While it is true that all animals communicate in some way, the complex spoken language It is one of the most human characteristics. We are able to modulate and create oscillations with our vocal chords much more stable than other primates. That’s because evolution has caused us to lose the membranes of these cords and air sacs, which are common to all non-human primates, according to a study published in the journal Science.
“In non-human species, vocalizations with the so-called ‘non-linear vocal phenomena’ (NLP, for its acronym in English) sound harsh, and it has been hypothesized that they reduce the perceived pitch of the voice, exaggerating the speaker’s body size for the listener. These NLPs have a prominent role in competitive interactions”, he tells SINC Harold Gouzoulesauthor of a perspective article on this study and scientist at the Faculty of Arts and Sciences at Emory University (USA).
O human vocalization it is based on the same acoustic and physiological principles as other terrestrial vertebrates – air in the lungs drives the oscillation of the vocal cords in the larynx – but the way people speak has several distinct characteristics. The oscillations of our vocal cords are much more stable and they lack the jagged oscillations and abrupt frequency transitions that are common in most other mammals.
“Although the vocal repertoires of many non-human primate species include some clear, harmonically structured calls, their vocalizations often branch into sub-harmonics at higher intensities,” notes Gouzoules.
These attributes, combined with increased neural control, allow humans to create the wide range of sounds that speech and spoken language allow. However, identifying the evolutionary adaptations that gave rise to human speech has been a challenge.
Unfortunately, we cannot say when this feature was lost, as it never fossilizes, nor does it leave traces in fossilized bones. We expect genetic analyzes to be carried out in the future
“Unfortunately, we cannot say when this feature was lost, as it never fossilizes, nor does it leave traces in fossilized bones. We hope that in the future genetic analyzes will be carried out”, he explains to SINC Takeshi Nishimurabiologist at Kyoto University (Japan) and lead author of the study.
On why other primates have not lost this membrane in the vocal cords, Gouzoules points out: “Perhaps it is because the selective pressure to do so would only occur before other prerequisites for language (e.g. cortical neuronal control of the vocal cords) . vocalizations), which most non-human species lack.
An icy upright and vocalizing. / Kate Grounds
Compare primate larynges
Nishimura’s team used footage from MRI and computed tomography (which uses a special X-ray machine and creates images) to examine the larynx of 29 genera and 44 species of primates. They found that all non-human taxa had a vocal membrane which is totally absent in us.
After observing the activity of this membrane during primate vocalizations, they developed anatomical and phonic models to compare the acoustic effects of its vibration.
“Our computer simulation analyzes confirmed that the vocal membrane contributes to the phonation (the vibrations of the vocal membranes and vocal cords) are ‘economical’. This means that they begin to vibrate due to a lower pressure of the airflow in the lung, compared to humans who do not have a vocal membrane”, says the Japanese biologist.
Non-human primates are required to make a loud call as a social behavior rather than small talk as in humans.
Thus, the evolutionary loss of this membrane resulted in a simpler larynx and a stable vocal source that allow humans the ability to produce the many harmonic-rich sounds that characterize speech.
“Nonhuman primates are required to make a loud call as a social behavior, rather than small talk as in humans,” concludes Nishimura.
Evolving does not mean being more complex
Evolutionary biology textbooks emphasize that natural selection does not inevitably produce greater complexity. For example, Mexican cave fish no longer have eyes, and there is genetic, developmental, and physiological evidence for adaptive regression of eyes in this species and in other cave animals.
In essence, cavemen represent a ‘use it or lose it’ evolutionary scenario. The interesting thing about the loss of eyes in cave fish is that their eyes no longer had the adaptive function they had before.
“Essentially, cavemen represent a ‘use it or lose it’ evolutionary scenario. The interesting thing about eye loss in cave fish is that their eyes no longer had the adaptive function they had before,” says Gouzoules.
With the loss of vocal cord membranes in humans, presumably there was still some communicative benefit to having this tissue, but it became more adaptable to shrink and eventually eliminate it. The proof is that this contributed to the evolution of language, “which clearly has enormous value”, emphasizes the researcher.
Reference:
Takeshi Nishimura et al. “Evolutionary loss of complexity in human vocal anatomy as adaptation for speech”, Science2022
