Plato classified humans as, “featherless bipeds”. Darwin rattled the cage about as hard as anyone when he suggested that humans evolved through the lineage of apes, and that the key variable that drove us towards our modern physical presentation was bipedalism. We are a bit of an odd animal in many ways. When it comes to other animals, there is typically some other creature that is very similar to them that we can use as a comparison that can help us understand them better. Other than avians, we are the only biped going, but the way in which humans move around is so drastically different from the strategies used by birds that the comparisons are incredibly difficult. Our closest living relative is the chimpanzee, and at some point in the historical record we shared a common ancestor (somewhere around 5 to 8 million years ago). Climate change appears to be the underlying reason that there was a divergence between humans and other great apes millions of years ago. It seems as though there was significant drying of the African climate, and with that the rain forests receded, and the open woodlands of the Savannah came into prominence. Chimps stuck to the rain forest and continued to eat a diet made up almost completely of fruit; whereas, the animals that became hominins and humans ventured out into the open terrain in search of other types of food. The ancestors of modern humans had to figure out a mode of locomotion that would be as economical as possible, because all of a sudden, they were having to travel many miles a day on foot to acquire foods such as yams and other tubers. Traversing this amount of distance on a daily basis is substantially more than what chimps do, as they rarely move more than a mile each day. The adaptive processes of evolution display themselves much more prominently when the going gets tough for a species, and this period of climate change and need to find new types of food with radically different strategies was a major stressor for our ancestors. Over time, there were three enormous shifts in the structure of the skeleton that helped our ancestors become amazing featherless biped apes who maximized economy in locomotion to increase our potential to survive and thrive on this shifting, variable, somewhat inhospitable spinning aqueous rock that hurtles through space revolving around an enormous fireball, that we call Earth. Those changes largely took place at our spines, pelvis, and feet.
Chimps are 4 times less energy efficient with long duration locomotion compared to humans. It costs a chimp about 140 Kcal more to traverse 6km compared to an average sized human female. Chimps are climbing quadrupeds compared to humans being walking bipedal animals. When you look at the spine of a quadruped, what you see is that it is long and close to being straight. There is a degree of curve to a quadruped spine, but for the most part, the anterior side of a quadruped spine is concave (gentle kyphosis almost throughout). The bipedal human spine features an “S” shape, which is the result of significant lordotic curves at the lumbar spine and cervical spine. If a quadruped attempts to rear up on its hind legs, the straight spine causes the thorax to be in front of the pelvis, and the center of mass is always falling forward and back down to the ground. The human lumbar spine has more lumbar vertebrae compared to a chimp spine (5 for a human, 3 to 4 for a chimp), and the shape of human lumbar vertebrae is more wedge like compared to squared off vertebrae of a chimp. The optimal human lumbar lordotic curve is 30 degrees, and this shape, combined with the subsequent thoracic kyphotic sweep back to the posterior side creates a situation where the thorax can be centered over the pelvis during upright posture. When we are looking at the neck of a chimp, we see that it emerges from the back side of its skull. The formen magnum of a chimp’s skull is positioned in a manner that is much more posterior compared to a human. This arrangement of a chimp’s foramen magnum and neck to skull position creates a more horizontal orientation of a chimp’s neck compared to the vertical orientation of the human neck. The optimal human cervical spine shares the same amount of lordosis (30 degrees) as the lumbar spine, and when these lordotic curves are coupled with a more anterior foramen magnum on the skull, we see an arrangement where the skull is stacked over the middle of the thorax, and the thorax is stacked over the middle of the pelvis in an upright bipedal presentation. The sagittal curves of the lumbar and cervical spine set the stage for humans to be able to create forward propulsion in locomotion with pendular walking and spring mass model running, without having to excessively contract the muscles of the thigh, hip, and back to prevent toppling forward and back down to the ground with our hands.
