Why did kings marry their sisters in so many historic societies, like ancient Egypt, Hawaii, the Inca kingdoms, pre-industrial Thailand, and several African realms? Why is royal incest so common?
Incest sets the king above society. If a king can break society’s most basic rules, he stands above everyone else. Plus, a truly lofty king has no peer other than his sister, since only she shares his exalted birth. A noblewoman couldn’t stand beside him as his queen and near equal, and neither could a princess from a lesser dynasty. So the propaganda of mighty kingship sometimes demands incest.
royal incest: King Chulalongkorn of Thailand and his sister/queen, Saovabha Bongsri
King Chulalongkorn of Thailand (1853-1910) and his sister/wife, Queen Saovabha Bongsri
Incest is god-like. The Greek god Zeus married his sister: the goddess Hera. So did the Egyptians’ Osiris, marrying his sister Isis. The Inca god-king Manco Capac married his sister too. The same goes for a long list of gods from across the world. So by marrying his sister, a king becomes god-like.
Royal incest keeps down the supply of rival families. By marrying their sisters, kings keep noble families from claiming semi-royal status through marriage links with the royal family.
Incest isn’t as bad as you think, genetically speaking. Most children of incest live perfectly healthy lives. It’s only after many generations that the genetic odds stack up against them.