Siblings that walk on all fours use a human gait

A man from a family with 19 children walking on his hands and feet in Hatay, Turkey, in 2005. (Anatolian/Reuters)

A man from a family with 19 children walking on his hands and feet in Hatay, Turkey, in 2005. (Anatolian/Reuters via the Washington Post)

Last week, a report was published in PlosOne that analyzes the walking gait of siblings from rural Turkey that walk on all fours. [Big thanks to my friend Bing Shaw for alerting me to this via the WaPo.] Walking on all fours is so unusual among human adults that the affected siblings from the Ulas family have received a great deal of attention. Locomoting on all fours is not only exceedingly rare among adults but is unusual at any age. Most babies crawl on their on their hands and knees rather than on their hands and feet.

Before getting to the contribution of the new research, let me share a bit of background on this neurobiological mystery. For those interested, there is a BBC documentary on the “Family that walks on all fours”.

There is also a scholarly monograph on the affected Ulas family members, written by Nicholas Humphrey, John R Skoyles, and Roger Keynes. This monograph is more concerned with the evolutionary implications, or lack thereof, of this unique condition rather than on the neurobiology of the condition, which is our focus here.

The challenge of cerebellar hypoplasia:

Five of 19 children (all now adults) born to parents in rural Turkey walk on their hands. MR imaging of the affected individuals shows a cerebellum that is much reduced in size, termed cerebellar hypoplasia. Particularly small in size is the vermis, the central portion of the cerebellum that is critical to coordinated walking. While the cerebellum and in particular the vermis is needed for coordination of walking, it is not needed for walking per se. Indeed the BBC documentary (at about 25:30 in the show) shows an Italian boy with no cerebellum (complete agenesis of the cerebellum) who walks, albeit in an uncoordinated manner. This fits with our idea that walking is the product of a type of circuit known as a “central pattern generator” or CPG. The output of CPGs produces a patterned stereotyped movement such as walking, swallowing, chewing, and so on. CPGs for different movements are present in the spinal cord and brainstem and are part of the motor hierarchy. The cerebellum modifies future CPG output to accommodate changing external (e.g. walking on sand vs walking on concrete) and internal (e.g. fresh and energized state vs tired and fatigued state) conditions. Without the cerebellum, movement including walking would not adjust to conditions, even routine conditions, and would always appear jerky and uncoordinated. With the cerebellum, walking is modified to match conditions, appearing smooth and coordinated and remaining so within one or two steps of a change in conditions (e.g. step off a boardwalk onto a beach).

Beyond coordinating gait, the vermis is also critical to postural balance. Because we are bipedal, our locomotion involves large doses of both gait and balance. [The challenge of balance for quadrupeds is much less than for bipeds because of the far greater support surface, and in many cases, a lower center of mass.] As with coordinated gait, balance requires the cerebellum. The cerebellum uses information from the inner ear’s vestibulum as well as visual and proprioceptive information to ensure that we don’t fall over as we move about. The cerebellum is constantly checking and adjusting motor output so that we remain upright while standing, locomoting, jumping, reaching, and so on. The beauty of the cerebellum is that it corrects errors before they happen. The congenital cerebellar condition suffered by the Ulas siblings renders maintaining balance while walking, and even while just standing, a very challenging proposition indeed.

What explains walking on all fours in the Ulas family?

The Turkish individual who first publicized the Ulas siblings proposed that this was a case of de-evolution, a glimpse into our evolutionary ancestry. In my opinion, this is not a scientific proposition. A group from the London School of Economics proposed a scientifically reasonable explanation for the walking pattern of the Ulas siblings:

  • Cerebellar hyperplasia, a condition that makes balance exceedingly difficult
  • Bear-crawling runs in the Ulas family: Most babies crawl on their on their hands and knees but approximately 5% use a bear-crawl where they get around on the hands and feet. The bear-crawl tends to run in families. According to the Ulas matriarch, all 19 of her kids used the bear-crawl.
  • A family environment that did not push the affected individuals to switch to a bipedal gait at a young age.

I asked my NeuroMOOC class if the above was a reasonable hypothesis and most felt it was. The most common comment was that students’ families were mesmerized by the story, often watching the BBC documentary together. I think that the most controversial idea was how to view the family and rural environment. Some felt that it was shameful that better medical care was not available or that the parents did not push their children to walk bipedally. I felt that it was quite unfortunate that the people in the town shunned the affected Ulas siblings. This appeared to cause the siblings quite a bit of distress. It was less clear to me how much distress, if any, their quadrupedal gait would have caused them in the absence of the social rejection.

