Thursday, June 07, 2007

Genes for tones

Two "learning outcomes" for this post today: 1) "genes for" cognitive functions appear to be even rarer than is typically thought and 2) getting money to do science requires doing some of the work for free or cheaply here in the UK.

So - on to point one: Pure Pedantry reports on the [PDF] Dediu and Ladd study into genetic correlates of features of language.

No correlates were found for most features (the presence of dialects, phoneme distribution etc). Only one correlation has been found: different alleles of the genes ASPM and Microcephalin are correlated with whether or not language is tonal.

Figure 1 in the PDF paper neatly shows the relationship between haplogroups (specific sets of alleles) and the use of tone in language. Having low frequencies of allele (type) 'D' of the gene ASPM in the population is correlated with tonality. Having high frequencies of Microcephalin allele 'D' is correlated with the absence of tonality. The authors conclude that:


"We assume that any such bias is very small at the individual level and becomes manifest only at the population level through the process of cultural transmission. We also assume that the bias is probabilistic in nature and that many other factors, including language contact and history, also govern the process of language change and affect its outcome. Our findings therefore do not support any racial or deterministic interpretation. Finally, note that this bias could be either for or against tone, but the fact that nontonality is associated with the derived haplogroups (Fig. 1) suggests that tone is phylogenetically older and that the bias favors nontonality."


So the older alleles are correlated with tonality, but there are fewer tonal "phenotypes" than non-tonal ones. It would be tempting extrapolate from this that tonal languages are older than non-tonal languages. But the authors state clearly that they have only found a correlation, not a causal relationship, between certain alleles of ASPM and Microcephalin. That is, there is no evidence that certain alleles of ASPM and Microcephalin "make for" tonality in the brain.

Language Log is pretty sceptical of the meaning and provenance of this correlation. A response by the paper's authors can be found here. The authors' justification for searching for this correlation, whilst ignoring gene function studies at this stage is illuminating, and brings us on to learning outcome 2:

"[W]e knew that ASPM and Microcephalin are involved in brain development. So if it was a hunch, it was a reasonably well-grounded hunch... [O]ur geographical correlations would mean more if they had proceeded from some experimental demonstration of some sort of genetically linked, language-related, cognitive/behavioral/perceptual difference. But given the widespread assumption (rooted in the Boasian tradition, but with a significant contemporary boost from Chomsky) that the human language faculty is absolutely uniform across the species, it's very unlikely that we would have been able to get funding to look for such a difference first. So we started by doing something we could do on our own without such support, namely testing the apparent correlation. Having done that, we hope we are now in a better position to apply for funding for the expensive part of the research. This might seem backwards, but it's a pretty common way of doing genetic mapping studies: start from your phenotype, use correlational studies to identify plausibly associated genetic markers, and then try to understand experimentally what the genetic markers actually do."

(Emphasis mine)

This makes perfect sense. Do the quick and cheap investigation first, especially if the odds appear to be against finding something. Once you have more data, get the money to do the expensive stuff. It does mean that most UK academics end up doing "weekend research" or "slush fund research" just to get to the point where they can actually get the money to do the work that they have in fact already begun. It's one of those pragmatic compromises that is far from perfect but seems to work. Like democracy.

1 comment:

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