Jan 27, 2016

An Exploration of the Link between Language and Genetics

via Majority Rights

A study in the Proceedings of the National Academy of Sciences (PDF), has illustrated the relationship between between geography, linguistics, and genetic data. By comparing geographic data for phonemes and alleles, they have come to the conclusion that in most parts of the world, languages and genes exist in the same locations and often appear to have travelled along the same migration routes.

PNAS-2015-Creanza figures A - E

Their abstract reads:
A comparison of worldwide phonemic and genetic variation in human populations, PNAS 2015 112 (5) 1265-1272; published ahead of print January 20, 2015, doi:10.1073/pnas.1424033112:
Linguistic data are often combined with genetic data to frame inferences about human population history. However, little is known about whether human demographic history generates patterns in linguistic data that are similar to those found in genetic data at a global scale. Here, we analyze the largest available datasets of both phonemes and genotyped populations. Similar axes of human geographic differentiation can be inferred from genetic data and phoneme inventories; however, geographic isolation does not necessarily lead to the loss of phonemes. Our results show that migration within geographic regions shapes phoneme evolution, although human expansion out of Africa has not left a strong signature on phonemes.
Worldwide patterns of genetic variation are driven by human demographic history. Here, we test whether this demographic history has left similar signatures on phonemes—sound units that distinguish meaning between words in languages—to those it has left on genes. We analyze, jointly and in parallel, phoneme inventories from 2,082 worldwide languages and microsatellite polymorphisms from 246 worldwide populations. On a global scale, both genetic distance and phonemic distance between populations are significantly correlated with geographic distance. Geographically close language pairs share significantly more phonemes than distant language pairs, whether or not the languages are closely related. The regional geographic axes of greatest phonemic differentiation correspond to axes of genetic differentiation, suggesting that there is a relationship between human dispersal and linguistic variation. However, the geographic distribution of phoneme inventory sizes does not follow the predictions of a serial founder effect during human expansion out of Africa. Furthermore, although geographically isolated populations lose genetic diversity via genetic drift, phonemes are not subject to drift in the same way: within a given geographic radius, languages that are relatively isolated exhibit more variance in number of phonemes than languages with many neighbors. This finding suggests that relatively isolated languages are more susceptible to phonemic change than languages with many neighbors. Within a language family, phoneme evolution along genetic, geographic, or cognate-based linguistic trees predicts similar ancestral phoneme states to those predicted from ancient sources. More genetic sampling could further elucidate the relative roles of vertical and horizontal transmission in phoneme evolution.
The overall result seems to be that language and ethnicity do share common geographic boundaries, if the effects of recent colonial history are ignored.

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