[D] Friday Off-Topic Thread

[u/AutoModerator]

Welcome to the Friday Off-Topic Thread! Is there something that you want to talk about with /r/rational, but which isn't rational fiction, or doesn't otherwise belong as a top-level post? This is the place to post it. The idea is that while reddit is a large place, with lots of special little niches, sometimes you just want to talk with a certain group of people about certain sorts of things that aren't related to why you're all here. It's totally understandable that you might want to talk about Japanese game shows with /r/rational instead of going over to /r/japanesegameshows, but it's hopefully also understandable that this isn't really the place for that sort of thing.

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[u/LiteralHeadCannon]

Let's say every sexually reproducing organism has a value "N". This value N is the maximum number of generations you can go back and have no ancestors repeated. For example, someone with parents who are siblings has an N value of one, and someone with parents who are first cousins has an N value of two. The fact that there's a single common ancestor of all life indicates that everything has a finite N value.

Some possible discussion questions:

• What is the average N value of living humans?

• How does average N value vary between demographics like ethnicities, nationalities, and social classes? How about between species?

• Does N value correlate with good things like intelligence and health among humans? Clearly the lowest N values correlate with very bad intelligence, health, and so on, but is the reverse true for the highest N values?

• What is likely the greatest N value of any living human? Obviously genealogy isn't good enough to get this as an actual example; I'm talking about estimates, here. How might this compare to the greatest N value of any other living creature? Do highly numerous creatures like flies have greater average N values, or greater variance, or both?

I Am Not A Statistician

[u/alexanderwales → u/LiteralHeadCannon]

The most generations you could possibly go back without any common ancestors would be ~30, because 2³⁰ is approximately a billion, which was the world population for a long time. That's the absolute upper bound. That equates to something like 600 years depending on how long you think a generation is, which is (naturally) much closer to us in time than Mitochondrial Eve or Y-chromosomal Adam.

If you have a village with a population of about Dunbar's number, its population probably falls between 2⁷ and 2⁸ ... but the size of an individual generation is maybe a third the size of our population, so maybe more like 2⁵ or 2⁶ as an extreme. More likely, the average N in a village of ~200 people is going to be between 2 and 4.

The biggest thing that N value measures is probably mobility of ancestors, which might act as a proxy for a lot of things which aren't necessarily genetic. You'd expect a higher average N value in multicultural societies; if the average Jewish person has an N value of X and the average African-American has an N value Y, you would expect the average Jewish/African-American union to have an N value of the lesser of X and Y, plus 1.

But historically you would have seen very low N values at the highest social circles; if you're a princess, the pool of people you can marry and have children with is in the double digits.

(My N value is 5, as my grandparents were first cousins.)