glottochronology n : the determination of how long ago different languages evolved from a common source language; "he mapped the glottochronology of the Romance languages"
Glottochronology refers to methods in historical linguistics used to estimate 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 put forward 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 then yields an estimated date of origin for those languages. Glottochronology is an adjunct to lexicostatistics, with which it has been sometimes confused.
HistoryThe 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 long 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 Krustal, Dyen and Black (1973). The assumption of a single-word replacement rate can distort the divergence-time estimate when borrowed words are included; but more realistic models have been used.
Chretien purported to disprove the mathematics of the model. At a conference at Yale in 1971 his criticisms were shown to be invalid.
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.
Word ListThe 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 ConstantLees 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 borrowed 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 TimeThe basic formula of glottochronology in its shortest form is:-
- t = \frac
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).
ResultsGlottochronology was found to work in the case of Indo-European, accounting for 87% of the variance. It is also said 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.
ControversySince its original incarnation, glottochronology has been rejected by many linguists and is mostly rejected today by all Indo-Europeanists .
1. However, 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.
2. 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 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:).
This global assumption has been modified and downgraded to single words even in single languages in many newer attempts (see below).
3. 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.
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).
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:
- t = \sqrt \frac
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 EstimationThe 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".
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- Bergsland, Knut; & Vogt, Hans. (1962). On the validity of glottochronology. Current Anthropology, 3, 115-153.
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- Gray, R.D. & Atkinson, Q.D. (2003): Language-tree divergence times support the Anatolian theory of Indo-European origin. Nature, 426, 435-439.
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- Holm, Hans J. (2007). The new Arboretum of Indo-European 'Trees'; Can new algorithms reveal the Phylogeny and even Prehistory of IE?. Journal of Quantitative Linguistics 14-2:167-214
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- Lees, Robert. (1953). The basis of glottochronology. Language, 29 (2), 113-127.
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- McMahon, April and McMahon, Robert (2005) Language Classification by Numbers. Oxford: Oxford University Press (in particular p. 95).
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- Renfrew, C., McMahon, A., & L. Trask, Eds. (2000). Time Depth in Historical LInguistics. Cambridge, England: The McDonald Institute for Archaeological Research.
- Sjoberg, Andree; & Sjoberg, Gideon. (1956). Problems in glottochronology. American Anthropologist, 58 (2), 296-308.
- Starostin, Sergei. Methodology Of Long-Range Comparison. 2002. pdf
- Swadesh, Morris. (1955). Towards greater accuracy in lexicostatistic dating. International Journal of American Linguistics, 21, 121-137.
- Swadesh, Morris (1972). What is glottochronology? In M. Swadesh, The origin and diversification of languages (pp. 271–284). London: Routledge & Kegan Paul.
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glottochronology in German: Glottochronologie
glottochronology in Spanish: Glotocronología
glottochronology in Galician: Glotocronoloxía
glottochronology in Dutch: Glottochronologie
glottochronology in Japanese: 言語年代学
glottochronology in Norwegian: Glottokronologi
glottochronology in Portuguese: Glotocronologia
glottochronology in Russian: Глоттохронология