Comment by godelski

The bottom of that link has a video that is far more meaningful[0]

It asks the question if the presidents are more related to one another than to another random group. The answer to this is no.

This is probably pretty obvious if you actually look at population sizes through time[1]. There's 8 billion people alive today, but we have a billion less in 2010, 1999, (5) 1986, 1974, 1960, 1927, 1800. So in the last 100 years we grew 6 billion people! But in the last 200 years only 7 billion. In 1200 (approximately the time of King John) there was 360 million people in the world. Which is like taking the entire US and distributing across the globe. For reference, there were only 68 million people in Europe[2], which is about the current population of the UK[3] or about the combined population of Tokyo and Delhi (add Shanghai and Sao Paulo if you require city proper).

So you can probably just guess through how quickly population exploded that you're going to have convergent family trees without going back very far. Honestly, I'm more surprised it takes 800 years and not less.

[0] https://www.youtube.com/watch?v=9shzqqcfvfw

[1] https://www.worldometers.info/world-population/world-populat...

[2] https://en.wikipedia.org/wiki/Medieval_demography

[3] https://www.worldometers.info/world-population/population-by...

[4] https://en.wikipedia.org/wiki/List_of_largest_cities