Using digital enhancements of skull fragments from five prehistoric individuals dating to more than 350,000 years ago, anthropologists argue that these human ancestors probably had hearing similar to that of people today.
Since the ears of social mammals are typically designed to perceive sounds made by fellow species members, the humanlike hearing of these ancient folk probably was accompanied by speech, contend Ignacio Martínez of the University of Alcalá in Spain, and his colleagues in an upcoming Proceedings of the National Academy of Sciences.
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“We think that these [Stone Age] people had the vocal-tract features necessary for speaking, and we’ll try to show it in future investigations,” Martínez says.
Until now, anthropologists had focused on the question of whether full-fledged speech emerged solely in Homo sapiens or whether it also appeared in Neandertals. It’s generally thought that H. sapiens arose around 200,000 years ago, while Neandertals lived from about 130,000 to 26,000 years ago.
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Hearing comparable to that of people may have evolved in the last common ancestor of Neandertals and H. sapiens, Martínez and his colleagues propose. That ancestor lived at least 500,000 years ago.
For their study, the researchers digitally enhanced a set of fossils from a Spanish site called Sima de los Huesos. The fossils derive from Homo heidelbergensis, a species regarded by Martínez’s team as ancestral to Neandertals but not to H. sapiens.
The researchers used a computerized tomography scanner to measure preserved ear structures on three skulls and two cranial pieces. Using anatomical data from living people to model soft tissue surrounding ear bones, they then assembled three-dimensional models of the prehistoric ears.
The scientists generated a comparable ear model for a living chimpanzee and, to establish anatomical extremes, they created ear structures of two theoretical creatures—a chimp with humanlike ears and a person with chimplike ears.
Finally, the investigators built an electrical circuit that they used to calculate the acoustic frequency of sounds transmitted through each ear model.
Reconstructed ears of the Spanish fossils and of the modeled human with chimplike ears could handle virtually the same range of sounds as do the ears of living people. A different acoustic signature appeared in the living chimp and the model of a chimp with humanlike ears.
These results provide a “convincing argument” that human ancestors evolved distinctive, speech-related hearing capacities by 350,000 years ago, remarks anthropologist Lynne Schepartz of the University of Cincinnati. This scenario fits with evidence of symbolic thought early in the Stone Age (SN: 5/22/04, p. 328: Available to subscribers at Humanity’s Strange Face), she says.
The evolutionary origins of language remain murky, cautions anatomist Jeffrey T. Laitman of Mount Sinai School of Medicine in New York City. Earlier studies reported marked differences between both the ear bones and reconstructed vocal tracts of Neandertals and Stone Age people, Laitman notes. Therefore, he says, it’s unclear why Neandertals’ ancestors would have had ears that worked just like those of people. He also notes that a vocal tract capable of speech as we know it may have evolved after humanlike ears did.