" When the Church banned marriage to in-laws, classifying them as “siblings” to make such unions incestuous, the bonds between kin-groups were broken by the death of either spouse, since the surviving wife or husband was prohibited from incestuously marrying any of their affines. "

― Joseph Henrich , The WEIRDest People in the World: How the West Became Psychologically Peculiar and Particularly Prosperous