Cousin relationships Marriages and sexual relationships between first cousins are stigmatized as incest in some cultures, but tolerated in much of the world. There are some cultures in Asia which stigmatize cousin marriage, in some instances even marriages between second cousins or more remotely related people.

Is second cousins inbred?

First cousins have an inbreeding coefficient of 0.0625. Anything at or above 0.0156, the coefficient for second cousins, is considered consanguineous; that includes relationships between people and their nephews and nieces.