This is a new paper in PNAS that finds, after controlling for the obvious underlying population genetic relationships, an association between allele frequencies of both ASPM and Microcephalin alleles and populations with tonal vs. non-tonal language. They also figure out that non-tonal languages are recently derived. The idea that the ancestral human languages were tonal and then many languages became non-tonal (in Europe) reminds me of the idea that the !Kung clicks are an ancestral form of human language (i.e. older hominin species or early H. sapiens communicated that way)
Razib has also got some commentary on this at GNXP. The authors have a website where they go through their argument, and they have some good world maps, like this one that shows locations of people that have tonal languages (grey) and non-tonal (yellow):
and here's the "money passage" from the authors' website:
"By comparing nearly 1000 genetic markers and 26 linguistic features, we were able to show that, as most people would expect, there is generally no correlation between population genetics and language typology – but the relation between tone and the two genes under study emerged as especially strong in all our analyses. It’s because there generally isn’t a correlation between population genetics and language typology that the correlation we’ve found may be interesting. This relationship remains important and statistically highly significant even when we consider the correlation between tone and ASPM and Microcephalinsimultaneously, after we take into account the fact that neighbouring populations tend to share both genes and languages, plus some more tests."
Linguistic tone is related to the population frequency of the adaptive haplogroups of two brain size genes, ASPM and Microcephalin
Dan Dediu and D. Robert Ladd
PNAS, Early Edition May 30
Abstract: The correlations between interpopulation genetic and linguistic diversities are mostly noncausal (spurious), being due to historical processes and geographical factors that shape them in similar ways. Studies of such correlations usually consider allele frequencies and linguistic groupings (dialects, languages, linguistic families or phyla), sometimes controlling for geographic, topographic, or ecological factors. Here, we consider the relation between allele frequencies and linguistic typological features. Specifically, we focus on the derived haplogroups of the brain growth and development-related genes ASPM and Microcephalin, which show signs of natural selection and a marked geographic structure, and on linguistic tone, the use of voice pitch to convey lexical or grammatical distinctions. We hypothesize that there is a relationship between the population frequency of these two alleles and the presence of linguistic tone and test this hypothesis relative to a large database (983 alleles and 26 linguistic features in 49 populations), showing that it is not due to the usual explanatory factors represented by geography and history. The relationship between genetic and linguistic diversity in this case may be causal: certain alleles can bias language acquisition or processing and thereby influence the trajectory of language change through iterated cultural transmission.