Two separate teams have published analyses in science journal Nature that compare the evolution of language with biological evolution. According to their findings, frequently-used words evolve slower than their less-used counterparts:
[Erez Lieberman, a specialist in evolutionary maths at Harvard University] was struck by this idea when he learned that the ten most common verbs in English (be, have, do, go, say, can, will, see, take, get) are all irregular. Instead of their past tenses ending in '-ed', as do 97% of English verbs, they take the peculiar forms of was, had, did, went, said, could, would, saw, took and got.
Researchers suppose that this is because often-used irregulars are easy to remember and get right. Seldom-used irregulars, on the other hand, are more likely to be forgotten, so speakers often mistakenly apply the '-ed' rule. The most commonly used word that they found this happened to was the verb 'to help' – the past tense used to be 'holp', but is now 'helped'.
Lieberman then sought to quantify the effect:
[Lieberman] and his team looked at 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. 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.'
Meanwhile, a separate research group led by Mark Pagel of the University of Reading in the United Kingdom began a similar undertaking with 200 words from several Indo-European languages. The group found that words used less frequently evolved faster, and that frequency explained half the rate of evolution. According to Pagel, "The easiest way to think about it is that changes to the higher-frequency words are less likely to be accepted." He adds, "If I say there are two guys coming over the hill to kill us, and in fact there are 20, we might end up dead."