A Genetic Basis for Language Tones (fwd)

[phil cash cash]

Scientific American
May 29, 2007
		
A Genetic Basis for Language Tones?
http://www.sciam.com/print_version.cfm?articleID=D87BB853- 
E7F2-99DF-3CE5ED42E188F867
		
Scottish scientists uncover a striking link between genes for brain  
size and tonality in spoken language
		
For the most part, the thousands of languages in the world today fall  
into one of two categories (notable exceptions being Japanese, some  
Scandinavian dialects and northern Spain's Basque tongue): tonal or  
nontonal.

Two linguists believe they know the genetic underpinnings for these  
differences. During a study of linguistic and genetic data from 49  
distinct populations, the authors discovered a striking correlation  
between two genes involved in brain development and language  
tonality. Populations that speak nontonal languages (where the pitch  
of a spoken word does not affect its meaning) have newer versions of  
the genes, with mutations that began to appear roughly 37 thousand  
years ago.

"You can consider this as the first of the many possible studies that  
we could do to try to find a genetic basis for language and language  
typology and the different populations that speak a language," says  
Patrick Wong, an assistant professor of communication sciences and  
disorders at Northwestern University, who was not involved in this  
study.

In English, the pitch at which a word is spoken conveys emotion but  
usually does not affect its meaning. But in many sub-Saharan Africa,  
Southeast Asian and Latin American languages tone changes the meaning  
of words. For instance, the Chinese word huar said in a high pitch  
means flower, but in a dipping pitch means picture.

The new research, published this week inProceedings 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 colleague Dan Dediu, a fellow linguist at the university,  
focused on one particular variation of each of these two genes.  
"They're versions of these genes that are not only newer, but also  
show signatures of strong natural selection in modern humans," Ladd  
says. In their report, the authors note that previous studies  
indicate that these popular new mutations do not appear to affect  
intelligence, brain size or social ability. But based on their strong  
correlation with language tone, they surmise that they may contribute  
to slight differences in the cerebral cortex, the outermost layer of  
the brain, which, among many other functions, plays a role in our  
ability to understand language.

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.

Northwestern's Wong says that in a field in which researchers  
struggle to determine whether differences arise from experience or  
genetics, the new study "gives us an idea that there is a genetic  
side to things." He says the research indicates that small  
differences in brain organization determined by genetic makeup may be  
amplified by cultural factors and contact with other languages  
through war or migration, creating today's dichotomy in language  
tonality.

"Even remarkable correlations can arise by coincidence—or, in this  
case, possibly by prehistoric migration factors that are currently  
unknown to anthropology and archaeology—so we can't rule that out,"  
Ladd says. "The next step is to attempt to correlate individual  
genotypes with measurably different behaviors on experimental tasks  
that are plausibly related to language and speech."