I wonder what implications -if any- this finding has on attempts to date the PIE language before the dispersal of its speakers. After all, PIE is constructed based on words found in several (at least two) daughter languages, and thus will tend to use words that are conserved more (since they have survived in more than one language). The implication of this article is that conserved words are replaced at a slower rate. Hence, it is important to take into account the rates of evolution of different terms when trying to figure out how long ago two languages shared a common ancestor.
Nature 449, 717-720 (11 October 2007) | doi:10.1038/nature06176; Received 30 April 2007; Accepted 17 August 2007
Frequency of word-use predicts rates of lexical evolution throughout Indo-European history
Mark Pagel et al.
Greek speakers say "ουρα", Germans "schwanz" and the French "queue" to describe what English speakers call a 'tail', but all of these languages use a related form of 'two' to describe the number after one. Among more than 100 Indo-European languages and dialects, the words for some meanings (such as 'tail') evolve rapidly, being expressed across languages by dozens of unrelated words, while others evolve much more slowly—such as the number 'two', for which all Indo-European language speakers use the same related word-form1. No general linguistic mechanism has been advanced to explain this striking variation in rates of lexical replacement among meanings. Here we use four large and divergent language corpora (English2, Spanish3, Russian4 and Greek5) and a comparative database of 200 fundamental vocabulary meanings in 87 Indo-European languages6 to show that the frequency with which these words are used in modern language predicts their rate of replacement over thousands of years of Indo-European language evolution. Across all 200 meanings, frequently used words evolve at slower rates and infrequently used words evolve more rapidly. This relationship holds separately and identically across parts of speech for each of the four language corpora, and accounts for approximately 50% of the variation in historical rates of lexical replacement. We propose that the frequency with which specific words are used in everyday language exerts a general and law-like influence on their rates of evolution. Our findings are consistent with social models of word change that emphasize the role of selection, and suggest that owing to the ways that humans use language, some words will evolve slowly and others rapidly across all languages.