Father Tongue hypothesis
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The Father Tongue hypothesis is an ethnolinguistic and population genetic hypothesis about language dispersal. A correlation was first reported between Y chromosal haplogroups and the distribution of language families by a team of population geneticists led by Estella Poloni. On the basis of these and similar findings by other geneticists, the hypothesis was elaborated by historical linguist Georg van Driem in 2010 that languages and entire language families were disseminated geographically more often by male than by female speakers. Consequently, many language communities speak father tongues rather than mother tongues, and the teaching by a mother of her spouse’s tongue to her children is a mechanism by which language has preferentially been spread over time.
Focussing on prehistoric language shift in already settled areas, examples worldwide  show that as little as 10-20% of prehistoric male immigration can (but need not) cause a language switch, indicating an elite imposition such as may have happened with the first farmers or metalworkers in the neolithic, bronze and iron ages.
The hypothesis in detail
Genetic variation of different genetic markers corresponds well to the historical and prehistorical migration patterns and with other factors, such as the geographical distribution or linguistic affinities of populations. However, the distribution of language families and linguistic subgroups more frequently correlates with the distribution of the haplogroups of the Y chromosome than with the distribution of the haplogroups of mitochondrial DNA. It is thus more often possible to predict the linguistic affinity of a male when only his Y chromosomal haplogroup is known, than to predict the linguistic affinity of a female when only her mtDNA haplogroup is known. The Y chromosome follows a patrilineal line of inheritance, meaning it is only passed on among males, from father to son. Mitochondrial DNA on the other hand follows a matrilineal line of inheritance, meaning it is only passed on from the mother to her children and from her daughters to their children, etc. The Father Tongue hypothesis is an interpretation of this observed phenomenon, that Y haplogroups correlate more frequently with linguistic subgroups than do mtDNA haplogroups. The historical linguist George van Driem interpreted this correlation of Y chromosomal haplogroups and language families as indicating that the spread of language families was often mediated by male-biased migration, whether these intrusions were martial or something less glamourous. He conjectured that the majority of language communities spoke father tongues rather than mother tongues.
Origin of the hypothesis
Even as early as 1919 scientists attempted to study ethnic differences on the basis of genetic markers. The first genetic marker studied for analysing ethnic differences was blood groups. Later other genetic polymorphisms were used, for example polymorphisms of proteins of the blood plasma, polymorphisms of human lymphocyte antigens or polymorphisms of immunoglobulins. After the advent of DNA sequencing technology and its rapid advancement in the 1970s and 1980s, other genetic markers followed, such as mitochondrial DNA types, Y chromosome polymorphisms, β-chain haemoglobin and DNA polymorphisms in nuclear genes, i.e. restriction fragment length polymorphisms. By the end of the 1980s it was commonly accepted among researchers that there are three points of view on human evolution and dispersals, namely an archaeological, linguistic and a genetic point of view, all of which paint a slightly different picture of the past. Population geneticists such as Luigi Luca Cavalli-Sforza, Paolo Menozzi, Alberto Piazza or biostatistician Robert Reuven Sokal propagated the idea that when looking at population movements in prehistory, the findings of all three disciplines must be taken into equal account for a most complete picture of the past. Many population geneticists have taken up the task and have compared various genetic markers in correspondence with geographical, linguistic and archeological findings. Although it had been observed by other researchers simultaneously, Estella Poloni and her team in 1997 reported that they had found a strong correlation between the Y-Chromosome sequence P49a,f/Taql haplotypes and linguistics, while not being able to find such a correspondence for the mtDNA haplogroups. Poloni et al. proposed in that essay for the first time the possible consequences of such a correlation, i.e. the Father Tongue hypothesis:
- "As a consequence, the female-specific diversity of our genome would fit less well with geography and linguistics than would our male-specific component. [...] If that were to prove to be the case, then the common belief that we speak our mother's tongue should be revised in favor of the concept of a ‘father's tongue’."
Poloni also discussed the father tongue in a talk at EvoLang 3, the 3rd International Conference on the Evolution of language in Paris in April 2000. At the same time from the late 1980s leading up to the early 2000s, a number of geneticists under the lead of Peter A. Underhill in Stanford, California or Michael F. Hammer in Tucson, Arizona had been analysing a steadily growing number of samples of Y chromosomes increasing the number of known Y chromosome polymorphisms and the number of Y chromosomal haplogroups. All the while linking the Y haplogroups to geographical occurrence. In 1997 Peter A. Underhill and his team published a small Y chromosome haplotype tree, which featured 20 haplotypes from 22 polymorphisms. More refined versions of the Y chromosome tree were published in November 2000 and finally in January 2001. The tree from November 2000 featured 116 haplotypes from 167 polymorphisms grouped into 10 distinct haplogroups, while the tree published only two months later in January 2001 featured 131 haplotypes from 218 polymorphisms in 10 distinct haplogroups. It was this tree from the January 2001 article which gained wide recognition among researchers of the field and was considered a breakthrough, though it was chronologically speaking only the third Y chromosome tree to be published in scientific literature. The most recent and refined version of the Y chromosomal haplogroup tree was published in a joint effort by Peter A. Underhill and Michael F. Hammer in 2008 also detailing the geographical occurrences of all the known haplogroups. The observation of a correlation between Y-chromosomal markers and the geographical distribution of languages by Poloni and her team in 1997 and 2000 led to the formulation of the Father Tongue hypothesis by historical linguist George van Driem at the Indo-Pacific Prehistory Association conference in Taipei in 2002. He proposed that
- "a mother teaching her children their father’s tongue has been a recurrent, ubiquitous and prevalent pattern throughout linguistic history, […] some of the mechanisms of language change over time are likely to be inherent to the dynamics of this pathway of transmission. Such correlations are observed worldwide."
