Hello Cousin!

I know I’m diverging from finishing the Miss Anne Powell train of stories, but I thought I’d throw this post out there. A part of my focus in writing this blog is to give new family history researchers some helpful tips and interesting information. This post fits that focus. I was watching some YouTube videos from Vsauce the other day and one of the videos reminded me of the issue I’m writing about here. If you are new to genealogy, you may not have come across the concept of “pedigree collapse”. The following is an excerpt from my forthcoming book, Genealogy Basics for Canadian Family History Researchers. I’ve added some links so that you can go read more about the concept.

Let’s Do Some Math

Wouldn’t it be wonderful to be able to trace your family back 500 years? 1,000? Would it even be possible to trace all of your unique ancestors on both sides of your family back so far? For most of us, the answer is “probably not”, and not only because there are no historical documents to trace your lineage that far back.

Your family tree is, at its simplest, two separate pedigrees, one for your father and one for your mother. If we consider a generation to be about 25 years, we would be thinking about 20 generations for 500 years of history and around 40 generations for 1,000 years of history. Now consider this: for every generation we go backward the number of our ancestors doubles. You’re number one, you have two parents, four grandparents, eight great-grandparents, sixteen great-great-grandparents, and so on. By the time you go back 500 years, you would be looking for more than half a million people. If you could go back another 500 years to 1,000 years ago, you would be looking for 550 billion people (and by the way, I did the math using a spreadsheet, so please feel free to correct me if you think my math is wrong). Now stop and think about that. There are 7 billion people in the entire world today; the highest number in history. How could you have 550 billion unique ancestors? The short answer is: you can’t.

Pedigree Collapse

In genealogy there is a concept called “pedigree collapse”. This means that, at some point in the past, both your father’s line and your mother’s line will have a single common ancestor and the unique pedigree for each collapses. In other words, both of your parents are descended from the same person at some point.

According to Rhode, et al., in a letter published in the journal Nature, the most recent common genealogical ancestor of everyone living today came from Taiwan about 2,300 years ago. This means that if we could trace our family history back 2,300 years genealogically, each of us could name this person as an ancestor. According to another source, if you go back 20 generations, one-third of your ancestors will be duplicates. So if you could go back 500 years (20 generations), approximately 175,000 of your potential half million ancestors would be common to both your family lines. In fact, anyone in your country in the same ethnic group likely will be your relative. If you’re European in descent, the point where the number of possible ancestors is the same as the estimated population (the entire population, not just the adult population) occurs sometime during the mid-fourteenth century. So, as you can see, it is impossible in this respect to trace your family tree as two separate pedigrees back 1,000 years. Somewhere along the line they are going to converge into a common ancestor.

I have one client whose family I traced back to 1800. This client’s father’s direct ancestor in the surname line had come to Canada from the United States around that time. I wasn’t researching the client’s mother’s line, because the research objective was to prove a bit of family lore about a First Nations ancestor in the father’s line. Surprisingly, when I researched the client’s paternal grandmother and grandfather’s lines to the early 19th century, I discovered that they converged at the same individual, the one who arrived in Canada from the U.S. in 1800. This is an example of pedigree collapse.

Of course, this is only one small part of all this client’s ancestry. There were certainly other immediate ancestors who were in no way so obviously related to that first ancestor in 1800. Early 19th century Upper Canada had a population of, according to the Library and Archives Canada website, 70,718, and so had an equally-limited population available for marriages. This type of limited pedigree collapse is a fairly likely occurrence for most people who trace their ancestry through both lines to early Upper Canada or the same area of another part of early Canada. Further, such convergence demonstrates why the number of your ancestors can never be more than the population of a given ethnic group, country or continent at any given point in history. Thank goodness for immigration.

Til next time, take care Cousin.


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