While there are two major ways in which language enables communication among humans, spoken language is the predominate form. In her chapter on the anatomical and physiological basis of language in The Oxford Handbook of Language Evolution, Ann MacLarnon writes:
“Humans use rapid, highly variable, extended sound sequences to transmit the complex information content of language. Speech is a very efficient communication medium: it costs little energetically, it does not require visual contact with the intended receiver(s), and it can be carried out simultaneously with separate manual and other tasks.”
Spoken language is a reflection of the unique human anatomy: it is made possible by a vocal tract anatomy which enables humans to make a large variety of different sounds. Spoken language is simply a stream of pressurized puffs of air which produce a wide range of sounds.
There is no single anatomical feature that makes spoken language possible. In his book The Accidental Species: Misunderstandings of Human Evolution, Henry Gee writes:
“The complicated arrangement of the larynx, the resonant chambers in our nose and mouth, the shape of our throat, the musculature that controls our lips and tongue with great precision and delicacy—all seem to be refined to a degree seen nowhere else, suitable for conveying the infinite subtleties of language.”
In her book The First Word: The Search for the Origins of Language, TChristine Kenneally describes the process of producing spoken language this way:
“Speech starts simply enough with air in the lungs. The air is forcefully expelled in an exhalation and it makes a sound because of the parts of the body it blows over and through—the vibrating vocal cords, the flapping tongue, and the throat and mouth, which rapidly opens and closes in an odd, yapping munch. It’s easy to underestimate the athletic precision employed by; the many muscles of the face, tongue, and throat in orchestrating speech.”
This is a complicated process. Christine Kenneally also writes:
“It takes at least ten years for a child to learn to coordinate lips, tongue, mouth, and breath with the exacting fine motor control that adults use when they talk.”
In his book The Story of the Human Body: Evolution, Health, and Disease, Daniel Lieberman notes that the human vocal tract is unique for two reasons:
“One is that our brains are exceptionally skilled at rapidly and precisely controlling the movements of the tongue and other structures that modify its shape. Additionally, the distinctive short and retracted face of modern humans gives our vocal tract a unique configuration with useful acoustic properties.”
Larnyx and Pharnyx
The larynx (voice box), made from four different kinds of cartilage, houses two folds of mucous membrane (vocal cords) which produce the sounds of spoken language. In speaking, muscles in the larynx contract and the vocal cords vibrate when air is expelled from the lungs. In his book The Origin of Humankind, paleoanthropologist Richard Leakey reports:
“Humans are able to make a wide range of sounds because the larynx is situated low in the throat, thus creating a large sound-chamber, the pharynx above the vocal cords.”
In her book The Canon: A Whirligig Tour of the Beautiful Basics of Science, Natalie Angier writes:
“The evolution of human language was made possible by our larynx dropping down from its previous primate position, thereby opening up a larger air space to facilitate elaborate sound production.”
The larynx is much lower in the neck in humans than in other mammals. The vertical and horizontal tubes are equally long in humans, an arrangement which is quite different from chimpanzees. Daniel Lieberman writes:
“A vocal tract with two tubes of equal length produces vowels whose frequencies are more distinct and which require less precision to make properly. In effect, the human configuration allows you to be able to be a little sloppy when speaking yet still produce discrete vowels that your listener will recognize correctly without having to rely on context.”
One of the other features of the vocal tract that is unique to humans and is especially adapted for language is the kind of muscle fiber in the vocal cords. Christine Kenneally reports:
“They don’t twitch like most muscle fibers but contract in a precise, graded fashion.”
This is different from the muscles found in the vocal cords of other mammals.
In his book Thumbs, Toes, and Tears and Other Traits that Make Us Human, Chip Walter writes:
“While the larynx gives our voices pitch and character, we sculpt sounds into phonemes after they have made their way through our vocal cords and up into our throats.”
With regard to the pharynx, James Hurford, in his book The Origins of Language: A Slim Guide writes:
“The typical primate larynx is up close to the back of the mouth, near where the nasal passage and the oral passage join. In humans, the lower position of the larynx allows a hollow space, the pharynx, up between it and the back of the mouth.”
James Hurford goes on to report
“The pharynx provides an extra shape-shiftable chamber through which passes the air carrying the vocal buzz.”
The tongue can change the shape of the pharynx producing a double resonator system. The tongue root can be pulled backward which produces a narrow pharynx and a wide oral cavity, or the tongue can be pushed high in the mouth producing a narrow oral cavity and a wide pharynx. James Hurford writes:
“Thus, the airflow from the lungs can pass either through a narrow cavity first, then into the next and wider oral chamber, or through a wider cavity first and then through a narrowed oral chamber.”
The Tongue
In making the many sounds of spoken language, the tongue is critical. Without a tongue, articulate human speech is not possible. Ann MacLarnon writes:
“The unique form of the tongue within the vocal tract in humans is considered to be a key factor in the speech-related flexibility of our supralaryngeal vocal tract.”
In other mammals, the tongue is flat and has a primary function of moving food around in the mouth so that it can be chewed, and then to move food to the back of the mouth so that it can be swallowed. The human tongue also functions in this way, but in addition it is an important structure in producing the variety of sounds that are needed for spoken language. With regard to the anatomy of the tongue, Ann MacLarnon writes:
“In humans, however, the tongue is a curved structure, lying part horizontally in the oral cavity and part vertically down an extended pharynx, where it attaches to a much lower hyoid, just above a descended larynx.”
Human tongues are quite different from those of chimpanzees, our closest living relatives. One of the differences is the position of the tongue. Natalie Angier writes:
“Whereas a chimpanzee’s tongue is contained entirely within the mouth, the back of the human tongue forms the upper edge of the volume tract, giving it flexibility in shaping and articulating sounds.”
Christine Kenneally describes the flexibility of the tongue this way:
“It can be moved up, down, and back; it can be bunched up or extended, widened or curled. Whenever the tongue changes shape, the whole vocal tract is altered, and each different configuration results in a different sound.”
James Hurford writes:
“Humans have uniquely complex control over the shape and movement of their tongues.”
It is this control that makes spoken language possible. But when did it evolve? James Hurford writes:
“Humans at some stage developed far finer control over tongue movements than chimpanzees, who cannot produce anything passable as human consonants; but dating the emergence of this fine control has so far eluded us.”
Hyoid Bone
Another important part of the human speech apparatus is the hyoid bone. The larynx is suspended from the hyoid (a tiny floating bone) at the base of the tongue. In her book The First Signs: Unlocking the Mysteries of the World’s Oldest Symbols, Genevieve von Petzinger describes it this way:
“This horseshoe-shaped bone is located in the throat below the chin, near the thyroid gland. It acts as an attachment point for the muscles of the lower mouth, tongue, and larynx, as well as several other throat muscles.”
The hyoid bone in humans is different than in other apes. In his book The Origins of Language: A Slim Guide, James Hurford reports:
“In the other apes, the hyoid bone has a spoon-bowl-shaped extension pointing outward from the middle of its U-shape. This extension is the ‘hyoid bulla’. Gorillas, chimpanzees, bonobos, and orangutans all have a bulla on their hyoid. The human hyoid has no bulla. It is more likely that our species lost its bulla than that the other apes independently gained one during their evolution.”
In searching for the origins of language, a human-like hyoid bone may provide an important clue regarding the potential for spoken language. The hyoid is, of course, a bone, and thus, in theory, following death it may be present after the flesh has decomposed. In reality, it is small and fragile and is rarely found in ancient remains. Paleoanthropologists have found the well-preserved hyoid bone of an Australopithecine dated to about 3.3 million years ago. This hyoid bone shows features similar to that of an African ape, including a pronounced bulla. This suggests that the vocal tract of the Australopithecines was more ape-like than human-like, indicating that they probably did not have spoken language.
