Glottochronology is a method that tries to calculate when two languages separated in the past. It is analogous to a kind of linguistic Carbon-14 test, but it usually cannot give absolute dates. The later term lexicostatistics is often used synonymously with glottochronology, though occasionally it simply refers to any kind of statistical comparison of lexical items from two languages.
It is obvious that languages change over time. Consider the opening lines of this poem by Chaucer written circa 1360. (The spelling has been standardized, and a modern rendition given to the right):
Almightly and all mercyable queen [Almighty and merciful queen],
to whom that all this world fleeth for socour [to whom everyone in the world runs to for help], to have release ofsin, of sorrow, and teene [for release from sin, sorrow, and hurt],
Glorious virgin of flowers flower [Glorious virgin and flower of all flowers],
To thee I flee confounded in error [To you I come, confused and in error].
Even though this poem was written almost seven centuries ago, it is no doubt transparent to any native English speaker today, and only a few archaic words are found. However, if we go back another few hundred years to Old English, things begin to look more and more like a foreign language as more and more of our familiar words drop out. Proponents of glottochronology argue that we might be able to measure the time depth of languages if we examine this rate of disappearance.
The glottochronology project rests on a number of assumptions. The first is that some words are more stable than others. Thus, an examination of basic core vocabulary will be more reliable than words that are more likely to change. There have been several proposed lists, based on several criteria, but a 100- or 200-word list is most commonly used. It includes terms referring, for example, to body parts, numbers, pronouns, and universal geographic features.
The second major assumption is the rate of change—that is, the loss of basic cognates (forms that have a common historical origin)—is the same for all languages at all times. Early proponents like Robert Lees and Morris Swadesh, comparing languages for which historical time depths were known, like the divergence of the Romance languages from Latin, conclude that anywhere from 80% to 86% would be retained over a thousand years. Using languages for which the time of separation was accurately known, they proposed the following logarithmic formula:
t = log c / 2 log r,
where time depth (in years) is represented by t, c the percentage of cognates shared between the two languages in question, and r the assumed retention rate (percentage).
As an example, we might compare five modern words from German and English, all core vocabulary items:
animal (Tier), four (vier), head (Kopf), I (ich), sun (sonne)
We find 60% agreement, as two pairs (animal/ Tier and head/Kopf) do not appear to be related. If we assume that languages change at the rate of 85% every 1,000 years, after looking up the appropriate logarithms, the above formula gives:
t = log (60%) / 2 log (85%) =-.511 /2 x—.163 = 1561
In other words, English and German diverged 1,561 years ago, around the year 400 CE.
Glottochronology was been used to track the time frames of many languages and families, from Native American languages, the languages of the Pacific, to Indo-European. Thus, for at least the more modest goals of obtaining relative dates of separation or for looking at languages within specific families, glottochronology seems to have proved it usefulness.
However, there are at least five important criticisms—or limitations—that might be leveled at glottochronology, both at the level of assumptions and practice. First, the list, whether the 100- or 200-item variety, invariably is not culturally neutral. Words for sun, moon, or certain colors, for example, no doubt carry varying symbolic weight across languages. Second, the method looks only at cognate lexical items and does not include an examination of pronunciation or grammar or changes in meaning over time. Third, it ignores borrowing and language contact, and this could easily skew results. For example, anywhere from 5% to 10% of the daily vocabulary items used in Japanese may come from English, including words for numbers and colors. Thus, a lexical statistical analysis might suggest that Japanese and English are more closely related than they actually are.
Fourth, it is not clear that the rates of retention are the same for all languages. Nor are we sure that even a single language will change at the same rate throughout its history. For example, the rate of change of English on a 200-word list is about 76% per 1,000 years, as is Coptic. However, German is 85%, Chinese 79%, and Greek 83%. But some languages are more retentive, such as rural Icelandic’s 97% and Armenian’s 94%. However, there are also less retentive languages, such as East Greenlandic, which appears to only hold 34% of its vocabulary over 1,000 years.
Finally, because of the nature of logarithms and the size of the word lists, the estimations tend to get more mathematically imprecise the further back in time you go. In fact, there is even a kind of linguistic “event horizon” (like that surrounding a black hole in physics, from which no light or information can escape), beyond which no comparisons can theoretically be made. This is around 25,000 years of separation (though even the most ardent glottochronologist would probably not trust figures past 10,000 years)
Because of these difficulties, there have been many critics of glottochronology, some particularly harsh. For example, the noted structural linguist George Trager (1972) claimed that in its enthusiastic and polemical history, the mathematical basis of glottochronology has proved untenable “and the supposedly ‘acultural’ and universally usable set of basic vocabulary . . . is, anthropologically speaking, a chimera, and is often unuseable….Where it has been taken seriously, it has sometimes led to ridiculously long or short periods of separation … [which are] just as likely to result from chance resemblance as a real relationship” (pp. 175-176).
Despite these attacks, there has been renewed interest in glottochronology in recent years. Dyen, Kruskal, and Black, in an exhaustive lexicostatistic study of the Indo-European family, found that glottochronology reflects the generally accepted language classifications made by other means, suggesting that the method may be more accurate than critics suppose. Various new methods of constructing phylogenetic trees (as in biostatistical research) have been added to glottochronology’s arsenal, so it “may be that the 21st century will see increasing application of these methods in work on language prehistory” (Wang, 1994, p. 1450).
And when there are few other avenues of investigation open, sometimes only glottochronology can offer insights. For example, Edda Fields, a social historian of Africa, reconstructed the early history of the coastal Guinea-Conakry area with the help of lexicostatistics, as there were no good methods of dating oral narratives and no written documents before the entry of the Portuguese in the 15th century. She examined how rice-planting vocabulary was borrowed among the local languages to examine lines of culture contact, trade, and technological innovation. She used glottochronology to establish a tentative history of the Guinea coast, concluding that coastal speech communities have not migrated very far from their present-day locations, thus giving a picture of a settlement pattern very different from oral narratives that tell of the ancestors migrating from the interior seeking to grow rice. In the absence of other evidence, this may be the only resource we have to find out about this important, but largely unknown, period of African history.
- Bynon, T. (1977). Historical linguistics. Cambridge: Cambridge University Press.
- Fields, E. (2001). Cutting down the trees and sowing seeds: A social history of costal Guinea, 2000 BCE to 1889 CE. Doctoral dissertation, University of Pennsylvania, Department of History.
- Hymes, D. (Ed.). (1964). Language in culture and society: A reader in linguistics and anthropology. New York: Harper & Row.
- Trager, G. (1972). Language and languages. San Francisco: Chandler.
- Wang, W. S.-Y. (1994). Glottochronology, lexicostatistics, and other numerical methods. In R. Asher (Ed.), Encyclopedia of language and linguistics (Vol. 3, pp. 1445-1450). New York: Pergamon Press.