The Nation - How English adds the '-ed' - Researchers find irregular verbs change in a predictable manner.

Tracing the evolution of English verbs over 1,200 years -- from the Old English of "Beowulf" to the modern English of "The Princess Diaries" -- researchers have found that the majority of irregular verbs are going the way of Grendel, falling to the linguistic equivalent of natural selection.

The irregular verbs, governed by confusing and antiquated rules, came under evolutionary pressure to obey the modern "-ed" rule of regular verb conjugation, according to a report today in the journal Nature.

That the English language has undergone dramatic change over a millennium will come as no surprise to generations of high school students who have struggled to decipher "Beowulf," which dates to the 9th century, or Chaucer's "The Canterbury Tales," written about 1200.

Linguists have constructed elaborate "family trees" showing how English has developed over time but have been unable to detect the principle driving irregular verbs toward regularity.

The researchers, led by Martin A. Nowak, an evolutionary theorist at Harvard University, discovered that irregular verbs evolve in a predictable manner -- just like genes and living organisms. Analyzing databases containing millions of words, Nowak and colleagues showed that the patterns of change depended on how often irregular verb forms were used.

Infrequently used irregular verbs were quickest to evolve. For instance, "holp," the past tense of "help," became the modern "helped." Similarly, "chode" became "chided" and "swole" became "swelled."

Researchers found they could compute the precise rate by which irregular verbs became "regularized" in the same way physicists calculate the half-life of radioactive materials.

In general, they discovered, a verb used 100 times less frequently evolved 10 times as fast.

Coauthor and Harvard graduate student Jean-Baptiste Michel said irregular verbs were like fossils that could reveal how linguistic rules -- and perhaps cultural rules -- were born and then died.

The research brings the field of linguistics, which inspired Charles Darwin as he pondered biological evolution, full circle, said W. Tecumseh Fitch of the University of St. Andrews in Britain, who wrote a commentary accompanying the report.

In the 18th and 19th centuries, he said, linguists were focused on how languages developed over time. Their crowning achievement, Fitch said, was a comprehensive "family tree" that showed how such modern languages as English, Russian, Spanish and Hindi diverged from Indo-European, a dead ancestral tongue spoken about 10,000 years ago. This elaborate construct informed Darwin's thinking.