# Average distance to common ancestor **URL:** \ **Category:** Factual Questions\ **Created:** [June 23, 2023, 10:03am UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987 "2023-06-23T10:03:23Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Danger\_Man](https://avatars.discourse-cdn.com/v4/letter/d/6de8d8/32.png) [@Danger\_Man](https://boards.straightdope.com/u/Danger_Man)\ **Post date:** [June 23, 2023, 10:03am UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987/1 "2023-06-23T10:03:24Z")
I’m wondering if there are any numbers available for how far on average you have to go back to find a common ancestor in different populations. I was intially interested in my own country, Norway, which is pretty homogeneous, but also other places that are similar. Do these numbers exist? ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [June 23, 2023, 11:18am UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987/2 "2023-06-23T11:18:06Z")
I would think this would be difficult in a local population (e.g. Norway) since you have migration and invaders into the country over the centuries as well as their own forays invading other towns and countries and sometimes bringing women from other places back with them as part of their loot. I’m not sure you can get a “pure” enough community to say they all came from a common ancestor. We do have a notion of Mitochondrial Eve and Y-chromosome Adam who are common ancestors to us all (every human on earth has them as their great, great, great, great…grandparents) but they lived several hundred thousand years ago (and they almost certainly didn’t know each other). ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 23, 2023, 2:44pm UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987/3 "2023-06-23T14:44:26Z")
Yeah, Norway might be pretty homogeneous, but I’d still wager that there are a few immigrants from Australia, Asia, and Africa living there, and it doesn’t take very many before you’re probably looking at the common ancestor of all of humanity. You might be able to phrase it as something like “common ancestor for 95% of the population”, or the like. But in that case, the answer might vary significantly for different chosen percentages. ---
**Author:** ![Danger\_Man](https://avatars.discourse-cdn.com/v4/letter/d/6de8d8/32.png) [@Danger\_Man](https://boards.straightdope.com/u/Danger_Man)\ **Post date:** [June 23, 2023, 3:13pm UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987/4 "2023-06-23T15:13:04Z")
That is not exactly what I am after. It’s more like if you take two random individuals, what is the average distance to their common ancestor. So it doesn’t need to be the same common ancestor for eveyone living there. Or maybe we could try for something a little different, like “50% of the population has a common ancestor no more than 10 generations ago”. I think what I want to do is to visualize how interconnected the population is. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [June 23, 2023, 3:31pm UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987/5 "2023-06-23T15:31:54Z")
Iceland is so interrelated that an app was created to let people know how closely related they are to a potential date. > **[Kissing cousins? Icelandic app warns if your date is a relative | CBC News](https://www.cbc.ca/news/business/kissing-cousins-icelandic-app-warns-if-your-date-is-a-relative-1.1390256)** > > You meet someone, there's chemistry, and then come the introductory questions: What's your name? Come here often? Are you my cousin? ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [June 23, 2023, 7:15pm UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987/6 "2023-06-23T19:15:31Z")
This article discusses that question > **[Humans Are All More Closely Related Than We Commonly Think](https://www.scientificamerican.com/article/humans-are-all-more-closely-related-than-we-commonly-think/)** > > Humanity’s most recent common ancestor and so-called genetic isopoint illustrate the surprising connections among our family trees And states that: Two people with recent European ancestry are descendants from everyone in Europe in 1000AD who has any descendants today. For the whole world population the point where everyone living at that time is the ancestor of everyone alive today (or no one) is “somewhere between 5300 and 2200 B.C” ---
