Role of ASPM and Microcephalin on Linguistic Tone

I want to share with you news about some yet to be released research on the role of two genes, ASPM & Microcephalin, in language tone, which has just hit the press releases. ASPM & Microcephalin are known to play a role in brain development of primates. The role of these two genes in language tone has not been investigated until now.

Language tone has direct tangents to both human evolution and linguistic anthropology. Now that I think of it even cultural anthropology has a lot to do with language tone. Not convinced? Well check out what Razib has found… an excellent example, plucked from a TimesOnline article, that describes this tangent,

“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.

The new findings from the University of Edinburgh also suggest that the very first human languages were probably tonal, sounding more like modern Chinese or Zulu than English or French. The genetic profile that appears to predispose to nontonal languages evolved only about 5,800 years ago, implying that all languages were probably tonal before that.”

So understanding the genetic origins and differences of language tone between human populations can tell us a lot about how genes have influenced which languages are spoken around the world today. Two linguists, Dan Dediu and D. Robert Ladd have been searching to find the genetic foundations for the differences tone, as heard in modern day languages,

“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.”

Their work will soon be published in PNAS, but until that happens you’re gonna have to run with my examples if you don’t quite understand what’s going on.

UPDATE, the paper has been published, “Linguistic tone is related to the population frequency of the adaptive haplogroups of two brain size genes, ASPM and Microcephalin”  — so feel very free to ignore my ramblings below. I’ll do my best to report what I do understand.

So people who have particular alleles of ASPM & Microcephalin, tend to speak nontonal languages such as English with greater affinity than tonal languages. While those with a different set of alleles, or version of these genes, people are more or less predisposed to speak tonal languages such as Chinese better. That’s simple to follow, and fairly simple to analyze too. I imagine Dediu and Ladd just sampled, isolated, amplified, and sequenced ASPM & Microcephalin from peoples that speak tonal and nontonal languages and then did an allelic frequency comparison.

What I don’t quite get, and what is causing my brain to hurt is how they determined the ancestral allele and the derived allele and how it correlates to tonal and nontonal languages. My confusion stems from these two press quotes, “nontonal languages evolved only about 5,800 years ago, implying that all languages were probably tonal before that,” and “nontonal languages have newer versions of the genes, with mutations that began to appear roughly 37 thousand years ago.” Something just doesn’t seem to add up here.

Linguistic anthropologists have classified groups of languages, or language familiesHuman Language Families, related by descent from a common proto-language, into what resembles a phylogram or pedigree. We know that tonal languages predate nontonal languages, but how did Dediu and Ladd estimate the ages of the genes and how they correlate to language tone? Where did they get the dates from?

They got these dates from Bruce Lahn, who showed,

“that there are two alleles, one for each of these two genes, which emerged fairly recently (estimated 6,000 years ago for ASPM and 37,000 years ago for Microcephalin) and that these new alleles seem to be spreading quickly in the human species (and are therefore probably “adaptive”, or favored by natural selection). They also showed that these “derived” alleles (as they are known) are unevenly distributed in the world’s populations, being especially rare in sub-Saharan Africa and most common in Europe, North Africa and Western Asia.”

This quote kinda clarified my confusion. ASPM‘s variant emerged 6k years ago and 37k year ago, Microcephalin‘s allele emerged and with these new variants there is a correlation to tonal to nontonal language transition. Interesting. But, now how does this gap of umm 31,000 years explain what’s happening in tonal to nontonal language transition?

I can’t help but to think one gene must have initiated the transition, so does that make Microcephalin our key player? I don’t know really, that maybe the wrong question to ask. The authors made an effort to make sure they are not not suggesting that language is involved in the selective pressure for the “derived” alleles of ASPM & Microcephalin.

I obviously have a lot of questions about this study because I do not have the first hand report yet. I hope many of my confusions will be resolved once I get the paper. Until then, this research seems like a very interesting and creative way to relate genes and their functions in a complex human behavior, language. In this study, there seems to be a positive correlation with certain alleles and the propensity to a certain language tone.

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