# How many ancestors did I have 1000 years ago?

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:

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.

## 43 thoughts on “How many ancestors did I have 1000 years ago?”

1. This of course depends on the nature of your pedigree.

To take a trivial example, if your father’s parents are Swedish and Nigerian, while your mother’s parents are Chinese and Arab, you will have many more ancestors than if all your grandparents come from one stock.

• Harry Keough says:

You will have exactly the same number of ancestors no matter what your ancestry is. You would in this case have a more diverse gene pool, of course!

• Rob Lynn says:

Way to show that you either didn’t read or didn’t understand the article

• L says:

Do you think perhaps some people were counted twice? In the past, in villages the whole village can be related, meaning, that the same ancestor could be in different lines of the tree (for example, he is the ancestor to both my mother and my father). So he is counted twice. Am I thinking right or no?

2. mskitty says:

Darel on the DNA-NEWBIEs list had this to say: “To put some perspective on the number of ancestors 1000 years ago being nearly 1 billion or 500 million pairs (husband & wife), estimates for the total human population in Europe is around 40 million people in 1000 AD and total world population is estimated to have been between 300 or 400 million. Unless those estimates are WAY off, the “numbers” of ancestors may be around a billion, but more likely far less than that if you filter duplicate names….The family tree is actually shaped more like a diamond or one of those old lava lamps?”

3. Perhaps you’ll like this take on the question as well. I used a model (based on royal genealogy, since most human populations have been practicing first-to-fourth cousin marriage) and projected it back with the same growth curve back to the identical ancestors’ point.

• mskitty says:

Great video! Thanks for posting it here!

4. And as Israel Pickholtz says, the curve goes up faster or slower depending on the population(s) your ancestors belong to. Eventually we all get to the identical ancestors’ point, but some more isolated lines will merge with the rest of our common ancestral population when the global population was lower.

• KAAffleck says:

What a great article! On my Icelandic/Norwegian side, I too am related to King Harald! As well as Ragnar Lothbrok..(my 31st Great Grandfather), Robert the Bruce, just to name drop a few! I was curious to know how many we had so far back….i’m gonna need a bigger Tree to fill out!! Lol! I find this genealogy so fascinating! If it weren’t for these generations of ancestors and their struggles to survive, we wouldn’t be here discussing them!

• Gina says:

I’m related to Robert the Bruce as well. How cool. My 20th ggrandfather. That is if all the lines that far back are correct!

5. joyce lawson says:

My ancestors have been traced back to queens and kings of sweden..england..

6. Dan says:

“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.”

This is only one of millions of paths of your direct ancestors. 1 path is 27 generations, there may be thousands more paths that are 35 generations. To say your ancestors 1000 years ago is only 27 generations for you is nonsense and defeats the object of this article.

7. kevin says:

Whilst the figures appear logical and mathematical I dont believe them, back track maybe 5 generations but no more. As an aside your back at the tenth generation… with 1000 plus ancestors whom in turn will have children etc etc… so just how many descendants would be roaming the Earth today.

• mskitty says:

Yes Kevin, that is the point. Our ancestors start duplicating after a while. Read the Joseph Chang paper or the more readable Brian Pears series.
Also we are all cousins … so share most of those ancestors 1000 years ago.

• L says:

Whilst YOU don’t have to believe, it is what it IS.

8. With my Scots-Irish-German background and my wife being Asian we don’t look for too many common ancestors we might have between us.

• Although not definitive, 23andme says my Japanese/American daughter is more than 50% European…

9. Ann Stanley says:

Fascinating website. Glad I found it.

• LaNell says:

Yes, it is!

10. I’m from Cherokee NC and I’m half Cherokee,my mother was fullblood.the term local convention use to describe the pedigree. The other side or half is Scottish,irish,German and English. Western north Carolina in the Appalachian mountains was settled by this side or half. According to are legend we have always been here from the beginning of time. The scientists have proof that we have been here 12,000 to 14,000 years. My ancestors thought of seven generation ahead when making decisions. This article has made me look at my own generations in a new light

• “My ancestors thought of seven generation ahead when making decisions.”- I love that!