Hyoid bones have also been found with the remains of Neanderthals at El Sidrón (Northern Spain, dated to 49,000 to 43,000 years ago) and Kebara (Israel, dated to 60,000 years ago). Like the hyoid bones of modern humans, these hyoids have no bulla. These hyoid bones strengthen the case for Neanderthals having at least the potential for spoken language.
Neanderthals, of course, are not directly ancestral to Homo sapiens, but the two species share a common ancestor dating back to 600,000 to 700,000 years ago. Current data suggests that this common ancestor was most likely Homo heidelbergensis. In Spain, paleoanthropologists found two hyoid bones from Homo heidelbergensis which were similar to those of modern humans. James Hurford reports:
“The implication is that the human vocal tract had evolved to something like its modern shape already in Homo heidelbergensis, over half a million years ago.”
It would appear that human ancestors at this time were developing vocal tracts which may have supported spoken language.
Choking
Unfortunately, this rearrangement in the throat which allows humans to speak has some other consequences. Situated below the larynx are two tracts: the windpipe (essential for breathing) and the digestive tract (essential for eating). To make sure that the food or liquid consumed by humans passes into the digestive tract, when humans swallow, the larynx closes. This means that, as humans, we cannot breathe and swallow at the same time and attempting to do so results in painful choking and even death.
In newborns, the larynx is high which allows them to breathe while suckling at their mother’s breast. At about three months of age, the larynx descends to a position low in the throat. Steven Pinker, in his book The Language Instinct: How the Mind Creates Language, writes:
“This gives the tongue the space to move both up and down and back and forth, changing the shape of two resonant cavities and defining a large number of possible vowels.”
While this enhances the ability for spoken language, it also means that simultaneous drinking and breathing is no longer possible. It is now possible to choke. With regard to choking, Chip Walter writes:
“This made it the sixth-leading cause of accidental death. A chimpanzee, however, will never choke to death, at least not because the banana it was eating went down the wrong way.”
James Hurford puts it this way:
“The lowered larynx actually brings with it a slightly greater risk of choking on food, as if the larynx is not carefully covered during swallowing, food can go down the wrong pipe, the trachea (windpipe) instead of the oesophagus (foodpipe). The evolutionary pressure to communicate outweighed the risk of choking.”
Breathing
Air passing through the vocal tract and producing the many sounds of spoken language requires control over the breathing process. Spoken language is produced during the exhalation process of breathing and requires an extended period of exhalation and very short periods of inhalation. Ann MacLarnon writes:
“Humans have enhanced control of breathing compared with non-human primates, which they use to extend exhalations and shorten inhalations during speech, as well as to modulate loudness.”
Ann MacLarnon goes on to report:
“Enhanced breathing control therefore contributes to the human ability to produce fast sound sequences, and to generate a whole variety of language-specific patterns and meanings, communicated through the intonation and emphasis of phrases or specific syllables.”
With regard to human control of breathing, James Hurford writes:
“While in other animals in-breaths and out-breaths are of roughly the same duration, human breathing while speaking is about 90% exhalation, with only about 10% of time saved for quick in-breaths. The exhalation itself is finely controlled, with a thin flow of air maintained at speeds and volumes conducive to vibrating vocal cords as desired and yielding the appropriate pressure for plosive and fricative consonants, all while producing subtle intonation patterns. Other mammals have no such fine control over their breathing even when vocalizing.”
James Hurford also points out:
“When walking, humans do not maintain any close coordination between their paces and their breathing. Indeed, we can easily talk in long sentences while walking. Even in running, while there tends to be some constant relation between pacing and breathing, it is not the one-pace-to-one-breath relationship typical of quadrupedal walkers.”
This suggests that bipedalism may have been important in the evolution of controlled breathing by providing a preadaptive platform on which the controlled breathing needed for spoken language was built.
More Human Origins
Human Origins: How children learn language
Human Origins: Protolanguage
Human Origins: Fossil Evidence
Human Origins: Clothing
Human Origins: Teeth
Human Origins: Humans as naked apes
Human Origins: Sex
Human Origins: Alfred Russel Wallace and Charles Darwin