Early humans heard sounds differently than we do today, according to new research that provides intriguing clues on the environments our ancestors were living in, and how prehistoric humans communicated with each other.
A key finding of the study, published in the journal Science Advances, is that our ancestors living in South Africa around 2 million years ago were extremely sensitive to close-range sounds, hearing them more keenly than both our species and chimpanzees do now.
"We concluded that Australopithecus africanus and Paranthropus robustus had a heightened sensitivity to sound between 1.0-3.0 kHz compared with both chimpanzees and humans," lead author Rolf Quam, an assistant professor of anthropology at Binghamton University, told Discovery News.
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He added that these early humans "were capable of hearing softer sounds" than our species and chimps can.
Quam and colleagues made the determination after reconstructing the internal anatomy of the ears of the two prehistoric humans. To do so, the researchers used CT scans and virtual computer reconstructions based on fossils. The particular human species were selected for the study because their remains include preserved ear bones.
The sensitivity to short-range sounds likely would have facilitated up close communication in an open habitat. Prior research on the tooth enamel of the prehistoric humans found evidence for consumption of foods found in both forests and savannahs, so our South African ancestors must have divided their time between these two environments.
Retreating to the forest might have been necessary, since humans were on the menu at the time for a wide range of large predators, such as leopards, lions and hyenas.
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In terms of how the prehistoric humans would have been communicating with each other, there is a general consensus among anthropologists that the small brain size, ape-like cranial anatomy and vocal tract of these individuals would not have given them the capacity for language.
Like other primates, though, they would have been emitting meaningful vowel-based calls. Quam and his team propose also propose that they could have used what are known as "voiceless consonants."
"These are consonants that are produced solely by air flowing through the lips, teeth and tongue, such as the sounds in English associated with the letters "t," "k," "f" and "s," Quam explained. "These are considered 'voiceless consonants' because the vocal chords do not move when they are produced."