• LaNell says:

They thought seven generations ahead? You are being deliberately comical. Right?? Since they were only thinking of food through the winter…

• Isabelle PRENAT says:

Really?
Were you there?
Are you aware that Indigenous people only harvested only 20% of any single plant for food for example, so that the plant could reproduce and be productive the following year and into the future???
That is only one of the things they did as they thought 7 generations ahead…
No, I didn’t think that you knew that…

11. Viens, Michael says:

It is important to remember that the number of ancestors lived through a thousand year period. The final number doesn’t mean that there were more than a billion people on the planet 1000 years ago but a billion people that lived over the course of 30 generations. Lets break it down to basic math. My parents each had parents meaning going back two generations I had 2+4=6. To figure out 30 generations you would multiply 4 (mothers parents+fathers parents)×30(number of generations )+2 (mom and dad)=122. The chart doubles the previous amount. That is simply contrary to common sense. Each child can only have 4 grandparents and 2 parents. The chart suggests that children have multiple parents and grandparents. It’s not compound math but simple math. Basic addition… Even if you go back 100 generations there would be 402 ancestors.

• mskitty says:

Michael –
No the chart does not suggest multiple parents and grandparents. It is just counting the number of ancestors in each generation.
Your 4 grandparents each had 2 parents which makes 8 people in that generation. Those 8 people also each had 2 parents so 16 in the next generation. Thus each generation of your ancestors going back is double the size of the previous generation.

• Alan says:

Wow Michael – your basic maths is terrible!!
It doubles each generation, it’s not rocket science.

• 1-me- my generation
2-parents- 2nd gen back
4-3rd
8-4th
16-5th
32-6th
64-7th
128-8th
256-9th
512-10th
1024-11th
2048-12th
4096-13th
6192-14th
16384-15th
32768-16th
65536-17th
131072-18th
262144-19th
524288-20th
1048576-21st
2097152-22nd
4194304-23rd
8388608-24th
16777216-25th
33554432-26th
67108864- 27th
134217728-28th
268435456-29th
536,870,912- direct ancestors in the 30th generation {barring incest}
These figures are just off the top of my head quickly. Feel free to check them with a calculator!

• Kitty says:

Those numbers are already listed above … but many of us know that we have the same 7th grandparents more than once in our tree, etc

12. Momo says:

40 generations of ancestors for just one current day person total just over 2.4 billion from memory… so for approximately 3 random current day persons, there would have been 7.5 billion ancestors for 40 generations…which is about the current world population….go figure.. wtf ??

• Kitty says:

and that Momo is why we know that it is a family braid not a family tree. Many of your ancestors are the same people as I say in the article “So your ancestors must be duplicated numerous times on your family tree”

13. Assume you lived on a desert island where people have been living with a steady population of 1000 people for 30 generations. And no one could leave the island. How many ancestors would you need to have?

• Isabelle PRENAT says:

Ask the people who lived on Easter Island before contact…

14. Richard says:

Thanks Rod!
Holy Crap! And I thought living within a 1 hour radius to my In-laws was scary!

15. Richard says:

Unfortunately for me, my family genealogy doesn’t go back very far at all.
I’ve been told that my Great, Great, Great Grand parents came from a remote tribe of Cannibals living in the North-Eastern part of Australia.

The words ‘Begotten’ and ‘BeEaten’ sound very similar to me.
Invitation cards that say “why don’t you come over for dinner to celebrate” scare the heck out of me!

16. So the conclusion is that many of our ancestors were not from separate families. Families must have interbred since there were not enough people in a specific island to support 30 generations of people. The conclusion is you better marry a foreigner or you children will end up with many inbred defects. Fortunately as an Englishman I married an Asian.

• LogicalHeathen says:

“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.”

This argument is fallacious, the maths doesn’t postulate that everyone of your ancestors was alive 1000 generations ago, it is saying that this amount of people (2 x people having successful sexual intercourse) had a descendant leading to you over x generations.

• Tom Christie says:

Spurious conclusion – if it were true we would all have inbreeding defects by now. Actually, it’s most advantageous to marry your 6th cousin, in terms of genetic distance.

• JEFFREY L CONWAY says:

Very interesting. Time to google if interracial marriages produce children with less birth defects than average. The sure would mess with “racial purists.”

17. LaNell says:

This HAD entered my mind, definitely. Glad to know there’s a name for it. Pedigree collapse. Brilliant! My Hall/Primrose 1700s immigrant couple from Scotland? Seems Cpt. Thomas Hall, married to Lady Catherine Primrose…his father was also married to a Primrose lady of the same line.

18. Gino says:

Genesis 15:16 say that 1 generation = 100 years

• Rod C says:

A “generation” is the time interval between ages of parents and children so were your parents 100 years old when you were born? Lifespan has shortened a lot since Genesis.

19. Larry says:

Wow this is amazing topic, I am impressed as to how people can’t follow the logic of this concept. We are all bound together today by ancestry. Do the math, then take it back to 100 generations.

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