Could Neandertals have chatted about the weather or the mammoth that got away? Last year, scientists at Duke University proposed that these heavyset hominids, who vanished about 35,000 years ago, might have been able to talk like modern humans, based on the large size of a pair of bony passages that channeled nerves to their tongues. But a new study suggests that the size of so-called hypoglossal canals says little, if anything, about speech capability.
David DeGusta, a graduate student in the Laboratory for Human Evolutionary Studies at the University of California, Berkeley, and colleagues did cross-section measurements of the hypoglossal canals in skulls of 75 nonhuman primates, four extinct hominids called australopithecines, and 104 modern humans.
They found that canal size varied widely in the humans, from 4.4 to 36.5 mm2. When the researchers measured the canals of the 3.2-million-year-old australopithecines, a hominid to which few anthropologists would attribute the gift of speech, they found that one had an area of 17 mm2, decidedly above the average for modern humans. The nonhuman primates also undermined the theory: Canals in 40 of these species were within the human range "both absolutely and after correction for oral cavity size," the authors report in the 19 February Proceedings of the National Academy of Sciences. "Despite all the sound and fury," says DeGusta, "the size of the hypoglossal canal signifies nothing."
The Duke team demurs. DeGusta's analysis "amounts to saying" that so long as there is any overlap between species, there's nothing significant about the mean differences, says Duke anthropologist Richard Kay. He draws an analogy with brain size comparisons. Human cranial capacity ranges from 800 to 1250 cubic centimeters, a range that encompasses the primitive Homo erectus. "But no one argues that there's not a significant difference" in mental ability between the two hominids, whose average brain size was very different.
Anatomist Jeffrey Laitman of Mount Sinai Medical Center in New York says he finds the hypoglossal canal theory "tantalizing," but that the new study raises a cautionary note, highlighting risks of drawing conclusions from "a relatively limited sample [and] a relatively limited part of the body."