The Kurdish siblings, aged between 18 and 34 and from the rural south, 'bear crawl' on their feet and palms.
Researchers have found a genetic condition which accounts for their extraordinary movement.
And it could provide invaluable information on how humans evolved from a four-legged hominid into a creature walking on two feet.
Two of the daughters and a son have only ever walked on two palms and two feet, but another son and daughter sometimes manage to walk upright.
The five can stand upright, but only for a short time, with both knees and head flexed.
Their remarkable story is told in a television documentary, to be screened next week, which shows scientists studying their movement, but also their struggle to fit in with modern society.
The five are all mentally retarded. Their mother and father, who are closely related are believed to have handed down a unique combination of genes which result in the behaviour.
One wonders how they are able to dress themselves and otherwise carry on normal tasks if they can't walk upright or stand upright for any length of time.
One also wonders how they can hunch themselves over like that without straining their backs. I tried bending over in that position and couldn't duplicate it. Of course, the fact that I can't, doesn't mean that it's impossible, if their muscles have developed that way.
I'm still sceptical about whether we're being hoaxed the way we were about the primitive Tasaday tribe in the Philippines.
On the other hand, if it's true, we've got some potential Liberal leadership candidates!