Sunday, November 18, 2012

Literature Review: Gonzales-Ruiz et al., 2012

  I can't believe I've only done one lit review so far... Time to fix that with a discussion of a fun paper (Gonzalez-Ruiz et al., 2012) that was brought to my attention recently on the haplotypes of people buried in Pazyryk graves (The Pazyryk culture is the one that gave us the dozens of golden deer statues I discussed previously. Ethinically, they were "Eastern Scythians", a.k.a. Saka.). The best part is that it's in PLOS ONE, which is a completely open source peer-reviewed journal. No paying $30+ for an article when you don't have a university library to use. :) I won't go into detail since you can read the entire thing for yourself with a click of a button, but here are the main points. If you aren't a geneticist, don't worry about the methods; there's a lot of jargon involved. Try reading the introduction, then skipping to the discussion.

  Haplotypes are particular sequences of DNA which are very useful in biogeographic studies of humans. They evolve at just the right rate to tell us about the worldwide expansion of our species throughout, then out of, Africa when considering particular combinations of haplotypes (haplogroups). The haplotypes used for these type of studies have pervaded the populations they evolved in. Some of them were carried to new regions when a population migrated or when adjacent groups sequentially interbreed, thus transporting the haplotype that way even if the original population didn't move much.

  Central Asia and the adjacent steppes are at a crossroads between "Europe" and "Asia" insofar as the ethnicities living there are concerned (despite the name of the region itself). There are high number of diverse ethnicities living there- some seem more European and some seem more Asian. The purpose of this paper was to add more information to our understanding of the ancient genetic flow in the region.
  The authors extracted DNA from skeletal material in Iron Age Pazyryk burials and compared it to other DNA from both Bronze Age and Iron Age burials in Central Asia. What they found is that during the Bronze Age- after humans had initially expanded into the Far East- the Altai mountains were acting as a barrier. East was east, west was west, and there's no evidence for any genetic flow between them. At some point in the Iron Age, things changed. The haplogroups go from being East Eurasian (i.e. Turkic nomads) on the east side of the mountains and West Eurasian (i.e., Iranian nomads) on the west side of the mountains to about half and half on both sides.
  Today, steppe nomads are Turkic. The few remaining ethnicities in the same larger language group as the Iranian steppe nomads are sedentary now. They were driven off the steppes and diminished in prominence by the westward-expanding Turkic nomads within history. What this study shows is that during prehistory, it was the Iranian nomads who did the expanding (toward the East). They initially stopped at the Altaic mountains, then the groups living in that area started expanding outwards-or rather, their genes did. There were no new West Eurasian haplotypes showing up, just the local ones increasing in geographic range. This study adds another line of evidence for our understanding of the ancient biogeography of steppe nomads (on top of cultural and linguistic data), and give us some hard boundaries (both spatial and temporal).


  1. I'll have to check that article out. Thanks for the review. Speaking of Pazyryk articles, I ran across this on on the symbolism of animal style ornament while I was researching some things for a felt rug I was making. You might find it interesting.