Why Do They Say ‘Blue Blood’?

Why Do They Say 'Blue Blood'?

People have been referring to aristocrats as ‘blue bloods’ for centuries. The general meaning of the phrase is the blood which flows in the veins of old and aristocratic families.

Blue bloods come from privileged, noble families that are wealthy and powerful. The word blood has long referred to family ties: people you are related to share the same blood. One specific type of family is composed of blue bloods: members of the aristocracy.

But what’s the origin of this weird term? What did the noble’s blood had that made our ancestors view it as blue? Let’s find out.

Can a Person Have Blue Blood?

We all know blood is red.

Despite how it looks when we peer at our veins, we don’t have any blue blood in our bodies; oxygen-rich blood is bright red, while oxygen-depleted blood is slightly darker color (but still red).

As it turns out, there’s a simple reason why we never have any blue blood come leaking out of our veins: none of our blood is actually blue.

Why then We See Our Veins Blue?

If all blood is red, then why do veins appear blue?

It turns out that the color of our veins is due less to the blood inside them, and more to the skin that separates them from the outside world. Our skin absorbs more red light than blue light; the veins reflect the blue light back to the outside world, so we see the veins as blue.

If you were to strip the skin away, you’d find that arteries and veins both look the same color (this is just a thought experiment; don’t do this in real life!).

So, no blue blood in people.

What’s the Origin of the Phrase ‘Blue Blood’?

Why Do They Say 'Blue Blood'?

‘Blue blood’ is a literal translation of the Spanish ‘sangre azul’. This was the designation attributed to some of the oldest and proudest families of Castile, who claimed never to have intermarried with Moors, Jews, or other races.

During the 8th century A.D., Spain, as well as a large portion of Europe, was ruled by Moors – the Muslim population of North Africa, Sicily, Portugal, Malta and the Iberian Peninsula. At the time, Spanish people were white in color but when they started mixing with the Moors, they began producing the dark-skinned people we now see in Spain.

Certain members of the Spanish aristocracy however, chose not to intermarry with the Moors and were allowed to live in the mountains of Castile. While in the Castile mountains, they not only geographically set themselves apart from the foreigners, but they also tried to differentiate their appearance by deliberately avoiding the sun in order to preserve their light skin. You see, people with dark-skin were seen as low-class workers because they were descendants of the invaders who had to work outdoors, under the sun.

This gave the aristocrats a pale skin which basically allowed their blood vessels to show through their skin in blue color – just like any normal pale skin human. Because these blue veins were only seen at the nobles and upper-class people of Spain, people started to refer to them as “blue bloods”.

The nickname stuck throughout the centuries and got into the modern language when the English learned about it and applied it to their own royal families.

Who Has Blue Blood in Reality?

So, as we have already mentioned, no blue blood in people.

However, this doesn’t hold true for every living being, and there is one striking example of blood that is truly blue… and incredibly valuable.

Horseshoe Crab blood is the fourth most expensive liquid on Earth!

Why Do They Say 'Blue Blood'?

When people talk about how “the blood of kings is blue”, it’s this guy that they’re really discussing. Fun fact: if a horseshoe crab claimed the Throne of England, there’s no legal way to stop him.

Our blood is red because of the hemoglobin molecule, which contains iron. Most animals also use iron in their blood – but not all of them.

The horseshoe crab, for example, uses hemocyanin to carry oxygen through their bodies. This molecule contains copper, rather than iron – which makes it blue. Horseshoe crabs really do have blue blood!

Horseshoe crab blood, along with being blue, is also incredibly sensitive to pathogenic bacteria. Every year, many thousands of crabs are collected and drained of about 30% of their blood, which is used to test for the presence of bacteria such as E. coliSalmonella, and others. Given the difficulty of obtaining it, horseshoe crab blood is worth about $60,000 per gallon.

There’s a fun fact to share with coworkers!

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