There is the possibility that the affected Ulas siblings may yet learn to walk on two feet, probably with the assistance of a walker. Toward the end of the BBC documentary, we see scenes where the affected siblings get access to parallel bars, walkers and basic physical therapy. Because of the continued flexibility inherent in cerebellar function and because others with similar or even worse cerebellar conditions can walk, there remains the hope that the affected individuals may yet have the opportunity to learn to walk upright.

Analyzing the Ulas family gait:

Now on to the work by Liza Shapiro and colleagues. This study is very simple. It analyzes the Ulas family gait from available movie frames. The analysis is not particularly simple or easy to understand but essentially the time when each limb is in contact with the ground is measured. If two limbs on the same side land and take off at the same time, this is a perfect pace. If the diagonal pairs of limbs land and take off at the same time, this is a perfect trot. Most gaits are neither perfect trots or paces and certainly the Ulas family gait is neither a trot nor a pace. The important finding is that all affected Ulas family members spent at least 75% of their walking in one type of gait (lateral sequence, diagonal couplet or LSDC). In contrast, non-human primates use a different type of gait for walking (diagonal sequence, diagonal couplet or DSDC). This boils down to the forelimb landing after contralateral hindlimb, and before ipsilateral hindlimb (non-human primates) vs the forelimb landing after ipsilateral hindlimb, and before contralateral hindlimb (Ulas family members). To put it in more concrete terms: either the right arm lands after the left leg and before the right leg or after the right leg and before the left leg. In fact the gait of healthy humans asked to walk on all fours is the same as that of affected Ulas family members. The authors conclude that “quadrupedal gait preferences in humans are best understood as a function of biomechanical constraints, rather than genetic mutations.” In sum, the gait of the affected Ulas siblings has nothing to do with evolution. The siblings are simply using the most expedient biomechanical approach to getting around without falling over.

The Ulas family illness:

Many of you may have noticed that the Ulas family siblings are often referred to as suffering from so-called Uner Tan Syndrome. I find this term objectionable for several reasons. First, Uner Tan is the individual who publicized the Ulas siblings as evolutionary throwbacks, missing links. As this idea is without any scientific merit and is more than a little mean-spirited, I am loathe to credit the man with his would be eponymous syndrome. More significantly, I am greatly influenced by the view of Sherwin B. Nuland, a physician and National Book Award-winning author, who has written, “There’s a big difference between what we call ‘disease’ and what we call ‘illness.’ A disease is a pathological entity; an illness is the effect of the disease on the patient’s entire way of life.” In Dr Nuland’s framework, the disease that the Ulas siblings have is cerebellar hypoplasia (and possibly additional and associated brain abnormalities). They have reacted to having a much diminished cerebellum by changing their lives, including walking on all fours. The walking on all fours part is theirs, their chosen path, the illness that they have.



  1. Thank you for this follow-up, as this was most impressionable during your course, and the conflicting issues surrounding this family. I am still amazed at the ability of this “scientist’ to have created and as well as been accepted by the scientific community the labeling of Uner Tan syndrome.


  2. Thanks for the update. You & Dr. Shapiro are of course right about Ulas syndrome (?). But I completely understand and respect why Uner Tan believed it “de-evolution” It was a fascinating guess. How exciting it would have been to have discovered such a thing! Reminds me a bit of “cold fusion”. Do we know whether Tan named the condition after himself?


  3. Indeed, the brain is soooo cool. Have you seen the below documentary film about this amazing young person from the UK and his phenomenal brain functions ? It blew me away.

    The Boy with the Incredible Brain

    –From a most appreciative 2014 neuroMOOCer


    • I watched the documentary that you mention. Really interesting. It made me think of a book that I saw mentioned, Struck by Genius by Jason Padgett, which I now plan on reading. I agree with one of the speakers that the whole savant phenomenon has revealed the underlying truth of intelligences. I think the speaker actually said “intelligence” but I would argue that the right way to think about it is in terms of multiple forms of learning/knowing capacities aka intelligences. The other individual briefly mentioned in the film who was able to recall days of the week and weather for any date illustrates to me the incredible variety of intelligences. Another story that comes to mind is one from The Man Who Mistook His Wife For A Hat by Oliver Sacks about someone who appears to have transiently lost normal (for humans) inhibition of the olfactory system. He is able to smell his way around the city and to identify people by smell. I suspect that something pays the price for the unleashed olfactory ability but nonetheless the story illustrates the variety of abilities that lurk in our nervous systems.


