How Did The Human Ancestors Hear? 2-Million-Year-Old Fossil Reveals Details

Human ancestors that lived about 2 million years ago had hearing abilities similar to those of chimpanzees, but their ears had some slight differences that made their hearing more human-like, a new study finds.

The finding — based on virtual models of early hominin (the ancestors of modern humans), modern chimp and human ears — suggests that, unlike chimps, these now-extinct human ancestors had a remarkable sensitivity to high-frequency sounds. These types of sounds are used in modern-day human communication — including the sounds made by the letters “K,” “T,” “Th,” “F” and “S” — and could have helped hominins detect short-range vocal communication during their time, the researchers said.

The authors suggested that the ability to hear short-range communication would have favored the open savanna, adding evidence that early hominins once lived there.

“[The hominins’] hearing pattern is similar to a chimpanzee[‘s], but slightly different,” said lead researcher Rolf Quam, an assistant professor of biological anthropology at Binghamton University in New York. “That difference seems to be in the direction of humans.”

Previous studies have examined the differences between human and chimp ear anatomy and auditory abilities, but less is known about the hearing skills of early hominins, Quam said.

To learn more, the researchers traveled to South Africa, where they took computerized tomography (CT) scans of early hominins, including the remains of two Australopithecus africanus individuals and one Paranthropus robustus individual. They also used CT scans from 10 modern humans (Homo sapiens) and 11 chimps (Pan troglodytes) — modern humans’ closest living relatives.

The researchers used these scans to make virtual reconstructions of the ears that included soft tissue. However, their models included some guesswork.

Other scientists have measured the “fleshy dimensions” of modern human ears (such as cartilage and skin), largely to gain a better understanding of hearing and to develop better hearing aids, Quam said. But nobody has extensively measured the fleshy parts of chimp ears, and unsurprisingly, these parts have long since decayed in the hominin samples, he said.

So, the researchers used the human data for all of the species. In the end, they based about half of each model on the species’ skeletons and half on the human data, Quam said.

Unexpectedly, the chimpanzee model produced accurate results, he said.

“So the model works for chimpanzees — and, therefore, [for] any possible human ancestor, it should also provide reliable results,” Quam told Live Science.

Credit: LiveScience