There's a family who lives in a remote region of Turkey with some members who walk on all fours. At the time of BBC's 2006 documentary about the Ulas family, scientists thought this was an example of "devolution," but more recent research offers another suggestion instead.
"The Family That Walks on All Fours" consists of five quadrupedal siblings, but the Ulas family has many other siblings that walk in a normal, upright position. Instead of these individuals going backward on what some scientists consider the evolutionary scale, Lisa Shapiro, an anthropologist at the University of Texas in Austin, thinks this trait is an adaptation on the part of the siblings.
In a recent study published in the journal PLOS One, Shapiro and other researchers pointed out that people with Uner Tan Syndrome, like some in the Ulas family, do not walk in the same pattern as nonhuman primates that use both their arms and legs to get around. Even if individuals with this syndrome exhibited the same gait as nonhuman primates, the researchers wrote that it still wouldn't be enough to "support the conclusion of evolutionary 'reversal.'"
“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,” Shapiro said in a statement. “As we have shown, quadrupedalism in healthy adults or those with a physical disability can be explained using biomechanical principles rather than evolutionary assumptions.”
To reach this conclusion, researchers analyzed the gait of 518 quadrupedal strides in video of people with UTS. What they saw was that these individuals almost exclusively used a lateral, not diagonal, sequence of gait.
Severe UTS, according to the study, is also characterized by cerebellar hypoplasia, loss of balance and coordination, and impaired cognitive abilities.
Turkish psychologist Defne Aruoba, who worked with BBC on its documentary, wrote that the Ulas family is "mystery to the scientific community," and "[e]very once in a while, a new scientist appears in the village and offers a new treatment or asks for the father Resit's permission to do more testing."
Aruoba wrote that he doesn't say yes or no, but that his only concern for his children with this disability is who will take care of them when he dies.
"And he is right. These adult individuals are completely dependent, not because they lack the necessary skills to take care of their own basic needs, but because they haven't been rehabilitated," Aruoba said.
Here's the BBC's hour-long documentary on this syndrome and the family that exhibits this unusual trait: