The scientific world was astonished when in 2005, five siblings— aged between 19 and 35, were discovered in an undisclosed, remote location in rural Turkey. The one unique trait they shared is that they walked on all-fours.
Interestingly, there were a total of 19 siblings in the Ulas family, yet only 5 of them were observed to be afflicted by a mysterious condition that affected their gait.
Instead of walking or running on their feet, the condition forced the family members to do a “bear crawl”.
The media sold the news as the biggest anthropological find in modern history, suggesting that the members of this family “evolved backward” and represented a snapshot of human evolution millions of years ago where our ancestors were claimed to have had quadrupedal locomotion before walking upright.
It was an “evolutionary throwback”, so to speak.
The implications would be immense, and the finding sent the Scientific community into a flurry and the family eventually came in the spotlight of a BBC documentary, “The Family that walks on all fours”.
What is Uner Tan Syndrome or “reverse evolution”?
The siblings walked around on their hands and feet for all their lives and could barely speak. Instead, they communicated with one another using a form of language they invented.
While their form of walking would tire most people out in moments, the Ulas family can ‘bear crawl’ for kilometers and only stand on two feet for mere moments with knees and head flexed.
One of the first scientists to research the family was Uner Tan, an evolutionary biologist at Cukurova University Medical School in Adana, Turkey. He was quick to proclaim that the family’s gait and “primitive” speech was a result of “reverse evolution”.
In a 2006 article published in the Journal of Neuroscience, he claimed that due to a genetic abnormality, the family had returned to the walking style of the great apes, and named the condition “Uner Tan Syndrome”, after himself.
Similarly, Professor Stefan Mundlos who is a geneticist based in Berlin too believes that a gene responsible for bipedalism must be missing in these 5 siblings.
Because millions of years of evolution have allowed humans to resist the forces of gravity to stand and walk on two feet, Tan believes how the Ulas family walks must be due to a regression in evolution.
Not “living fossils” but an untreated medical condition
Almost 9 years after their discovery, the diagnosis was debunked in 2014. When other researchers began investigating the Ulas family, they discovered numerous holes in Tan’s hypothesis.
A group of American researchers pointed out the crucial fact that the family walked by putting their weight on their wrists, not their knuckles like primates. English psychologist, Nicholas Humphrey, and John Skoyles, an evolutionary psychologist, believes it to be cerebellar ataxia— a form of brain damage to the cerebellum.
The part of the brain which is responsible for spatial orientation and balance, in other words, the way you walk. Their colleague, Roger Keynes, zoned in that the damage must be on the cerebellar vermis, disturbing their balance and gait.
They went on to say that their condition was the result of their parents being cousins. This resulted in them inheriting an autosomal recessive mutant present from both parents. Therefore, 5 out of the 7 siblings, suffered from the effects two-fold whereas one brother who inherited the same defect, still managed to walk upright, albeit clumsily.
Another article by Liza J. Shapiro published in PLOS One showed that the siblings’ do not walk like primates. Primates walked diagonally, which means they put a hand on one side and a foot on the other to walk. The siblings walked laterally, just like other quadrupeds.
She hopes that this ends the debate on the idea of “reverse evolution” and instead contends that the siblings suffer from a rare medical condition called disequilibrium syndrome (DES), which Tan and his colleagues deny. She told the Washington Post,
The siblings today
In a 60 Minutes Australia segment aired in October 2018, it appears that the siblings have undergone physical therapy, and with the aid of a walker, are beginning to show improvements in their condition. They are now able to stand and walk with medical assistance.
Professor Nicholas Humphrey, the researcher on the family notes that it’s unfortunate that their conditions were allowed to carry on for so long without intervention.
With a proper healthcare system, what would have been a medical condition that, although rare, would have been discovered and treated earlier rather than subjected to such intense media-fueled, scientific scrutiny.
One of the first people involved in debunking Tan’s study recently reflected on the impact of his peer’s work, Humphrey told BBC,
Turkish psychologist Defne Aruoba, who was involved in caring for and researching the family shares a stark observation. According to Aruoba,