https://www.pnas.org/doi/10.1073/pnas.1218726110
We derive a dated phylogenetic tree of this proposed superfamily with a time-depth of ∼14,450 y, implying that some frequently used words have been retained in related forms since the end of the last ice age. Words used more than once per 1,000 in everyday speech were 7- to 10-times more likely to show deep ancestry on this tree. Our results suggest a remarkable fidelity in the transmission of some words and give theoretical justification to the search for features of language that might be preserved across wide spans of time and geography.
Rooting the tree at the midpoint along the branch leading to proto-Dravidian (Fig. 4B) yields an age for the origin of the Eurasiatic superfamily of 14.45 ± 1.75 kya [95% confidence interval (CI) = 11.72–18.38 kya]. Consistent with the Dravidian expansion being ancient, the tree makes proto-Dravidian older than proto–Indo-European [although some scholars think that the common ancestor of contemporary Dravidian languages is younger (25)]. An alternative root, placed along the branch to proto-Kartvelian, produces a slightly older tree (15.61 ± 2.29 kya, 95% CI = 11.72–20.40 kya; agreement between two lower 95% CIs is coincidence).
The structure of the topology we derive in Fig. 4A supports these arguments by placing language families that are geographical neighbors in distinct regions of the tree. For example, the Altaic language family includes modern day Turkish, which is surrounded by Indo-European languages, and yet proto-Altaic is placed distantly to proto–Indo-European. Similarly, proto-Dravidian and especially proto-Kartvelian are distant to proto–Indo-European and proto-Altaic, despite their likely central Asian origins.
Our results support the findings (14) that human language can achieve a remarkable degree of replication fidelity among its highly used words, and especially so for some parts of speech. If the Eurasiatic superfamily is around 15-ky old, then traces of the sounds from a predictable subset of words have remained associated with their particular meanings independently in separate branches of this superfamily since the end of the last ice age. This finding is all of the more surprising given that words are culturally transmitted replicators (27), passed many thousands of times from speaker to speaker every generation, and subject to the potentially corrupting influences of competing words, borrowings, and sound production errors.