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Genetic variant linked to osteoarthritis favored in cold climates

Like many others, I've been rewatching the "Game of Thrones" television series in preparation for the start of the seventh season later this month. So I don't think it's all that odd that an image of Jon Snow's first trip to the jaw-dropping Wall of ice (which rises 700 feet high) in the frozen north of Westeros popped up in my head as I began research for my latest release about human evolution, migration and genetic selection.

You see, like Snow, our early human ancestors moved north out of Africa into the much colder climates of Europe and Asia tens of thousands of years ago. And as their surroundings and weather changed, they adapted to these changing conditions by passing on genes that would enhance their descendants' chances of survival. Paradoxically, however, this fancy genetic footwork seems to have favored a DNA sequence that not only reduces human height, but also increases the risk of osteoarthritis. It seems somewhat contrary to the "survival of the fittest" mantra that we all learned in high school.

The researchers, Stanford developmental biologist David Kingsley, PhD, and Harvard human evolutionary biologist Terence Capellini, PhD, Harvard graduate student Jiaxue Cao, and former Stanford postdoctoral scholar Hao Chen, PhD, published their findings today in Nature Genetics.

From our release:

Now, researchers at the Stanford University School of Medicine and at Harvard University have shown that, despite its association with the painful joint disease, this genetic variant has been repeatedly favored as early humans migrated out of Africa and into colder northern climates. At least half of Europeans and Asians harbor the gene variant, which is relatively rare in African populations. [...]

A more compact body structure due to shorter bones could have helped our ancestors better withstand frostbite and reduce the risk of bone fracture from falling, the researchers speculate. These advantages in dealing with chilly temperatures and icy surfaces may have outweighed the threat of osteoarthritis, which usually occurs after prime reproductive age.

It wasn't just our early human ancestors who hit upon this solution, the researchers found. Our even more ancient cousins, the Neanderthals and the Denisovans, also singled out this same gene variant (through a process known in genetic circles as positive selection) when they left Africa about 600,000 years ago. Its evolutionary popularity means it is now present in billions of people.

As Kingsley explained:

The potential medical impact of the finding is very interesting because so many people are affected. This is an incredibly prevalent, and ancient, variant. Many people think of osteoarthritis as a kind of wear-and-tear disease, but there’s clearly a genetic component at work here as well. Now we’ve shown that positive evolutionary selection has given rise to one of the most common height variants and arthritis risk factors known in human populations.

Previously: From whence the big toe? Stanford researchers investigate the genetics of upright walking, It's a blond thing: Stanford researchers suss out the molecular basis of hair color and Comprehensive review of humans' expansion out of Africa could lead to medical advances
Photo by Jeff S. PhotoArt at HDCanvas.ca

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