Sounds Wild and Broken Read online

  Unity and Diversity

  In the moment of our birth, we are dragged across four hundred million years of evolutionary time. We turn from aquatic creatures to dwellers of air and land. We gasp, sucking the alien gas into lungs previously filled with warm, salty ocean. Our eyes are pulled from the dim, reddish glow of the deep into jabbing brightness. The chill of evaporation slaps our drying skin.

  No wonder we wail. No wonder we forget, burying the memory in the soil of the subconscious.

  Our earliest and only experience of sound before birth was the hum and throb of an aquatic cocoon. Our mother’s voice found us, as did the sounds of her surging blood, breath flowing in lungs, and churning digestion. Fainter were the sounds of the world beyond our mother, from places then unimaginable to our mostly unformed brains. High tones were attenuated by the enclosing walls of flesh and fluid, and so our first sonic experiences were low and often rhythmic as her body pulsed and moved.

  In the womb, hearing develops gradually. Before twenty weeks, our world is silent. At about twenty-four weeks, hair cells start to signal through nerves running to rudimentary auditory centers in the partly developed brain stem. Cells tuned to low-frequency tones mature first, and so our hearing starts with bass throbs and murmurs. Six weeks later, furious growth and differentiation of tissues result in a frequency range of hearing similar to that of an adult. Sound flows from mother’s fluids into ours, directly stimulating the nerve cells in the innermost part of our ears, unmediated by ear canals, drums, or middle ear bones.

  All of this gone, in a moment.

  Birth removes us from our watery surrounds, but our final aural transition to air happens hours later. The fatty vernix that swaddles us at birth lingers in the ear canal, muffling airborne sound for a few minutes or, for some, days. Soft tissues and fluid likewise recede over hours from the bones of the middle ear. When these vestiges of our fetal selves finally dissolve, our ear canals and middle ears are filled with the dry air that is our inheritance as terrestrial mammals.

  Yet even in adulthood the hair cells of our inner ears are bathed with fluid. We keep a memory of the primal ocean and womb inside the coils of our inner ear. The rest of the ear’s apparatus–pinnae, middle ear chamber, and bones—delivers sound to this watery core. There, deep inside, we listen as aquatic beings.

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  I lie belly-down on the wooden dock. The splintery boards toast me with the stored heat of the summertime Georgia sun. In my nose, the sulfurous, ripe aroma of salt marsh. The flowing water under the dock is turbid, a mud soup sweeping past on a falling tide. I’m on Saint Catherines Island, a barrier island whose eastern shores face the Atlantic. Here, on the western side of the island, ten kilometers of salt marsh separate me from the flood-prone piney woods of the mainland. In the humid air, these woods are mere haze on the horizon. Salt marsh grasses, interrupted by narrow, twisting tidal creeks, cover the intervening distance. These grasses grow knee or waist high on all the mudflats, as thickly packed and as deep green as lush fields of young wheat.

  The marshes seem monotone, their uniform verdure spiced only by snowy egrets stalking the creek edges and the pumping wing beats of glossy ibises passing overhead. But these are the most productive habitats known on Earth, capturing and turning into plant material more sunlight per hectare than the lushest of forests. Marsh grasses, algae, and plankton thrive in the happy confluence of fertile mud and strong sun. Such abundance supports a diverse animal community, especially of fish. More than seventy fish species live in these tidal marshes. Ocean-dwelling fish also swim here to spawn. Their larvae grow in the protection and plenty of the marshes, then catch a ride to adulthood on an outbound tide.

  For all terrestrial vertebrate animals, rich salt water such as this was our original home, first as single-celled creatures, then as fish. About 90 percent of our ancestry was underwater. I clamp headphones over my ears and drop a hydrophone from the dock. I’m taking my ears back to where they came from.

  The heavy capsule, a waterproof rubber and metal ball containing a microphone, sinks quickly, pulling the cable after it. I wedge a cable loop under my knee, holding the hydrophone above the creek bottom’s mud and debris, about three meters down in the opaque water.

