Communications on a National Project
3/16/2004 3:33 PM (This is copyrighted materials that is for scholarly review
only)
Once upon a time, there were
very few human languages and perhaps only one, and if so, all of the 6,000 or
so languages spoken round the world today must be descended from it.
If that family tree of human
language could be reconstructed and its branching points dated, a wonderful new
window would be opened onto the human past.
Yet in the view of many
historical linguists, the chances of drawing up such a tree are virtually nil
and those who suppose otherwise are chasing a tiresome delusion.
Languages change so fast,
the linguists point out, that their genealogies can be traced back only a few
thousand years at best before the signal dissolves completely into noise:
witness how hard Chaucer is to read just 600 years later.
But the linguists' problem
has recently attracted a new group of researchers who are more hopeful of
success. They are biologists who have developed sophisticated mathematical
tools for drawing up family trees of genes and species. Because the same
problems crop up in both gene trees and language trees, the biologists are
confident that their tools will work with languages, too.
The biologists' latest foray
onto the linguists' turf is a reconstruction of the Indo-European family of
languages by Dr. Russell D. Gray, an evolutionary biologist at the University
of Auckland in New Zealand.
The family includes extinct
languages like Hittite of ancient Turkey, and Tokharian, once spoken in Central
Asia, as well as the Indian languages and Iranian in one major branch and all
European languages except Basque in another.
Dr. Gray's results, published
in November in Nature with his colleague Quentin Atkinson, have major
implications, if correct, for archaeology as well as for linguistics. The shape
of his tree is unsurprising — it arranges the Indo-European languages in much
the same way as linguists do, using conventional methods of comparison. But the
dates he puts on the tree are radically older.
Dr. Gray's calculations show
that the ancestral tongue known as proto-Indo-European existed some 8,700 years
ago (give or take 1,200 years), making it considerably older than linguists
have assumed is likely.
The age of
proto-Indo-European bears on a longstanding archaeological dispute. Some
researchers, following the lead of Dr. Marija Gimbutas, who died in 1994,
believe that the Indo-European languages were spread by warriors moving from
their homeland in the Russian steppes, north of the Black and Caspian Seas,
some time after 6,000 years ago.
A rival theory, proposed by
Dr. Colin Renfrew of the University of Cambridge, holds that the Indo-Europeans
were the first farmers who lived in ancient Turkey and that their language
expanded not by conquest but with the spread of agriculture some 10,000 to
8,000 years ago.
Dr. Gray's date, if
accepted, would support the Renfrew position.
Several linguists said Dr.
Gray's tree was the right shape, but added that it told them nothing fresh, and
that his dates were way off. "This method is not giving anything
new," said Dr. Jay Jasanoff, a Harvard expert on Indo-European. As for the
dates, Dr. Jasanoff said, "The numbers they have got seem extremely wrong
to me."
Dr. Don Ringe, a linguist at
the University of Pennsylvania who has taken a particular interest in computer
modeling of language, said that Dr. Gray's approach was worth pursuing but that
glottochronology, the traditional method of dating languages, had "failed
to live up to its promise so often that convincing linguists there is anything
there is an uphill battle."
In the biologists' camp,
however, there is a feeling that the linguists do not yet fully understand how
well the new techniques sidestep the pitfalls of the older method. The lack of
novelty in Dr. Gray's tree of Indo-European languages is its best feature,
biologists say, because it validates the method he used to construct it.
Most historical linguists
know a few languages very well but less often consider the pattern of change
affecting many languages, said Dr. Mark Pagel, an evolutionary biologist at the
University of Reading.
"The field is being
driven by people who are not confronted with the broad sweep of linguistic
evolution and is being invaded by people like me who are only interested in the
broad sweep," Dr. Pagel said.
Glottochronology was
invented by the linguist Morris Swadesh in 1952. It is based on the compiling
of a core list of 100 or 200 words that Swadesh believed were particularly
resistant to change. Languages could then be compared on the basis of how many
cognate words on a Swadesh list they shared in common.
Cognates are verbal cousins,
like the Greek podos and the English foot, both descended from a common
ancestor. The more cognates two languages share, the more recently they split
apart. Swadesh and others then tried to quantify the method, deriving the date
that two languages split from their percentage of shared cognates.
The method gave striking
results, considering its simplicity, but not all of the findings were right.
Glottochronology suffered from several problems. It assumed that languages changed
at a constant rate, and it was vulnerable to unrecognized borrowings of words
by one language from another, making them seem closer than they really were.
