Little is known about the hypothetical protolanguage from which all modern ones descended, which could date back 50,000 years. However, Merritt Ruhlen of Stanford University and Murray Gell-Mann of the Santa Fe Institute in New Mexico argue that the word order must have been subject-object-verb. In a family tree of 2200 languages, living and dead, based on how similar sounds were used to convey similar meanings, they found that subject-verb-object (I drink beer) languages always descended from subject-object-verb (I beer drink) ones – never the other way round.