March
16, 2004, Tuesday
SCIENCE
DESK
Correction Appended
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.
Correction: March 18, 2004, Thursday An article in Science Times on Tuesday about
efforts to construct a genealogy of the world's languages referred incorrectly
to the Indo-European family. While it includes most of the European languages,
Basque is not the only exception.
CAPTIONS: Chart: ''The Spread of Language, by Swords or Plowshares''
WARRIOR THEORY -- Languages were spread by a warrior people, the Kurgan
culture, who lived in the Russian steppes sometime after 6,000 years ago. They
conquered peoples in what is now India, Turkey and Europe, imposing their
language, proto-Indo-European. This evolved into the Indo-European language
family.
AGRICULTURE THEORY -- Original speakers of proto-Indo-European were farmers who
probably lived in what is now Turkey. Their language spread not by conquest,
but with the spread of new farming technologies, which had just been invented.
Approximate periods when Indo-European language families emerged, according to
this theory:
Chart shows branches and development of the Indo-European languages.
(Source by Nature)
(pg. F4)