Reconstructed for the first time the hearing of the first hominids

It has been made with three dimensional models of the ear cavities by an international team with the participation of one researcher from IPHES. The study concludes that early hominids had a hearing similar to chimpanzees, but with differences that already closer to modern human. The impact of the previous study about the acoustic capabilities of the preneandertals at Atapuerca has allowed the realization of this research in  Australopithecus and Paranthropus.

In human evolution there are still many open questions about how the different traits that characterize Homo sapiens have emerged. One is our hearing capabilities that are close linked to speech. Scientists strive to know when our capabilities for hearing have evolved, how kind and how it was developed. Now, one research published in the journal Science Advances in its issue of Friday 25 September, brings some light on this process.

The study concluded that early hominids had a hearing similar to chimpanzees, but with slight differences that already closer to modern human. The research was conducted by an international team which has participated Carlos Lorenzo, a researcher IPHES (Catalan Institute of Human Paleo-Ecology and Social Evolution) and professor at the URV (Rovira i Virgili University of Tarragona).

The study focuses on fossils belonging to two different hominids (bipedal primates) that are predecessors of the genus Homo: Australopithecus and Paranthropus, genera that lived between 4-2 million years ago and 2.5-1 million years ago, respectively.

3D reconstruction from fossils of Australopithecus africanus and Paranthropus robustus found in South Africa, specifically at Sterkfontein and Swartkrans, dated between 3 and 2 million years ago, has allowed us to analyze the internal anatomy of the ear. It has been observed that those species had auditory capacities similar to those of chimpanzees, but with slight differences that are closer to humans. "The first hominids could use vocalization systems similar to chimps, but does not seem to have abilities to hear an articulated language as complex as that of modern humans", says Carlos Lorenzo.

Humans are different from most other primates, including chimpanzees, having better acoustic capabilities in a frequency range generally between 1.0 to 8.0 kHz. Within this frequency range, covering many of the sounds emitted during the spoken language, chimpanzees and most other primates have lower sensitivity compared to humans. These capabilities are known through laboratory studies that allow to obtain audiograms from chimpanzees and humans.

The three-dimensional reconstructions that have been carried out by the IPHES researcher were made from CT scans of fossils. "With these 3D models we can infer if they have the same sensibility in the hearing frequencies that modern humans use when we speak", said Carlos Lorenzo.

This research project, about the auditory abilities of our ancestors, began in 2004 with the study of the auditory capacities of the preneandertals found in the Sima de los Huesos (Atapuerca, Burgos). "Thanks to the consolidation of the results obtained and the prestige of the Atapuerca research team we have now been able to study the South African fossils of Australopithecus and Paranthropus", observes Carlos Lorenzo who has been working at Atapuerca during the last 25 years.

Citation: Quam, R., Martínez, I., Rosa, M., Bonmatí, A., Lorenzo, C., de Ruiter, D.J., Moggi-Cecchi, J., Conde Valverde, M., Jarabo, P., Menter, C.G., Thackeray, J.F. & Arsuaga, J.L. (2015). "Early hominin auditory capacities". Science Advances, 25 September: 1-12.