bilby
Fair dinkum thinkum
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You don't need to go back as much as 1,000 years to find that everyone in Europe is related.
Everyone alive today with a fairly recent European ancestor is almost certainly descended from King John. And it's vanishingly unlikely that they are not descended from Julius Caesar.
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001555
Everyone with a recent English ancestor is very likely a descendant of every English person (who has left descendants) prior to 1500CE.
Everyone alive today with a fairly recent European ancestor is almost certainly descended from King John. And it's vanishingly unlikely that they are not descended from Julius Caesar.
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001555
We have shown that typical pairs of individuals drawn from across Europe have a good chance of sharing long stretches of identity by descent, even when they are separated by thousands of kilometers. We can furthermore conclude that pairs of individuals across Europe are reasonably likely to share common genetic ancestors within the last 1,000 years, and are certain to share many within the last 2,500 years. From our numerical results, the average number of genetic common ancestors from the last 1,000 years shared by individuals living at least 2,000 km apart is about 1/32 (and at least 1/80); between 1,000 and 2,000ya they share about one; and between 2,000 and 3,000 ya they share above 10. Since the chance is small that any genetic material has been transmitted along a particular genealogical path from ancestor to descendent more than eight generations deep —about .008 at 240 ya, and 2.5×10−7 at 480 ya—this implies, conservatively, thousands of shared genealogical ancestors in only the last 1,000 years even between pairs of individuals separated by large geographic distances. At first sight this result seems counterintuitive. However, as 1,000 years is about 33 generations, and 233≈1010 is far larger than the size of the European population, so long as populations have mixed sufficiently, by 1,000 years ago everyone (who left descendants) would be an ancestor of every present-day European. Our results are therefore one of the first genomic demonstrations of the counterintuitive but necessary fact that all Europeans are genealogically related over very short time periods, and lends substantial support to models predicting close and ubiquitous common ancestry of all modern humans.
Everyone with a recent English ancestor is very likely a descendant of every English person (who has left descendants) prior to 1500CE.