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No, Walking on All 4 Limbs Is Not a Sign of Human 'Devolution'

New quantitative analysis reveals that people with Uner Tan Syndrome don't actually walk like primates at all.
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(Photo: BBC)

(Photo: BBC)

In 2005, an evolutionary biologist named Uner Tan happened upon several adults in a remote corner of Turkey who had taken to locomotion on all fours. After naming the rare disability after himself, he attempted to make a grandiose argument about how they represented ancient stepping stones between primates and humans. The phenomenon, he argued, was a special sign of human "devolution." "The recently discovered 'UNERTAN SYNDROME' consists of quadrupedal gait, severe mental retardation, and primitive language," he wrote in the abstract of a paper that outlined his theory. "This syndrome can be considered as devolution of human being, throwing a light into the transition from quadrupedality to bipedality with co-evolution of human mind."

BBC visited five of the siblings afflicted with the condition and spoke to scientists debating the varying implications of the phenomenon:

Though the condition is certainly real, Tan's lame explanation regards the disability as some kind of curious evolutionary side-show rather than focusing on the human struggle to adapt to extraordinary biomechanical and cognitive constraints. It also happens to ignore the basic precepts of evolution. "'Devolution' doesn’t make any sense to me in evolutionary biology – it’s not the way we refer to evolutionary changes," Liza Shapiro, a University of Texas-Austin anthropology professor who recently did a quantitative analysis of the gait, says in an email. "Species can (re)evolve traits that may resemble earlier traits of their ancestors, but they are not 'devolving,' and certainly, individuals don’t 'devolve.'" Tan's theories ring more of eugenics than science. A theory about time machines might be counted as more rigorous.

After putting aside these facts and accepting the dimwitted premise, the problem with this half-baked theory is that it doesn't even get its half-bakedness right. The gait, according to Shapiro's new analysis, just isn't the same as that of a non-human primate. In fact, adults who don't have the syndrome move in a similar fashion when asked to walk on all fours in an experimental setting.

The new study, published last week in PLoS One, analyzed frame-by-frame video footage from the BBC documentary and discovered that Tan likely didn't have a firm grasp of the basic locomotion concepts of sequence and couplets when he was crafting his theory. "Contrary to the published claims that the Turkish individuals with UTS used 'primate-like' [diagonal sequence diagonal couplets] walking gaits, only 1% of the 513 strides quantified across Participants 1–5 from Family 'A' were categorized [this way]," the researchers conclude. In other words, the locomotion patterns of the Turkish subjects did not match diagonal sequences of non-human primates. "I don’t know why they would claim this without testing it," Shapiro says. "As we discussed in the paper, they took a superficial view of limb positioning (based on still images) and interpreted it as a diagonal sequence gait, when it was in fact a lateral sequence gait with diagonal COUPLETS."

In service to his faux-revolutionary theory, Tan seems to have only seen what he wanted. Meanwhile, people with Uner Tan Syndrome continue to adapt to their own reality.