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Comment by quickthrower2 | Hacker News Reader

This makes some crazy assumptions that not only do people not have kids with their first cousins (they do!) but they don't with there Nth cousins for N going into the dozens, with the family tree organizing itself into a perfect inverted pyramid. Also a generation can be 15-50 years, and is unique to each parent-child pair in the DAG (to use the term from the sister comment).

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I'm kinda wrapping my head around the DAG thing (but still have no clue how large of an effect it has on the overall calculation) but don't get how 25 years per generation is off. I know that in the last few centuries people have been having children at older and older ages but you're saying that an average like that doesn't hold for the long-term? Or maybe it's just very complicated? E.g. some 60 year-old man gets a 20 year-old woman pregnant 700 years ago and it has a dramatic change on the calculation?

Historically, having your first child around 27 was average except for the wealthy. The post war period was a historical aberration of young marriage.

> fathers consistently older (30.7 years) than mothers (23.2 years)

https://www.science.org/doi/10.1126/sciadv.abm7047

Those numbers from the abstract are average generation times, which is very different than the average age of having the first child.

Try the awesome numberphile video "EVERY baby is a ROYAL baby" [1] https://www.youtube.com/watch?v=Fm0hOex4psA

The problem isn't so much the average generation length but that generations are not coordinated waves each only having kids with the same generation.

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