Like a skyscraper skeleton that goes up overnight--but doesn't get windows for another decade--languages evolve in fits and starts, according to a new study.
The idea that languages evolve in bursts, rather than gradually, isn't new. When applied to species, it's called punctuated evolution. But the idea is controversial in both fields--and proof has been hard to come by.
Now, scientists in the United Kingdom say they've mustered the power of mathematics to demonstrate the phenomenon in the evolution of languages. The researchers, headed by evolutionary biologist Quentin Atkinson and mathematician Mark Pagel of the University of Reading, looked at related versions, or homologs, of common words in three of the world's major language families: Indo-European, Bantu, and Austronesian. Like species, changes in languages can be tracked through the fate of certain words, just as mutations in key genes can tell a species' history.
The words the researchers tracked are from the so-called Swadesh lists: compilations of heavily used words denoting things such as numbers or body parts that change little over time and are rarely borrowed, making them good clues about how one language relates to another. An example from the Indo-European language family is the words for "water" in English, German ("Wasser"), Hittite ("watar"), and Russian ("voda"). Despite many borrowings, English is much further from Latin languages such as French, according to the Swadesh lists. Consider, for example, the French for water--"eau."
The team used this vocabulary data to construct evolutionary trees showing how new languages sprouted from root languages. English, for example, notes Atkinson, arose when the Saxons moved to the British Isles from the European continent, separating themselves from their parent Germanic language.
The researchers applied the same mathematical models to language evolution that they previously used to show that biological speciation can occur in bursts (Science, 6 October 2006, p. 119). They concluded that lineages with many "nodes," or offshoots, change faster over time than language families that have few offshoots. Pagel says most of this speed-up comes about the time the new languages break off from their ancestral lines. For example, in their study--published in the 1 February issue of Science--the researchers estimate that 31% of the vocabulary differences among Bantu languages arose about the time they split from their parent languages.
Anthropologist Tecumseh Fitch of the University of St. Andrews in Fife, U.K., calls the study "a beautiful example of the potential for cross-pollination between evolutionary biology and … linguistics." He says the work marks "the emergence of a new body of mathematics that applies to all evolutionary systems, whether the replicators are genes, words, or ideas."