How many years back are these Gedmatch European matches?

Question

I got many matches on the Gedmatch website that are from the same heritage background (Irish/English/Dutch/German/Spanish/French). The total cM of shared DNA runs from 10 to 32 cM. The most common chromosome of all the matches and me is chromosome 15 and all the matches' connections' go back from 4 to 7 generations.

My question is that I am from Algeria. I have 13% Iberian (Spanish and Portuguese) DNA and 56% North African (Amazigh) and 20% Middle East and the Levant (Arab) and 9% African. I was wondering is these people who matched with me mean that I have a foreign 4’s grandfather or grandmother from those countries and how many years this common ancestry goes back. Or if these far away connections are normal in Algerian people?

I read that Amazigh Berber DNA have some Irish in them but is this the reason that I have those matches or does it have to be a closer relationship to have many matches like that? Note that the largest cM shared is 32 cM. I had another bigger one on Family Tree DNA at 46 cM. I also read about how the Barbary slave trade refers to the slave markets that were lucrative and vast on the Barbary Coast of North Africa, which included the Ottoman provinces of Algeria. At that time they took people from Ireland and Europe as slaves to North Africa between the 16th and the middle of the 18th century. After that the French occupation of Algeria started. So am really not sure where this blood line started, I would appreciate any help.

Answer 1

You've asked a great question but one that is very difficult to answer because it depends so much on a very complex history of Algeria and other parts of North Africa. A history you have outlined very well.

When you're assessing matches like these, it's very important to look at the segment lengths. FamilyTreeDNA is notorious for overstating matches because they count every segment they can find. Gedmatch is better. Basically, don't count anything less than 5 cM. Many people say don't count segments under 7 cM.

When looking at Gedmatch, be sure to do a one-to-one comparison with your matches. The one-to-many listing is very useful for an overview but the numbers for the total cM matches are often wrong. I don't know why this is and I've tried to figure it out but it's not straightforward. The one-to-one matching appears to be correct. Leave it at the default settings.

You also want to look at the largest segment, as this is a clue as to how many generations back the match is. A match with a single segment of 32 cM is likely to have a more recent shared ancestor than a match with 1 segment of 7 cM and 5 segments of 5 cM. This is not a given though. Segments are always "real" but they may not mean what you think they mean (sometimes they can be mishmashes of more than one ancestor).

Does FTDNA give you any European ancestry outside of Iberian? If not, then you aren't likely to have a grandparent or great grandparent who is European. Your matches with Europeans may be because you have a European ancestor further back or it could be that your matches have a North African ancestor.

Because of the French occupation, and all the other interactions between North Africans and Europeans (in addition to the Iberian area), mixed ancestry of Algerians is going to be really common. It's just hard to tell what's what in your case from the DNA alone.

The fact that you've been able to narrow down the chromosome is great. Do the matches match each other in the same place that they match you? Checking this out is called triangulation and I highly recommend doing it, though it is time consuming. Gedmatch has some tools to make it easier (their early ones didn't work as they should have and I haven't worked with the newer ones). Some tools might be behind their paywall. A $10US donation will get you a month's access.

Do your matches show up as 100% European? This is another clue that will help you figure out where the connections are. Though not an easy one to suss out.

A place to explore this in more depth is the International Society of Genetic Genealogy (ISOGG) facebook group. Lots of professionals there who can answer your questions in more depth than I can.

I also recommend pounding the paper trail as best you can. Perhaps you'll come across a European surname or other clue.