What the researchers found was that the frequency with which a word is used relates to how slowly it changes through time, so that the most common words tend to be the oldest ones.
For example, the words "I" and "who" are among the oldest, along with the words "two", "three", and "five". The word "one" is only slightly younger.
Interesting, but a bit dubious. Mark Liberman (HT, by the way!) is inspired to provide a precise distinction between lies and "bullshit" (see original post) and comments:
Though I still hold out some hope that Prof. Pagel is being systematically misquoted, I'm afraid that I'm now reluctantly coming to believe what a colleague of his told me in confidence: "He knows better, but he just doesn't care".