Humans Might Be So Sickly Because We Evolved to Avoid a Single Devastating Disease

Humans Might Be So Sickly Because We Evolved to Avoid a Single Devastating Disease

Hundreds of thousands of years ago, our ancestors evolved a simple trick that could have helped thwart a major infectious disease. It probably saved our skins, but the change was far from a perfect solution. New research has uncovered evidence that mutations arising between 600,000 and 2 million years ago were part of a complex of adaptations that may have inadvertently made us prone to inflammatory diseases and even other pathogens. An international team of researchers compared around a thousand human genomes with a few from our extinct cousins, the Neanderthals and Denisovans, to fill in missing details on the evolution of a family of chemicals that coat the human body's cells. Sialic acids are a diverse group of carbohydrates that blossom like leaves from the tips of proteins covering the surfaces of human cells. This canopy of sugars is typically the first thing you'd bump into if you were the size of a virus or bacterium, so it's no surprise that these chemicals serve as a security badge, identifying friend from foe. Changes in sialic acid markers can give rise to a number of diseases. But it was one specific change particular to all humans that the researchers here were most keen to gain an understanding of. Most mammals – including closely related apes – have a compound called N-glycolylneuraminic acid, or Neu5Gc. We've known for some time that the gene for this version of sialic acid is broken in us, leaving its precursor form, N-acetylneuraminic acid (Neu5Ac), to do its ...
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