In 2001, Ajit Varki drank a bunch of pig spit. What does drinking the extraction of pig salivary glands give you? Sialic acid, something every mammal in the world produces except humans. Why are we left out?

As it turns out, we humans lost the genes which make the enzyme which modifies the existing sialic acid, caled Neu5Gc, we have in our bodies. By drinking pig saliva, Varki showed everyone how we have it. When we consume animal proteins, the special sialic acid becomes part of our cells, making it into every part of our bodies.

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That’s a problem. The immune system sees these acids, stored on the edges of sugars inside cells, as a threat. This, according to Ajit Varki and his wife and co-researcher Nissi Varki, is what cause atherosclerosis. It’s the result of our own immune system attacking the Neu5Gc sialic acid in our cells.

So the question is, why did humans get the evolutionary shaft? Why, of all the mammals, did we end up being the ones with a genetic code that turns meat into poison? According to the Varkis, our immune system isn’t the only one on the look-out for sialic acid. Viruses, including malaria, use sialic acid as a signpost guiding them to the best cells. By eliminating one form of sialic acid, early humans may have managed to gain immunity from certain viruses, including malaria. Unfortunately, all things adapt, and we got stuck with malaria again as well as an immune system that overreacts to meat.

[Via The Man Who Touched His Own Heart]

Image: USDA.

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