The New World was the last habitable part of the globe to be settled by humans. Today, Alaska is separated from eastern Siberia by the Bering Strait, which is 55 km (18 miles) wide, but this has not always been the case. Throughout the period from 25,000 years ago until as late as 10,000 years ago, sea levels were so low that the strait and parts of the adjoining Chukchi and Bering Seas became dry land. The result was a landmass stretching from the Verkhoyansk Range in eastern Siberia to the Mackenzie River in northwestern Canada (Hoffecker, et al., 1993). Known as Beringia, this so-called ‘land bridge’ was 1,600 km (1,000 miles) from north to south and linked Asia to North America. The region remained dry and cold, but free of ice. It is thought to have been an open landscape covered with grasses and herbaceous tundra and steppe vegetation (Guthrie, 2001; Zazula, et al., 2006). It is via the Beringia land bridge that humans are long believed to have first reached the New World, but the number of migrations and their timing have been hotly debated for many decades.
Much of our understanding of these migrations has come from archaeological and genetic data. The genetic results suggest that the New World was populated in three migrations: a major migration associated with the First Americans or Paleoindians; a second migration associated with Na-Dene language speakers distributed mainly in northwestern Canada, Alaska and along the Pacific Coast; and a third migration associated with Eskimo-Aleut language speakers, who are restricted to the Aleutian Islands and the Arctic (Reich, et al., 2012).
A third approach to understanding prehistoric migrations is comparative linguistics. In 1986, the American linguist Joseph Greenberg (1986) used this method in an attempt to identify the number of migrations into the New World. It has long been known that languages evolve over time, and that there are language ‘families’ or groups of languages that share common origins. Greenberg began by assuming each group of migrants spoke their own language and that over time a language family arose from each founding language. In earlier work going back to the 1960s, Greenberg claimed that there were three language families: Amerind, Na-Dene and Aleut-Eskimo. His conclusion – now vindicated by genetics – is that there were three migrations.
Up until now, however, linguists have been unable to link the three language groups to those in Asia. It has long been suspected that there is a linguistic connection between the Na-Dene languages and the Yeniseian languages of Siberia, but it remains unproven. A new study has investigated the possible relationship, using phylogenetic methods to build up a linguistic family tree. In the last decade, computational phylogenetic tools developed primarily to study relationships in evolutionary biology have been adapted for use in the field of historical linguistics. These new techniques have been used to study prehistoric migrations and language classifications as far back as the latter part of the last Ice Age.
The researchers applied the technique to 40 languages spoken across North America and Asia. The resulting family tree was used to test various migration hypotheses. The results suggested that there was an early dispersal of Na-Dene populations along the North American coast and a Yeniseian migration back into Siberia. This was followed by a dispersal of Na-Dene languages into the North American interior. The study does not contradict the widely-accepted scenario that the New World was settled from Beringia, but complicates it with the insight that some groups in Beringia migrated back in the opposite direction (Sicoli & Holton, 2914).
References:
1. Hoffecker, J., Powers, R. & Goebel, T., The Colonization of Beringia and the Peopling of the New World. Science 259, 46-53 (1993).
2. Guthrie, D., Origin and causes of the mammoth steppe: a story of cloud cover, woolly mammal tooth pits, buckles, and inside-out Beringia. Quaternary Science Reviews 20, 549-574 (2001).
3. Zazula, G. et al., Vegetation buried under Dawson tephra (25,300 14C years BP) and locally diverse late Pleistocene paleoenvironments of Goldbottom Creek, Yukon, Canada. Palaeogeography, Palaeoclimatology, Palaeoecology 242, 253–286 (2006).
4. Reich, D. et al., Reconstructing Native American population history. Nature 488, 370–374 (2012).
5. Greenberg, J., Turner, C. & Zegura, S., The Settlement of the Americas: A Comparison of the Linguistic, Dental, and Genetic Evidence. Current Anthropology 27 (5), 477-497 (1986).
6. Sicoli, M. & Holton, G., Linguistic Phylogenies Support Back-Migration from Beringia to Asia. PLoS One 9 (3), e91722 (2914).
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