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 have gone the way of Grendel, felled by 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 from the ninth century, or Chaucer’s “The Canterbury Tales,” written about 1200.

Linguists have constructed elaborate “family trees” showing how language has morphed over time but have been unable to detect the principle governing such changes.

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.

Still unresolved in the latest study is why the -ed rule emerged as dominant over at least seven other classes of irregular verbs, each governed by specific rules, or in some cases (as in “go” and “went”) no rule at all.

Lead author Erez Lieberman, a Harvard graduate student, said the answer might lie in the simplicity of the -ed rule, which is far easier to remember than, say, the rule governing the conjugation of “grow” to “grew.” (In one-syllable words that begin with two consonants, keep the first two letters and add -ew. )

New verbs entering the English language, such as the verb “to google,” almost always follow regular conjugation rules, he said. But there are exceptions: “snuck,” the past tense of “sneak,” slipped into the language in the late 19th or early 20th century, Lieberman said, possibly influenced by the conjugation of “struck,” the past tense of “strike.”

Some irregular verbs are so embedded in everyday language that they will never regularize, researchers said. Although less than 3 percent of modern verbs are irregular, the 10 most common verbs (be, have, do, go, say, can, will, see, take, get) are irregular, researchers said. They calculated the half-lives of “be” and “have” at 38,800 years, making them the least mutable of the irregular verbs.