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lynmc5 t1_j1v9yrk wrote

Reply to comment by Dorocche in What is the ‘widest’ ancestral generation? by vesuvisian

Given the propensity of people to stay near where they were born and also the propensity of people to marry within social circles, the "expectation" of the number of generations back for every ancestor being unique is probably quite small.

2**15 = 32,768, 15*20 years/generation = 300 years. So 300 years ago, if your community of eligible ancestors was 32,768 or more, each one could be unique. I guess that's not unreasonable depending where they lived, but it doesn't seem likely.

2**20 = 1,048,576, 20*20 years/generation = 400 years. It seems unlikely to me that your community of eligible ancestors 400 years ago would be over 1 million.

Anyway, that's my uneducated guess.

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WilliamMorris420 t1_j1vdlat wrote

There was one teacher, in Somerset, England. Whose relatives have moved about 0.5 miles, in 9,000 years.

https://www.thearchaeologist.org/blog/mesolithic-skeleton-known-as-cheddar-man-shares-the-same-dna-with-english-teacher-of-history

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Octavus t1_j1wd7i8 wrote

Cheddar Man lived before the human isopoint, if he has one living descendant then every single person on the planet is also his descendant. At some point 7,300 to 5,300 years ago if someone had a living descendant, then all of humanity is their descendant.

https://www.scientificamerican.com/article/humans-are-all-more-closely-related-than-we-commonly-think/

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WilliamMorris420 t1_j1wef86 wrote

So why is he the only one, noted as a descendant and not everybody else?

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Octavus t1_j1wgus9 wrote

He has the same mitochondrial DNA haplotype as Cheddar Man, which isn't passed down by males so isn't actually evidence at all that he is a descendant of Cheddar Man. Only that the share the same female ancestor.

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Minniechild t1_j1x4a8f wrote

I would suggest because he lives within walking distance of where Cheddar Man’s remains were found, and also due to the similarities in their faces which make for a nice Personal Interest Piece

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WilliamMorris420 t1_j1x7xdb wrote

They already knew that he was a descendant or at least related. The visual reconstruction, came after the DNA tests.

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Frozen_Watcher t1_j1x4fy6 wrote

This is an optimistic estimate that casually ignores physical/cultural barrier and lack of movements. This estimate only applies if people move around often and for a long distance to leave descendants around a big area all over the world like in modern world which isnt really applicable to ancient past. I seriously doubt some native american living at that time is a common ancestor of most people living in eurasia right now.

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thephoton t1_j20ak83 wrote

> At some point 7,300 to 5,300 years ago if someone had a living descendant, then all of humanity is their descendant.

Weren't, for example, Native Americans, isolated from Europe for more than 7,300 years?

So if you consider someone living in the Andes with pure Native American ancestry, how are they descended from Cheddar Man?

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Octavus t1_j20c6b6 wrote

There isn't believed to be anyone left in the Americas or Tasmania who does not have any European ancestry from the last 500 years.

Going the other direction Paleo Eskimo bridged the gap for a while between the Americas and Asia. Their culture spanned from Russia through Alaska into Greenland.

There was a continuous but some gene flow between Australia and South East Asia. Any other isolated groups of humans have only been isolated for a few hundred years.

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thephoton t1_j24ijax wrote

> There isn't believed to be anyone left in the Americas or Tasmania who does not have any European ancestry from the last 500 years.

OK, but take the Andean's great-to-the-nth grandmother from 7300 years ago (one of the ones who lived in the same region all those centuries ago). Is that grandmother also an ancestor of the teacher in Somerset? And of some villager in a remote village in Tibet?

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Octavus t1_j24z5w5 wrote

Their ancestry would spread to Alaska present day Alaska on only a few hundred years. Paleo Eskimo, who lives from Russia through Alaska into Greenland. They acted as the bridge between the old and new worlds 4,500 and 1,500 years ago.

The world has been much more interconnected than what most would believe. It takes only one person after complete mixing to spread an entire continent of ancestry. Do not underestimate just how much mixing occurs in 1,000 years, that is enough time to completely mix all of Europe.

