The human vocal tract is well built for maximizing the number of different sounds it can produce. Particularly notable is the way the tongue can move freely in the mouth and the modifications that support the abillity.
I'm always happy when there is a new paper by Bart de Boer. He studies the mechanics of producing speech sounds, and in the next issue of the Journal of Evolutionary Psychology he has a review paper on the human vocal tract (draft here). As it is available online, I will limit myself to reporting data that caught my eye:
Does that point mean that we evolved our vocal tract's present anatomy for some reason other than for proper speech? De Boer thinks not. He has made a series of calculations concerning the relation between vocal tract and position of the larynx and concludes that "there is indeed a larynx depth that results in the largest possible acoustic area covered" which happens to match human female anatomy. There was "a path of ever increasing fitness from a chimpanzee-like anatomy to the human (female) anatomy."
This fitness path suggests that there has been a specific evolutionary trend toward maximizing the range of possible signals:
… a population of communicators can always be invaded by mutants that can produce a slightly larger range of signals. … The mutants can… produce more distinctive signals, or produce the same signals with less effort… If communication confers fitness (as it is usually assumed when discussing the evolution of language) mutants with a larger signaling space will invade populations of individuals with a smaller signaling space.
This process of replacing a narrow range with a wider one until the range was maximized appears to be exactly what happened. ("…human anatomy and human vocal abilities agree with a maximization of articulatory abilities.")
Choking to death is a famous risk of speaking, usually attributed to the lower larynx. But de Boer says the crucial change was in separating the velum and larynx so that the larynx can no longer link to the velum. This change allows "the rounded tongue freedom of movement." Tecumseh Fitch has famously pointed out that other mammals besides humans have a lowered larynx, "However, in all the cases that Fitch presents, the animals in question are still able to connect the larynx to the velum and are (presumably) able to swallow and breathe at the same time. Furthermore their tongues are ordinary flat mammalian tongues."
In the discussion section, de Boer continues, "As soon as there is a gap between the velum and the larynx—something which is necessary for enhanced freedom of motion of the tongue—there is a danger of food falling in the lungs. But once this risk exists, the evolutionary cost has been paid, so to speak, and the larynx position [can] evolve toward a position that produces the largest range of signals."
Even after four years of working on this blog I am still learning things.
The difference between male and female articulation has been reported before on this blog. The presumed reason for the lower larynx in males is to give men deeper voices, suggesting a bigger size. This leads to my favorite fact in the paper. A study "found that men are more impressed by perceived body size than women, and any adaptations for size exaggeration are therefore most likely the result of male-male competition for dominance, rather than the result of men trying to impress women." The final placement of the male larynx in a non-optimal position is likely "a compromise between articulatory range and size exaggeration."
A number of other vocal tract adaptations are listed in the paper besides the well known lowering of the larynx and inability to seal off the lungs from the mouth: "fine control over breathing … the anatomy of the vocal cords… [neurological] ability for vocal imitation… [neurological] ability to control vocalizations consciously … a rounded tongue, a 90 degree angle between mouth and pharynx."
One last thought as I mount an old hobby horse of mine. This transition from chimpanzee vocal tract to human tract did not require just a generation or two. If you want to agree with the generativists and the archaeologists who argue that speech is at most only a hundred thousand years old, you must account for the fact that we had already gotten rid of our chimpanzee vocal tract. Perhaps it was a pre-adaption but please, tell us what led to its formation.