SCIENCE
05/14/2013 11:15 am ET

Ear Bone Fossils Expected To Yield Key Clues About Human Evolution

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By Michael Balter

Researchers debate when language first evolved, but one thing is sure: Language requires us not only to talk but also to listen. A team of scientists now reports recovering the earliest known complete set of the three tiny middle ear bones—the malleus ("hammer"), incus ("anvil"), and stapes ("stirrup")—in a 2.0-million-year-old skull of Paranthropus robustus, a distant human relative found in South Africa.

ear bones
Ear bones from Paranthropus robustus.

Reporting online today in the Proceedings of the National Academy of Sciences, the researchers found that the malleus of P. robustus, as well one found earlier in the early human relative Australopithecus africanus, is similar to that of modern humans, whereas the two other ear bones most closely resemble existing African and Asian great apes. The team is not entirely sure what this precocious appearance of a human-like malleus means. But since the malleus is attached directly to the eardrum, the researchers suggest that it might be an early sign of the high human sensitivity to middle-range acoustic frequencies between 2 and 4 kilohertz—frequencies critical to spoken language, but which apes and other primates are much less sensitive to.

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