Why Did so Many of History’s Kings Marry their Sisters?

by | Oct 4, 2011 | Ancient History, Special Historical Studies, Pre-Columbian Americas

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?

  1. 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.
  1. 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.

  1. 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.
  1. 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.
  1. Most kings had large, diversified portfolios of children, so they could afford a few risky investments. Kings generally get to sleep with lots of women. So historic kings had a good chance of fathering many children, born to mothers who are not related to them. They could risk a few unhealthy offspring.
  1. Many royal siblings didn’t know each other well. Royal siblings often grow up with limited contact. Nature usually prevents attraction among children raised in the same household, but that doesn’t necessarily prevent attraction between a king and a sister he hardly knows.

© 2011, 2018 by David W. Tollen. All rights reserved.

See also, Star Wars and History: Father vs. Son in Myth

KEY SOURCE: National Geographic, The Risks and Rewards of Royal Incest (Sept., 2010).


  1. Mhasekho Resu

    For me I don’t think that incest not a bad thing, it is our own choice . No one can stop or critisise another.

  2. ericaling666

    Not unusual for religion, dynastic tradition to dictate activities lesser mortals would eschew. In our ” enlightened era ” we commoners,” dregs, deplorables ” accept far worse-ritual sacrifice of infants, modern slavery, starvation of millions, child sexual exploitation, while others spend $ millions on exotic food. I find it difficult to evince virtuous indignation, for our ancestors.



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