The Family That Walks on All Fours: Setting the Record Straight

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In 2006, the BBC released a documentary about five members of a Turkish family who walk on all fours. Turkish neuroscientist Uner Tan, who discovered the family, shaped the sensational hypothesis with which this discovery was presented: That these people are examples of reverse evolution, a “throwback” to an earlier state of human development.

The documentary’s claims had been bothering UT anthropologist Liza Shapiro since the show aired. The evolutionary reversal hypothesis “was really insulting—and strange,” she says. And as Shapiro and her collaborators show in a new paper available online in the journal PLOS One, it’s also wrong.

“We weren’t the first people to call the evolutionary reversal idea ridiculous,” Shapiro says. The idea “was kind of like Bigfoot.”

The Ulas family members, and others with Uner Tan Syndrome (UTS), have a genetic mutation that leads to mental disability and difficulty in balance. When Tan’s papers began extending the evolutionary reversal hypothesis to families without the genetic mutation that walked quadrupedally, says Shapiro, the “claims became more and more absurd.”

But it wasn’t until Tan began citing Shapiro’s own research that she decided to set the record straight.

Shapiro, who studies primate locomotion, could tell from the BBC footage that the quadrupedalism in the Ulas family members differs from that of nonhuman primates. Since Tan’s theory made the leap from suggesting that the siblings move like primates to the conclusion that the family members exhibit evolutionary reversal, a simple study was enough to break the causal link.

Apes and monkeys walk in a diagonal sequence, placing a foot down on one side and then a hand on the other side. Humans walk in a lateral sequence, putting a foot down and then a hand on the same side.

After extensive analysis of the walking strides of people with UTS and healthy adults walking around a laboratory on all fours, the research was conclusive: Those with UTS walk in lateral sequences, moving as any human forced to walk quadrupedally would.

Shapiro chalks the Ulas family’s quadrupedal adaptation up to cultural differences. The Ulas family lives in a remote, rural region of Turkey, and without access to physical therapy or walking aids, quadrupedalism was the best biomechanical adaptation available.

“The body is adaptable. Your body can compensate for disadvantages,” says Shapiro, citing the acclimations made by a dog without hind legs and monkeys trained to walk bipedally.

While Shapiro’s research debunks the original claims, she is quick to point out that evolutionary reversal is an untenable idea, period. “We’re showing that they don’t walk like primates, but even if they did, it wouldn’t demonstrate evolutionary reversal.”


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