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Glottochronology is an approach in historical linguistics for
estimating the time at which languages diverged, based on the
assumption that the basic (core) vocabulary of a language changes
at a constant average rate. This assumption, originally suggested
by Morris
Swadesh, is based on an analogy with the use of carbon
dating for measuring the age of organic materials, in that a
"lexical half-life" is
estimated. The method estimates the length of time since two or
more languages diverged from a common earlier proto-language,
by counting the number of words that have been replaced in each
language. This yields an estimated date of origin for those
languages. Glottochronology is an adjunct to lexicostatistics, with which it has
been sometimes confused.
Methodology
Word list
The original method presumed that the core vocabulary of a
language is replaced at a constant (or near constant) rate across
all languages and cultures, and can therefore be used to measure
the passage of time. The process makes use of a list of lexical
terms compiled by Morris Swadesh assumed to be resistant against
borrowing (originally designed as a list of 200 items; however, the
refined 100 word list in Swadesh (1955) is much more common among
modern day linguists). This core vocabulary was designed to
encompass concepts common to every human language (such as personal
pronouns, body parts, heavenly bodies, verbs of basic actions,
numerals 'one' and 'two', etc.), eliminating concepts that are
specific to a particular culture or time. It has been found that
this ideal is not in fact possible and that the meaning set may
need to be tailored to the languages being compared.
The percentage of cognates (words that have a common origin) in
these word lists is then measured. The larger the percentage of
cognates, the more recently the two languages being compared are
presumed to have separated.
Glottochronologic
constant
Lees obtained a value for the "glottochronological constant" of
words by considering the known changes in 13 pairs of languages
using the 200 word list. He obtained a value of
0.806 ± 0.0176 with 90% confidence. For the 100 word list
Swadesh obtained a value of 0.86, the higher value reflecting the
elimination of semantically unstable words. This constant may be
related to the retention rate of words by:-
- L = 2ln(r)
where L is the rate of replacement, ln is the logarithm
to base e, and r is the glottochronological constant
Divergence
time
The basic formula of glottochronology in its shortest form
is:-

where t = a given period of time from one stage of the
language to another, c = proportion of wordlist items
retained at the end of that period, and L = rate of
replacement for that word list.
By testing historically verifiable cases where we have knowledge
of t through non-linguistic data (e. g. the approximate
distance from Classical Latin to modern Romance languages), Swadesh
arrived at the empirical value of approximately 0.14 for L
(meaning that the rate of replacement constitutes around 14 words
from the 100-wordlist per millennium).
Results
Glottochronology was found to work in the case of Indo-European,
accounting for 87% of the variance.[1] It is
also postulated to work for Hamito-Semitic (Fleming 1973), Chinese
(Munro 1978) and Amerind (Stark 1973; Baumhoff and Olmsted 1963).
For the latter, correlations have been obtained with radiocarbon
dating and blood groups as well as archaeology.
Indo-European tree according to glottochronological results (Gray
& Atkinson)
Discussion
The concept of language change is old and its history is
reviewed in Hymes (1973) and Wells (1973). Glottochronology itself
dates back to the mid-20th century (see Lees 1953; Swadesh 1955,
1972) An introduction to the subject is given in Embleton (1986)
and in McMahon and McMahon (2005).
Glottochronology has ever since been controversial, partly owing
to issues of precision, as well as the question of whether its
basis is sound (see e.g. Bergsland 1958; Bergsland and Vogt 1962;
Fodor 1961; Chretien 1962; Guy 1980). These concerns have been
addressed by Dobson et al. (1972), Dyen (1973) and Kruskal, Dyen
and Black (1973). The assumption of a single-word replacement rate
can distort the divergence-time estimate when borrowed words are
included (Thomason and Kaufman 1988). Chrétien purported to
disprove the mathematics of the Swadesh-model. At a conference at
Yale in 1971 his criticisms were shown to be invalid.[2] The
same conference saw the application of the theory to Creole language
(Wittmann 1973). An overview of recent arguments can be obtained
from the papers of a conference held at the McDonald Institute in
2000. See Renfrew, McMahon and Trask, 2002. These presentations
vary from "Why linguists don't do dates" to the one by Starostin
discussed above. Since its original inception, glottochronology has
been rejected by many linguists, mostly Indo-Europeanists of the
school of the traditional comparative method. Criticisms have
been answered in particular around three points of discussion.
- Criticism levelled against the higher stability of lexemes in
Swadesh lists alone (Haarmann 1990) misses the point, because a
certain amount of losses only enables the computations (Sankoff
1970).
- Traditional glottochronology did presume that language changes
at a stable rate.
- Thus, in Bergsland & Vogt (1962), the authors make an
impressive demonstration, on the basis of actual language data
verifiable by extra-linguistic sources, that the "rate of change"
for Icelandic constituted around 4% per
millennium, whereas for closely connected Riksmal (Literary
Norwegian) it would amount to as much as 20%. (Swadesh's proposed
"constant rate" was supposed to be around 14% per millennium).
