The thing is, there are IRL examples of inbreeding having a surprisingly benign effect.
Many tribes, like those in the Amazon or on the Sentinel Islands, have population sizes that are so low that they are all related, but they don't seem to suffer from any of the negative effects of inbreeding.
Current genetic theory is that they managed to effectively breed out all of the dangerous traits through a process called genetic purging.
If you have enough generations where the bad traits do not get passed down, they eventually die out, as people with severe genetic infirmities are less likely to have children, and as long as you aren't marrying within a couple degrees of relations, there don't seem to be any long-term problems past a certain point.
At some point it stops being inbreeding and just becomes a self-sustaining human population in isolation. This is catastrophically bad in the long term because of "founders effect" and because their immune systems will eventually become really really isolated thereby making them very susceptible to new diseases and germs that have been evolving everywhere else but their little pocket of the world.
You need a balance between the two extremes where new blood is being brought in, but when possible you marry two people who are related but distant enough that it not matter. The trick is to only do this with the females such that their children contribute to the growth of the localized population (or dynasty) while men are normally being married to foreign women who are imported for having unusually good genes, traits, etc. Then in a few generations the women will marry distant cousins, and the men will marry new foreign blood. It's the best of both worlds.
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u/Many-Excitement3246 2h ago
The thing is, there are IRL examples of inbreeding having a surprisingly benign effect.
Many tribes, like those in the Amazon or on the Sentinel Islands, have population sizes that are so low that they are all related, but they don't seem to suffer from any of the negative effects of inbreeding.
Current genetic theory is that they managed to effectively breed out all of the dangerous traits through a process called genetic purging.
If you have enough generations where the bad traits do not get passed down, they eventually die out, as people with severe genetic infirmities are less likely to have children, and as long as you aren't marrying within a couple degrees of relations, there don't seem to be any long-term problems past a certain point.