A Turkish family of five brothers and sisters, ages 18 to 34, walk on all fours, but scientists say they don’t move like quadruped primates and therefore can’t be suffering from “reverse evolution.”
The Ulas family of Hatay Province in southern Turkey move about by “bear crawling” on their feet and palms with their knees and head flexed.
Some theories about why included “a backwards stage in human evolution,” but American scientists say it's more likely the Ulas’ suffer from a rare genetic disorder. Their unusual gait is likely an adaptation to cerebellar hypoplasia, which affects their sense of balance. This condition is called Uner Tan syndrome (UTS).
The family moves laterally when they walk, whereas primates walk in a diagonal sequence, moving the hand on one side and foot on the other, researchers said in a report published in the journal PLOS One.
The Ulas’ walk by moving their left foot, left hand, and then right foot and right hand. Apes and nonhuman primates walk by moving the right foot, left hand, and then left foot and right hand.
"Although it's unusual that humans with UTS habitually walk on four limbs, this form of quadrupedalism resembles that of healthy adults and is thus not at all unexpected," said head researcher Liza Shapiro, an anthropologist at The University of Texas at Austin.
"As we have shown quadrupedalism in healthy adults or those with a physical disability can be explained using biomechanical principles rather than evolutionary assumptions," she said.
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