Greg Laden's Blog

Blue blood is an English expression recorded since 1834 for noble birth or descent; it is a translation of the Spanish phrase sangre azul, which described the Spanish royal family and other high nobility who claimed to be 'pure', free of Moorish or Jewish blood, being of Visigothic descent. There is no connection between the phrase and the actual blood color of nobility; however, in the ancient agricultural societies of Europe the whole upper class had superficial veins that might be more visible and appear bluish by comparison to the rest of the pale-pinkish skin, as the skin itself was not tanned.... [which feels like something added to an otherwise nice piece of wiki-work ... ] An alternative traditional explanation, argyria (a disease causing a blue-grey skin tone after digestion of silver), is considered less valid, as table silverware was not regularly used by much of the nobility. [and, I might add, does not happen today among those who use silver all the time...]

Robert Lacey explains the genesis of the blue blood concept: "It was the Spaniards who gave the world the notion that an aristocrat's blood is not red but blue. The Spanish nobility started taking shape around the ninth century in classic military fashion, occupying land as warriors on horseback. They were to continue the process for more than five hundred years, clawing back sections of the peninsula from its Moorish occupiers, and a nobleman demonstrated his pedigree by holding up his sword arm to display the filigree of blue-blooded veins beneath his pale skin--proof that his birth had not been contaminated by the dark-skinned enemy. (Robert Lacey, Aristocrats. Little, Brown and Company, 1983, p. 67) [this, I will run down ... nice implementation of the race concept by those Spanish guys....] ...