For example, hepatolenticular degeneration in the offspring of general marriage, the chance of disease is only one in four million, and in the offspring of cousin marriage, it is as high as one in 64, and the incidence of genetic disease in the offspring of close marriage is 150 times higher than that of non-close marriage. In addition, the birth mortality rate of children born to close relatives is more than twice as high as that of children born to non-close relatives.
Therefore, there is a scientific reason why close relatives should not marry.