Again, every religion prohibits marriage between blood relations, though the rules vary somewhat; as, for instance, in the West, marriage between an uncle and his niece is sometimes permitted, a union usually considered unlawful in the East, as by some other Western religions. However, certain modern social revolutionaries are now questioning the laws which make blood-relationship a bar to marriage. These laws are nevertheless rooted in truth; for where there is no expansion, there is no progress.