- This and several other similar examples effectively proved that
Swadesh's formula would not work on all available material—a
serious accusation considering that evidence that can be used to
"calibrate" the meaning of L (i. e. language history
recorded during prolonged periods of time) is not overwhelmingly
large in the first place.
- It is highly likely that the chance of replacement is in fact
different for every word or feature ("each word has its own
history", among hundreds of other sources:[3]).
- This global assumption has been modified and downgraded to
single words even in single languages in many newer attempts (see
below).
- A serious argument is that language change arises from
socio-historical events which are of course unforeseeable and,
therefore, uncomputable.
- New methods developed by Gray & Atkinson avoid these
issues, but are still seen as controversial, primarily since they
support the Anatolian origin of the
Indo-European people over the more popular Kurgan
hypothesis.
Modified
glottochronology
Somewhere in between the original concept of Swadesh and the
rejection of glottochronology in its entirety lies the idea that
glottochronology as a formal method of linguistic analysis becomes
valid with the help of several important modifications. Thus,
inhomogeneities in the replacement rate were dealt with by Van der
Merwe (1966) by splitting the word list into classes each with
their own rate, while Dyen, James and Cole (1967) allowed each
meaning to have its own rate. Simultaneous estimation of divergence
time and replacement rate was studied by Kruskal, Dyen and
Black.
Brainard (1970) allowed for chance cognation and drift effects
was introduced by Gleason (1959). Sankoff (1973) suggested
introducing a borrowing parameter and allowed synonyms.
A combination of these various improvements is given in
Sankoff's "Fully Parameterised Lexicostatistics". In 1972 Sankoff
in a biological context developed a model of genetic divergence of
populations. Embleton (1981) derives a simplified version of this
in a linguistic context. She carries out a number of simulations
using this which are shown to give good results.
Improvements in statistical methodology related to a completely
different branch of science – changes in DNA over time – have sparked a
recent renewed interest. These methods are more robust than the
earlier ones because they calibrate points on the tree with known
historical events and smooth the rates of change across these. As
such, they no longer require the assumption of a constant rate of
change (Gray & Atkinson
2003).
Starostin's
method
Another attempt to introduce such modifications was performed by
the Russian linguist Sergei Starostin, who had proposed
that
- systematic loanwords,
borrowed from one language into another, are a disruptive factor
and have to be eliminated from the calculations; the one thing that
really matters is the "native" replacement of items by items from
the same language. The failure to notice this factor was a major
reason in Swadesh's original estimation of the replacement rate at
under 14 words from the 100-wordlist per millennium, when the real
rate is, in fact, much slower (around 5 or 6). Introducing this
correction effectively cancels out the "Bergsland & Vogt"
argument, since a thorough analysis of the Riksmal data shows that
its basic wordlist includes about 15–16 borrowings from other
Germanic languages (mostly Danish) – exclusion of these elements
from the calculations brings the rate down to the expected rate of
5–6 "native" replacements per millennium;
- the rate of change is not really constant, but actually depends
on the time period during which the word has existed in the
language (i. e. chances of lexeme X being replaced by lexeme Y
increase in direct proportion to the time elapsed – the so called
"aging of words", empirically understood as gradual "erosion" of
the word's primary meaning under the weight of acquired secondary
ones);
- individual items on the 100 wordlist have different stability
rates (for instance, the word "I" generally has a much lower chance
of being replaced than the word "yellow", etc.).
The resulting formula, taking into account both the time
dependence and the individual stability quotients, looks as
follows:

In this formula, −Lc reflects the gradual slowing down
of the replacement process due to different individual rates (the
less stable elements are the first and the quickest to be
replaced), whereas the square root represents the reverse trend –
acceleration of replacement as items in the original wordlist "age"
and become more prone to shifting their meaning. The formula is
obviously more complicated than Swadesh's original one, but, as
shown in Starostin's work, yields more credible results than the
former (and more or less agrees with all the cases of language
separation that can be confirmed by historical knowledge). On the
other hand, it shows that glottochronology can really only be used
as a serious scientific tool on language families the historical
phonology of which has been meticulously elaborated (at least to
the point of being able to clearly distinguish between cognates and
loanwords).
Time-depth
estimation
The problem of time-depth estimation was the subject of a
conference held by the McDonald Institute in 2000. The published
papers (Renfrew, McMahon and Trask, 2002) give an idea of the views
on glottochronology at the time. These vary from "Why linguists
don't do dates" to the one by Starostin discussed above. Note that
in the referenced Gray and Atkinson paper, they argue that their
methods can not be called "glottochronology".
References
- ^
Language-tree divergence times support the Anatolian theory of
Indo-European origin, Russell D. Gray & Quentin D. Atkinson,
Nature 426, 435–439 2003
- ^
See the published proceedings under Dyen (1973) in the
bibliography
- ^
Kirk JM, St Anderson, & JDA Widdowson, 1985 Studies in
Linguistic Geography: The Dialects of English in Britain and
Ireland. London: Croom Helm
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pdf
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External
links
See also