The ilium bones of a human are fairly squared off. The insides (medial surface) of the human ilium bone face each other and the outsides (lateral surface) face away from each other. A chimp’s ilium bones are rotated on a transverse axis, so that the, “medial side”, faces forward, and the, “lateral side”, faces backwards. As a result of this, a chimp’s glute medius faces posteriorly (a human’s faces laterally), and is unable to provide frontal plane control for the axial skeleton. Due to the direction glute med faces on a chimp, when a chimp tries to stand upright and walk forward, they lurch side to side like a penguin or a drunk. The thorax of a chimp rocks back and forth laterally and falls outside its base of support (feet) during gait, which is incredibly energy inefficient. The human glute med faces laterally, and integrates pelvis with thorax during single leg stance, preventing the center of mass of the thorax from laterally rocking during forward propulsion in gait. Humans with movement impairments, and who are carrying excess mass (extreme muscle hypertrophy or obesity) often times demonstrate some form of compensatory frontal plane motion of their axial (excess sway) or appendicular (imaginary lat syndrome) skeleton, which is probably some form of seeking an older evolutionary strategy of movement more reminiscent of how a quadruped would move if forced to try to stand upright. When a human is capable of keeping the axial skeleton inside the base of support from a frontal plane perspective during forward propulsion, they are able to rhythmically raise and lower their center of mass, which allows for tremendous energy conservation due to cycling back and forth between collection of potential uphill energy and release of downhill kinetic energy as they transition through the phases of stance and swing.
The feet of a chimp have a great toe that is almost perpendicular to the other toes. This is similar to how the thumb is offset from the other fingers on our hands, and is oriented in an oblique to horizontal direction compared to the fingers. This offset first digit on a foot or a hand is a great arrangement to facilitate grasp. So when you see a foot and toes that are shaped the way a chimps are, you can conclude that the animal needs to be able to climb trees. The human foot, with the great toe in line with the other toes indicates that grasp and climbing is not the primary function of that particular body part. The human foot has a longitudinal ligament that helps create the arch of our foot. Human toes have vertically oriented, rounded metatarsophalangeal (MTP) joints. Chimps do not have an arch, and the shape of their MTP joints prevent them from being able to hyperextend their toes. This combination of no arch and toes that cannot hyperextend forces chimps to try to walk on the outsides of their feet (almost as if they were on both sides of a Bosu ball). The human arch in many separates the rear foot (calcaneus) from the forefoot (ball of the feet and toes). The function of the arch during gait and other movement tasks of humans is to be able to stiffen as we transition from our heels to the balls of our feet. During normal gait, we strike with our heel, which sets off the neural cascade response that stiffens our arch, and allows the forefoot to be able change shape to receive the body mass and then propel body mass forward. Without an appropriately stiff arch, the functionality of our rear foot and forefoot is impaired, and we resort to compensatory movement patterns.
Our ancestors, who lived outdoors in the wild, moved a lot. They walked and ran miles and miles a day, and they reposed in deep kneeling, seated, and squatting positions. They assumed postures that we tend to avoid in our seated in chairs modern world, and they put us to shame with their activity levels. We are built to be upright and move for a large part of our day, and then to rest on the ground. The stereotypical behaviors that our species engaged in drove the genetic evolutionary pathway that led to the presentation of our skeletal arrangement explained in this article. When we go through life and don’t stress ourselves in the right way with enough and appropriate movement, and we don’t find repose in natural ways on the ground, we are deviating from providing our genome with critical environmental signals that are necessary for displaying our optimal phenotype. When you cease behaving like the humans from which you preceded you in your ancestry, you start going further back in time from a mechanical perspective, and you start going chimp. The bad movers in our society rock back and forth side to side as they try to walk and look like Tweedle Dum, or a penguin, or a chimp. With these people, we need to find interventions that can be driven into their electrochemically wired, water filled anti-gravity meat suits, which are constrained by the skeleton. When a person can experience reorganization of their nervous system to reposition their pelvis and rib cage, typically we see a situation where the pelvis is more squared away, the lordotic curves of their spine are restored, and their feet appropriately receive load and propel the body through space. Deliberate, sensory rich contractile behavior of the meat suit coupled with thoughtful, full excursions of the ventilatory process are the underlying methods I use to take those of us who have gone full chimp mode and bring them back to being human. Mechanical restoration of dysevolved humans is a major tool in my toolbox for restoring health to the system and reducing unnecessary stress from the performance of simple functions.