Disorder causes 5 siblings to walk on all fours

Since the siblings were first discovered by scientists in 2005—and featured in a BBC documentary in 2006—one popular explanation of their unusual quadrupedal gait was “reverse evolution”—meaning they could be living proof that we can essentially devolve. But new research published this week suggests that theory is false, and that the condition is instead an adaptation to a rare disorder, reports the Washington Post.