Two groups of researchers have uncovered the law of language evolution by finding that the more a word is used, the less likely it is to change over time, and vice versa. In one paper, researchers at Harvard University focused on the evolution of English verb conjugations over a 1,200-year period.
In a separate study, a team at the University of Reading in England reviewed cognates - similar sounding words in different languages for the same object or meaning - to determine how all Indo-European tongues progressed from a common ancestor that existed between 6,000 and 10,000 years ago.
"What our frequency effect allows us to do is identify...ultraconserved linguistic elements. Namely, they're the words we use all the time," Nature quoted Mark Pagel, an evolutionary biology professor at Reading.
In their search for cognates, Pagel and his team examined some 200 words in 87 Indo-European languages. Narrowing their focus to the frequency of use of each of the words in just four Indo-European languages—English, Spanish, Greek and Russian, the team found that they were used at similar rates universally even if the words with the same meaning were not cognates.
By combining their data, the researchers determined that it would take as little as 750 years to replace less-used words and up to 10,000 years for new words to evolve in place of the most frequently used ones.
They found that an irregular verb used 100 times less frequently is regularized 10 times as fast. For the more mathematically inclined, this can be expressed as: 'The half-life of irregular verbs is proportional to the square root of their frequency.'1
The Harvard researchers specifically studied the roots of English, tracing 177 verbs with varying frequencies of use that were irregular in Old English, and examined how many had been regularized into the '-ed' past tense by the eras of Middle and Modern English.
Over the years, several past tense forms of verbs have died out in English and now only one persists as a rule: adding "-ed" to the end of verbs.
Lead researcher, Erez Lieberman, a specialist in evolutionary maths at Harvard University, and his team found that an irregular verb used 100 times less frequently is regularized 10 times as fast. In mathematical words, the half-life of irregular verbs is proportional to the square root of their frequency.'
Lieberman predicts that the next verb to fall into line will be wed, the past tense of which will regularize from wed to wedded.
He adds that both papers call attention to the similarities between language change and the evolution of species. Leiberman even refers to early English as a "primordial soup" of verb forms in his paper.
"By being more frequent, a verb is more stable. Both studies, illustrate this profound effect that frequency has in the survival of a word," Leiberman says.
Both studies are published in Nature.