Someone recently posed the question “How many ancestors did I have 1000 years ago?” in conjunction with the assumption that the various genetic origins programs include about 1000 years worth of ancestry … my answer, of the billion possible maybe a million, maybe far fewer …
Very simply, if you postulate that 1000 years was 30 generations ago then your theoretical number of ancestors is two to the 30th, or just over a billion: 1,073,741,824.This is impossible as nowhere near that many people were alive back then. Plus not everyone who lived a thousand years ago has descendants today. So your ancestors must be duplicated numerous times on your family tree; this is known as pedigree collapse. Brian Pears points out in his article The Ancestor Paradox, that “even if every marriage in every generation was between second cousins, a quite unbelievable situation, we would still run out of people to be our ancestors within 29 generations.”
Kenneth W. Wachter came up with an interesting mathematical model for this, described in Stephen Lewis’ blog post How many ancestors do I have. To somewhat paraphrase, “Going back 30 generations… Wachter’s model calculates that [an Englishman] would have 952,279 distinct ancestors in 1077 – only around 0.09% of the maximum but representing fully 86% of the total estimated English population [at that time] of 1.1 million.”
More recently (1999), Yale statistician Joseph Chang wrote a paper analyzing pedigree collapse that postulated that we Europeans all have a common ancestor who lived in about 1400 AD. Warning, that paper has lots of math in it.
I am not so convinced of these generation estimates however, since in my own tree my ancestors living in about 1000 AD are only my 25th grandparents; so 1000 years is 27 generations for me rather than 30. But then I am descended from many a youngest child. Click here for my relationship path to a Norwegian 25th grandfather who lived in the year 1000, the grandson of King Harald the Finehair, and another 25th grandparent in France from that same time period.
Here are a few very readable articles about the number of ancestors we might have had 1000 years ago:
- Family Tree Magazine, “What is Pedigree Collapse?”
- The Royal We
- Charlemagne’s DNA and Our Universal Royalty
- and the series of articles by Brian Pears: – Our Ancestors, Conceptions, Misconceptions and a Paradox, The Ancestor Paradox Revisited and The Ancestor Paradox Yet Again
In tracing my Norwegian side, I have found much evidence of pedigree collapse among my Etne, Hordaland ancestors, many of them starting to repeat at 7-9 generations back. The DNA shared with other folk from Etne almost always makes the relationships look closer than they are, when in fact there are multiple common ancestors, often on the same lines. Farms Ve, Fatland, Frette, and the Koll (Skiftun) clan keep reappearing in the tree. Plus the Rieber and Galtung family which traces back to royalty, of course.