It seems another link has been found between humans and chimpanzees. Two million-year-old fossils indicate that early humans had a hearing pattern that resembles that of chimpanzees.

Using hominin fossils excavated from two sites known as Sterkfontein and Swartkrans in South Africa, researchers reconstructed an aspect of sensory perception to study the internal anatomy of the ear. The two million-year-old early hominin species Australopithecus africanus and Paranthropus robustus were used for this study, according to a news relase.

"We know that the hearing patterns, or audiograms, in chimpanzees and humans are distinct because their hearing abilities have been measured in the laboratory in living subjects," Rolf Quam, assistant professor of anthropology at Binghamton University, said in the release. "So we were interested in finding out when this human-like hearing pattern first emerged during our evolutionary history."

Compared to other primates, including chimpanzees, humans have a better hearing ability across a wider range of frequencies, generally between 1.0-6.0 kHz. Basically, this range includes much of spoken language. Quam and his colleagues have previously studied hearing abilities of hominin individuals from a fossil site in Spain. These fossils were dated to be about 430,000 years old and represent ancestors of Neanderthals that had hearing abilities almost identical to living humans, the release noted. 

However, the most recent older fossils examined from South Africa represent hearing abilities more similar to chimpanzees. The only difference found was that the human's maxium hearing sensitivity was shifted towards a slightly higher frequency. This means that they could hear better and within a frequency range of 1.0-3.0 kHz.

Based on their diet, the hominin fossils indicate that the species lived in the savanna. This short-range auditory pattern would have been favorable for people living in more open environments such as this, where sound waves don't travel as far, the researchers noted. While the researchers don't believe hominins had a specified language, they do argue that these hearing patterns suggest a short-range communication of sorts. 

"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," Quam said in a statement

A video explaining their findings can be found online. Their study was recently published in the journal Science Advances

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