**Author:** ![Banksiaman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/banksiaman/32/3334_2.png) [@Banksiaman](https://boards.straightdope.com/u/Banksiaman)\ **Post date:** [June 23, 2023, 10:30pm UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987/7 "2023-06-23T22:30:38Z")
One way to approach it is to consider how many generations you could have without sharing ancestors. Broadly, if you take 25 years as a generation, in 250 years you have 10 ancestral generations. That 10th generation of ancestors has your 1024 great great … grandparents. Global population in 1800 CE was [maximally 1 billion people](https://en.wikipedia.org/wiki/Estimates_of_historical_world_population), so reasonable likelihood of your ancestors and someone else’s being distinct. Another 250 years back to 1500 CE, you have 1 million ancestors in your 20th generation. Your friend also has a million. The global population is 425-600 million. The odds of sharing someone are that much much higher. Another 5 generations to 1400 CE and you have 32 million in your 15th antecedent generation in a world with 350-500 million people. Before 1400 population stayed (relative to now) more or less static for centuries, while with each generation back you and your friend each double the number of your ancestors. Its another 4 generations (29 gens - 1300 CE) when your potential max ancestors exceed the global population. In reality you will be connected to some individuals in that 29th gen in many multiple ways. And it is quite possible that you will still have no genetic connection to anyone in the Americas, Australia or the Pacific, and probably no one in the eastern half of Asia or sub-Saharan Africa at that point, just because of the way people were isolated. So if you both connect to a relatively constrained area with fair internal mobility - say Europe - I’d expect you’d have a probable shared ancestor in the past 500 years, and an even chance in the past 250 if you come from the same region or country. ---
**Author:** ![Baker](https://avatars.discourse-cdn.com/v4/letter/b/bb73d2/32.png) [@Baker](https://boards.straightdope.com/u/Baker)\ **Post date:** [June 23, 2023, 11:31pm UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987/8 "2023-06-23T23:31:27Z")
I can’t truly tell you if there is an answer to the the OP, but if you are into genealogy at all you might be surprised. Back in the 1880’a an ancestor wrote about the history of our one family name. I traced two very distant relations, beginning with a common ancestor who crossed the Atlantic in 1722, He had several sons. From one of them I am descended. From another I know of a third cousin five times removed. In the latter part of the 19th century that guy was prominent in government. And while watching a PBS show I saw a woman with that name and managed to get in touch. Turns out her husband was a descendant of a third son of that common ancestor, and we were seventh cousins once removed. ---
**Author:** ![mbh](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@mbh](https://boards.straightdope.com/u/mbh)\ **Post date:** [June 23, 2023, 11:38pm UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987/9 "2023-06-23T23:38:14Z")
My mother once took a class in genealogy at the local Mormon center. They told her that, if you take any two white people in the United States, and trace back 10 generations, you can find a common ancestor. ---
**Author:** ![Baker](https://avatars.discourse-cdn.com/v4/letter/b/bb73d2/32.png) [@Baker](https://boards.straightdope.com/u/Baker)\ **Post date:** [June 24, 2023, 2:35am UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987/10 "2023-06-24T02:35:07Z")
I’m not surprised. In my previous response it was eight generations, at the most. ---
**Author:** ![Blindmellowjelly](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blindmellowjelly/32/13920_2.png) [@Blindmellowjelly](https://boards.straightdope.com/u/Blindmellowjelly)\ **Post date:** [June 24, 2023, 5:09am UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987/11 "2023-06-24T05:09:49Z")
Especially, from my First Cousin Grandma and Grandpa, it is unique. I don’t neccessarily know how to explain it. But as a family, we are like twins. There is a genetic cleavage and kin. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 24, 2023, 12:59pm UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987/12 "2023-06-24T12:59:58Z")
> [@Banksiaman](#): > > Broadly, if you take 25 years as a generation, in 250 years you have 10 ancestral generations. That 10th generation of ancestors has your 1024 great great … grandparents. Except that you might not have 1024 10th-degree ancestors. That’s far back enough that it’s fairly likely that some of those ancestors were the same people. Take two people from sufficiently-separated populations, and they might end up overlapping with themselves more than with each other. ---
**Author:** ![Banksiaman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/banksiaman/32/3334_2.png) [@Banksiaman](https://boards.straightdope.com/u/Banksiaman)\ **Post date:** [June 24, 2023, 1:15pm UTC](https://boards.straightdope.com/t/average-distance-to-common-ancestor/985987/13 "2023-06-24T13:15:22Z")
> [@Chronos](#): > > Except that you might not have 1024 10th-degree ancestors. That’s far back enough that it’s fairly likely that some of those ancestors were the same people. Take two people from sufficiently-separated populations, and they might end up overlapping with themselves more than with each other. I agree - which is why I said that in the second last para.