New York: Early humans who lived around two million years ago had hearing abilities similar to chimpanzees but with some slight differences in the direction of modern humans, new research that looked into ancient human fossils has revealed.
Humans are distinct from most other primates, including chimpanzees, in having better hearing across a wider range of frequencies, generally between 1.0-6.0 kHz.
Within this same frequency range, which encompasses many of the sounds emitted during spoken language, chimpanzees and most other primates lose sensitivity compared to humans.
“We know that the hearing patterns in chimpanzees and humans are distinct because their hearing abilities have been measured in the laboratory in living subjects,” said Rolf Quam, assistant professor of anthropology at Binghamton University who led an international research team.
They were interested in finding out when this human-like hearing pattern first emerged during our evolutionary history.
Quam and the team reconstructed an aspect of sensory perception in several fossil hominin individuals from the sites of Sterkfontein and Swartkrans in South Africa.
The study relied on the use of CT scans and virtual computer reconstructions to study the internal anatomy of the ear.
The results suggest that the early hominin species - Australopithecus africanus and Paranthropus robustus - both of which lived around 2 million years ago - had hearing abilities similar to a chimpanzee.
How do these results compare with the discovery of a new hominin species, Homo naledi, announced just two weeks ago from a different site in South Africa?
"It would be really interesting to study the hearing pattern in this new species. Stay tuned,” Quam added.
In the South African fossils, the region of maximum hearing sensitivity was shifted towards slightly higher frequencies compared with chimpanzees.
The early hominins showed better hearing than either chimpanzees or humans from about 1.0-3.0 kHz.
It turns out that this auditory pattern may have been particularly favourable for living on the savanna.
In more open environments, sound waves don't travel as far as in the rainforest canopy, so short range communication is favoured on the savanna.
“We know these species regularly occupied the savanna since their diet included up to 50 percent of resources found in open environments,” Quam noted.
The researchers argue that this combination of auditory features may have favoured short-range communication in open environments.
Does this mean these early humans had language?
"No," said Quam. “We are not arguing that. They certainly could communicate vocally. All primates do, but we're not saying they had fully developed human language, which implies a symbolic content,” he pointed out.
“We feel our research line does have considerable potential to provide new insights into when the human hearing pattern emerged and, by extension, when we developed language," the authors concluded.
The study was published in the journal Science Advances.