In low trust societies, there is an incentive for keeping marriages within the extended family. Islam exacerbates this with its institutionalization and celebration of cosanguinary marriage, even between first cousins. Some have argued that the West was made unique by the church banning all marriages between close relations. It certainly changed the politics because it forced rulers to look further for mates. Look up the book, *The Weirdest People In the World* by Joseph Henrich, where weird stands for Western, Educated, Industrialized, Rich and Democratic which gives an insight into how Western civilization differs from the rest. Review https://quillette.com/2020/09/08/the-weirdest-people-in-the-world-a-review/ Journal article https://www2.psych.ubc.ca/~henrich/pdfs/WeirdPeople.pdf