Ancient humans had hearing like chimps

By TONY WU Senior Staff Writer

Imagine the difficulty of living a life without sound. As one of the five fundamental senses, hearing is a crucial part of everyday life.

However, scientists are uncertain about the process through which humans developed our current hearing patterns. Recent research on human fossils indicate that two million years ago, human and chimpanzee hearing patterns closely resembled one another. It was also at this time that differences in their respective hearing patterns began to emerge.

In humans, our hearing range is between 20 hertz (Hz) and 20 kilohertz (kHz), but we can also perceive frequencies between one and six kHz better than other primates. It is important to note that the range of one to six kHz includes many sounds utilized in spoken languages.

These auditory differences between humans and primates were obtained in laboratory experiments, but until the analysis of fossils found in Spain and South Africa, scientists did not know how they evolved.

The researchers looked at fossils of human ancestors, which were estimated to be around 430,000 years old and which were found in northern Spain. These remains possess hearing patterns that are almost identical to the modern human pattern.

The fossils excavated from Spain came from the Sima de los Huesos (Pit of Bones). Scientists think that they represent ancestors of some of the later Neanderthals that lived.

On the other hand, when they examined South African fossils that are around two million years old they found a hearing pattern that is closer to chimpanzees.

The two species that scientists looked at in South Africa were Australopithecus africanus and Paranthropus robustus. Both species lived around the same time. The fossils were dug up at the sites of Sterkfontein and Swartkrans in South Africa.

The scientists used CT scans and computer reconstructions of the inside of the ears of these fossils in order to determine what the hearing range of these early hominids may have been.

They noted that the maximum hearing sensitivity in these older remains was shifted towards a higher frequency when compared to that of chimpanzees. In addition, these hominins, the human branch of primates, have better hearing at the range of one to three kHz.

These discoveries had several implications. The researchers concluded that the differences in auditory patterns may develop from a life in the savanna. In these wide, open environments, sound waves dissipate quickly, traveling much shorter distances than in the rainforest.

As a result, short range communications through high frequencies is preferred. This is further supported by evidence that early hominins scavenged up to 50 percent of their diet from the savanna.

Secondly, these communications indicate that early hominids may have used vocal communications. However, the scientists clarified that these vocal communications were not a developed human language. All primates communicate, but a fully developed language would meant the inclusion of symbolic content. In fact, evidence suggests that small brain size, coupled with differences in vocal tracts, indicate that early hominins did not have the ability to understand language.

“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,” Rolf Quam, an assistant professor at Binghamton University and the lead author of the study, said in a press release.

Quam is also hopeful that someone will be able to study the hearing pattern of the newly-found human ancestor, Homo naledi. Fossils of this hominin species were found recently in South Africa. This research could spark new discoveries. “It would be really interesting to study the hearing pattern in this new species,” said Quam. “Stay tuned.”