A theory for bipedal gait ? Ipsilateral interference between the foot and hand in quadrupedal gait.


Human quadrupedalism is not an epiphenomenon caused by neurodevelopmental malformation and ataxia: Uner Tan Syndrome, Part 3

* Alert: Before you read this blog post you will do yourself a great degree of mental service by reading our 2 prior blog posts on this video.  There is an important learning progression here. Here are the links:



Note that in this video there is ipsilateral interference between the foot and hand in this quadrupedal gait. In this diagonal quadrupedal locomotion (QL) the forward moving lower limb is impaired from further forward progression by the posting up (contact) hand of the same side. This would not occur if the QL gait was non-diagonal (ie. unilateral), the forward progression of the lower limb would be met with same time forward progression of the upper limb, allowing a larger striding out of both limbs.  This would enable faster locomotion without increasing cadence (which would be the only way of speeding up in the diagonal QL), at the possible limitation of necessitating greater unilateral truncal postural control (which is a typical problem in some of these Uner Tan Syndrome individuals who typically have profound truncal ataxia).  

As the video progresses one can see that bipedal locomotion IS IN FACT POSSIBLE in Uner Tan syndrome individuals. 

This is the excerpt from the embedded video:

“Two adult siblings from a consanguineous famiy in Kars, Turkey, exhibited Uner Tan syndrome with severe mental retardation, and no speech, but with some developmental differences.. 
There was no homozygocity in the genetic analysis, but the extremely low socio-economic status suggested epigenetic changes occurred during pre- and post-natal
Quadrupedal locomotion in cases with Uner Tan syndrome exhibit interference between the ipsilateral extremities, and this also occurred in all tetrapods with diagonal sequence QL since this form of locomotion appeared around 400 MYA. 
The ipsilateral limb interference might have been the triggering factor for bipedal locomotion in our ancestors, and walking upright would enhance their chances of survival, because of the benefits in the visual and manual domains. The ipsilateral interference theory is a novel theory for the evolution of bipedalism in human beings, and was first proposed by Uner Tan in 2014.”

As Karaca, Tan & Tan (1) discussed in their article:

“In discussions of the origins of the habitual QL observed in Uner Tan syndrome, it was argued that this quadrupedalism might be an epiphenomenon caused by neurodevelopmental malformation and severe truncal ataxia (Herz et al., 2008). The present work will show that this argument may be untenable, presenting two individuals with QL who do not exhibit ataxia, and who have entirely normal brain images and cognitive functions.”

As we mentioned in our last blog post,

“Tan and Ozcelik mentioned in their recent research, in UTS the obligate diagonal QL was associated with some genetic mutations and cerebellovermial hypoplasia, and was seen as an adaptive self-organizing response to limited balance. On the other  hand, the present work showed that human QL may spontaneously occur in humans with an unimpaired brain, probably using the ancestral locomotor networks for the diagonal sequence preserved for about the last 400 million years. (Shapiro and Raichien, 2005; Reilly et al., 2006)." (1)

Kind of brings some new "slap in the face” thoughts to the rehab “bird dog” exercise doesn’t it !  Driving a 400 million year old quadruped motor pattern (ya, ya, we know it is a early-window primitive cross crawl infant neurodevelopmental pattern, we have been to Pavel Kolar seminars. Don’t try to argue, just think past all this. Go get a beer or walk in the park and cogitate on this a bit, it is important.)

If you want to dive deeper into this kind of work,  you may want to go and look at some of our recent work on Arm Swing here. But don’t forget to watch this video above again and pay close attention to what we mentioned here.

We received this video on Monday (March 3, 2014) directly from Dr. Uner Tan himself in Turkey. We are very grateful for all that he has been sharing with us behind the scenes and we are grateful for his research and for this budding relationship.  Thank you Dr. Tan !  

Dr. Shawn Allen, one of The Gait Guys


1. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3480821/