  When I first release the hydrophone, all I hear is the high gurgle of streaming water. As it descends, the swirling sounds fall away. Suddenly I’m plunged into a pan of sizzling bacon fat. Sparkles surround me, a sonic shimmer. Every glistening fragment is a fleck of sunlit copper, warm and flashing. I’ve arrived in the acoustic domain of snapping shrimp.

  This crackling is common in tropical and subtropical salt waters worldwide. Its sources are the hundreds of species of snapping shrimp that live in seagrass, mud, and reefs. Most of these animals are half the length of my finger or smaller, equipped with one hefty claw for snapping and a lighter one for grasping. I’m hearing a chorus of claws.

  As the claw snaps shut, a plunger slams into a socket, shooting forward a jet of water. In the wake of this jet, water pressure drops, causing an air bubble to pop into existence, then collapse. This implosion sends a shockwave through the water, the snap that I’m hearing. The sound pulse lasts less than a tenth of a millisecond, but it is strong enough to kill any small crustacean, worm, or fish larva within three millimeters of the claw tip. Shrimp use the sound as a territorial signal and jousting weapon. As long as they keep a centimeter away from their neighbors, they can spar unharmed.

  The combined racket of snapping shrimp is, in some tropical waters, loud enough to befuddle military sonar. In World War II, US submarines hid among the snapping shrimp beds off Japan. To this day, navy spies deploying hydrophones must work around the sonic haze of shrimp claws.

  My first lesson in this sonic immersion is that the underwater world can be a boisterous place. Before I donned the headphones, airborne sound came to me in bursts: squalls of whistles from boat-tailed grackles, pulses of cricket and cicada sound, occasional nasal caws from fish crows, and the melodies of distant songbirds. Underwater, the shrimp innervate their surroundings with unflagging sonic energy. There are no silent spaces between song phrases or cries. Sound travels more than four times faster in salt water than in air, adding to the sense of brightness. This is especially true at close range, between the reflective surfaces of the muddy bottom and the upper water boundaries, where sounds have not been attenuated by the viscosity of water.

  Into the cloud of shrimp sound come stammering bursts of knocks. Each batch lasts a second or two, a cluster of ten or more taps. Then a pause of five or so seconds, more regular taps, interrupted by occasional hesitations. The taps sound like an impatient fingernail drumming on a hardcover book, sharp and low, with a touch of resonance. The sounds come from silver perch close by. These finger-length fish come to the salt marsh to spawn before returning in late summer to the deeper waters of the estuary and offshore. Alongside these knocks come faster bursts of tapping, almost purrs, the calls of the Atlantic croaker, a bottom-feeding fish that grows as long as my forearm.

  Waa! The bleat of a lamb, but quieter. These complaints occasionally poke into the background of shrimp, perch, and croaker, and come from an oyster toadfish, probably hiding in its lair on the bottom of the tidal creek. Like their namesake, toadfish are scaleless and warty, with huge gulping mouths. Their fist-sized heads and tapered bodies are also well endowed with spines. Males call to attract females to shallow burrows. After mating, males stay with the fertilized eggs for weeks, defending them and cleaning the nest. The one I hear now is muffled and soft. He must be at some distance from the hydrophone, perhaps burrowed into debris around the dock’s pilings.

  All three of the fish that I hear through my hydrophone make sound by vibrating their swim bladders. Each bladder is an air-filled sac running inside the fish, stretching for about one-third of the body length below the spine. Muscles pressed against the thin walls of these bladders shiver, a
nd these motions evoke squeaking or grunting sounds from the air within. The muscles are among the fastest known in any animal, contracting hundreds of times per second. Sound waves from the swim bladder flow into the fish’s tissues and then into the water. For these fish, the whole body is an underwater loudspeaker.

  The acoustic realm of these shrimp and fish seems alien to me. I’m used to the melodies, timbres, and rhythms of humans, birds, and insects. Here, though, percussive sounds dominate: the sparkle of thousands of hammer blows by shrimp claws, the knocks of perch and croaker, and the unmodulated burr of the toadfish.

