There are not many cases, but there are, there are. There are some human beings who still move on all fours as opposed to the usual bipedal form. In 2005, the neuroscientist and evolutionary biologist Uner Tan described the case of a Turkish family of 19 siblings, five of whom showed impaired cognitive abilities, a speech difficulty known as dysarthria, and a neurological disorder called cerebellar hypoplasia. In addition, they also walked regularly on feet and hands.
This condition became known as “Uner Tan Syndrome” (UTS) , and the scientist linked the symptoms to an evolutionary perspective, suggesting that they were an expression of our primate ancestry, an example of evolutionary reversion to a primitive state, or “return”.
To support hypotheses, Tan and his colleagues asserted that people with UTS use “primate-like” diagonal sequence quadrupedalism, a type of gait that distinguishes primates from most other mammals. This form consists in that when walking, the right arm moves simultaneously with the left leg and the left arm with the right leg.
However, about a decade later, a team led by Liza Shapiro of the University of Texas conducted a rigorous study in which quadruped in healthy or physically disabled adults was explained using biomechanical principles rather than evolutionary assumptions. .
In essence, Shapiro observed that those affected walked with weight on their wrists, not on their knuckles, unlike non-human primates. He also analyzed 518 quadruped strides of the images of the Turkish family diagnosed with Tan Syndrome and saw that they almost completely used the lateral movement sequence (right arm with right leg; left arm with left leg), like cats and dogs. .
This suggested that his symptoms had to do with a hereditary and neurological condition that complicates his sense of balance, developing quadrupedalism as a strategy. Nothing to do with an evolutionary reversal.
