A combination of ape-like and human-like features in the bones inside the ear of two ancient hominin species suggests they may have begun to evolve what earlier so-called austrolopiths lacked -- a sensitivity to the midrange frequencies that modern humans use for speech, they said.
The tiny bones in the middle ear of Australopithecus africanus and Paranthropus robustus showed modern human features that may be related to the evolution of language, palaeoanthropologist Rolf Quam of Binghamton University in New York said.
The similarity between the two species -- Australopithecu from 3.3 to 2.1 million years ago and Paranthropus from 1.8 million years ago -- points to a "deep and ancient origin" of this feature, Quam says.
"This could be like bipedalism: a defining characteristic of hominins," he said in a university release Tuesday.
Quam and his colleagues say they plan to use CT scans of the fossils and 3D virtual reconstruction of the ear anatomy to work out more precisely what the world sounded like to our distant ancestors.