The Wave Leaps From Flesh To Air

Try speaking without air from the lungs, squirming tongue, or dancing lips. Attending to the differences between vowels and consonants gives us a sense of the importance of each part of the vocal tract. In each case, the larynx provides raw sounds that the mouth then sculpts. Khoomei singers, known in the West as Tuvan throat singers, take this to an extreme, using constrictions created by their tongues to filter out all but a few overtones while their tightened larynx drones. Theirs is a sophisticated vocal art that builds on the interplay of the larynx and mouth we all use as we speak or sing. The same is true for other mammals. When dogs or wolves throw back their heads to howl or squirrels lower their jaw and pull in their cheeks to chitter, they are shaping sound with their vocal tracts. None of the structures that we use to speak are unique to our species. Our chests are more amply supplied with nerves for the fine control of breath than most primate species, but this is an elaboration, not an innovation. Our chimpanzee relatives also drop their hyoid bones and larynges. The descent is lower, though, in humans, opening a more voluminous resonant space in our throats. This, combined with protuberant faces of chimpanzees, means that the chimpanzee vocal tract is dominated by the mouth, with very little resonance in the throat.

All Or Nothing

In humans, the resonant spaces in mouth and throat are about of equal size. Human and chimpanzee tongues are similar, although ours is more domed and larger relative to the size of our mouths. Anatomically, human speech is based on subtle changes in the proportions of structures present in other species. Contrast this with birdsong, which flows from a syrinx unique to modern birds. The evolution of both birdsong and human speech was a striking and novel expansion of the sonic diversity of the world. Theirs is the product of radical anatomical innovation, ours of tinkering. Evolution used a heavier hand in our brains, creating new linkages that allow us to speak. These, too, build on talents and predispositions present in our close relatives. All great apes are keen learners. Infants take years to learn all they need in order to thrive within the social and ecological environment. This social transmission of behavior and tradition constitutes culture. But unlike in humans, the cultures of other great apes are founded almost entirely on close visual observation and tactile participation.

I Don't Believe A Word

Although other great apes are vocal, they do not, as far as we know, convey complex knowledge through sound. Our human ancestors connected vocal expression to culture. This union of two preexisting great ape abilities, vocalization and social learning, is the foundation of human language. We do not know exactly when this revolution took place. The hyoid bone was in modern form and position in ancestral humans, including Neanderthals, about five hundred thousand years ago. But there is nothing magical about the exact shape and position of this bone. Ancestors with higher hyoids and larynges might not have been quite as articulate as we are, but they had the anatomical capacity needed for complex sound making, just as other great apes do. The conjunction of vocal production, learning, and culture left its mark in our brains and genes. Unlike in other primates, the nerves that control the larynx in humans thread directly into the motor cortex, the part of our brain that controls voluntary movements. These connections give us finer control and, most important, bring vocal production into the realm of learning. We also have substantial and complex brain connections among the laryngeal nerves and those involved in vocal interpretation, sonic memory, and the control of body movements involved in speech such as those in the tongue and face. The gene acts as a regulatory hub, stimulating and suppressing the actions of other genes that guide the growth and interconnections of nerve cells that coordinate muscular action, sensory input, memory, and interpretation.

Warning Signs

Neanderthal ears were similar to those of modern humans. Reconstructions suggest that the middle and inner ears were, like ours, tuned to the frequencies of human speech. Brain networks, greatly elaborated in humans compared with other primates, allow humans to draw together vocal production, interpretation, and memory in ways that other species cannot. We are not alone in this talent. Many birds, and perhaps other vocal learners such as whales and bats, also have direct connections from the vocal organ to the motor portions of the brain, along with elaborated connections among regions of the brain concerned with memory, perception, analysis, and production of sound. In reading these words, you take this human talent for integration one step further. Breath turned to ink. Three hundred milliseconds after you gaze on a word, electrical energy courses through the visual cortex of the brain. Four hundred milliseconds after that, the auditory cortex fires, swiftly followed by brain regions that interpret sound and language. Within less than a second of attention to the written word, silent reading provokes a frenzy of activity in the listening portion of the brain. Silent reading thus opens us to apparitions, the ghosts of writers’ voices. As your eye moves over these clusters of letters, sound no longer travels through air but in waves of electrical activation along wet, fatty cell membranes in a mammalian brain. Now speak these words aloud. The wave leaps from flesh to air. Just as it always has, sound moves from one being to another, from one medium to another, connecting and transforming. In the animal sounds around us, we hear the diverse physicality of the world. The songs of birds contain within them the acoustic qualities of vegetation and the voices of the wind. Mammal calls reveal how predators and prey hear one another in the varied terrains of forests and plains. Water’s many moods are expressed in the forms of whale and fish songs. The inner structure of plant material is manifest in the vibratory signals of insects.