Tuesday, May 29, 2007

ASPM & Microcephalin & tonal languages?   posted by Razib @ 5/29/2007 01:08:00 PM

Note: The authors have a website which summarizes their research (via Language Log).

Speaking in tones? Blame it on your genes:

People who carry particular variants of two genes involved in brain development tend to speak nontonal languages such as English, while those with a different genetic profile are more likely to speak tonal languages such as Chinese.

In tonal languages, which are most common in South East Asia and sub-Saharan Africa, subtle differences in pitch can change the meaning of vowels, consonants and syllables. Nontonal languages, which prevail in Europe, the Middle East and North Africa, use pitch only as a way of conveying emphasis or emotion.
He cautioned, however, that the research had so far found only an association that appears to be more than chance, and that more work was needed to confirm a causal effect.

I first started hearing stuff this sort of research (i.e., the correlations between particular alleles and language forms) in 2006, so I'm not too surprised. We'll see how this pans out, look for it in PNAS.

But, which alleles on which genes? From Scientific American:
The new research, published this week in Proceedings of the National Academy of Sciences USA ties this difference to two genes, ASPM and Microcephalin. The exact functions of both genes are still open to debate, but they are known to affect brain size during embryonic development. "They presumably have something to do with brain structure, because there are deleterious mutations of the genes that lead to microcephaly" (a condition in which a person's brain is much smaller than the average size for his or her age), says senior study author, Robert Ladd, a professor of linguistics at the University of Edinburgh in Scotland.
Ladd and Dediu compared 24 linguistic features-such as subject-verb word order, passive tense, and rounded vowels-with 981 versions of the two genes found in the 49 populations studied. Most of the language contrasts could be explained by geographic or historical differences. But tone seemed to be inextricably tied to the variations of ASPM and Microcephalin observed by the authors. The mutations were absent in populations that speak tonal languages, but abundant in nontonal speakers.

First, note that the authors here imply that derived (more recent) forms of the genes in question under strong selection are connected to the spread of non-tonal languages around 6,000 years ago. There's a lot of question begging here, are tonal languages ancestral? Is this association causal? But look, there's one thing that jumps out at me from a cursory examination of the various times suggested here: it sees possible that the rise to prominence of non-tonal languages (assuming their derived character) dovetails with the posited expansions of Indo-European and Afro-Asiatic languages around the core of the World-Island (Eurasia + Africa).

Here is the wiki info on the geography of tonality:
In Europe, only Norwegian, Swedish, Scottish Gaelic, the Limburgish language (according to some a dialect of Dutch), Lithuanian, Serbian, Croatian, and some dialects of Slovenian possess tonality, and only Lithuanian regularly marks it in text other than in dictionaries. The tones of Lithuanian are believed to be especially authentic, as they agree for the most part with the tones of Vedic Sanskrit, its ancient cousin. Another Indo-European tonal language, spoken in the Indian subcontinent, is Punjabi.

Most languages of sub-Saharan Africa (notably excepting Swahili in the East, and Wolof and Fulani in the West) are tonal. Hausa is tonal, although it is a distant relative of the Semitic languages, which are not.

There are numerous tonal languages in East Asia, including all the Chinese "dialects", Thai, Vietnamese and Burmese (but not Mongolian, Cambodian, Malay, standard Japanese or standard Korean). In Tibet, which is riven by harsh geography, the Central and Eastern dialects of Tibetan (including that of the capital Lhasa), are tonal, while the dialects of the West are not. Much speculation has been generated over the reasons for this partial tonogenesis.

Some of the native languages of North and South America possess tonality, especially the Na-Dene languages of Alaska and the American Southwest (including Navajo), and the Oto-Manguean languages of Mexico. Among the Mayan languages, which are mostly atonal, Yucatec, with the largest number of speakers, has developed tones.

Finally, from the authors' website:
The next step is to do experiments in which we look for evidence of the nature of the predisposition or bias. The work of Patrick Wong and his colleagues provides one possible lead here: they have shown that some monolingual adults find it much harder than others to learn an artificial language vocabulary that makes use of tone or pitch distinctions, and that the differences between these groups show up in subtle differences of brain structure as well. If we could show that these differences also reflect differences in genetic make-up, it would go some way to showing that the correlation we have found is based on a real causal link.

Related: This is Bruce Lahn's brain on ASPM and MCPH1. ASPM, Microcephalin, and intelligence. Developmental cell biology of ASPM. Brain size & genes.