      • Thank you so much for that reference–I have been all through Padgett’s website and will definitely also read his story, not least because my final project for the MOOC was on the TBI of Michael Schumacher with, for now, the much more common outcome which is unfortunately not positive at all. So how can a blow to the head (or a seizure) apparently produce these effects in an extremely minute number of (lucky) individuals ? Do they have some predisposition to becoming a savant ? Is it the specific way they are injured ? Or both ? Or other factors ? And all these different types of savants: the history ones, the math ones, the guy whose nose is for a while on par with that of a beagle…which could open up vast career possibilities. And here is another question related to that documentary: how many people think of a number or numbers as being a specific color ? For me, for instance a 5 is definitely red; 6 would never be red, but blue. But why ? Did I remember something on the wall in the kindergarten classroom or from some child book; from where else are these associations coming from and are they in any way useful ? Could one better remember a telephone number by thinking in color ? If 100 000 people were surveyed would there be any statistically significant color/number patterns ? In any case, am doing the MOOC on Learning how to Learn right now (UC San Diego, course started yesterday) and there is some interesting brainy stuff in there to reflect on.


  4. My comment is two-fold:
    1. With regard to the diagnosis of “Uner Tan Syndrome”, I was glad to see your response to the publication of that “premature diagnosis”. Too often these days doctors, scientists, researchers, etc. are so quick to publish something before it is completely verified, and deliberately do so. I believe that a thirst for publicity, a competition with colleagues or perhaps an unethical attempt to attract funding drives professionals to do this. Unfortunately, one of the hazards of such ‘worthless’ publications is that they are readily accepted by the general layperson who naively believe everything that is written or posted to the web. But often the general public fails to catch any retractions or corrections that may be posted at some point in the future (sometimes months or years after the initial claim has been made), and they continue to believe what they originally read. The “Uner Tan Syndrome” claim may have compromised the safety of the Ulas family in Turkey, and fueled further anniliation by their neighbors and members of the local villages.

    2. I felt that “The Family That Walks On All Fours – Documentary”, while controversial for many and for a variety of reasons, was very well done, and has served and will continue to serve many purposes. Yes, the documentary called attention to the family, but they have been receiving all kinds of help because of the attention. Also, it discounted the Uner Tan Syndrome papers and several other theories that were being tossed around, and didn’t settle on the first or easiest explanation for the ‘bear crawl”. I was grateful that after the main body of the documentary concluded there was a follow-up showing some of the siblings walking on two feet via the use of parallel bars provided by the documentary team, and walkers. It is too bad that it took 36+ years for simple tools like these to be suggested, even though there had to have been hundreds (if not thousands) of people in Turkey that were aware of this family’s issues, a number of which were in the medical profession.


  5. Please see the following article I recently published on this topic:

    Tan U. Quadrupedal Locomotor Characteristics of Uner Tan Syndrome Cases, Healthy
    Humans, and Nonhuman Primates in Evolutionary Perspectives. WebmedCentral NEUROSCIENCES


    Uner Tan syndrome (UTS) consists of
    quadrupedal locomotion (QL), impaired intelligence,
    and dysarthric or no speech. Previously, I described
    the walk of cases with UTS as diagonal sequence (DS)
    because of ipsilateral limb interference, which is
    mostly observed in nonhuman primates with DS QL.
    The only gait analysis previously performed for UTS
    was of a few cases from only one family. They
    exhibited lateral sequence (LS) QL. The current work
    presents a gait analysis of UTS in more cases from
    more families, to obtain a representative sample.

    Hip and knee angles during quadrupedal
    standing were measured in UTS cases, healthy
    controls with requested QL, and nonhuman primates.
    Limb phases were assessed from video footages, as
    the percent of the hind limb’s stride durations.

    UTS cases and nonhuman primates
    exhibited quadrupedal standing with straight legs
    nearly perpendicular to the ground. Healthy individuals
    could not walk quadrupedally like the UTS cases, but
    could perform QL only with flexed legs. UTS cases
    and healthy individuals with free (flexed-leg) QL used
    predominantly lateral sequence-diagonal couplet
    (LSDC) walks. Terrestrial primates preferred DS gaits.
    The healthy individuals with free QL were similar to
    arboreal primates in quadrupedal posture.

    Healthy individuals could not imitate the
    QL of the UTS cases, so a comparison of the UTS
    cases with healthy individuals is not justified. Although
    these results do not seem to support the thesis of
    locomotor evolution in reverse, nobody knows with
    certainty who our ancestors were or how they walked,
    and so the possibility of UTS as an example for the
    ancestral reappearance of QL in human beings cannot
    be positively excluded. This locomotor evolution in
    reverse was supported by experimental evidence that
    proved reverse evolution occurs as a scientific fact.


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