Scientists have spotted the oldest-known living form of cancer, and it's an odd one—passed sexually from dog to dog over the past 11,000 years, the Smithsonian reports.

By decoding the cancer's genome, British researchers found that it dates back to a dog with short, dark fur and the look of a modern-day Alaskan malamute, reports the BBC.

And while it's old, it only started traveling the world around the time of Christopher Columbus, probably because dogs were taken along on sea voyages. It's also the time when "humans were really manipulating dogs and breeding them strongly for some product—whether it was a lap dog, a purse dog, or a hunting dog," an evolutionary geneticist tells Nature.

The disease is unlike most human cancers, because it underwent a stunning 1.9 million mutations (compared to the several thousand found in ours) and is not too scary—typically disappearing from dogs that get it, The Loom notes.

That's quite unlike the world's only other known contagious cancer in the wild, a facial tumor that spreads among Tasmanian devils and typically kills them in a matter of months.

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