Thousands of years ago, an early human ventured deep within a cave, where sound reverberated off the walls. Perhaps by either speaking or walking, they generated the sound reminiscent of a hoof. To represent this sound, they drew a hoofed animal.
They would have been using the same skills that prompted the earlier development of language, theorizes a new study.
Published in the journal Frontiers in Psychology, the paper suggests cave art was made in acoustic "hot spots" because early humans were converting acoustic sounds into drawings.
"Our research suggests that the cognitive mechanisms necessary for the development of cave and rock art are likely to be analogous to those employed in the expression of the symbolic thinking required for language," says Cora Lesure, a linguist at MIT and one of the study's authors.
Essentially, Lesure says, the cognitive functions needed to transfer acoustic sounds to pictures are the same cognitive functions needed in language.
"In this sense, cave and rock [art] would represent a modality of linguistic expression," says Lesure.
Whether or not this art would have shaped how language further developed is speculative.
Modern Homo sapiens developed around 200,000 years ago, and the study's researchers note that language is thought to have evolved around 100,000 years ago. The oldest forms of cave art found date back roughly 40,000 years.
"We could speculate that human language emerged as an abstract symbolic system, while its expression—in the form of cave and rock art, or any other modality—may have occurred very late," says Vitor Nobrega, a linguist at the University of São Paulo and author on the study.
In particular, their study looked at Blombos Cave in South Africa, which contains geometric engravings.
The markings, they suggest, are external representations of internalized thought.
It's a theory contrary to a belief among archaeologists and anthropologists that language doesn't fossilize, says Lesure.
Finding evidence of when and how humans began speaking is difficult. Anthropologists can study ancient skulls to see when certain lobes in the brain responsible for language began to take shape, but it's difficult say exactly when humans began speaking because it was likely spoken orally long before it was written.
Archaeologists have theorized early evidence of language can be found in objects like beads or altered bones that may have been used for anything from counting days to taking attendance.
"It's very likely that archaeoacoustics explains the placement of some art in some caves some of the time," says April Nowell, an archaeologist from the University of Victoria who studies the origins of art.
But saying that the cave acoustics inspired visual representations is a stretch, she says.
She notes that cave art has also been made within a cave's acoustic "hot spot," where ceremony and storytelling may have also taken place, suggesting the art was less a form of communication and more a form of decoration. Nowell notes that some of the common imagery seen inside caves noted in the study, like horses or other hooved animals, is imagery found on objects outside caves.
"The acoustic factor is an important one to consider," Nowell adds, "but I don’t think it was the only explanation for why people made marks in the places they did."
Lesure adds that their study doesn't outright say the cave art they looked at equates to language, only that the same cognitive functions may have been present.
"There's no doubt that the images were of symbolic value," says Genevieve von Petzinger, an anthropologist and National Geographic explorer.
She echoed Nowell's sentiments that it's not explicitly clear if the drawings were used as a form of communication, but notes: "It certainly wouldn't be beyond the realm of possibility that the sounds [in the cave] would have enhanced what they were doing."
Archaeologists are still searching for some of the first physical evidence of linguistic capabilities, and von Petzinger adds, "We're still searching for that holy grail."