Model results for chimpanzees, modern humans, and early hominins from 0.5 to 5.0 kHz. (A) The occupied band is similar in chimpanzees and early hominins, but is shifted toward slightly higher frequencies in the latter. Modern humans show a widened occupied band that is further extended toward higher frequencies. (B) The sound power transmission curves correspond to decibels at the entrance to the cochlea relative to P0 = 10?18 W for an incident plane wave intensity of 10?12 W/m2. The mean value ± 1.0 SD for each frequency position is shown for each group. Points higher along the curve indicate better sound power transmission and heightened auditory sensitivity. Individual results are provided in figs. S5 to S8. (Credit: Rolf Quam, Binghamton University)
Anthropologists from Binghamton University in New York conducted research into the sensory perception of early humans using several two-million-year-old fossil hominins to reveal how the human hearing pattern resembles chimpanzees, but with some slight differences.
Rolf Quam, PhD, assistant professor of anthropology at Binghamton University, led a study that looked at fossils of early humans from the sites of Sterkfontein and Swartkrans in South Africa and utilized CT scans and virtual computer reconstructions to investigate the internal anatomy of the ear. As explained in a study article published in the September 25, 2015 edition of the journal Science Advances, the team’s study results suggest that early hominin species Australopithecus africanus and Paranthropus robustus had better hearing than chimpanzees 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.
“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,” said Quam. “So we were interested in finding out when this human-like hearing pattern first emerged during our evolutionary history.”
Rolf Quam, PhD, Binghamton University
According to an announcement from Binghamton, Quam and colleagues also studied the hearing systems in several fossil hominins from the site of the Sima de los Huesos (Pit of the Bones) in northern Spain. These fossils are about 430,000 years old and are considered to represent ancestors of the later Neanderthals. The researchers found that hearing abilities in the Sima hominins were nearly identical to living humans, while the older South African specimens had a hearing pattern that was much more similar to living chimpanzees.
The researchers report that, 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. The team believes 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.
“We know these species regularly occupied the savanna since their diet included up to 50 percent of resources found in open environments” said Quam. The researchers argue that this combination of auditory features may have favored short-range communication in open environments. However, this does not necessarily mean that early hominins had language.
“They certainly could communicate vocally,” said Quam. “All primates do, but we’re not saying they had fully developed human language, which implies a symbolic content. 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.”
As reported by Binghamton University, the emergence of language is one of the most hotly debated questions in paleoanthropology, the study of human origins, since the capacity for spoken language is often held to be a defining human feature. There is a general consensus among anthropologists that the small brain size and ape-like cranial anatomy and vocal tract in these early hominins indicates they likely did not have the capacity for language.
Quam and his colleagues would be very interested in studying the hearing pattern of the newly discovered hominin species, Homo naledi, that was recently announced.
Watch the YouTube video from Binghamton University of Dr Quam discussing the team’s research here.
Source: Binghamton University
