I’d never heard of the Uner Tan Syndrome before reading this article. It is named after a Turkish scientist who discovered a family who walk on all fours:
The subject of bear crawling hibernated for many decades until a couple of Turkish doctors, in 2004, made a discovery that was more science fiction than science. In a rural village, they happened upon a group of siblings who had never stood up. Members of a family with 19 children, all of whom bear-walked in their infancy, these five brothers and sisters had never lifted up off their hands. They had walked like bears all their life. The siblings actually wrist-walked, with their palms pressed flat against the ground. (Think of someone doing the downward-facing dog yoga pose while walking.) No one had ever seen an adult human move like this before.
The siblings were able to stand upright if they really concentrated on it, an early report on them noted, “but they become unsteady if they try to walk bipedally, and soon go down onto their hands.” They were quadrupeds. To help support the family, the lone male bear crawler ranged as far as a mile from home collecting cans and bottles. While bear-crawling, he was indefatigable. “This contrasts markedly with normal adult humans,” the report noted, “who find such a gait—if and when they try it—tiring and uncomfortable even after practice.”
I’d also never heard of the term “reverse evolution,” but that is the phrase that was used in this academic paper on the syndrome.
More: a documentary on the bear-walking family.