Because of these and other
problems, many linguists have given up on glottochronology, showing more
interest in an ingenious dating method known as linguistic paleontology.
The idea is to infer words
for items in the material culture of an early language, and to correlate them
with the appearance of such items in the archaeological record. Cognates for
the word wheel exist in many branches of the Indo-European family tree, and
linguists are confident that they can reconstruct the ancestral word in
proto-Indo-European. It is, they say, "k'ek'los," the presumed
forebear of words like "chakras," meaning wheel or circle in
Sanskrit, "kuklos," meaning wheel or circle in Greek, as well as the
English word "wheel."
The earliest wheels appear
in the archaeological record around 5,500 years ago. So the proto-Indo-European
language could not have started to split into its daughter tongues much before
that date, some linguists argue. If the wheel was invented after the split,
each language would have a different or borrowed word for it.
The dates on the earliest
branches of Dr. Gray's tree are some 2,000 years earlier than the dates arrived
at by linguistic paleontology.
"Since `wheel' is
shared by Tocharian, Greek, Sanskrit and Germanic," said Bill Darden, an
expert on Indo-European linguistic history at the University of Chicago,
"and there is no evidence for wheels before the fourth millennium B.C.,
then having Tokharian split off 7,900 years ago and Balto-Slavic at 6,500 years
ago are way out of line."
Dr. Gray, however, defends
his dates, and points out a flaw in the wheel argument. What the daughter languages
of proto-Indo-European inherited, he says, was not necessarily the word for
wheel but the word "k'el," meaning "to rotate," from which
each language may independently have derived its word for wheel. If so, the
speakers of proto-Indo-European could have lived long before the invention of
the wheel.
His tree, Dr. Gray said, was
derived with the methods used by biologists to avoid problems identical to
those in glottochronology. Genes, like languages, do not mutate at a constant
rate. And organisms, particularly bacteria, often borrow genes rather than
inheriting them from a common ancestor. Biologists have also learned that trees
of any great complexity cannot be drawn up by subjective methods. Mathematical
methods are required, like having a computer generate all possible trees — a
number that quickly runs way beyond the trillions — and then deciding
statistically which class of trees is more probable than the rest.
Dr. Gray based his tree on
the Dyen list, a set of Indo-European words judged by linguists to be cognates,
and he anchored the tree to 14 known historical dates for splits between
Indo-European languages.
Many of the Dyen list
cognates are marked uncertain, so Dr. Gray was able to test whether omission of
the doubtful cognates made any difference (it did not). He also tested many
other possible assumptions, but none of them produced an age for
proto-Indo-European anywhere near the date of 6,000 years ago favored by
linguists.
"This is why our
results should be taken seriously by both linguists and anyone else interested
in the origin of the Indo-European languages," he wrote, in a recent reply
to his critics.
"We haven't repeated
the errors of glottochronology," Dr. Gray said in an interview. "What
we are doing is adding value, since we can make inferences about time depths
which can't be made reliably in other ways."
Dr. Gray said he had formed
collaborations with linguists and hoped they would give his tree a warmer
reception once his critics understood that he had not made the errors they
cited.
Some linguists are
interested in the biologists' approach.
"I think these methods
are extremely promising," said Dr. April McMahon of the University of
Sheffield and the president of the Linguistics Association of Great Britain, though
she expressed concern about Dr. Gray's emphasis on dating language splits.
If the biologists' methods
can date languages that existed 9,000 years ago, how much further back can they
probe?
"Words exist that can
in principle resolve 20,000-year-old linguistic relationships," Dr. Pagel
of Reading wrote in a recent symposium volume, "Time Depth in Historical
Linguistics," adding that "words that can resolve even deeper
linguistic relationships are not out of the question."
Many linguists believe that
once two languages have drifted so far apart that they share only 5 percent or
so of their vocabulary, chance resemblances will overwhelm the true ones,
setting a firm limit on how far back their ancestry can be traced.
"That's a mistaken
reasoning which shows the linguists are relying on a model of evolution they
trash when they see it written down," Dr. Pagel said.
He added that their argument
assumed a constant rate of language change, the very point they know is wrong
in glottochronology.
Geneticists believe modern
humans may have left Africa as recently as 50,000 years ago, perhaps in a
single migration with very small numbers. Reconstructing language of 20,000
years ago would be a big stride toward whatever tongue those first emigrants
spoke. But Dr. Gray has no plans in that direction.
"It's hard enough to
work out what happened 10,000 years ago, let alone 30,000 years ago," he
said.