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?