Valyrians in GoT :: why so inbred?

[Anthony Appleyard]

In the story, the heirs of Aegon the Conqueror married their sisters to keep the Valyrian stock pure, and thus suffered the effects of inbreeding.

But before the Doom,, Valyria had colonies on Essos, and a fair number of Valyrians would have to be posted to those colonies, to run and organize them, and likely their house dragons with them, and thus would be safely far away when the Fourteen Flames blew their tops. That would likely let the Targaryens in Westeros find Valyrian wives each generation without having to marry their sisters, even if during the century of wars  after the Doom, the only safe transport for news and important people between the Valyrian ex-colonies would be on dragonback safely above the heads of the dangers of land and sea travel.

 

[Masha]

In the WoI&F as well as F&B, it was mentioned that all Valyrian noble/dragonlords houses married in-the-family to keep "the blood pure". There were valyrians and there were Valyrians. Furthermore, it was mentioned it was some sort of event/holiday/election when the Doom happened so ALL dragonlords, noble houses and all their dragons were gathered at the Valyria, other than Targaryens, so they were all killed. Frankly, in retrospect seems if Doom wasn't natural catastrophe, the timing is so suspicious I'd say Faceless Men really were involved.

There were two Valyrien families left other than Targyriens - Velaryons and Centagar as well as Baratheon bastard - Oris. Early on Targyriens did intermarry with Velaryons but as those 2 other houses declined in power, they stopped. Basically, at this point all Valyriens left in Essos are Valyrien equivalent of small folk. At this point, Targyrien's first choice is in-house, second choice Westerosi noble families.