National Geographic : 2010 Sep
health and development problems that he didn't talk until he was four or walk until he was eight. He also had trouble chewing food and couldn't sire a child. e physical problems faced by Charles and the pharaoh Tutankhamun, the son of siblings, point to one possible explanation for the near- universal incest taboo: Overlapping genes can back re. Siblings share half their genes on aver- age, as do parents and o spring. First cousins' genomes overlap . percent. Matings between close relatives can raise the danger that harmful recessive genes, especially if combined repeat- edly through generations, will match up in the o spring, leading to elevated chances of health or developmental problems---perhaps Tut's partially cle palate and congenitally deformed foot or Charles's small stature and impotence. If the royals knew of these potential down- sides, they chose to ignore them. According to Stanford University classics professor Walter Scheidel, one reason is that "incest sets them apart." Royal incest occurs mainly in societies where rulers have tremendous power and no peers, except the gods. Since gods marry each other, so should royals. Incest also protects royal assets. Marrying fam- ily members ensures that a king will share riches, privilege, and power only with people already his relatives. In dominant, centralized societies such as ancient Egypt or Inca Peru, this can mean lim- iting the mating circle to immediate family. In societies with overlapping cultures, as in second- millennium Europe, it can mean marrying ex- tended family members from other regimes to forge alliances while keeping power among kin. And the hazards, while real, are not absolute. Even the high rates of genetic overlap generated in the o spring of sibling unions, for instance, can create more healthy children than sick ones. And royal wealth can help o set some medical conditions; Charles II lived far better (and prob- ably longer, dying at age 38) than he would have were he a peasant. A king or a pharaoh can also hedge the risk of his incestuous bets by placing wagers else- where. He can mate, as Stanford classicist Jo- siah Ober notes, "with pretty much anybody he wants to." Inca ruler Huayna Capac (-), for instance, passed power not only to his son Huáscar, whose mother was Capac's wife and sister, but also to his son Atahualpa, whose mother was apparently a consort. And King Rama V of ailand (1873-1910) sired more than 70 children---some from marriages to half sisters but most with dozens of consorts and concubines. Such a ruler could opt to funnel wealth, security, education, and even political power to many of his children, regardless of the status of the mother. A geneticist would say he was o ering his genes many paths to the future. It can all seem rather mercenary. Yet a ection sometimes drives these bonds. Bingham learned that even a er King Kamehameha III of Hawaii accepted Christian rule, he slept for several years with his sister, Princess Nahi'ena'ena--- pleasing their elders but disturbing the mis- sionaries. ey did it, says historian Carando, because they loved each other. ---David Dobbs When Western values pressed ashore, Hawaii's King Kamehameha III (above) donned a suit, but skirted a ban on royal incest. Thailand's King RamaV, posing with his half sister---and wife---and their children, faced no such prohibition.