French Canadians: What we mean by an "isolated population"

In Anthropology classes, you'll hear the French Canadians referred to as an "isolated population", meaning that there is little intermarriage/breeding with other ethnic/racial groups. (You'll also see the word "inbred", but we try to avoid that because it has negative connotations.) In truth, French-Canadian populations have long mixed with Native and other European communities, however, there is a tendency toward endogamy. Because of the "isolation" of French-Canadian communities, there are certain genetic markers associated with French-Canadian ancestry, as well as unusually high incidence of certain genetic diseases, particularly Tay-Sachs.

As I work on the genealogy of my French-Canadian ancestors, I'm getting a much more visceral understanding of what we mean by "isolated". My great-grandmother, Medora LeFebvre, was born in Maine, but her parents were both born in the area around Quebec City, and following their families back, with only one exception, every single one of her direct-line ancestors has their ultimate origin in Quebec City in the early to mid 1600s. (The one exception is an English soldier from the mid-1700s). Most of the French-speaking Catholic inhabitants of Quebec City married other French-speaking Catholics (whether of European or Native ancestry), making the effective breeding population quite small. Now, obviously, there were other French-speaking Catholic communities, and people were continuously moving between them. I'm only 1/8 French Canadian, for example, and there are lots of other people with mixed French-Canadian ancestry.

If we think about this mathematically, however, we can see why most French-Canadians have some overlapping heritage. Take the specific case of Quebec City: Quebec City was founded in 1608, but grew quite slowly. According to wikipedia, (granted, not the most impressive source), in 1665, the town only had 550 people, a quarter of whom were in religious orders. This means that only a little over 400 people made up the reproducing population of the city (and of course, many of those would have been children, so not yet of reproductive age). If we're generous, we can say that 350 years ago, or around 17 generations back, Quebec City had about 450 potential ancestors. Seventeen generations back, we each have a total of 131,072 ancestors. If all of your ancestry is in Quebec City prior to 1665, then you are likely related to almost everyone who lived in the city at that time, and most of them would be related to you through multiple lines (that is, they would repeat over and over in your family tree).

 Of course, many people's French-Canadian ancestors - even the ones from Quebec City - migrated into New France after 1665. But French migration was cut off when the French lost control of the city in 1763, at which time the population was about 8,000 people. That is 252 years ago, or over 12 generations back, when we each have 4,096 ancestors. Again, anyone whose ancestry is rooted in the French population of Quebec City is very likely to be related to almost anyone else with similar ancestry, since each of us is probably related to half of the inhabitants of the town in 1763. (OK, that's not quite true, because of repeats, but you get the idea).

The practical effect of this isolated population is that most French-Canadians - particularly if they are from the same region of French Canada - are related to each other on some level. When I see that a person has French-Canadian ancestry in Quebec City, I know I'm almost certain to have some connection. Wikitree.com has a fun feature that allows you to calculate your relationship to anyone who is in their system. Here are some tidbits from our family:

I am 9th cousins with the new Canadian Prime Minister, Justin Trudeau, through our common descent from Charles Cloutier, one of the early immigrants to Quebec City, who arrived in 1634. We have 46 known common ancestors in the last 25 generations.

Madonna (the singer) and I are 7th cousins, twice removed. We share 50 known ancestors in the last 25 generations, the closest being my eighth great-grandfather (her sixth), Charles Fortin, who was born in Quebec in 1656. I find this a particularly funny relationship because Madonna's family and mine (on my father's side) have deep roots in Bay City, Michigan. My grandmother knew her grandmother. But we're related through my mother's side.

Sticking with singers, Celine Dion and I are also 7th cousins (once removed). We have 125 known common ancestors in 25 generations, starting with Pierre Morin, born in Port-Royal, Acadia (eastern Canada) in 1662.

Hillary Rodham Clinton and I are 7th cousins, once removed. We share my 8th great-grandfather, Mathurin Gagnon, who was born in Perche, France, in 1606, and migrated to Quebec City sometime before 1641.

I'm sure there are a bunch more. If I run across any in the process of genealogy, I'll let you know.