There's an intriguing new paper at the AJHB on the paternal ancestry of a population from Iron Age China. It argues that the Han Chinese are the result of fairly recent admixture events, with Y-chromosome haplogroup Q1a1 entering the ancestral territory of the Han, the Central Plain of China, only around 3,000 years ago from the northwest. It's probably a sign of things to come, not only for the Han but many populations generally thought to be genetically homogeneous.
Note also how the Y-chromosome haplogroups appear to be associated with different burial customs and inferred social status. Q1a1 was found in the remains of three aristocrats and eight commoners, most of them buried in the extended prostrate position typical of Bronze and Iron Age steppe nomads of what is now western China. Most of the other remains were buried in the extended supine position, characteristic of the populations of the Chinese Central Plain at the time. I've put the details into a spreadsheet here.
It'll be interesting to learn about the genome-wide genetic structure of the people who introduced haplogroup Q1a1 into the ancestral Han gene pool. Were they perhaps in large part of Ancient North Eurasian (ANE) origin? The reason I say this is because Q is the most common Y-chromosome haplogroup in the Americas, where ANE peaks today. It's also the sister clade of haplogroup R, which is the paternal marker of Mal'ta boy, or the MA-1 genome, the main reference sample for ANE.
Indeed, haplogroup R was expanding in a big way across Europe and West and Central Asia at about the same time as Q1a1 in China. It also probably came from the steppe and was in all likelihood associated with the spread of ANE deep into Europe.
Objectives: Y chromosome haplogroup Q1a1 is found almost only in Han Chinese populations. However, it has not been found in ancient Han Chinese samples until now. Thus, the origin of haplogroup Q1a1 in Han Chinese is still obscure. This study attempts to provide answer to this question, and to uncover the origin and paternal genetic structure of the ancestors of the Han Chinese.
Methods: Eighty-nine ancient human remains that were excavated from the presumed geographic source of the Han Chinese and dated to approximately 3,000 years ago were treated by the amelogenin gene polymerase chain reaction test, to determine their sex. Then, Y chromosome single nucleotide polymorphisms were subsequently analyzed from the samples detected as male.
Results: Samples from 27 individuals were successfully amplified. Their haplotypes could be attributed to haplogroups N, O*, O2a, O3a, and Q1a1. Analyses showed that the assigned haplogroup of each sample is correlated to the suspected social status and observed burial custom associated with the sample.
Conclusions: The origins of the observed haplotypes and their distribution in present day Han Chinese and in the samples suggest that haplogroup Q1a1 was probably introduced into the Han Chinese population approximately 3,000 years ago.
Yong-Bin Zhao et al., Ancient DNA evidence reveals that the Y chromosome haplogroup Q1a1 admixed into the Han Chinese 3,000 years ago, American Journal of Human Biology, Article first published online: 18 AUG 2014, DOI: 10.1002/ajhb.22604
Lots of ancient Y-DNA from China
First genome of an Upper Paleolithic human (Mal'ta boy)
Ancient human genomes suggest (more than) three ancestral populations for present-day Europeans