Evolutionary Dynamics of Language

October 11, 2007

A pair of letters appeared in this week’s Nature which are quite interesting. Pagel et. al. have a piece on how the frequency of word-use predicts the rate of lexical change in Indo-European history [Nature 449:717-721]. This is complemented by the Lieberman et. al. piece on quantifying the evolutionary dynamics of language [Nature 449:713-716], which focuses in on the use of conjugation. There is also a corresponding News and Views written by W. Tecumseh Fitch which puts these two papers into the context of the larger field of linguistics.

The Pagel paper uses a Bayesian MCMC model that simultaneously accounts for uncertainty in the parameters of the model of cognate replacement and in the phylogenetic tree of the language. They are then able to link variation in the rate of lexical replacement to the frequency of word-use. Fitch points out that this observation is not new … but the use of models to quantify the relationship is novel.

The Lieberman work determines the regularization rate of groups of words showing similar usage levels. They observe a simple rule: a verb’s half-life scales as the square root of its frequency. Irregular verbs that are 100 times as rare regularize 10 times faster. They then predict (and show cute examples to demonstrate) that the word wed will likely be the next word to regularize.

Both papers are by laboratories whose primary interest is in evolution. It is therefore perhaps not surprising that these papers frame linguistic change in terms of evolution. For example, the Pagel paper states that some of the forces which are known to effect languages change include social status, size of the population, and levels of outside contact. The direct population genetics analogy to fitness, population size and migration seems clear. The ties between linguistics and evolution are deep and historical. In fact, as Fitch points out, an early tree of language was perhaps inspiration to Darwin. But it nevertheless highlights the fact that evolutionary processes are not restricted to biological entities. When evolution is viewed as a process of change over time (by relatively simple rules), it becomes applicable to a large number of historical studies (linguistic, cultural, technological, etc…).

Lieberman, E., Michel, J., Jackson, J., Tang, T., Nowak, M.A. (2007). Quantifying the evolutionary dynamics of language. Nature, 449(7163), 713-716. DOI: 10.1038/nature06137

Pagel, M., Atkinson, Q.D., Meade, A. (2007). Frequency of word-use predicts rates of lexical evolution throughout Indo-European history. Nature, 449(7163), 717-720. DOI: 10.1038/nature06176

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