enjoy friend  apparently old zoroastrianism used to do this too. i think it's repulsive beyond cousin marriage but eh whatever. this paper gives a quite simple mathematical model. inbreeding leads to new recessive mutations. outbreeding leads to literally destruction of the species.   ticles/pmc3275546/#:~:text=a%20cons equence%20of%20the%20model,could%20 ultimately%20only%20lead%20to
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