I recently had an Ancestry DNA test done. The process is clean, well-designed and private: 10ccs of spittle in a plastic container sent off in a pre-addressed package identifiable to the testers only by a reference number. Once the test is complete – only a matter of weeks – the results are available using the reference number.
Until recently, most genealogical DNA testing focused on the Y chromosome for direct male father-to-son descents, or mitochondrial DNA (mtDNA) for mother-to-daughter descent. In both cases, the tests seek out small inherited mutations. By comparing the results of large reference groups, it is possible to infer roughly when and where each mutation first arose and, by extension, the most recent common ancestor of everyone whose DNA includes that mutation. The rate of change on the Y chromosome is much faster than for mtDNA, and the inheritance from father to son mimics European surname inheritance, so Y DNA testing has long been the most genealogically useful.
What Ancestry does is different. It is an autosomal DNA test, taking samples from across the entire genome, all 23 chromosomes, rather than just part of a single sub-chromosome. They test 730,525 points, over 7% of the entire genome. Even three years ago, industrial DNA-testing on this scale was barely imaginable, and it makes possible broad-brush comparisons on a completely new scale.
What do those broad-brush comparisons tell you? Ancestry uses the results in two ways. First comes an “ethnicity estimate”, giving a percentage match to each of 26 ethnic groups. Second is a search across other Ancestry test results to uncover unsuspected 2nd, 3rd and 4th cousins.
So when I got the email saying my test was complete, I was like a child on Christmas morning. Would I be 40% Iberian, 10% Eastern European, 20% Finnish? Third cousins in Hawaii, please, please, please.
No. Apparently, I’m 98% Irish. After trying to choose which of my treacherous Brit fingernails to pull out in order to make the 100%, I took a closer look at the way the results are created. There’s a margin of error of +/- 5%. So I could actually be 103% Irish – Hiberniores Hibernicis ipsis, more Irish than the Irish themselves. Wrap the green flag round me, boys.
More seriously, that 98% points up the limits of autosomal testing. It is very broad, but also very shallow, its accuracy limited to four generations, great-great-grandparents. This is because you get half your DNA from each parent, who each got half from their parents and so on, halving with each generation. As a result, the amount you share with any of your great-great-grandparents is just 6.25%.
I already know who all my great-great-grandparents were and where they lived, all along the Galway/Roscommon border, God help them. Not a Finn or a Polynesian among them. So Ancestry was telling me nothing I didn’t know.
Ethnicity is also much slipperier and more dangerous terrain that Ancestry seems to realise. In the US, being “Irish” or “Italian” or “Polish” is an interesting twist on basic American-ness: it might be pistachio or vanilla, but it’s still ice-cream. In Europe, we spent most of the 20th century fighting genocidal wars that revolved around a toxic mix of ethnicity and nationalism. Not ice-cream at all.
The second part of the Ancestry DNA experience is genuinely useful, though. On Ancestry itself, I found four third-cousin families, all of whom have extended family histories about which I knew nothing.
And when I uploaded my results to the open-source GedMatch.com, I found even more, and closer connections.
The Ancestry test costs £99 and is well worth it, especially if your main interest is the broader extended family. Just take the ethnicity side of things with a grain of salt.