14 DAY TRIAL // Scientists have long debated whether backward evolution is possible. Occasionally there were some reports of such events happening in the animal kingdom, but this might be the first such example in case of humans.
Uner Tan of Cukurova University Medical School in Adana, Turkey, who discovered them, argued that this could have been produced by a mutation and that it might offer scientists an unprecedented glimpse into human origins.
"The children exhibiting this syndrome originated from a family having 19 children," he wrote. Five of these, aged 14 to 32 years, "walked on two palms and two feet, with extended legs? They could stand up, but only for a short time, with flexed knees and heads. The sitting posture was rather similar to an ape. They could not hold their heads upright; the heads were flexed forward with their skulls. They could not raise their heads to look forward. This head posture with flexed skull was rather similar to the head posture of our closest relatives, like chimpanzees."
While some researchers, including Tan, believe genetic faults caused the siblings to regress in a form of "backward evolution," other scientists claim genes triggered brain damage. This second hypothesis is also supported by Tan's observations:
"They were mentally retarded;" Tan wrote, "they could not count from one to ten. They were not aware of time and space. For instance, they did not know where they live (which country, which village, which city). They were unaware of year, season, day, and time."
However, Tan has mapped the genetic defect to a region of the genome called chromosome 17p, a region where some of the biggest genetic differences between humans and chimps are found. 17p had also been linked to bipedalism to 17p by several other studies. This adds more weight to the claim that this syndrome is indeed an example of backward evolution.
Backward evolution could occur in two ways: either by the organisms losing genes they had gained earlier in evolution; or by regaining a previously lost ability or structure, by reactivating certain genes that had fallen into disuse, but weren't completely lost.
Nicholas Humphrey, an evolutionary psychologist from the London School of Economics, told the Times that weeks of study indicate their method of walking is a long-term pattern of behavior and not a hoax.
"However they arrived at this point, we have adult human beings walking like ancestors several million years ago," Humphrey said.
Tan had made available a video of one of the women walking on all fours.
Photo credit: Uner Tan / International Journal of Neuroscience