Tuesday is an anniversary worth noting: On Jan. 30, 1868, Charles Darwin published a follow-up to his masterpiece On The Origin Of Species.This less-popular tome (897 pages!) contained a vexing puzzle:

Why do pets and livestock tend to have "drooping ears?"

Wolves, for example, have perky, upright ears. But the ears of many dogs are distinctly floppy. Darwin saw this odd trait in many domesticated species — "cats in China, horses in parts of Russia, sheep in Italy and elsewhere, the guinea-pig in Germany, goats and cattle in India, rabbits, pigs and dogs in all long-civilized countries."

"The incapacity to erect the ears," Darwin concluded, "is certainly in some manner the result of domestication."

A century later, an ambitious (and adorable) experiment in the Soviet Union proved him right. At the time, Vladimir Lenin's pseudo-scientific dogma had no room for classical genetics. So Russian geneticist Dmitry Belyayev disguised his own research as the study of animal physiology. He retreated to Siberia and attempted to domesticate the silver fox.

Belyayev took 130 foxes from fur farms and started a breeding program. He only picked the tamest foxes — those that seemed less jumpy around humans, and less likely to bite — as parents. When their pups were grown, he'd pick the tamest ones to breed again.

In just a few dozen generations, Belyayev's foxes were tame. And, lo and behold, their ears were distinctly floppier. Just as Darwin suspected, selecting for a change in behavior led to an unexpected change in appearance.

But what's behind this mysterious change? What possibly could link tameness and ear cartilage? Skunk Bear's latest episode shares one fascinating hypothesis that ties it all together, and explains shortened snouts and patchy coats along the way.

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