  But unity undergirds these differences.

  The shrimps’ stony, articulated exoskeleton bristles with fine sensory hairs. Sound also stimulates clusters of stretch receptors in their joints, where cilia transmit motion to nerves. At the base of antennae, tiny sand grains enclosed within gelatinous balls of sensory cells are stirred into motion by sound. Hearing, for snapping shrimps, is an experience for the whole body. Unlike human ears that detect pressure waves on our eardrums, shrimp and other crustaceans hear by detecting the displacement of water molecules, especially low-frequency motions. Sound, for them, arrives not as the push and shove of a wave, but as the tickle of moving molecules.

  Fish, too, hear through sensors spread all over their body surface. Cells capped with jelly-enclosed cilia line both the skin and watery canals just below the skin’s surface, a network known as the lateral line system. Unlike the touch receptors deeply buried in our dry, keratinous skin, these fish sensory cells live in intimate contact with the water around them. The lateral line system is especially sensitive to low-frequency sounds and wafts of flowing water. Rudiments of the lateral line system appear on human skin as embryos, but we lose any trace as we mature, shedding this sensory embrace of our surroundings long before we are born.

  Fish also hear using inner ears. These are the same structures that our ancestors brought with them when they came onto land. We humans hear with modified fish ears.

  Like the lateral line system, the fish’s inner ears unite sensation of sound and motion. Three looping semicircular canals detect body motion by sensing the flow of fluids in the canals over hair cells. Connected to these canals are two bulging sacs lined with sound-sensitive hair cells. In many fish species, tiny flat bones in the sacs overlay some of these hair cells. When the fish moves, the bone lags, dragging on the hair cells and magnifying the sense of motion. In many species, the swim bladder also gathers and transmits sound waves to the inner ears.

  Among land vertebrates, the fish’s flat ear bones and swim bladders are absent. The hearing sacs are elongated into canals, expanding the range of sound frequencies that the ear can perceive. In mammals, the canal is so long that it coils, forming what we now call the cochlea, from the Latin for “snail shell.” Our language divides sensations of “sound,” “body motion,” and “balance,” but they all emerge from hair cells in interconnected fluid-filled canals in our inner ears. The link in human cultures between music and dance, and between speech and gesture, is deeply rooted in both our bodies and in the evolutionary history of animals.

  Ancient kinship among vertebrates is present in sound making too. Although vertebrate animals make sound in very different ways, these processes share an embryological origin. A small segment of nervous tissue at the intersection of the hindbrain and the spinal column develops into the nerve circuit that controls sound making in adult animals. This circuit acts as the pattern generator for vocalization across animals with very different forms of sound making: from the swim bladders of fish, to the larynges of terrestrial animals, to the unique syringes in the chests of birds, along with thousands of sonic variations made by croaking and booming vocal sacs, strumming pectoral fins, and drumming forearms.

  The region of the spine that orchestrates vocalization also coordinates the actions of the pectoral region, the muscles of the front fins or limbs. This linkage reveals the need for fine control of timing in both vocalization and movement. All calls and songs have rhythmicity, from the steady hum of the toadfish to the layers of repetition in the song of a bird. The same is true for the coordinated movements of fins, legs, or wings. Just as hearing in vertebrate animals is closely allied with a sense of motion, sound production is linked to body movement. Rhythmicity of sensation and action shares an embryological root.

  When we humans talk and gesticulate, or sing and play musical instruments, we evoke ancient connections. When my hands thump out rhythms on piano keys or strum a guitar, I’m enacting the same bodily relationships among voice, limbs, and sound that create the bleats of a toadfish or the melodies of a forest songbird. When Henry Wadsworth Longfellow wrote that “music is the universal language of mankind,” he stated an embryological and evolutionary truth that far transcends the bounds of “mankind.”

  Lowering a hydrophone from the dock was a revelatory moment. The expansion of my awareness came from two intersecting directions. I understood that my unaided human senses utterly failed to convey to me the richness of the marshes. The water surface, especially when obscured by streams of opaque tidal mud, is a formidable barrier to human understanding. When I heard the lively below-water chatter, I pierced, for a moment, a sensory barrier. Now when I’m at the marshes, I imagine and feel their diversity and fecundity, despite the visual uniformity of their above-water plants. Listening below the water surface opened me to the previously hidden life of the marsh.

