Our Neanderthal cousins had the capacity to both hear and produce the speech sounds of modern humans, a new study has found.
Based on a detailed analysis and digital reconstruction of the structure of the bones in their skulls, the study settles one aspect of a decades-long debate over the linguistic capabilities of Neanderthals.
"This is one of the most important studies I have been involved in during my career," said palaeoanthropologist Rolf Quam of Binghamton University.
"The results are solid and clearly show the Neanderthals had the capacity to perceive and produce human speech. This is one of the very few current, ongoing research lines relying on fossil evidence to study the evolution of language, a notoriously tricky subject in anthropology."
The notion that Neanderthals (Homo neanderthalis) were much more primitive than modern humans (Homo sapiens) is outdated, and in recent years a growing body of evidence demonstrates that they were much more intelligent than we once assumed. They developed technology, crafted tools, created art and held funerals for their dead.
Whether they actually spoke with each other, however, has remained a mystery. Their complex behaviors seem to suggest that they would have had to be able to communicate, but some scientists have contended that only modern humans have ever had the mental capacity for complex linguistic processes.
Whether that's the case is going to be very difficult to prove one way or another, but the first step would be to determine if Neanderthals could produce and perceive sounds in the optimal range for speech-based communication.
3D model of modern human (left) and Neanderthal (right) ear anatomy. (Mercedes Conde-Valverde)
So, using a bunch of really old bones, this is what a team led by palaeoanthropologist Mercedes Conde-Valverde of the University of Alcalá in Spain set out to do.
They took high-resolution CT scans of the skulls of five Neanderthals to create virtual 3D models of the ear structures. They also modeled the ear structures in Homo sapiens, and a much older fossil - the skull of a Sima de los Huesos hominin, also known as the Sima hominin, the ancestor of Neanderthals, dating back to around 430,000 years ago.
A model of the hearing capacity of these structures from the field of auditory bioengineering was then employed to understand frequency range to which the ears were most sensitive, also known as the occupied bandwidth. For modern humans, the occupied bandwidth is the human vocal range.
The team found that Neanderthals had better hearing in the 4 to 5 kilohertz range than the Sima ancestor, and that the Neanderthal occupied bandwidth was closer to that of modern humans than that of the Sima hominin. This optimization strongly suggests that Neanderthals needed to hear each other's voices.
The occupied bandwidth of modern humans (blue), Neanderthals (grey) and the Sima hominin (red). (Conde-Valverde et al., Nat. Ecol. Evol., 2021)
"This really is the key," Conde-Valverde said. "The presence of similar hearing abilities, particularly the bandwidth, demonstrates that the Neanderthals possessed a communication system that was as complex and efficient as modern human speech."
Interestingly, the occupied bandwidth of Neanderthals extended into frequencies above 3 kilohertz that are primarily involved in consonant production. This, the team noted, would distinguish Neanderthal vocalizations from the vowel-based vocalizations of non-human primates and other mammals.
"Most previous studies of Neanderthal speech capacities focused on their ability to produce the main vowels in English spoken language," Quam said.
"However, we feel this emphasis is misplaced, since the use of consonants is a way to include more information in the vocal signal and it also separates human speech and language from the communication patterns in nearly all other primates. The fact that our study picked up on this is a really interesting aspect of the research and is a novel suggestion regarding the linguistic capacities in our fossil ancestors."
Having the anatomy capable of producing and hearing speech doesn't necessarily mean that Neanderthals had the cognitive ability to do so, the researchers cautioned. But, they point out, we have no evidence that the Sima hominins exhibited the complex symbolic behavior, such as funerals and art, that we've found associated with Neanderthals.
This difference in behavior parallels the difference in hearing capacity between Neanderthals and Sima hominins, which, the researchers say, suggests a coevolution of complex behaviors and the ability to communicate vocally.
"Our results," they wrote in their paper, "together with recent discoveries indicating symbolic behaviors in Neanderthals, reinforce the idea that they possessed a type of human language, one that was very different in its complexity and efficiency from any other oral communication system used by non-human organisms on the planet."
The research has been published in Nature Ecology & Evolution.