The Family That Walks On All Fours is a documentary that explored the science and the story of five individuals in the Ulas family in Turkey that walk with a previously unreported quadruped gait.
Debate exists as to the nature and cause of their walking, including controversial speculation in the form of the Uner Tan syndrome that it may be a genetic throwback to pre-bipedal hominid locomotion. Nicholas Humphrey, who accompanied the documentary makers, concluded that it was due to a rare set of genetic and developmental circumstances coming together.
First, their mother recalls that initially all of her 19 children started off walking with a bear-crawl (i.e. on their feet rather than their knees). Second, due to an inherited recessive genetic mutation, they have a non-progressive congenital cerebellar ataxia that impairs the balance children normally use to learn to walk bipedally. Not being able to manage the balance needed for bipedal walking, they perfected in its place their initial bear-crawl into an adult quadruped gait.