“Where Are My Old Country DNA Matches?” A Guest Post by John Motzi

A common lament is the lack of DNA matches from the “old country”: If only more people tested in the country of my ancestors, I could break down the brick walls for those ancestors.  Indeed, I have several matches whose trees point to relationships back in the old country, likely just one generation prior to my immigrant ancestors.  If more people in that country, that region, that town did DNA testing, wouldn’t that tell all?  It sounds like a plausible concept, but the reality is – it depends.

In my case, that ancestor would be my 3^rd great grandfather Giuseppe Mazzei.  I know the town where he lived.  I see in that town today several surnames of people in my tree as well as the trees of my matches.  I know that Giuseppe had seven children, and at least four of them immigrated to the US.  Of the ones that did not immigrate, some of their children immigrated.  So, the first reality is that most of the descendants of my 3^rd great grandfather are to be found in the US.  Therefore, most of the matches I should expect to see would be in the US.  To date all of the matches I have found are in the US (2C1R to 4C1R).

But what about those back in Italy?  Even if they tested (without my knowledge) what are my chances of finding them?  Contemporary descendants of my 3^rd great-grandfather would be my 4^th cousins.  According to the “cousin statistics” page of the ISOGG Wiki¹, the chance that I share ANY DNA with a 4C about 50-70%.  For 5^th cousins the chance of sharing is 15-30% so there is a greater likelihood of not sharing DNA than the likelihood of sharing any.  That indeed is cause for lament!  But that same wiki page also describes that the likely number of 4^th and 5^th cousins is huge!  On average (beware!) I should expect to find matches corresponding to 432 out of a theoretical 940 fourth cousins and 700 out of a theoretical 4,700 fifth cousins.  Of course, that’s only if they all tested.

Based on data from the DNAGeek², the size of the database at Ancestry is approximately 12.8 million and the sum of all of the other testing companies’ databases is about the same.  These are global figures but we know that the vast majority of testers at Ancestry are US based.  The current population in the US is 328 million people³, of which about 75% (246 million) are over the age of 18.  That means that the size of the Ancestry database is equivalent to 5.2% of the US adult population.  As a best case, let’s assume that someday, testers in other countries will test at the same rate as our very approximate rate for Ancestry in the US (5.2%).  We could expect to find 5.2% of our globally detectable DNA cousins which is 22 of our theoretical 940 fourth cousins and 36 of our theoretical 4,700 fifth cousins.  We can double those figures if we want to include all of the databases.

So what have we learned?  Formulating a strategy for finding matches pointing to ancestors in the “old country” depends on knowing how far back in time was the common ancestor & understanding where the descendants of that ancestor are likely living today.

Matches from the old country would be very useful if one’s unknown ancestor immigrated in the last 50 years.  Matches from the old country might be a very long shot if one’s ancestors immigrated over 300 years ago (my French ancestors in Canada – there are tens or hundreds of thousands of cousins right here in North America).  For many of us whose ancestors immigrated to North America in the latter part of the 19^th century – it’s a numbers game.  The situation might be that most of those cousins are sitting here in the US anyway.  I might eventually find a match back in Italy, but I don’t think I’ll be waiting for it as part of my genealogy strategy.

References:

1. 1. https://isogg.org/wiki/Cousin_statistics
   2. https://thednageek.com/database-sizes-september-2018-update/
   3. https://www.census.gov/popclock/

Note from Dana: John Motzi has been a tremendous help to me as I have shared the Leeds Method with our genealogy community. He can be reached via email at john.motzi@att.net or be found on Facebook as “John Motzi.”