I hope we can have a thoughtful discussion about this. Right up our alley (diversity, nurture/nature, migrations, prehistory...).
Linguistic tone is related to the population frequency of the adaptive haplogroups of two brain size genes, ASPM and Microcephalin
(Dediu and Ladd, 10.1073/pnas.0610848104 -- Proceedings of the National Academy of Sciences)
Heard about it through a Canadian science podcast, with Ladd being interviewed about their research. What I liked was that he was careful not to make the results sound too conclusive or the potential determinism too strict.
Dediu and Ladd have also put a special page up to prevent misunderstandings.