At a Loss For Words?
Graduate Students Poke Hole in Theory That Beetle-Browed Neanderthals Could Talk
By Robert Sanders, Public Affairs
Close human relatives known for their protruding brow and squat, heavy bodies, Neanderthals apparently branched off from our early ancestors some 400,000 years ago and disappeared about 30,000 years ago.
The original claim that Neanderthals could use language was made by a team of Duke University researchers based on an analysis of the size of the hypoglossal canal, a hole on either side of the base of the skull that accommodates the nerves innervating the tongue and controlling its movement.
In their April 1998 report in the Proceedings of the National Academy of Sciences, the Duke researchers asserted a correlation between speech and the size of the hole, assuming that larger holes mean larger nerves and more complex tongue function. They then argued that the hypoglossal canal in Neanderthals and early Homo sapiens is close in size to those of modern humans, suggesting that they used language as early as 400,000 years ago.
The Berkeley students refute that assertion in an article in the Feb. 16 issue of PNAS.
"If this hypothesis were right, then humans should have a bigger hypoglossal canal than monkeys, since monkeys don't talk," argued David DeGusta, a graduate student in the Laboratory for Human Evolutionary Studies of the Department of Integrative Biology at Berkeley. "But a lot of monkeys and apes have hypoglossal canals within the size range of humans."
Correcting for mouth size, like the Duke researchers did, the Berkeley group found 15 non-human primate species whose average hypoglossal canal size is larger than the modern human average. For example, relative to mouth size, the average gibbon, an ape, has a hypoglossal canal twice as large as the average modern human.
"More than half of the monkeys we measured have hypoglossal canals that are in the modern human size range, both absolutely and relative to mouth size," he added. "So if you find a Neanderthal with a canal also in the modern human size range, did it have human-like vocal abilities or monkey-like vocal abilities? Based on the hypoglossal canal, you can't say."
After examining skulls from many species of non-human primates, modern humans and million-year-old human ancestors, the authors found no correlation between canal size and language ability, leading them to conclude that the size of the hypoglossal canal simply does not reflect vocal capability or language usage.
According to F. Clark Howell, professor of anthropology and the National Academy of Sciences member who forwarded the paper to the journal, "This paper is a disclaimer. It says we can't use their (the Duke researchers') criterion to suggest language capability. It doesn't work."
The students conclude in their article that "the date of origin for human language and the speech capabilities of Neanderthals remain open questions."
DeGusta was very intrigued by the initial study, authored by Richard F. Kay, Matt Cartmill and Michelle Balow of the Department of Biological Anthropology and Anatomy at Duke University Medical Center.
Upon looking at skulls in the laboratory, however, the correlation between canal size and language didn't seem to hold. So he and co-authors W. Henry Gilbert, also of Berkeley's Department of Integrative Biology, and Scott P. Turner of the campus's Department of Anthropology, spent last summer looking at a slew of modern primate skulls.
They measured the size of the hypoglossal canal in 75 individual skulls representing 32 different species of non-human primate, including Old and New World monkeys, prosimians (lemurs) and the apes -- chimpanzees, gorillas, orangutans and gibbons. Most of the skulls came from the Museum of Vertebrate Zoology.
For comparison they also measured the hypoglossal canal size of 104 modern human skulls from different museum collections. The Duke researchers had studied 48 modern human skulls.
What the Berkeley researchers found was a large overlap between the sizes of the canals in humans and non-human primates. Even when the researchers corrected for the size of the tongue, as indicated by the size of the palate, the overlap remained.
"We found 40 different skulls of non-human primates that had hypoglossal canals both absolutely and relatively within the modern human size range," DeGusta said.
In addition, they found that the two canals in each skull are themselves often different sizes. In one modern human skull, the area of one hole was twice that of the other.
This and two other lines of evidence assembled by the Berkeley researchers argue that "the size of the hypoglossal canal is not a reliable indicator of speech," the authors wrote.