounded. He used to say that when he went traveling, he didn’t bring a camera; while everyone took pictures, he recorded the sounds of the places he went.

I particularly remember his shows about the 1964 World’s Fair, when he walked around recording the sounds of the different pavilions. At the time I was a constant visitor to the fair because I happened to live about two blocks from it, and I remember being excited listening to these shows because I knew
exactly
where he was talking from. I heard the songs from the Small World exhibit or the sounds of the extruding machines that made the plastic mold-a-rama dinosaur toys they sold at the Sinclair Oil Dinoland.

On one episode I liked, he started out by talking about a vendor named Ernie who sold popcorn in front of the press box
at Comiskey Park and was just as famous as some of the ball players. This was not a subject of particular interest to me, until he started imitating Ernie’s famous call and telling how it would echo all around the park, bouncing off the left-field wall and the scoreboard in right field, then echoing back through the “great cavern of the stands, just floating through the whole park, just part of the rich effluvia of life.” From there he led into talking about listening to the world from four thousand feet above the ground in a hot-air balloon. He talked about how he could hear dogs barking, conversations, kids rattling sticks on fences—things he never could have heard at ground level or from an airplane, where you’re enclosed and surrounded by throbbing engines. And he wondered why sound carried so well up there, saying that maybe an acoustician or a meteorologist could tell you but he didn’t know.

Decades later, I still remember that particular show, and realized that I could now answer his question.
²
Sound waves propagate through the air in a spherical pattern, widening out from whatever made the sound. In theory it could spread out nearly forever, losing energy based on the square of the distance from the sound source, but things get in the way, making the sound lose energy. Sound can be refracted, bent by things as simple as changes in the density of the air; reflected, bouncing off hard surfaces; or absorbed into a surface, adding a bit of heat
to the structure but losing the energy of the sound. As things refract, reflect, or absorb sound, the sound gets distorted, losing strength and cohesion. The more things that are in the way, the more the sound fades away. But the part of the sound that rises above the clutter on the ground is unobstructed, essentially giving listeners above the ground (and not surrounded by throbbing aircraft engines) a natural hearing aid. Just changing the place you listen from can radically affect what you hear, be it four thousand feet in the air, under the ground in a bat cave, or just in my office after I move a bookshelf from one place to another.

Aside from an appreciation of the way sound changes in different spaces and places, I picked up something else from his tales. When my wife and I travel, we usually have a camera stored somewhere, but more often we pack enough audio gear to make passage through the TSA checkpoint interesting. The most interesting time was when we were going off to record the Eiffel Tower—my wife is an artist whose work has a heavy focus on sound, and she wanted to record the actual sounds of the tower, including the low-frequency infrasound normally undetectable by humans. So after she got the requisite permission from the Société Nouvelle d’Exploitation de la Tour Eiffel (SNTE), we packed up four digital recorders, some in-ear binaural microphones, several hundred meters of cable, and eight geophones—seismic microphones normally used to record earthquakes and drilling operations. You know, just basic tourist stuff.

These were “can”-type geophones, relatively small but heavy brass cylinders with electrical leads on the ends. In other words, they look like pipe bombs. On 100-meter leads. Plus a lot of electronic gear with blinking lights and timers attached to them. Surprisingly, the security agent at Kennedy Airport in New York
simply asked what they were and then gushed about how much she loved Paris, wished us luck, asked where she could hear the recordings, and let us go. Then, on our second day in Paris, after I’d cleared everything with the local SNTE office and began duct-taping these geophones to the south pillar of the Eiffel Tower (while my French-speaking wife was off with the video crew), I heard some rather frantic voices yelling something I didn’t understand. Upon looking down, I saw a number of gendarmes directly under me, armed with machine guns and clearly insisting that I either do something or stop doing something. Waving my letter from the head of security (who had not informed the local gendarmerie) and saying “le papier!” repeatedly with a New York accent didn’t help much, but my wife managed to return and calm things down before I got shot in the name of acoustic research.

But it was worth it. We were allowed to record the tower’s ambient human-audible sounds and infrasonic vibrations from the base, from the apex, from the underground mechanical room (which was strictly off-limits at the time), and from the escape chute at the top of the tower under the radio antennas. If you go there and listen, the sounds you usually hear are those of the voices of thousands of visitors in their hundreds of different languages, the horns of the taxicabs whose drivers are blocking traffic in yet another strike, the two-toned European sirens as the police try to get traffic moving, and other sounds of the urban Parisian environment, ranging from the weather to the cooing and flapping of the omnipresent pigeons. But standing on the topmost platform, separate from most of the other visitors, I confirmed what I think of as the Jean Shepherd effect: when the wind died down I could occasionally hear conversations from
individuals almost a thousand feet below, their voices (in French) rising undistorted along a specific clear radian.

But the tower has an unheard voice of its own. You may think that 7,300 tons of metal, 2,500 tons of stone, and 50 tons of paint would keep the tower rock steady, but the massive structure vibrates constantly at subsonic frequencies. Gustave Eiffel claimed that his design for the structure was intended to minimize wind resistance, and his success is demonstrated by the fact that even in strong winds the tower only sways 2 to 3 inches (as opposed to the 10 to 12 feet the World Trade Center used to sway). But the tower responds to and propagates all sorts of low-frequency vibrations—the pounding of visitors’ feet, the motion of the giant chariots hauling the counterweights that lift the nineteenth-century elevators (still using most of the same technology that Gustave Eiffel installed), the wind shaking the antennas and lighting system.