I have taken several DNA tests for ancestry, including those provided by the FT-DNA, 23andMe, and Living DNA companies. Unusual for a tester, I am actually of a single population, very local, well documented ancestry here in East Anglia, South-East England. I'm not someone in the Americas or Australia, that might have very little clue what parts of the world that their ancestors lived in, previous to immigration. I know my roots, I'm lucky. I live them. You might ask, why did I feel the need to test DNA for ancestry? The answer is, curiosity, to test the documented evidence, fill the gaps, look for surprises, and in particular, to understand the longer term, to reach further back into my ancestry.
I have though, become a bit of a skeptic, even a critic, of autosomal DNA (auDNA) tests for ancestry. They are the tests presented by the businesses in results called something like Ancestry, Family Ancestry, Origins, Family, Composition, etc. Instead of testing the haplogroups on either the direct paternal (Y-DNA), or direct maternal (mtDNA), these tests scan the autosomal and X chromosomes. That's good, because that is where all of the real business is, what makes you an individual. However, it is subject to a phenomena that we call genetic recombination (the X chromosome is a little more complicated). This means that every generation circa 50% of both parents DNA is randomly inherited from each parent. I said randomly. Each generation, that randomness chops up the inherited segments smaller, and moves them around. After about seven or eight generations, the chances of inheriting any DNA from any particular ancestral line quickly diminishes. It becomes washed out by genetic recombination.
Therefore, not only are the autosomes subject to a randomness, and genetic recombination - they are only useful for assessing family admixture only over the past three hundred years or so. There is arguably, DNA that has been shared between populations much further back, that we call background population admixture. It survived, because it entered many lines, for many families, following for example, a major ancient migration event. If this phenomena is accepted - it can only cause more problems and confusion, because it can fool results into suggesting more recent family admixture - e.g. that a great grandparent in an American family must have been Scandinavian, when in fact many Scandinavians may have settled another part of Europe, and admixed with that ancestral population, more than one thousand years ago.
DNA businesses compare segments of auDNA, against those in a number of modern day reference populations or data sets from around the world. They look for what segments are similar to these World populations, and then try to project, what percentages of your DNA is shared or similar to these other populations. Therefore:
- Your results will depend on the quality and choice of geographic boundary, allocated to any reference population data set. A number of distinct populations of different ancestry and ethnicity may exist with in them, and cross the boundaries into other data sets. How well are the samples chosen? Do they include urban people (that tend to have more admixture and mobility than many rural people). Do they include descendants of migrants that merely claim a certain ancestry previous to migration?What was the criteria for sample selection?
- Your results might be confused by background population admixture.
- You are testing against modern day populations, not those of your ancestors 300 - 500 years ago. People may well have moved around since then. In some parts of the World, they certainly have!
It is far truer to say that your auDNA test results reflect shared DNA with modern population data sets, rather than to claim descent from them. For example, 10% Finnish simply means that you appear to share similar DNA with a number of people that were hopefully sampled in Finland (and hopefully not just claim Finnish ancestry) - not that 10% of your ancestors came from Finland. That is, for the above reasons, presumptuous. It might indeed suggest some Finnish ancestry, but this is where many people go wrong, it does not prove ancestry from anywhere.
This is my main quibble. So many testers take their autosomal (for Family/Ancestry) DNA test results to be infallible truths. They are NOT. White papers do not make a test and analysis system perfect and proven as accurate. Regarding something as Science does not make it unquestionable - quite the opposite. The fact of the matter is, if you test with different companies, different siblings, add phasing, you receive different ancestry results. Therefore which result is true and unquestionable?
A Tool for further investigation
So what use is DNA testing for ancestry? Actually, I would say, lots of use. If you take the results with a pinch of salt, test with different companies, then it can help point you in a direction. Never however take autosomal results as infallible. Critical is to test with companies with well thought out, high quality reference data sets. Also to test with companies that intend to progress and improve their analysis and your results.
For DNA relative matching, then sure, the companies with the best matching system, the largest match (contactable customer) databases, and with custom in the regions of the world that you hope to match with. There is also, GEDmatch. Personally, I find it thrilling when I match through DNA, but in truth, I had more genealogical success back in the days when genealogists posted their surname interests in printed magazines and directories.
The results of each ancestry test should be taken as a clue. Look at the results of testers with more proven documented and known genealogies. Learn to recognise what might be population background, as opposed to recent admixture in a family. Investigate haplogroup DNA - it has a relative truth, although over a much longer time, and wider area. Just be aware that your haplogroup/s represent only one or two lines of descent - your ancestry over the past few thousand years may not be well represented by a haplogroup. Investigate everything. Enjoy the journey. Explore World History.