About this Research Topic
A man with quadrupedal locomotion was first described by Childs  in 1917. Following a long-lasting silent period of nearly 100 years, six new cases exhibiting quadrupedalism were discovered in 2005 in Southern Turkey. These cases presented a never-before described novel syndrome with quadrupedalism, mental retardation, and dysarthric speech. This novel syndrome, referred to Uner Tan Syndrome (UTS), subsequently introduced to scientific community by about 15 articles describing eight more families [2, 3]. MRI generally showed cerebello-vermial hypoplasia. UTS cases exhibited diagonal-sequence quadrupedal locomotion, which is also used by most of non-human primates. Only the evolution of primates with diagonal-sequence quadrupedal locomotion was associated with a transition to bipedalism in human beings with well-developed hand skill and cognitive abilities. The phylogenetically oldest tetrapods, lived 395 MYA, exhibited diagonal strides, reflecting lumbering movements, consistent with a diagonal-sequence quadrupedal locomotion. The existence of this locomotion in primates suggests that the neural circuits for this locomotion is highly conserved during evolution. These neural circuits have been preserved for nearly 400 million years, beginning with the fish-like ancestors of the first tetrapods, to the emergence of primates. Neural networks responsible for diagonal-sequence quadrupedal locomotion have preserved for at least 395 million years since tetrapod-like fishes [4,5]. Evolutionary conservation of the enzyme for shaping the neural tube is associated with the evolutionary conservation of the neural networks for diagonal-sequence quadrupedalism. These neural networks may be represented in the central pattern generators (CPG) discovered in tetrapods, ranging from most primitive animals to primates. However, the concept of CPG did not find supporters among system theoreticians: ..the assumption of a built-in CPG does not explain the development of walking. If the program contains the instructions for the entire sequence of behaviors ahead of time, how can novel and adapted forms can be generated? . In light of dynamical systems theory, human quadrupedalism may be considered as an emergent property, resulting from some locomotor constraints. Emergence of human quadrupedalism, as a strange attractor, may occur randomly without any influence of a previously established genetic or neural code. The developmental emergence of the diagonal-sequence quadrupedal locomotion in humans may be the result of a neuronal group selection process following the principles of the adaptive self-organizing dynamic systems.
 Childs WJ. Across Asia Minor on Foot. William Blackwood and Sons, Edinburgh and London (1917).
 Tan U. 2010. Uner Tan syndrome: history, clinical evaluations, genetics, and the dynamics of human quadrupedalism. The Open Neurology Journal 4: 78-89.
 Tan U. 2012. Uner Tan syndrome: review and emergence of human quadrupedalism in self-organization, attractors and evolutionary perspectives. In: Latest findings in intellectual and developmental disabilities research. Uner Tan (Ed.), InTech Publ.
 Niedzwiedzki G, Szrek P., et al. (2010). Tetrapod trackways from the early Middle Devonian period of Polan. Nature 463: 43-48.
 Daeschler EB, Shubin NH, et al. (2006). A devonian tetrapod-like fish and the evolution of the tetrapod body plan. Nature 440: 757-763.
 Thelen E, Smith LB. (1996). A dynamic systems approach to the development of cognition and action. MIT Press/Bradford book series in cognitive psychology, p.10.