A team of researchers studies how primates perceive verbalizations to understand the evolution of human language | Science

Speech and language are unique abilities of the modern human being. Despite the fact that this ability evolved over millions of years, it is impossible to find traces of the process in the fossil record, as it leaves no tangible traces. However, to unlock the secrets of this mysterious ability, we can re-examine the modes of communication of our closest living relatives.

The fact that these relatives, the hominids, cannot speak makes this mystery even more unfathomable. Some scientists believe that in living primates More clues to the evolution of our language skills can be found than previously thought.

“It has always been thought that, although hominids are our closest living relatives, they are not useful for studying the appearance of language and speech because their verbal behavior is very different from ours”, explains Adriano Lameira, primatologist at the University of Warwick. , UK. “It’s something automatic, the result of a reflex, of a blind instinct.”

In his years of studying orangutans in their natural jungle environment, Lameira discovered that wild orangutans they can verbalize new and varied sounds, and he recently suggested that this depends on local population density. Novelty is essential when an individual needs to stand out, so hominoids living in densely populated areas express their individuality by articulating more distinctive and variable sounds.

tiger print sheets

In Indonesia, Lameira made an experience of moving on all fours in the jungle hidden under a printed tiger skin sheet. Lameira recorded the reactions of jungle hominoids and found that female orangutans carrying a calf remain silent when they identify “a tiger” that remains in their line of sight for two minutes. Once the tiger is gone, they drop alert calls for up to twenty minutes.

From this behavior he deduced that immediate verbalization would have endangered the orangutan calf. “A Sumatran tiger can climb ten meters high on a tree trunk in a second,” says Lameira. “Revealing your location can be very dangerous, especially when you have a newborn baby with you.”

By making a sound when the tiger is gone, the mother alerts the cub to danger and helps it make the appropriate association. The most curious thing about this behavior is that the female orangutan communicates in this way an event that has already happened, and not something that is happening in the current place and time. “It does not correspond at all to what we thought so far,” says Lameira.

This is an indication that orangutans are able to communicate past events, and possibly future events as well. If you possess this ability, endless possibilities open up. exchange of information. “This ability to communicate events that are not occurring at the current place and time may well be a trait shared by our last common ancestor.”

It is possible that other hominoids also possess this capacity, more or less developed. “Even if the communication about the past – or the future – only lasts twenty minutes, it can still pay off,” says Lameira. “Natural selection just takes a little nudge to do its thing and drive progress.” It is possible that hominoids could communicate that on a certain tree grows this or that fruit, although here we are entering the realm of speculation.

He talks about monkeys

In the south of France, Pascal Belin studies macaques and marmosets in captivity to investigate their perception of verbalizations. “The goal of the research is to better understand the evolution of the human brain,” says Belin, a neuroscientist at the University of Aix-Marseille (France). “We studied humans and three other types of primates – marmosets, macaques and baboons – to find differences and similarities between them, especially in terms of oral communication.”

One of the experiments involved teaching three macaques to lie still in an MRI machine so their brains could be scanned while listening to dozens of sounds, including the voices of other macaques.

“The brains of macaques and marmosets, like those of humans, appear to have regions that are particularly sensitive to specific oral sounds, that is, sounds made by individuals of the same species,” Belin explains. MRIs show areas that are activated when macaques hear other macaques, but not when it comes to nature sounds, marmosets or the like. A similar area is activated in our brain when we hear human voices.

If the same area of ​​the brain is activated in macaques and humans when they listen to another member of their species, this indicates that this area related to oral expressions evolved before they took different branches of the evolutionary tree.

Belin’s hypothesis is that the region of the primate brain that is responsible for processing oral information is quite similar to ours and therefore originates from a common ancestor that predates the time when ancient humans such that the standing man They appeared in Africa between two and three million years ago.

“This suggests that the last common ancestor of humans and macaques already had a precursor to this brain area responsible for oral sounds twenty million years ago,” says Belin.

Further experiments involving the surgical implantation of electrodes in macaques are planned to elucidate exactly which neurons are activated when they hear another macaque, but not when they hear other monkeys or other types of noises or of sounds.

The results of marmosets and macaques could even be compared to those of humans who have had this type of electrode implanted for medical reasons, as is the case with some people with epilepsy who do not respond to treatment, who are implanted so that neurosurgeons can see small areas of the brain that may need to be removed.

It would involve asking these people to listen to the same ninety-six sounds as marmosets and macaques while they are being monitored in a hospital, in order to study the brain’s response.

consonant contacts

Not only are the similarities interesting, but so are the differences. Hominids can articulate vowels, as is the case in monkeys, with the larynx. However, only hominins and humans can make consonant sounds, which rely less on the vocal tract and more on the lips.

Orangutans have a rich repertoire of farts and lip-smacking, which they combine with growls and other vowel sounds. “They combine verbal and non-verbal calls, the same way vowels alternate with consonants,” Lameira explains. “We believe that this communion between two different types of calls is very special and powerful, so much so that all languages ​​are based on this consonant followed by a vowel formula.”

As Lameira intuited, this repertoire formed the essential foundation upon which our ancestors began to develop what we know today as human speech and language. These common traits, argues Lameira, allow us to trace the evolutionary path that culminated in human speech and language and to understand the most critical milestones our ancestors took in speaking and evolution. of the brain.

Lameira encourages the scientific community to study gorillas, bonobos, and chimpanzees for similar traits, such as combinations of consonant and vowel sounds, or evidence of communication about recent events. Finding our primate relatives could help us uncover traces of our human ancestors and the origins of modern speech and language.

The research described in this article was financed by European funds.

Article originally published not Skyline, the Journal of Research and Innovation of the European Union. You can read the English version here.

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