  Alongside this understanding of the nature of a particular place, my sense of self changed. Lying on the dock and, later, reading about animal voices and ears, my thoughts and feelings about identity shifted. Evolution has drastically reworked the mammalian body as it transformed us from fleshy-finned swimmers to four-legged land lumberers. But under these terrestrial bodily accretions is unity with our distant aquatic relatives, unity not just of pedigree but of lived sensory experience. I’m a fish talking in air, strutting and breathing on land, yet experiencing the sea through trembling hair cells in coiled watery tubes in my ears. My hydrophone and headphones created a curious loop. In listening to the subaquatic world, I used tubes of modified seawater buried in my inner ears.

  But human ears are only one of the sound sensors present here. Earth’s sonic diversity is not only present in the varied voices of animals. Part of the world’s richness is the diversity of aural experience.

  As mammals, we inherited triplet ear bones and a long tightly curled cochlea. Birds have a single middle ear bone and a comma-shaped cochlea. Lizards and snakes have a short cochlea whose sound-sensitive hair cells are arranged in patches, not in a single smooth gradient as in our ears. These are three independently evolved mechanisms within the vertebrate clan for hearing in air, dating back about three hundred million years. Each lineage lives within its own construction of sound. Lab experiments on the behavior of captives give us a crude sense of what these differences might mean for perception. Compared with mammals, birds cannot hear as high. Birds are relatively unconcerned with the sequence of sounds but are highly attuned to rapid-fire acoustic details in each note in a song, picking out subtleties that human ears miss entirely. Birds are also especially adept at hearing how sound energy is layered into different frequencies, the overall “shape” of the sound, rather than attending to the relative pitches that are the particular focus of mammalian ears and brains. Where we discern a melody in bird or human song—shifting frequencies between notes—birds likely experience the rich nuances of the inner qualities of each note.

  Fish and shrimp are immersed in sound as the movement of water molecules directly stimulates their surface hairs and as sound waves flow unimpeded into and through their bodies. Bacteria and free-living eukaryotes, too, feel the vibratory signal on their membranes and cilia. On land, insects hear airborne sounds with hairs on their body surface and modified stretch receptor organs in their skeletons, the same organs used by both insects and crustaceans to feel motion and vibration in their
legs. Specialized hearing organs independently evolved at least twenty times in different groups of insects. Crickets have drumlike hearing organs in their front legs, but grasshoppers hear through membranes on their abdomens. Many flies hear with a sensor in their antennae. Among moths, hearing organs evolved at least nine different times, resulting in “ears” on wing bases, along the abdomen, or, in the case of the sphinx moths, on the mouthparts. We humans can feel vibrations on our skin and in our flesh as well as in our ears, but these are crude and blurry sensations compared with the nuanced whole-body hearing experience of these other beings.

  It is a convenient shorthand to say that the shrimp, fish, bacteria, birds, insects, and I “hear” the same sound. To hear is a verb that reveals the narrowness of our sonic perceptions and imaginations. We have no such limitation when we describe how animals move: They lope, strut, crawl, sidle, wing, creep, sashay, slide, trot, flutter, and bounce. Here is a lexicon that recognizes the diversity of animal motion. But we have an impoverished vocabulary for hearing. Hear. Listen. Attend. These words do little to open our imagination to the multiplicities of sonic experience.

  What is the verb for the sensation created by a snapping shrimp’s foreleg joints or the direction-sensitive hairs on its claws? When the bony plate in a croaker’s ears slides over a membrane covered in hair cells, what should we name the resulting experience? The ciliary hairs in the lateral lines of the fish are immersed in the water around them, surely yielding a different experience from the movement of a triplet of bones in our middle ears. We lack any word to convey the mystery of the sphinx moth’s mouth palpus when sensing an approaching bat.