Cienciaes.com: Evolution of the larynx and spoken language.

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A few weeks ago, we celebrated here the discovery two decades ago of the gene responsible for the production of the FOXP2 transcription factor, which is involved in the control of the neuromuscular connections involved in the movements necessary to generate speech. The human species is exceptional in that it possesses a variant of this gene that is different from variants found in other species, including higher apes. Apparently, the mutation that generated the human variant provided new properties that allowed the development of language.

A few days ago when I write this, I was surprised by the publication in the prestigious journal Science of a study that compares the vocal apparatus, particularly the larynx, of numerous species of primates and draws very interesting conclusions about the evolution of language. I could not miss the opportunity offered by the publication of the article to continue delving into the subject of the evolution of language, a topic that has always surprised me so much to the point of almost leaving me speechless, which according to Ángel is impossible, as confirmed by the fact that I have decided to talk about language again in this program.

The larynx is the vocal organ of mammals, which produce sounds by forcing air through it. The folds of tissue on the inner surface of that organ vibrate in response to the flow of air expelled from the lungs, producing the wide range of vocalizations we can hear on television documentaries, including the words of the commentator, who is often also a mammal.

Although certain specializations of the human vocal apparatus were well known and understood, such as the descent of the root of the tongue into the pharynx, which also entails changes in human vocalizations, the evolution of the larynx had not been studied in detail. This is what a large group of researchers in evolutionary biology from several countries on several continents set out to do, for which they study the vocal apparatus of Old and New World primates.

The researchers use magnetic resonance and computed tomography to analyze the anatomy of the larynxes of 25 genera (such as Homo or Macaca) and 43 species of primates (such as sapiens and mulata, for example). Scientists confirm that, in the human larynx, two folds of tissue, the so-called vocal cords, are responsible for the production of sound. However, the rest of the primates also have additional folds in the form of fins, called membranes or vocal lips, which also participate in the production of sound. Humans are the only primates that lack these vocal membranes and only produce sounds through the vocal cords.

The function of the vocal membranes was unknown, and to find out, the researchers conducted various experiments and computer simulations. First, they used three chimpanzees, who had unfortunately died in the zoo where they lived, to force air through their larynxes and analyze via time-lapse video the vibration of their laryngeal vocal cords and membranes. They also analyzed the larynxes of live chimpanzees making sounds while awakening from anesthesia (needed to place the camera in their larynx without much protest) and other similarly treated primate species.

The acquired data were used to generate a computer-simulated larynx model that allowed analyzing the sounds produced by the larynxes of primates under different airflow conditions and also modifying the laryngeal anatomy at will. To this simulated larynx, the researchers could add or remove the vocal membranes, although only in a simulated way, and analyze what happened in their presence… or in their absence, that is, in the case of the human larynx.

The conclusions of this study were clear. The vocal membranes possessed by all primates, except humans, produce a greater range of sounds when they vibrate, but they behave in a chaotic way that prevents acoustic stability and the possibility of modulating the sound produced in a controlled manner, resulting in essential to be able to codify the information in vocalizations in a coherent way, and thus allow the language to be understandable by whoever listens to it.

The study authors speculate that primate vocal membranes evolved to allow the production of a wide range of loud sounds, suitable for communication over distances typical of forest or savannah, but at the cost of some unpredictability when generating them. The loss of the vocal membranes had an impact on the amount of vocal frequencies that humans can produce, and also on the volume of those vocalizations, but it allowed better control in the production of sound frequencies and ended up making spoken language possible and , later, the writing, which made it possible to spread the enormous amounts of nonsense that we can see published on social networks. No one could have suspected that the disappearance of simple membranes in the larynxes of primates some six million years ago could have the enormity of the consequences that it has had, and will have, because if language is a blessing for our species, it is equally a blessing. severe curse that many insist on amplifying.

So far the scientific data. Now let’s look at some of the mysteries, speculations, and possibilities that these data generate. The first mystery is which gene or genes are responsible for the generation of vocal membranes. These genes are not known, but they must be present and functional in all primates except humans, or humans have functional variants, but in a different way than in other primates. We will have to wait, hopefully not too long, for these genes to be identified to see if, in effect, they function in the same way in all primates except Homo sapiens.

If this aspect is confirmed, an interesting conclusion would be that evolution does not always take place through the gain of genes or new functions, but also through their loss, provided that this occurs in the right environment and also at the right time. Both, time and environment, allowed not only the survival, but the expansion of mutant primates that lacked vocal membranes. We must consider that the mutation that originated everything probably occurred within a single family of our ancestors, and that the descendants of that or those few mutants lacking vocal membranes acquired such an evolutionary advantage, perhaps because they were able to communicate better with each other than their counterparts. congeners and thus form more cohesive groups, which ended up dominating the entire species.

However, that evolutionary advantage could only have occurred in an environment or under conditions probably different from those that make vocal membranes necessary for communication and for the survival of wild primates even today. Those conditions are still dominant in the natural environment where most primates live, or else those vocal membranes would have disappeared in other primate species as well, which might have thus evolved their own spoken language. This, however, has not happened. We will also have to wait for new studies that illuminate this still obscure aspect of the evolution of human speech.

Jorge Laborda (08/27/2022)

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