By JOHN NOBLE WILFORD
While scientists agree that speech is probably the most important behavioral attribute that distinguishes human beings from other animals, they have been at a loss to determine when and how that transforming evolutionary step occurred.
They have probed the human brain and compared it with casts of the braincase from ancient fossil skulls. They have compared bones and muscle attachment points in the throats of humans, apes and ancestral human skeletons. Archeologists have examined patterns in early stone tools for clues to when humans might have developed the creativity and the self-awareness usually associated with communication skills like speech.
All they had been able to agree on is that the earliest unambiguous evidence for human speech is found in the cave art and other artifacts, particularly in Europe and Africa, that began appearing some 40,000 years ago.
Now scientists at Duke University have explored a new avenue of fossil anatomy and found surprising evidence suggesting that vocal capabilities like those of modern humans may have evolved among species of the Homo line more than 400,000 years ago. By then, their research shows, human ancestors may have had a full modern complement of the nerves leading to the muscles of the tongue and so could have been capable of forming speech sounds.
The new findings, moreover, indicate that the Neanderthals, relatives of modern humans, could have had the same gift for speech. Their extinction about 30,000 years ago has often been attributed in part to speech deficiencies, restricting their ability for cultural innovation.
In a report being published Tuesday in The Proceedings of the National Academy of Sciences, the Duke anthropologists say that if their interpretation of the tongue nerves is correct, "then humanlike speech capabilities may have evolved much earlier than has been inferred from the archeological evidence for the antiquity of symbolic thought."
The research was conducted by Dr. Richard F. Kay and Dr. Matt Cartmill at the Duke Medical Center in Durham, N.C., with the assistance of a former student, Michelle Balow. The results were also described earlier this month in Salt Lake City at a meeting of the American Association of Physical Anthropology.
"This is evidence for the proposition that Neanderthals could talk," Cartmill said in a telephone interview on Sunday. "Did they sound like modern humans? I don't know."
Anthropologists familiar with the research said the findings were interesting and exciting. Some were reserving judgment, but not Dr. Erik Trinkaus, an anthropologist at Washington University in St. Louis, who specializes in Neanderthal studies.
"I think it's not only a reasonable conclusion," he said, "but one long overdue."
Trinkaus said previous research had been based on deficient anatomical reconstructions, none of which adequately took into account the neurological aspects for controlling the vocal track to allow for speech. As for the possibility of speech by archaic Homo sapiens 400,000 years ago, even before Neanderthals, he said this was consistent with a significant enlargement of brain size in that period, the appearance of a more complex tool technology and migrations into colder climates, where life probably depended on greater planning that could be related to advances in communications skills.
On the other side, Dr. Philip Lieberman of Brown University, an authority on early language, has argued that the Neanderthal throat would not have been well suited for the production of the vowels a, i and u. But Trinkaus contended that a species would not have needed modern English's range of vowels to have speech and language.
Even the discovery in Israel a decade ago of a Neanderthal skeleton with a large hyoid bone, which is in the throat and associated with speech, had not settled the issue of Neanderthal speech. Scientists had said there was still insufficient fossil evidence to enable an understanding of how the large hyoid bone might have influenced the production of vocalizations.
Cartmill himself cautioned that the new evidence for earlier human speech "is suggestive but, in the present state of our knowledge, it is not proof."
Other scientists noted that other, independent evolutionary developments, including a lengthened larynx, enlarged prefrontal brain lobes and some reconfigurations of the brain, would have been critical to the emergence of speech. The size of the brain of Neanderthals was well within the range of that of modern humans.
The Duke scientists directed their research at the hypoglossal canal in all primates. It is a hole at the bottom of the skull in the back, where the spinal cord connects to the brain. Through the canal run nerve fibers from the brain to the muscles of the tongue.
It occurred to the scientists that the size of the hypoglossal canal might serve as an index of the vocal abilities of modern and early humans. The wider the canal, they assumed, the more nerve fibers there could be to control the tongue muscles. And the more nerves, they further suggested, the finer control the species could have over its tongue for the purpose of making speech sounds.
On the basis of comparative measurements of hypoglossal canals of modern humans,
apes and several human ancestor fossils, the researchers concluded that the canals
of modern humans are almost twice as large as those of modern apes -- the chimpanzee
and the gorilla -- which are incapable of speech. They also found that the canal
size of austrolopithecines, earlier human relatives
that died out about one million years ago, did not differ significantly from that of chimpanzees.
The results, the scientists reported, "suggest minimum and maximum dates for the appearance of the modern human pattern of tongue motor innervation and speech abilities."
To narrow the range, the scientists examined skeletons of Neanderthals and also of species of the Homo genus that lived as much as 400,000 years ago. These included Kabwe specimens from Africa and Swanscombe fossils from Europe. Their hypoglossal canals fell within the range of those of modern Homo sapiens.
"By the time we get to the Kabwe, about 400,000 years ago, you get a canal that's
a modern size," Cartmill said. "And that's true of all later Homo species, including
Tuesday, April 28, 1998
Copyright 1998 The New York Times
Maintained by Francis F. Steen, Communication Studies, University of California Los Angeles