Analysis of ear bones from fossilised skulls at least 350,000 years old has shown that their hearing was attuned to pick up the same frequencies as those used in modern human speech.

The findings, by a team led by Ingacio Martínez, of the University of Alcalá in Spain, suggest that early human beings’ capacity for a simple form of speech had probably evolved by about 500,000 years ago. While complex spoken language of the sort we would recognise today did not emerge until much later, the hominids living half a million years ago had probably developed a pattern of intricate vocalisations and calls that was significantly different to those of other animals.

In the study, Dr Martínez’s team examined the hammer, anvil and stirrup bones in the ears of Homo heidelbergensis fossils found at Sima de los Huesos, in the Sierra de Atapuerca in Spain.

Homo heidelbergensis, also known as Boxgrove Man, after a habitation site in Sussex, is not a direct ancestor of modern Homo sapiens but lived widely throughout Europe and is thought to be a progenitor of another human cousin, Neanderthal man.

The researchers used the arrangement, size and shape of the ear bones, which are used to turn sounds into electrical signals of the brain, to construct a model of the frequencies that H. heidelbergensis was best adapted to hear. The results, details of which are published today in the journal Proceedings of the National Academy of Sciences, indicate that the hominids’ ears were much more similar to our own than to those of chimpanzees.

This offers strong support to the theory that H. heidelbergensis made intelligible vocalisations that could be regarded as an early form of speech. The need to listen to and understand such sounds would have driven the evolution of ears that were well equipped to pick them up.

As H. heidelbergensis and Neanderthal man lie on a slightly different branch of the human family tree to Homo sapiens, the similarity between the ears suggests this quality was inherited from a common ancestor that lived perhaps 500,000 years ago.

Modern human hearing is noticeably different from that of chimpanzees and other apes in that it is particularly good at discerning sounds at frequencies between 2 and 4 kilohertz (kHz), the range that covers normal speech.

While chimpanzees can hear sounds in this range, their ability to do so is limited and their ears are tuned particularly to two acoustic peaks, at 1kHz and 8kHz. The H. heidelbergensis ears, like those of modern human beings, were good at frequencies around 1kHz, but also in the range 2 to 4kHz. “Our results show that the skeletal anatomy in these hominids is compatible with a human-like pattern of sound transmission through the outer and middle ear at frequencies up to 5kHz, suggesting that they had auditory capacities similar to those of living humans in this frequency range,” Dr Martínez said. This indicated a potential for rudimentary language. The findings support a hypothesis advanced recently by Robin Dunbar, Professor of Evolutionary Psychology at Liverpool University, that hominids became capable of a rudimentary form of speech about 500,000 years ago.

In his book The Human Story, Professor Dunbar argued that changes in the anatomy of the nerve that controls the tongue, and in the vertebrae that allow breath control, occurred at about this date. These changes would have been essential to the development of vocalisations that went on to become speech.

“I’m happy to see these results, as they add another layer of anatomical evidence that complex vocalisations . . . may have evolved at this time,” he said yesterday.

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