Genes for Language

You would think that language as a general phenomena in the human species is genetically prescribed, but the peculiarities of individual languages -- such as whether a people uses a particular phoneme or not -- is the result of historical or geographical factors.

Dediu and Ladd, publishing in PNAS, have shown that is true with one exception: whether the language spoken by a population is tonal or not may be related to the genetic structure of that population. (A tonal language is one in which particular phonemes can mean different things depending upon the tone in which they are spoken. An example is Chinese. English is an example of an atonal language.)

In the study, they looked at Single Nucleotide Polymorphisms (SNPs) in two genes, ASPM and Microcephalin, both of which are involved in brain development. An SNP is a sequence variation, an allele, for a gene that differs across a populations. Then they looked at the languages spoken by different populations around the world and related those to the different SNPs present in the genes of those populations.

What they found is interesting. After you remove factors like geography and historical factors, the association of the majority of features of the languages -- such as the presence or absence of dialects -- with SNPs disappear. However, a clear association was found between the genetics in the population and whether or not the population speaks a tonal language.

In their words:

In the present study, we performed statistical tests of this hypothesis on the basis of a large database comprising 983 alleles and 26 linguistic features collected for 49 world populations (see Materials and Methods), controlling for geographical and historical factors. We considered linguistic features rather than linguistic groupings (dialects, languages, linguistic families, or phyla), because our hypothesis concerns specifically the interaction between linguistic typological diversity and population genetic diversity. We found that, in general, the relationship between these two diversities is fully explained by geographical and historical factors, whereas, in the specific case of tone, ASPM-D, and MCPH-D, there is an important and significant correlation between their distributions even after controlling for geography and history. Therefore, we propose that this relationship is causal; that is, the genetic structure of a population can exert an influence on the language(s) spoken by that population. Further experimental support is required, but these findings suggest a fundamental direction for future research targeted at understanding the complex relationship between genetic factors, cultural evolution, and linguistic phenomena.

Now, let me just say that interpreting this work is destined to be controversial because proving genetic causality from what is fundamentally a genetic correlation is very difficult.

Language Log brings up one of the issues. If you go around searching for correlations, and you check enough SNPs you are bound to find one of them. This does not mean that correlation is causal. The Dediu and Ladd respond to Language Log's criticisms here. Their response is that they didn't go on a fishing expedition, that the statistics by which significance is determined are fluid (another one of Language Log's objections), and that they realize very much that the connection must be confirmed by other means.

Let's set aside the debate about causality, and ask what the implications would be if these results are true.

Basically, the authors argue that genes represent a cognitive bias in the population that affects the language it develops. This flies straight in the face of research by Noam Chomsky and others that the language faculty in the human species is essentially uniform. If shown to be true, that is a truly unprecedented finding.

The research was also covered by the Economist here.

Hat-tip: Marginal Revolution.

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This flies straight in the face of research by Noam Chomsky and others that the language faculty in the human species is essentially uniform.

well, we know that to some extent that's not totally true. the SAT verbal has a normal distribution ;-) (ok, so it is scaled in a way to be normalized)

btw, i wouldn't be surprised if the causation was inverted. the language was the selective bias upon the genes. in fact, that's what i believe. it is similar to LCT (lactase persistence).

You'd think a pure pedant would know the singular is phenomenon.

What is the basis for that, razib?

I disagree. Language changes constantly. For instance, in today's generation language is quite different than from how our parents spoke it. But what about our genes? The allele frequency in this generation is pretty much exactly like that of our parents generation. Biological evolution works slowly with respect to the number of generations passing. If one thing can change very quickly, and one only very slowly, it is much more likely that the quickly changing thing is a result of the slowly changing thing than vice versa, simply based on probability.

Of course, I don't buy that there's causation here at all. Are the individuals within those genetic populations that do not have those genes, such as immigrants who are fluent? Do they show more difficulty with the language than say, immigrants from countries that have those genes?

the authors argue that genes represent a cognitive bias in the population that affects the language it develops. This flies straight in the face of research by Noam Chomsky and others that the language faculty in the human species is essentially uniform.

Chomsky and friends never argued that there should be no genetic variation in the language faculty, UG is only an idealization of the basic design. Pinker and Bloom makes this point in their paper Natural Language and Natural Selection:

"True, grammars for particular languages, and universal grammar, are often provisionally idealized as a single kind of system. But this is commonplace in systems-level physiology and anatomy; for example the structure of the human eye is always described as if all individuals shared it and individual variation and pathology are discussed as deviations from a norm. This is because natural selection, while feeding on variation, uses it up (Ridley, 1986; Sober, 1984). In adaptively complex structures in particular, the variation we see does not consist of qualitative differences in basic design, and this surely applies to complex mental structures as well (Tooby and Cosmides, 1989)."