How Many Interfamily Marriages Are in Your Database?

How many interfamily marriages do you have in your genealogy database? I currently have 79 couples. Just an interesting fun fact, right?

Not so fast. Interfamily marriage is defined as marriage between people with common ancestors, aka cousin marriage, and this is how pedigree collapse occurs.

Pedigree Collapse

What is pedigree collapse, you ask. If you count your ancestors, you should theoretically double the number for each generation you go back. Two parents. Four grandparents. Eight great-grandparents. And so on.

However, if you actually look at your family tree, the deeper you go, the less likely this calculation is to be valid.

Why?

Before too many generations, your number of many-times great-grandparents would exceed the number of all people living at that time.

So, what actually happened? Interfamily marriages.

One expert estimates that nearly 80 percent of all marriages in the past occurred between first or second cousins.¹ This means that the spouses’ ancestors appear in their descendants’ family trees multiple times. So, there are actually fewer ancestors than expected based on the simple calculation referenced above. Instead of an ever-expanding pedigree, you get points where the pedigree has collapsed.

I’ve seen this in action on both sides of my family tree. On my father’s side, I’m descended from Andrew Walker Sr. and his wife Catharine Margaret Fetzer three times through their children: John and his wife Mary Lucas, Catherine and her husband George Walker, and Mary Ann and her husband John Mayes. I am allegedly descended from Johann Michael Haudesheldt and his wife Maria Dorothea Seitel through two of their sons: Lawrence and Michael.

On my mother’s side of the family, I’m descended from Johann Michael Klein Sr. and his second wife Maria Catharina Kuntz twice through their daughter Maria Magdalena and her husband Conrad Brey, and their son Johann Jacob and his wife Eva Elisabetha Heilig. I’m descended from David Yeakel and his wife Susanna Heydrick through sons Johannes Henrich and his wife Susanna Heydrick,² and Jeremias and his wife who was a Wolf. In fact, Jeremias serves as a point of collapse, too, because I descend through two of his daughters: Charlotte who married Andrew Schultz, and Catharine who married Conrad Wolf.

Yeakel and Heydrick (Heidrig) appear elsewhere in my pedigree with Rosina Yeakel, daughter of Balthasar and Regina (John) Yeakel, wife of Rev. Christopher Schultz, and Anna Heidrig who was the wife of Melchior Krauss, whose grandson Balthasar Krauss married Susanna Yeakel, daughter of Johannes Henrich and his wife Susanna Heydrick. It’s likely that if I were to trace these families back through Germany, I’d find additional points of collapse.

These are just the families I’ve found in my direct ancestry. Collateral lines have additional cousin marriages. And then there are those relations who are yet unproven. For instance, I have “Hartzel” and “Hertzel” ancestors who were said to be brothers. How many more points of collapse will I find as I go further back?

Why is This Important?

That interesting fun fact is actually useful in your research. Related families often moved and settled together. Cousin marriages one or two generations on were not uncommon. From our perspective, working backward through our family lines, these marriages may not appear to be cousin marriages. Our ancestors may or may not have known they were cousins, but we don’t. It’s only after we get back another generation or two that we finally make the connection and see the relationships.

It may not even be your line that reveals the relationship. So, if you’re stuck, researching those around your brickwall—friends, siblings, neighbors, associates—may be more help than you think. Check out the in-laws, too. Who knows, they may just be family.

• Category: Research
• Tag: Maternal Line, Paternal Line