On the basis of the ongoing work on population genetics, van Driem elaborated the Father Tongue hypothesis in his ethnolinguistic publications and in population genetic publications which he has co-authored.
Examples of father tongues
There are several salient examples where the diffusion of a language family correlates strongly with the diffusion of Y chromosomal haplogroups. The dispersal of Indo-European, for example, from an original homeland in the Pontic-Caspian steppe seems to be linked to the spread of various subclades of the R haplogroup not just to Europe, but certain R haplogroup subclades, specifically R1a and R2, reflect the penetration of the Indo-Aryans into the Indian subcontinent. Further, the Y chromosomal lineage L likely reflects an earlier patrilingual dispersal of Elamo-Dravidian emanating from a region which encompassed the Bactria and Margiana of later prehistory. Austroasiatic speakers show a high frequency of the O2a haplogroup subclade. For example, Munda speakers in north and northeast India show high frequencies of O2a, not found in their regional neighbours who speak languages other than Austroasiatic, whilst their mtDNA haplogroups seem to be the those frequent in their region independent of language affinity. Yet another example, a population genetic study of 23 Hàn populations has shown that the Hàn expansion southward during the sinification of what today is southern China, was predominantly male-biased and is an uncontroversial example of the Father Tongue hypothesis. It has also been suggested that Bantu and other Niger-Congo languages correlate well with Y chromosomal haplogroups.
Exceptions to Father Tongue hypothesis
Genetics does not determine the language spoken by a human being, and the link between Y chromosomal haplogroups and linguistic affinities is an observed correlation and not a causal link. Therefore, it must be assumed that, while father tongues predominate, exceptions to father tongues exist in the world. Two very well known exceptions are the Balti in northern Pakistan and Hungarians. The mtDNA haplogroups most frequent among Balti are the same as those of the neighbouring Tibetan communities, whereas the Y chromosomal haplogroups most frequent in Balti males appear to have entered Baltistan from the west with the introduction of Islam. The Balti speak among the most conservative dialects of Tibetan. The language of the Baltis corresponds with the mtDNA and not with the Y chromosome and is in effect a salient example of a mother tongue. The other well known exception is Hungarian. The N1c haplogroup of the Y chromosome, distinguished by Tat-C deletion is found at a high frequency throughout Uralic language communities, but it is virtually missing in Hungarian males. Therefore, while the intrusion of the Magyars into what is today Hungary is historically attested and has left clear linguistic evidence, genetically the Magyar intrusion has left no salient genetic traces. Instead, from a genetic point of view, Hungarians strongly resemble a Western Slavic language community.
Implications of the Father Tongue hypothesis
The Father Tongue hypothesis has far reaching implications for several processes in linguistics such as language change, language acquisition and sociolinguistics. The Father Tongue hypothesis has implications for linguists’ understanding of language change. It must be assumed that the dynamics of language change whereby mothers pass on the language of their spouses to their offspring differ from the dynamics of language change in a monolingual community and even from the dynamics of change in a bilingual community where mothers pass on their own language to their children. As a consequence, such dynamics can introduce a discontinuity with the past. For example, it has been observed that Michif, genetically an Algonquian language was relexified by Métis women with French, the language of their husbands, and so the genetic affinity of Michif has come to be almost unidentifiable. If the process of relexification went beyond the possibility of linguistic reconstruction, the dynamics of such a process may preclude the true linguistic heritance of a community. The Father Tongue hypothesis has implications for understanding the dispersal of populations, languages and cultures because many linguistic dispersals appear to be largely male-biased. The premise of a Father Tongue may have a number of sociological or sociolinguistic consequences in terms of what aspects of a culture and language are and can be dispersed, since it must be assumed that these aspects are not the same as they might be in dispersals of entire populations consisting of both sexes and children, or female-biased dispersals. The Father Tongue hypothesis also has implications for language acquisition, as the hypothesis suggests an evolutionary explanation for why females may be better in some aspects of language performance and acquisition.
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