One of the members of the Ulas family, from Turkey, some of whom walk on all fours.
Credit: Nicolas Humphrey
SYDNEY: More than four million years ago, hominids made the crucial transition from walking on their hands and feet to walking upright on two feet.
Along with tool making, speech and enlarged brain capacity, bipedal posture has long been regarded as an identifying human trait.
But in 2004, five of 19 siblings in a remote village in southern Turkey were found to walk on their feet and hands, the first human quadrupeds.
Once thought to be genetic
Turkish scientists led by Tayfun Ozcelik from Bilkent University, in Ankara, suggested that a mutation in a single gene might result in quadrupedalism. However, since then more families - three in Turkey and one in Iraq - have been discovered with multiple members who 'walk' on all fours.
"We see quadrupedal locomotion as an adaptive - and undoubtedly effective - compensation for problems with balance," said Nicholas Humphrey, a theoretical psychologist at the London School of Economics.
He and his colleagues, who studied the families and reported their findings in the journal Proceedings of the National Academy of Sciences in 2008.
Now thought to be a balance issue
Further study confirmed their earlier finding and revealed that individuals have a mutation at one of three locations in the genome, each resulting in balance problems, reported Humphrey and his colleagues in the journal PLoS Genetics in 2009.
"We believe that the fact that this gait has not been 'corrected' in the families under study must be attributed to the local cultural environment."
Despite the geographic separation of the families, the method of quadrupedal walking is similar: legs and arms held fairly straight, and bottom in the air. They put much of their weight on the heels of their palms, which are rough and calloused.
They can 'run' quickly
The Iraqi siblings "are able to walk on two legs for several steps, [but] they tend to tumble into a quadrupedal position quickly, complain of lack of balance and occasionally fall from a sitting position," Humphrey says.
They also have difficulty with stairs and descend feet-first. However, researchers also report seeing quadrupeds 'running', moving agilely over rough terrain and travelling long distances.
Researchers have also found that a quadrupedal gait is accompanied by varying degrees of mental retardation and difficulties with language, and parents of quadrupeds are often closely related, Humphrey reports, suggesting cerebral deficits may also play a part.
Walking upright is a complex skill, which takes about seven years for most people to master, according to Humphrey. "Although many mammals and other animals can stand or walk bipedally for shorter or longer periods of time, the manner in which humans do so is unique," he said. "We are always a second or two from falling down."
Humans who walk on all fours
This article is essentially about the Uner Tan syndrome first described in 2005 in five siblings (from a consanguineous family with 19 children) exhibiting habitual walking on hands and feet (quadrupedal locomotion), dysarthric speech and mild to severe mental retardation including no conscious experience (1). Despite that, Uner Tan syndrome is not even mentioned once in the Cosmos article.
My reactions to the statements in the article are as follows:
Cosmos: “But in 2004, five of 19 siblings in a remote village in southern Turkey were found to walk on their feet and hands, the first human quadrupeds.”
Tan: The affected siblings had been under the eyes of many physicians and scientists for at least 35 years (the age of the oldest case), and their existence was reported in newspapers and on Turkish TVs much earlier than 2004, without any scientific publication. So, they were not found in 2004, but that was the year the work published in the 2005 paper was done (1).
The statement “the first human quadrupeds” also does not reflect the truth, because the first quadruped man was first found by an English traveler, W.J. Childs, in 1914, in a Greg village in the Turkish Northeastern Black Sea Coast, and was described in Childs’ book, published in 1917 (2). Moreover, Muybridge had already described, in 1901, a child walking on all fours with a paralyzed leg, cited by Tan (3). This case did, however, not exhibit Uner Tan syndrome, because the child had a paralyzed leg due as a post-polio sequel, and was quite normal in cognitive abilities. Actually, Muybridge observed and photographed this case much earlier, in 1888. So, the first human quadrupeds were found in 1888 in England, and in 1914, in Turkey.
Cosmos: "We see quadrupedal locomotion as an adaptive - and undoubtedly effective - compensation for problems with balance," said Nicholas Humphrey.”
Tan: No, I do not agree with this argument. I see the quadrupedal locomotion as a developmental process, which may occur even in normal children without any balance problems and no impairments in the cognitive domain (4).
Cosmos: "We believe that the fact that this gait has not been 'corrected' in the families under study must be attributed to the local cultural environment."
Tan: No, I do not agree: although most of the families belonged to lower socio-economic class, one family was relatively well off. One of the relatives of this family was a physician, who attempted physical treatment of the affected children, but with no success at all. The mother attempted to force her daughter to walk upright, but again, without success. The cases with a paralyzed leg strongly preferred walking on all fours, despite serious pressures from their fathers to use crutches or a wheelchair (5).
Cosmos: “They put much of their weight on the heels of their palms, which are rough and calloused.”
Tan: No, this argument is not scientific, because there are no published results about the weights under the hands and feet. Rough and callused palms, which were observed only in one of the affected individuals (1/22), may not be an indicator for more weight-bearing under the heels of their palms than under the feet. The man with calluses in the palms spent time running around many kilometers every day. I have measured the pressures under hands and feet, and found more weight under the feet than under hands (unpublished observations).
Conclusions: The emergence of the human quadrupedal locomotion during locomotor development may be explained by the principles of the self-organization process within the framework of the dynamical systems theory. That is, a dramatic process of adaptive self-organization may play a role in the emergence of the human quadrupedalism; no previously established neural code, or any other motor program, or genetic code alone may be responsible for the emergence of the human quadrupedalism. Rather, the attractor, quadrupedalism, may result from the dynamic interactions of many subsystems, such as genetics, environmental constraints, central pattern generators, posture, balance, body constraints, muscle strength, extensor and flexor motor systems, perceptual processes, cognition, and motivation, not depending upon the prior existence of instructions embedded within the central nervous system and/or coded in certain genes.
(1) Tan U (2005). Unertan syndrome: quadrupedality, primitive language, and severe mental retardation; a new theory on the evolution of human mind. Neuroquantology, 4: 250-255.
(2) Childs WJ (1917). Across Asia Minor on Foot. William Blackwood and Sons, Edinburgh and London. p. 27.
(3) Tan U. (2010). A post-polio paraplegic couple: a woman with palmigrade, saltatoric locomotion; a man with inability to walk; a dynamical systems theoretical perspective. WebmedCentral NEUROLOGY; 1(11) WMC001176.
(4) Tan U, Tan M. (2009). A new variant of Unertan syndrome: running on all fours in two upright-walking children. Int J Neurosci 119: 909-918.
(5) Tan U. (2010). Uner Tan syndrome: history, clinical evaluations, genetics, and the dynamics of human quadrupedalism. The Open Neurology Journal 4: 78-89.