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Walking on All Fours Is Not Backward Evolution, Study Shows

July 18, 2014
Image Caption: These images show a comparison of footfall sequence in primate (baboon, above) and nonprimate (cat, below). Footfall sequence is depicted numerically, beginning with the right hind limb in each animal. The primate is walking in diagonal sequence (RH-LF-LH-RF), and the nonprimate is walking in lateral sequence (RH-RF-LH-LF), where R=right, L=left, H=hind limb, and F=forelimb. Credit: Images are from Muybridge E (1887) . Animal Locomotion: An Electro-photographic Investigation of Consecutive Phases of Animal Movements, 1872-1885: 112 Plates. Published under the auspices of the University of Pennsylvania

The University of Texas at Austin

Contradicting earlier claims, “The Family That Walks on All Fours,” a group of quadrupedal humans made famous by a 2006 BBC documentary, have simply adapted to their inability to walk upright and do not represent an example of backward evolution, according to new research by Liza Shapiro, an anthropologist at The University of Texas at Austin.

Five siblings in the family, who live in a remote corner of Turkey, walk exclusively on their hands and feet. Since they were discovered in 2005, scientists have debated the nature of their disability, with speculation they represent a backward stage of evolution.

Shapiro’s study, published online this month in PLOS ONE, shows that contrary to previous claims, people with the family members’ condition, called Uner Tan Syndrome (UTS), do not walk in the diagonal pattern characteristic of nonhuman primates such as apes and monkeys.

According to a theory developed by Uner Tan of Cukurova University in Turkey, people with UTS are a human model for reverse evolution, or “devolution,” offering new insights into the human transition from four-legged to two-legged walking. Previous research countering this view has proposed that the quadrupedalism associated with UTS is simply an adaptive response to the impaired ability to walk bipedally in individuals with a genetic mutation, but this is the first study that disproves claims that this form of walking resembles that of nonhuman primates.

The study’s co-authors are Jesse Young of Northeast Ohio Medical University; David Raichlen of the University of Arizona; and Whitney Cole, Scott Robinson and Karen Adolph of New York University.

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Source: The University of Texas at Austin



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