07 May 2019

The DNA Problem We Aren't Talking About

Everybody in the gene pool! You're all my ancestors.

Are you chasing a pair of magic ancestors who don't exist? You find a strong DNA match. You expect to find a shared set of 4th great grandparents or so. But is there a common set of great grandparents at all?

If you and your DNA match come from an endogamous culture, the answer may be "Sorry. No."

Endogamy is the practice of marrying within a specific group, over and over again. Let's say a small town has 200 families. When each child comes of age, they marry someone from one of the other 199 families in the town.

In some cultures and some geographies, intermarriage was the only choice.
In some cultures and some geographies, intermarriage was the only choice.
Imagine keeping up that practice for centuries. The 200 families' DNA would be so blended together that they may be hard to tell apart.

The International Society of Genetic Genealogy (ISOGG) Wiki says endogamous populations include:
  • Jews
  • Polynesians
  • Low German Mennonites
  • the Amish
  • Acadians
  • French Canadians
  • the people of Newfoundland
  • many Arab countries
  • people from many islands.
None of those groups include my ethnicity. But I've seen firsthand that endogamy was a necessity when you lived in a rural, isolated town in the 1700s or 1800s. In my ancestors' towns, intermarriage of families was the only choice. Sometimes a man married a woman from the next town. But most of the time, he married a woman from his own little neighborhood.

Think about their DNA segments getting all twisted together in knots. It's like that tangled-up ball of Christmas lights. You'd rather throw it out and get a new set than wrestle with it all day.

The ISOGG says that people "from endogamous populations … will typically have large numbers of matches in the DNA databases. … [Their] relationships will often be more distant than predicted."

More distant than predicted. Let that sink in. If your people practiced endogamy, their relationships may be more distant than predicted.

My parents' ancestors came from a few neighboring endogamous towns. My parents share 37 centimorgans across 4 DNA segments. That can make them many things. According to Ancestry DNA, my parents could be:

Got shared DNA? There are so many ways you may be related.
Got shared DNA? There are so many ways you may be related.

And here I've been trying to find that one magic couple. That one set of my 4th or 5th great grandparents that belong to each of my parents.

What if that couple doesn't exist? What if my parents share DNA because their entire region of Italy shares DNA?

LegacyTree tells us that people from endogamous groups often "share multiple ancestors in common with each other. They also may descend from the same ancestral couple multiple times."

DNAeXplained adds that if you match someone from an endogamous population, "it's because you share so much of the same DNA…not because a particular segment comes from one specific ancestor."

How does this change your genealogy research? If you have ancestors who married within their small town or tribe for centuries, what should you do?

I've been researching my ancestral hometowns since 2005. I saw right away that there was a ton of intermarriage. The only way to sort out my ancestors was to document the entire town. I did that for my maternal grandfather's town. Now I'm piecing together every extended family relationship from my paternal grandfather's town. The 2 towns are so close that you can see one from the other. But traveling from one to the other is hard. Even to this day.

It's official. I no longer expect to find one magic couple shared by my parents.

The Leeds Method and DNA Painter showed me that the last names of Pozzuto and Zeolla from my paternal grandfather's town have the closest DNA ties to my mother. So I'm going to continue doing what I've been doing.

These 4 shared segments can mean a long list of possible relationships.
These 4 shared segments can mean a long list of possible relationships.
I'm adding every Pozzuto baby to my family tree one at a time. I'm piecing together their ancestors until I can tie them to someone already in my tree. Now that random, unrelated baby is my distant relative.

I'm paying special attention to families that:
  • have both the Pozzuto and Zeolla names through marriage.
  • have one spouse from one of my father's towns and the other spouse from one of my mother's towns.
When that rando-baby becomes a relative, their descendants may tie me to one of my DNA matches. If that DNA match has a connection to both my parents, I've got something special.

It won't be that one magic couple. But it may be a highly condensed bucketful of the shared gene pool. The pool that has my entire Italian region as card-carrying members.

Are you seeing a lot of the same last names marrying one another in your extended family tree? Keep endogamy in mind when your search for one magic couple is feeling like anything but magic.

Don't miss out! Please follow me on Twitter or Facebook. Thank you!

No comments:

Post a Comment