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Additional-Fee1780 t1_j25u0tt wrote

That’s not true. Australian aborigines have been isolated for something like 50 ky.

EDIT: this is now known untrue. Thanks /u/Octavus!

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Octavus t1_j25ymfi wrote

They have not been completely isolated for 50,000 years, there has been several periods of limited contact.

The most significant is ~10,000 years ago was when Australia was finally culturally split from New Guinea, there is also linguistic evidence as 90% of Australian languages are within the same family and split only a few thousand years ago. However this is before the isopoint so not related.

What is important is genetic and trade evidence between India, South East Asia, and the northwest cost of Australia. This trade and gene flow occurred ~4,300 years and gave enough time for Australia and Tasmania to become completely mixed in the 1,000-3,000 years before the contact.

This is technically only evidence of India -> Australia but the evidence points towards continue contact and not a one off event. Continued contact points to the people returning from Australia to the homelands which allows for gene flow the other direction. It simply takes one person to make the trip and have descendants.

The dingo has only been in Australia for 4,000-10,000 years. If Australians have been isolated for 50,000 years where did this non-native animal come from?

Genome-wide data substantiate Holocene gene flow from India to Australia

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swami78 t1_j1xsoic wrote

Many years ago I was contacted by a German researcher who told me I am a descendant of 40 odd skeletons found in the Lichenstein Hole (a family tomb in a sealed cave) dating from 2500 years ago. They found another descendant less than 5kms from that cave. They were thought to have been Visigoths or Frisians.

I have read that some 60% of English people can find Edward the Confessor in their lineage - and even slightly more French can find Charlemagne in theirs. We're all related anyway - Mitochondrial Eve.

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WilliamMorris420 t1_j1xuwpj wrote

What you find is that as you go back, that you have so many great, great, great.... grandparents. So Edward was born 1020 years ago, which is roughly 40 generations. In that time you "should" have had 1 trillion ancestors. Which is about 10 times more people who have ever lived. Because the same people keep turning up on different branches of your family tree. Especially when you get to about the tenth generation.

Essentially we have so many ancestors that as long you have children and they have children. Your line will continue indefinetly and you'll have millions of descendants.

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sagramore t1_j1yjfdh wrote

Isn't what you've described here exactly what OP's original question states and asks about?

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swami78 t1_j21f2bs wrote

I was hoping someone would do the math! Thanks.

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PicardTangoAlpha t1_j1vqya6 wrote

Whats the widest it can be in a place like North America with large influxes from overseas?

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guynamedjames t1_j1w0dsr wrote

You'll get your widest from interracial households, especially when you get multiple generations of interracial mixing. So your African grandma, dutch grandpa, Chinese grandma and Indian grandpa type families are realistically going to be very far apart generically. And within that, historically people from cities will have more diverse genes than those from the country

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MetricJester t1_j1xr8dq wrote

Also: three of those grandparents could also be children of Genghis Khan.

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Artanthos t1_j1xbtka wrote

If you are talking a small island (Guam) it would be much lower numbers.

If you are talking about Hollars in WV, it might only be 3-4 generations. The Hollar I am familiar with had 2nd cousins marrying and only about a dozen families in total.

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lynmc5 t1_j1xdjit wrote

On the other hand, if you don't require every ancestor to be "unique", that is, not relatives by ancestry, but just want to know the number of unique persons who are ancestors, my simple formula isn't very helpful. If cousins marry and produce a grandchild, that grandchild has 2**3 - 2 great-grandparents instead of 2**3.

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Rolldal t1_j1yrojg wrote

It largely depends on when. During the middle ages under the feudal system it was difficult for all but itinerant workers (tinkers, travelling merchants, etc.) to move but as the feudal system collapsed this changed. During the English civil war many ordinary people moved about, travelled to the new world etc. Also often occupation dictated movement. My Potter ancestors generally stayed put but my miner ancestors moved as mines ran out of coal, lead, tin or whatever they happend to be mining.

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A_Notion_to_Motion t1_j1yeorb wrote

This stuff is hard for me to wrap my head around tbh. It doesn't help that I now have that family tree song stuck in my head for some reason...

"I'm my own grandpaaaaa!!!"

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