East meets West, and vice versa

2 minute read

Here’s a nice, symmetrical pair of stories:

DNA testing on 2,000-year-old bones in Italy reveal East Asian ancestry
Prowse's team cannot say how recently he, or his ancestors, left East Asia: he could have made the journey alone, or his East Asian genes might have come from a distant maternal ancestor. However, the oxygen isotope evidence indicates that he was definitely not born in Italy and likely came here from elsewhere in the Roman Empire.
In addition to the mystery the find uncovers, Prowse sees the broader scientific impact for archaeologists, physical anthropologists, and classicists: The grave goods from this individual's burial gave no indication that he was foreign-born or of East Asian descent.

OK, that’s one way. Now the other:

Skeleton of Western Man Found In Ancient Mongolian Tomb
Consider an older gentleman whose skeleton lay in one of more than 200 tombs recently excavated at a 2,000-year-old cemetery in eastern Mongolia, near Chinas northern border. DNA extracted from this mans bones pegs him as a descendant of Europeans or western Asians. Yet he still assumed a prominent position in ancient Mongolias Xiongnu Empire, say geneticist Kyung-Yong Kim of Chung-Ang University in Seoul, South Korea, and his colleagues.
This long-dead individual possessed a set of genetic mutations on his Y chromosome, which is inherited from paternal ancestors, that commonly appears today among male speakers of Indo-European languages in eastern Europe, central Asia and northern India, Kims team reports in an upcoming American Journal of Physical Anthropology. The same man displayed a pattern of mitochondrial DNA mutations, inherited from maternal ancestors, characteristic of speakers of modern Indo-European languages in central Asia, the researchers say.

Hmmm… it’s almost like they’re reading from the same script…

It’s not obvious what these finds are uncovering. Is this evidence of very rare migration across very long distances? Is it a weak pattern of long-distance genetic similarity that has been partially masked by later expansions of populations?

It would help if the stories gave some assessment of how unexpected such finds would be today. Both with regard to the mtDNA-Y chromosome “ancestry” axis, and with respect to the autosomes. Bower mentions work on Kurgan burials which is more informative:

Add to those discoveries a report in the September 2009 Human Genetics. Geneticist Christine Keyser of the University of Strasbourg in France and her colleagues found that nine of 26 skeletons previously excavated at 11 Kurgan sites in northeastern Russia possess a Y chromosome mutation pattern thought to mark the eastward expansion of early Indo-Europeans. That same genetic signature characterizes the Duurlig Nars man.

That’s a frequency. The more singular finds are much harder to deal with statistically. I also worry about PCR errors when a result is only present in one or two specimens. Looking at dozens of individuals, low-likelihood errors start to become more and more likely.