Scientists have discovered a family that walks on all fours – millions of years after its ancestors stood up and walked on two legs.
Evolutionary psychologist Professor Nicholas Humphrey, one of the scientists leading the research into the family, said: "This could be hugely important – a living example of how our ancestors walked before they became bipedal.
"As such, it might teach us so much about our distant past."
The family is very poor, has had little medical help and lives in a small village in Turkey. The parents, who are closely related, have had 19 children.
Most were normal, but six were born with what looks like brain damage. Five of these, aged between 18 and 34, walk quadrupedally. Family members are treated as outcasts by many of the villagers.
The BBC was given exclusive access to the family and is to tell the extraordinary story in a documentary film to be broadcast this month.
The documentary features interviews with scientists from across the world, and their response has been mixed – the only thing they do agree on is that this is not a hoax.
American paleanthropologists think that the family's skeletons could hold vital clues about the origin of man. A Turkish neurophysiologist believes that they are wholesale genetic throwbacks – a living 'missing link'.
But UK researchers contend that no single faulty gene could produce the first human quadrupeds the modern world has seen.
Producer Jemima Harrison, of Passionate Productions, which made the film for the BBC, said: "The family raises profound questions about what it is to be human. They walk like animals and that's very disturbing at first. But we were also very moved by this family's tremendous warmth and humanity."
The Family That Walks On All Fours is on BBC2 on Friday, 17 March at 9pm.