“Bad design” of the human mouth enables us to speak
|July 6, 2018||Posted by News under Design inference, Human evolution, Intelligent Design|
From Philip Lieberman at The Scientist:
In On the Origin of Species, Darwin noted “the strange fact that every particle of food and drink which we swallow has to pass over the orifice of the trachea, with some risk of falling into the lungs.” Because of this odd anatomy, which differs from that of all other mammals, choking on food remains the fourth leading cause of accidental death in the United States. This species-specific problem is a consequence of the mutations that crafted the human face, pharynx, and tongue so as to make it easier to speak and to correctly interpret the acoustic speech signals that we hear.
In humans, however, a developmental process that spans the first 8 to 10 years of life forms the adult version of the SVT. First, the skull is reshaped, shortening the relative length of the oral cavity. The tongue begins to descend down into the pharynx, while the neck increases in length and becomes rounded in the back. Following these changes, half the tongue is positioned horizontally in the oral cavity (and thus called the SVTh), while the other half (SVTv) is positioned vertically in the pharynx. The two halves meet at an approximate right angle at the back of the throat. The tongue’s extrinsic muscles, anchored in various bones of the head, can move the tongue to create an abrupt 10-fold change in the SVT’s cross-sectional area. (See illustration below.)
During the first 8 to 10 years of life, the relative length of the oral cavity shortens and the tongue extends down into the throat. This gives the adult human supralaryngeal vocal tract (SVT) two parts of nearly equal lengths that meet at a right angle: the horizontal portion of the oral cavity and the vertical portion associated with the pharynx. At the intersection of these two segments occur abrupt changes in the cross-sectional area of the SVT that allow humans to produce a range of sounds not possible for infants and nonhuman animals.
As it turns out, the configuration of the adult human tongue’s oral and pharyngeal proportions and shape allow mature human vocal tracts to produce the vowels [i], [u], and [a] (as in the word ma). These quantal vowels produce frequency peaks analogous to saturated colors, are more distinct than other vowels, and are resistant to small errors in tongue placement.5 Thus, while not required for language, these vowel sounds buffer speech against misinterpretation. This may explain why all human languages use these vowels. More.
We’re told that the design of the human larynx, trachea, and oral cavity is poor because humans can choke to death. True, but it is not one of the common causes of death. As noted at ENST,
to put things in perspective, according to the National Safety Council, “5,051 people…died from choking in 2015,” which works out to 0.0018 percent of all deaths in the United States, and of those “2,848 were older than 74.” (See here and here.) There is no doubt some relationship to the prevalence of age-related conditions like Alzheimer’s disease. More.
Yes, many of the deaths from choking occur among elderly people. That fact will inflate choking death statistics in an era like ours when people live longer.
As one expert source notes, “Choking in the elderly is a serious issue and is one of the leading causes of death for adults over the age of 76.” It’s awkward, to say the least, to attribute the death of a human being over seventy-five years of age to “bad design” when mortality is a built-in feature of the world of life. The same person could otherwise die of cancer…
In any event, optimization is all we can hope for in a transient world, no matter who designed it or didn’t. It’s surprising how often that fact gets overlooked.
Nathan Lents, call your office.
Lents’s recent book is Human Errors: A Panorama of Our Glitches, from Pointless Bones to Broken Genes.
See also: At Skeptic: Five Questions about Human Errors for Proponents of Intelligent Design
External testicles another instance of bad design? Oddly, in making such a dramatic claim (“there is no good reason that sperm development has to work best at lower temperatures”), Lents does not quote any expert on the subject of temperature and sperm development.
Jonathan Wells on Lents’s claim that the human eye is wired backwards