Though close relatives marrying is bad for the children's health, it's actually a slight benefit for the grandchildren, great-grandchildren, etc. Why that's tr

Though close relatives marrying is bad for the children's health, it's actually a slight benefit for the grandchildren, great-grandchildren, etc. Why that's true: The reason inbreeding is bad is that the child is at risk of inheriting two copies of a nasty recessive mutation, in a region of their genome where both versions came from the same recent ancestor. However, if the child goes on to successfully reproduce, it's more likely that they had zero copies than two--and in that case the grandchildren have zero copies, which is good for them.