The Corner

Genes and Tones

I wrote in NRODT a year or so ago about geneticist Bruce Lahn’s finding that some genes apparently involved in brain development have (a) within just the past few thousand years turned up in new varieties, which (b) seem to confer strong selective advantages to those possessing them, and (c) are not evenly distributed across all human populations, the founder group of modern humans having scattered by the time they appeared.

The actual function of these genes was, however, as I said at the time, not completely understood.  That they are connected with brain development is strongly suggested by the fact that defects in them are known to be associated with microcephaly, a congenital infant condition in which the brain fails to develop properly.  But what, in their healthy form, do these genes **do**?  That the historically-new variants Lahn turned up apparently do better?   (Based on the high rate at which they have spread through their host populations, which suggests that they confer some strong survival advantage.)

To find out, you compare population A1, in which the new variants occur at high frequency, with population B1, in which they occur with low frequency, and look for brain-related differences.  If you think you’ve found one, you test against different high- and low-frequency populations A2 and B2, to see if your hypothesis holds up… and so on until your research budget runs out.  Then, if you’ve got anything worth a damn, you publish.  Basic science.

Proceeding thus, previous researchers have ruled out direct connections to intelligence, brain size (when the genes are functioning normally) and the processing of social information.  So what the heck do they do?

Now a couple of Scottish linguists have come up with a new hypothesis:  these recent mutations may allow us to speak nontonal languages.  There is a write-up in here.

There are some languages–famously Chinese, in all its dialectical varieties, but there are plenty of others–in which you change the meaning of a word by changing its “tone.”  That’s a combination of pitch (low, medium, high) and contour (rising, level, falling).  Cantonese, for instance, has seven tones:  high-level, high-rising, high-falling, medium-level, low-level, low-rising, low-falling.  The word pronounced “yee” might, depending on tone, mean “aunt,” “chair,” “clothing,” “idea,” “two,” “ear,” or “suspicion.”  (Or a great many other things.  Even allowing for tone differentiation, meaning-to-syllable is a many-one mapping.)  Yoking syllables together reduces the ambiguity, but not totally:  “yee-gah” means “now,” but with different tones, “clothes rack.”

Well, according to these researchers–their names are Ladd and Dediu–”The [newer] mutations [of these two genes] were absent in populations that speak tonal languages, but abundant in nontonal speakers.” 

Why being able to speak a nontonal language gives you any survival advantage, as the genetic evidence suggests, I do not know, and the researchers don’t speculate.  It may be just a side effect of some tweak in brain ontogeny that confers a more obvious advantage in perception or cognition.

It’s interesting stuff, though.  It’s been known for a long time that some language features have biological correlates.  European populations whose languages have a “th” sound, for instance, like English and Greek, exhibit similar blood-group frequencies (I think that’s right–I’m working from memory).  So far as I know, though, this is the first study to suggest a linguistic correlation with identified genes.

This sort of thing is the most fascinating stuff going on in science now:  the slow uncovering of human nature in all its meaty & molecular actuality–the territory formerly squabbled over by philosophy, literature, and folklore yielding to cold biological fact.  It’ll be a long time happening, and it will turn up things we–liberals and conservatives both–won’t like, but it’s starting.