Irish Roots


February 17th 2014

Hazy Admixtures

John Grenham

The journal Science (sciencemag.org) recently published "A Genetic Atlas of Human Admixture History", an attempt to use statistical analysis of the human genome to identify what the authors call "admixture events". These are the relatively large-scale mixing of the genes of two distinct human groups due, for example, to invasion or migration.

By comparing the lengths of unmixed stretches of the genome, it is possible to date the events at (relatively) precise points within the last four millennia, and to begin to map them. Accompanying the article, a mapping website (bit.ly/1jc5roy) invites the public to play with target populations, events and percentage admixtures.

This kind of stuff is terrific fun, and there is no doubt that these techniques will eventually provide great evidence for migration history, perhaps even transforming it in the way aerial photography has transformed archaeology.

However, when I went to look at the data underlying their big orange circle that connects Ireland to Greece, I got a bit of a shock. The sample consisted of just seven Irish individuals. Digging further, it turned out that the total number of individuals covered in the entire Atlas was 1490. And buried in the footnotes are astounding margins of error, plus or minus four centuries in some cases.

I'm no statistician, but I know that generalizing from the genes of a sample group the size of Ballyhaunis to 4000 years of human history is just asking for trouble.

So you might expect some caution, or even humility, from the researchers behind the project. Not a bit of it. One of them is quoted by The New York Times as saying, "In some sense we don't want to talk to historians. There's a great virtue in being objective: You put the data in and get the history out."

Unlike historians, who just make it all up.


Comments and suggestions are welcome, to irishroots(at)irishtimes.com.

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