Glottochronology

Glottochronology, or lexicostatistics, is a quantitative method in historical linguistics that estimates the time of divergence between related languages based on the proportion of shared cognates in their basic vocabularies. Developed by Morris Swadesh in 1950, the method assumes that core vocabulary items change at a relatively constant rate over time, allowing linguists to calculate a 'time depth'—how long ago two languages shared a common ancestor. Though controversial due to its restrictive assumptions, glottochronology provides rough temporal estimates when archaeological or written records are unavailable.