Consanguinamory may have been pivotal to the creation of modern civilization

Brother-kings married sister-queens, [...] flouting a prohibition commoners will have felt to be natural. Lords and ladies of the earth flaunted superhuman invulnerability, constructing auras of power by haughty taboo-breaking. They did so especially when they had not yet invented the administrative and communications systems to enforce their rule by less colorful means. [...]

Polynesian peoples developed a number of high-chiefdom/almost-state societies in which brother-sister marriage for the high-ranking was politically salient. [...]

Where conditions for ranking were auspicious, a family that risked inverting taboo and ignoring aversion set in train a snowballing status improvement for its descendants and an evolutionary leap in social complexity for its society. Somewhere in the history of all early states we might expect to find royal brother-sister incest lurking.

-  Hill Gates, Inbreeding, Incest, and the Incest Taboo