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From thought to language

Help SPOKEN SPEECH and the INVENTION OF WRITING A Gene involved in Speech? Taking a closer look at the forkhead domain FOXP2 and the Evolution of Language
Language gene found Mutation of a gene called FOXP2 causes speech and language disorder Identification of the human FOXP2 gene
Molecular evolution of FOXP2, a gene involved in speech and language

First discovered in the KE family, several of whose members had specific language impairments, the FOXP2 (short for “forkhead box P2”) gene is the first gene that scientists ever associated with the human ability to speak.

The exact problems caused by mutations in this gene remain hard to identify , which is not surprising when you consider the family of genes to which this one belongs.The FOX family of genes are transcription factors, which means that they produce proteins that can regulate the expression of a number of other genes by binding directly to their DNA. (The binding ability of these particular proteins comes from their forked shape, from which the gene family gets its name.)

General form of the FOXP2 protein. The red segment marks the location of the mutation that caused the specific language impairments in members of the KE family.

Source: Dr. Simon Fisher

The FOXP2 gene would appear to play an important role in orchestrating the establishment of the neural pathways during embryonic development. And in fact, this gene is extremely well preserved phylogenetically: the protein that it produces is almost identical in mice and in primates, which are separated by some 130 million years of evolution.

Source: Dr. Svante Pääbo

The protein that the FOXP2 gene produces in humans differs by only two or three amino acids from the protein that it produces in other species. It is very likely these two or three amino acids that make the difference between animals that cannot speak and humans who can. Moreover, the mutations that caused this difference are estimated to have occurred between 100 000 and 200 000 years ago, roughly the time that articulate language first emerged in human beings.

By performing a detailed analysis of the defective FOXP2 gene sequence in several members of the KE family, scientists were also able to identify the precise site of the mutation that caused this gene to malfunction in these individuals. This mutation occurs on exon 14 of the FOXP2 gene, when the guanine in a nucleotide is replaced by an adenine. As it happens, the part of the gene where this mutation occurs is precisely the one that codes for the “forkhead” portion of the protein—the part that binds to the DNA on other genes. This change in a single nucleotide on the FOXP2 gene has a direct impact on this protein, causing the amino acid arginine to be replaced with a histidine.

In the hundreds of normal subjects tested, the protein produced by FOXP2 always has an arginine at this particular site, while in the members of the KE family who suffered from specific language impairments, it always had a histidine. Hence there is not a shadow of a doubt about the mutation that causes this disorder. That said, it is still amazing to think that the mutation of a single one of the 2 500 nucleic bases in the FOXP2 gene is sufficient to impair so vital a faculty as language!

Just around the end of World War II, the Italian population geneticist Luca Cavalli-Sforza began constructing genealogical trees that established relationships among populations throughout the world. This ambitious project supported certain hypotheses that broke fertile ground for further research. For example, by cross-tabulating data on several dozen genes, Cavalli-Sforza established a relationship between American Indians and Asians. This finding is consistent with the most common theory about how the New World was populated: by peoples who crossed from Siberia to Alaska when the Bering Strait was frozen over during the last great Ice Age, some 30 000 years ago.

Cavalli-Sforza’s findings assumed even greater importance when he correlated them with analogous studies on languages. When Cavalli-Sforza compared the genealogical trees established by geneticists with those established by linguists, he got some amazing results: with just a few exceptions, the people who speak each of the 15 major families of languages are genetically related as well. The obvious explanation for this remarkable concordance is, of course, that when a population migrates to a new territory, it takes its genes along as well as its language.

But there have been many criticisms of Cavalli-Sforza’s approach, and in particular his way of defining a population. In the works of Cavalli-Sforza and his followers, the first step is to define a population, by linguistic criteria among others. Correlations are then established between these populations and their languages, which seems like a dangerously circular approach. It has also been noted that these studies are more convincing on a small scale or a large scale, but far less so on an intermediate one. The reason is that it is easier to distinguish Inuit from Bantu, for example, than to differentiate the various populations that speak Bantu languages.

In addition, the DNA samples used in many studies come from blood banks, and the accompanying records may be biased or false, because for various reasons, when people give blood, they may report their ethnicity as different from what it actually is. Once again we see the risks that errors may be found when controls are applied to both linguistic and genetic data.

Link : Gènes et langues ont-ils la même histoire ? Link : Genetic Distance and Language Affinities Between Autochthonous Human Populations Link : The Great Human Diasporas: The History of Diversity and Evolution Link : On the origin of speeches Link : A tale of two scientists
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