Faith
To have blue eyes an individual must have a b gene and a b gene. You can't have a B and a b, that gets you brown, as does B and B. Well, if only bb's make up a newly isolated population they will only produce blue-eyed offspring and that will characterize that group in distinction to the parent group.
Your own arguement undoes your position for Noah's family being the only surviving race on earth.Otherwise you must explain how all the genetic diversity in humans like sickle cell anemia or cystic fibrosis or hemophilia could occur unless all these genetic disorders were present in Noah's family since they are about as genetically isolated as it gets eh?. This is just a sampling list of all the genetic disorders in humans.
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