Those of you who have read this weblog for a while know that ASPM is one of the genes that was once a major topic of interest. But the 2000s turned into the 2010s, and I kind of lost interest. There was some really strange result though that ASPM and tonal languages had some association. But there are all sorts of weird correlations. Nevertheless, in 2012 a study of Europeans found those with a particular ASPM allele were better at recognizing particular tones.
Curiouser and Curioser. Now in Science, a new study of Cantonese speakers, ASPM-lexical tone association in speakers of a tone language: Direct evidence for the genetic-biasing hypothesis of language evolution:
How language has evolved into more than 7000 varieties today remains a question that puzzles linguists, anthropologists, and evolutionary scientists. The genetic-biasing hypothesis of language evolution postulates that genes and language features coevolve, such that a population that is genetically predisposed to perceiving a particular linguistic feature would tend to adopt that feature in their language. Statistical studies that correlated a large number of genetic variants and linguistic features not only generated this hypothesis but also specifically pinpointed a linkage between ASPM and lexical tone. However, there is currently no direct evidence for this association and, therefore, the hypothesis. In an experimental study, we provide evidence to link ASPM with lexical tone perception in a sample of over 400 speakers of a tone language. In addition to providing the first direct evidence for the genetic-biasing hypothesis, our results have implications for further studies of linguistic anthropology and language disorders.
One thing that needs to be made clear, and is obvious in the above figure: the SNP within ASPM is statistically associated with a better perception of tones but has a smaller impact than IQ, and in particular, musicality. In other words, ASPM is not the “tone gene.” It’s just a gene that has a nontrivial (detectable) effect on one’s ability to recognize tones.
On the first reading of this paper I thought back to Terrence Deacon’s The Symbolic Species: The Co-evolution of Language and the Brain. Deacon takes a different tack that Steven Pinker in The Blank Slate, emphasizing that language emerges out of a gradual co-evolutionary dynamic, rather than being a distinct cognitive module that is “purpose-built” for the task. Deacon (and, to be fair Pinker and the Chomskyite tradition in general) emphasizes that the nature of linguistic phenomena is constrained and shaped by our neuro-cognitive architecture.
The authors seem to think their result has evolutionary implications:
In conclusion, we found direct evidence of gene-tone association, providing the critical direct evidence for the genetic-biasing hypothesis of language evolution. We hypothesize that ASPM is expressed in the pitch center of the auditory cortex (20), which would, in turn, enhance the lexical tone perception of carriers of the favored allele. Populations with a higher frequency of the favored allele would be more likely to have lexical tone in their language.
Al well and good. But we need to take a step back, as I did after reading the paper. First, the tone-enhancing T allele is the major allele in humans, and seems to be the ancestral one. In fact, the T allele is at a much higher frequency in Africa than it does in East Asia. You can confirm this in the 1000 Genomes Browser, but I also generated some frequencies from the HGDP: