2 million-years-old fossils reveal what our ancestors` hearing was like

Washington DC: Research into human fossils, dating back to approximately two million years ago, has revealed what our ancestors` hearing was like.

Rolf Quam of Binghamton University led an international research team in reconstructing 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, but with some slight differences in the direction of humans.

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.

People 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, said Quam, adding that so they were interested in finding out when this human-like hearing pattern first emerged during our evolutionary history.

In the South African fossils, the region of maximum hearing sensitivity was shifted towards slightly higher frequencies compared with chimpanzees, and 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 favorable 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 favored on the savanna.

The study is published in the journal Science Advances.