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Kayce Basques
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layout: base.njk | ||
title: "You have thousands of ancestors from the 1500s" | ||
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# {{ title }} | ||
<noscript> | ||
It looks like you have JavaScript disabled. This page uses JavaScript to | ||
redirect you to https://www.biodigitaljazz.net/blog/ancestors.html so I guess | ||
you can just manually redirect yourself instead? | ||
</noscript> | ||
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I usually think about lineages from the perspective of the ancestor. E.g. my | ||
grandpa had 5 kids; those 5 kids produced 9 grandkids; those 9 grandkids | ||
produced 3 great-grandkids (so far); 17 descendants in total. | ||
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Over the last few days, I've been having fun thinking about the situation in | ||
reverse, from the perspective of the descendant. Here's a quote from *Genes: | ||
A Very Short Introduction* by Jonathan Slack: | ||
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> Also, when considering 'roots', some of the basic mathematics of inheritance | ||
> needs to be borne in mind. With fully random matings the number of your | ||
> ancestors doubles every generation. Ten generations ago (250-300 years) we | ||
> might expect about 1,000 ancestors each contributing 0.1 percent of their | ||
> total variants to your genome... when the number of ancestors exceeds | ||
> 2,000-3,000 (12 generations would be about 4,000), it is likely that some | ||
> ancestral sections of DNA have been lost altogether... by about 15 | ||
> generations back many of the ancestors contribute no DNA variants at all but | ||
> they are still ancestors on the lineage. So, even though we all have an | ||
> ancestry running back to the origin of life on Earth, we do not necessarily | ||
> have any DNA variants from most of our ancestors. | ||
[original version of this post]: https://web.archive.org/web/20230905030056/https://kayce.basqu.es/blog/ancestors/ | ||
[Hacker News discussion]: https://news.ycombinator.com/item?id=37387341 | ||
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(In the [original version of this post] I did a thought experiment here to calculate | ||
when the number of ancestors starts to get nonsensical, i.e. if you double the | ||
number of ancestors every generation there's a point where the number of ancestors | ||
exceeds the total number of humans at that point. I've removed this thought experiment | ||
because I think it distracts from my main idea. See the [Hacker News discussion].) | ||
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[pedigree collapse]: https://en.m.wikipedia.org/wiki/Pedigree_collapse | ||
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Your exact number of ancestors depends on how much [pedigree collapse] there | ||
is in your lineage, but I'm pretty sure the basic premise of this blog post | ||
holds: you've got a lot of ancestors. | ||
<script> | ||
window.location.replace('https://www.biodigitaljazz.net/blog/ancestors.html'); | ||
</script> |
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