for National Geographic News
Editor's Note: The Family That Walks on All Fours documentary premieres in the U.S. Tuesday, November 14, at 8 p.m. on most PBS TV stations.
Five adult siblings who can walk only on all fours have been found in Turkey, researchers say. These human quadrupeds may provide clues to how humans evolved to stand on two feet.
The three sisters and two brothers may offer insight into the way our apelike ancestors moved, according to scientists. Human ancestors are believed to have begun walking on two legs more than three million years ago.
Discovered in a remote area of southern Turkey last summer, the family of ethnic Kurds has sparked a scientific debate, which will be covered in a BBC television documentary that is set to air on March 17 in the United Kingdom. The family's exact location and last name have not been disclosed.
Born with a genetic brain abnormality, two of the sisters and one of the brothers are thought to have only walked on all fours their entire lives. The two other siblings can walk upright for short distances.
The siblings' parents are closely related and have had 19 children in all.
This bizarre case is not a hoax, according to experts who have studied the family.
The cause of the four-limbed locomotion, however, is a bone of contention among the researchers.
Uner Tan is a neurophysiologista doctor specializing in the functions of the brain, spinal cord, and nervesat Cukurova University in Adana, Turkey.
He believes the siblings, who range in age from 18 to 34, are evolutionary throwbacksa "missing link" to our forebears. (Related reading: "Was Darwin Wrong?")
Meanwhile German geneticists believe the siblings' genetic abnormality may have knocked out the gene responsible for bipedalism, or two-legged walking, in humans.
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