In the book Hawaii, Michener describes the practice of marrying your sibling as practiced amongst the royalty of Hawaii traditionally. It is stated there that you have either exceptionally fine children or defective ones. They would simply drown the defective ones at birth.

I don't remember what he said the odds were...it vaguely seems like 50 50.

When I was an early pubescent teen I remember trying to sneak a peek at my older sisters, but I cannot remember ever having any notions about doing more than that.

The taboos are strong, but in the example you cite, it is difficult to see the harm, morally. I think such actions would be emotionally "playing with fire" though, perhaps.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.