It would seem simple enough to test. (Probably couldn't get PEOPLE to do it (except maybe those from one of them Appalchaian [sp is WRONG!] states that we Uber-men like to mock) but perhaps RABBITS.
Take 4 boys and girls and LET 'em go!
Rabbits have litters.
They can have far more offspring per unit of time than humans
In addition, the mix would have to be not 4 pairs but one pair (representing Noah and his wife), three male offspring of that pair and 3 semi-random females. Semi random because Noah and his family are not that far removed from Adam and Eve, thus putting an initial restriction on the possible genetic diversity.
That's why the genetic diversity is