The myths and ignorance about ethnicity estimates

[Mart 'n' Al]

I only found this ‘Family History Fanatics’ video today, but it explains all the myths and ignorance about ethnicity estimates.

https://www.youtube.com/watch?v=nlmK0X3I1Lo

It's an excellent presentation, especially the data simulation. It should become required watching for anybody before they give their DNA, hoping to get extreme details of their ethnicity. It counters the YouTube videos of shocked people opening their DNA results on camera. It would also go a long way to explaining statistics to people who shouldn't be gambling. I will be citing this video frequently. One thing that they don't mention is the absolute futility of researching your ancestry back more than a few generations because you are eventually going to encounter a non-paternal event, i.e. somebody is descended from a secret relationship and this is not recorded anywhere except in your DNA.  You only have to go back 5 or 6 Generations, and you have looked at 100 relationships. You only need one man or woman in those 100 or so relationships to have had an illicit relationship producing a child and it makes a mockery of your further research.
 
Martin

[IJDisney]

Thanks for re-posting this Martin. It deserves a thread to itself.

It is an interesting presentation, but he contradicts himself. At 4.20 he says "about three quarters of our six great grandparents we don't share any DNA with". That suggests we only share DNA with about 64 people out of the 256 ancestors at that generation. But later on, with his simulation from about 5 minutes in, the chart shows that we could actually share DNA with up to 93 out of our 256 six times great grandparents (which is over a third). A small point, but in mathematics a small variant can throw out a huge error in the long run. His math also doesn't allow for any cousin marriages (a huge missing factor in my opinion) which will throw his conclusions way out.

But I get the point. Basically, DNA can only prove part of our ancestry, since we don't inherit DNA from every one of our ancestors. Therefore ethnicity estimates are only based on the DNA markers we have inherited from a certain number of our ancestors (i.e. not all our ancestors). So even if the ethnicity estimates were accurate it would ignore a huge percentage of our ancestors whose DNA we have not inherited.

Therefore if I get told I'm 79% Irish/Scots and 21% North European, yet I believe that one of my 3 x great grandparents was Indian, and another was North African, I can ignore the estimate and go with my family knowledge (if I have document proof, of course). But the danger is if i didn't know about those ancestors, and believed the ethnicity estimates were accurate, then I might ignore possible future leads that would discover those Indian or African roots, because I would think "that can't be true because my ethnicity estimate shows I don't have any DNA from there"!

[hurworth]

NPEs have always occurred though.  The availability of DNA testing hasn't made studying generations back more than a few generation any more futile than it always was.

[Erato]

"makes a mockery of your further research"

Not necessarily or at least not entirely.  It depends what you think is most important or most interesting  -  nature or nurture.  If all you want is an animal husbandry style bloodline, then an unknown 'illicit' relationship is a big problem.  If you think historical, social, economic, religious, educational and other such factors are more interesting than DNA, the impact is much less severe.

[Mart 'n' Al]

Erato, DNA recently confirmed my grandfather's identity.  As my grandparents just had the one child, I would have no interest in the ancestry of my grandmother 's husband if he hadn't been my grandfather.  I do see your point though.

Martin