Genetic Basis for Tone

Bob Ladd, a linguist here at Edinburgh and a former professor of mine, has been doing some interesting research that's received a write-up in Scientific American:

Two linguists believe they know the genetic underpinnings for these differences. During a study of linguistic and genetic data from 49 distinct populations, the authors discovered a striking correlation between two genes involved in brain development and language tonality. Populations that speak nontonal languages (where the pitch of a spoken word does not affect its meaning) have newer versions of the genes, with mutations that began to appear roughly 37 thousand years ago.
...
Ladd and Dediu compared 24 linguistic features—such as subject-verb word order, passive tense, and rounded vowels—with 981 versions of the two genes found in the 49 populations studied. Most of the language contrasts could be explained by geographic or historical differences. But tone seemed to be inextricably tied to the variations of ASPM and Microcephalin observed by the authors. The mutations were absent in populations that speak tonal languages, but abundant in nontonal speakers.