I haven’t seen the original Nature article, but this post at Carl Zimmer’s “The Loom” website is interesting. Statistically it seems we all share an ancestor who lived about 2,300 years ago. This is a surprisingly recent date, and prompts a number of questions about the methodology used.
Of course we have to distinguish between genealogy and genetic history: with genes you get that random element which means that your great-great-grandchild could inherit none of your genes. Genes are (reasonably) identifiable, so it’s possible, as Cavalli-Sforza and others have done, to trace the movement of genes across populations. With genealogy, all you have is statistics, and some assumptions about the movement and degree of interbreeding of people throughout history. So, it would be an interesting question to ask the authors of the Nature article – and I don’t know if they discuss this or not – where this putative ancestor of ours might have lived. I imagine the answer would be somewhere on the Eurasian landmass, maybe the Middle East, at the centre of trade links and the site of expansionary empires. It implies that everyone on the American continent can trace an ancestor from outside America – possible – and similarly for Australian aborigines and the tribes of New Guinea – unlikely.
The trouble with statistical studies like this is, the answers they come up with tend to be advanced with more conviction than the assumptions warrant. Still, it’s fascinating stuff.
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