In 2005, a Turkish neuroscientist and evolutionary biologist named Dr. Uner Tan discovered a family with a very unique condition: five of them walked four legs with a quadrupedal gait. In addition to quadrupedalism, those affected had severe mental retardation and what he described as "primitive speech." The presence of these three characteristic symptoms is known as Uner Tan syndrome. The Ulas family was discovered in a small village near Iskenderun in southern Turkey. At the time of their identification, there were 12 normal children and 7 disabled children, one of whom died. Among the remaining 6 affected children, 5 of them showed habitual quadrupedal walking. The Ulas family is highly inbred (first cousins) and none of the founders exhibit any of the symptoms. This suggests that the genetic basis of Uner Tan syndrome is autosomal recessive (Harrison and Holt). A family in Brazil and another in Iraq also showed segregation for similar phenotypes at varying degrees of severity (Türkmen et al.; Ozcelik et al.). Habitual bipedal gait, articulate language, and the ability to form complex thoughts are characteristics that have long been thought to separate human beings from animals. When Dr Tan first described Uner Tan syndrome, he claimed that affected individuals were "genetic throwbacks". He hypothesized that a unique genetic mutation would be discovered in this family that could shed light on human evolution and the transition to bipedalism. Initially, the physical manifestations of the syndrome seemed to support this claim. The first clue was the fact that affected individuals walked with what is described as a diagonal sequence quadrupedal gait. It's an unusual foot...... middle of paper ... Nicholas, John R. Skoyles and Roger Keynes. Human Hand Walkers: Five siblings who never stood up. London, UK: London School of Economics and Political Science, 2005. LSE Research Online. Lemelin, Pierre, Daniel Schmitt and Matt Cartmill. “Step patterns and interlimb coordination in opossums (family Didelphidae): evidence for the evolution of diagonal sequence walking gaits in primates.” Journal of Zoology 260.4 (2003): 423-429. Ozcelik, T. et al. “Mutations in the very low density lipoprotein receptor VLDLR cause cerebellar hypoplasia and quadrupedal locomotion in humans.” Proceedings of the National Academy of Sciences 105.11 (2008): 4232-4236. Türkmen, Seval et al. “CA8 mutations cause a novel syndrome characterized by ataxia and mild mental retardation with predisposition to quadrupedal gait.” Ed. Gregory S. Barsh. PLoS Genetics 5.5 (2009): e1000487.