Glottochronology

Glottochronology (from Attic Greek γλῶττα "tongue, language" and χρóνος "time") is the part of lexicostatistics dealing with the chronological relationship between languages.

The idea was developed by Morris Swadesh under two assumptions: first; that there does, indeed, exist a relatively stable "basic vocabulary" (referred to as "Swadesh lists") in all languages of the world; and, second; that any replacements happen in a way analogous to radioactive decay, in constant percentages per time elapsed. Meanwhile, there exist many different methods, partly extensions of the Swadesh method, now more and more under the biological assumptions of replacements in genes. However, Swadesh's technique is so well known that, for many people, 'glottochronology' refers to it alone.