Chapter 6 The Gift of Tongue
This chapter is divided into three parts.
(1) Place human speech into the broader evolutionary framework of vocal communication.
(2) Focus on one apparent derived feature, our species-specific tongue. Also discuss studies of the vocal abilities of other species and recent studies on the development of the human tongue and SVT in infants and children.
(3) Discuss the speech production anatomy and phonetic repertoires of extinct hominids, particularly Neanderthals.
Human speech involves more than the larynx. But the larynx is a key element in the production of speech. In Victor Negus’ observation “ that the human embryo, when it is about 5 mm long, shows a slit in the pharyngeal floor much like that of the Lung Fish.”
Figure 6.1 illustrates hypothetical “branch points” in the evolution of the speech-producing anatomy. A branch point marks a point at which the course of evolution can change through selection that enhances fitness in a new setting. In addition, the writer use cars and computers to illustrate the theory of branch points.
Negus explored the anatomic bases of the first three stages of laryngeal evolution in Figure 6.1.
(1) The evolution of the larynx was the development of dilators that can pull the larynx open to allow more air into the lungs during breathing.
(2) The second functional branch point accounts for the larynx’s becoming a sound-generating device.
(3) The anatomic modifications that yield more efficient, controlled phonation and /or better breathing occur at branch point III in the figure.
Figure 6.2 shows the relative area of the trachea, or windpipe, which connects the larynx to the lungs, compared with the maximum opening of the larynx for a horse, a dog and a human being. And it also shows the laryngeal morphology that determines maximum opening. Horses have a larynx that has long arytenoids cartilages. These cartilages swing apart to open the larynx for respiration.
The optimum length of the arytenoids cartilages for maximizing the opening of the larynx relative to the trachea is about 0.7 times the diameter of the laryngeal opening. Human being have almost the shortest arytenoids cartilages of any mammal relative to their tracheal cross-section. The probable reason is phonation.
Many anatomic features differentiate human beings from earlier extinct hominids. The branch point at level IV denotes the modifications of the supralaryngeal vocal tract that typify anatomically modern Homo sapiens. The cost has been a greater probability of choking to death and perhaps less chewing efficiency.
Darwin recognized that the human suprolaryngeal airway differs from that of other primates and most mammals; it is an inferior swallowing machine. He may have known that human infants at birth have an SVT similar to an ape’s. Human newborns retain most features of the nonhuman SVT.(See Figure 6.3 and 6.4).
Figure 6.5 shows the risky food and pathway of an adult human being. We can’t simultaneously breathe and drink. The pharynx in humans is a common food-and-air pathway. However, the nonhuman supralaryngeal airway is better adapted for swallowing in any position.
Human beings and nonhuman primates follow two different paths after birth.
(1) In humans the tongue descends into the pharynx, taking the larynx down with it.
(2) The rotation of the facial block is one factor implicated in the restructuring of the human face and the human SVT.
The two-tube human SVT can be functionally divided into two sections: a horizontal section(SVTh)defined by the oral and oropharyngeal length and a vertical SVTv section defined by the vertical pharyngeal length. Between birth and age three years, the proportions of the SVT change from an SVTh/SVTv ratio of 1.5/1 to a ratio of 1.25/1. As children mature, the proportion of the tongue body in the vertical pharyngeal section continues to increase until the fully quntal adult SVTh/SVTv 1:1 ratio is attained between ages six and eight years.
A perceptual magnet pulls an ill-formed format frequency pattern toward the ideal exemplary of the language that a person is exposed to in the early months of life. In effect, our speech perception system cleans up sloppy signals.
Descent until Age Six to Eight Years
After the cranial base angles stabilizes between ages two and three, further descent of the tongue occurs and the proportion of the human tongue (SVTv) that is in the pharynx continues to increase relative to that in the oral cavity (SVTh) until age six to eight. That proportion is then maintained as the face and jaw attain their adult sizeds at about sixteen to eighteen years.
versus Tongue Descent
Figure 6.8 in the animals, the larynx descends either transiently during phonation or in some instances permanently because the distance between the hyoid bone and the larynx increases. However, the animals’ tongues remain positioned in their mouths. In contrast, in humans the tongue descends into the pharynx, changing its shape and taking the larynx down with it.
Descent and Signaling Size: How Big Am I?
Larynx lowering in these animals seems to be the result of natural selection for auditory size enhancement. Laryngeal descent, absent tongue displacement, lowers formant frequencies but does not increase phonetic range.
Significance of Lowering the Larynx
This SVT configuration is necessary to produce the quantal vowels 〔i〕,〔u〕, and〔a〕The term “quantal” needs clarification. The term was coined by Stevens to characterize speech sounds that have two useful properties.
(1) Quantal sounds have perceptually salient acoustic properties that can be produced with a certain degree of sloppiness on the part of a speaker.
(2) Speech communication would be perfectly possible without quantal sounds, but they enhance the robustness of the communicative process.
Capabilities of Nonhuman Tongues
Capabilities of Extinct Hominds
Limits and the Antiquity of Speech
A most Improbable Primate
The 1971 Neanderthal Reconstruction and Modeling Techniques
abstract of Chapter 7:
chapter focuses on the questions of evolution of the anatomic bases of human
speech, that is, the research of the airway above the larynx and the SVT. The
key element about this issue is the evolution of the tongue of human. The tongue
allows us to produce more kinds of sound. But following by the stand of human
caused man can produce so many, the more risks we are under for the epiglottis
is shorter so that it cannot always cover whole larynx. This fact is dangerous
to us but we exchange these risks with alert tongue to get higher language
abilities. And we can observe those ideas by the evolution of human.