(if you haven’t already, you can read part 1 of this series by clicking here)
Mammalian development can be seen as a microcosm of tetrapod evolution. Mammals begin life as fertilized eggs- as do fish, amphibians, reptiles, and birds. At the earliest stages of fetal development, mammals appear like tadpoles (amphibians) with buds for limbs.
The first muscles to activate are the spinal muscles, followed by their tendinous attachments. Eventually the limb muscles begin to differentiate and gain independence. The very last stage of mammalian development is the development/ differentiation of fascia. Mammals develop from the spine outward, much as tetrapod biomechanical evolution progressed from spinal muscles to limb muscles to fascia.
Human babies are born in an earlier state of development than most other placental mammals and so make for good study subjects. When a human baby is born, it cannot yet lift its own head- much like early fish/ tetrapod ancestors could not lift theirs. When a baby begins to crawl, it does so in the amphibian/ reptilian manner- right arm/ left foot together, left arm/ right foot together. If you’ve ever had a baby grab your finger with its little hand, you know that babies show a surprisingly strong grip. This is because when a baby grips your finger, it is doing so with full efficiency- all spinal action is being transferred fully efficiently (via tendons) to the baby’s hand. Fascia have not yet begun to function on their own, and you are feeling the full force of spinal action transmitted through limbs via tendons.
In a fully efficient system, this powerful grip action continues undiminished as the person matures, merely complemented and supplemented by the action/ formation of the fascia surrounding it. This is how a baby’s strong but undifferentiated hand (a baby cannot yet use one finger at a time), can grow and develop into a concert pianist’s.
(Note that human fingers do not have discrete muscles of their own- every movement is a combination of tendon and fascia. Note too how a master pianist makes it look physically easy to generate such power in the fingers- this is how an efficient biomechanical system, with power transmitted cleanly from spinal muscles through limb muscles, appears)
Mammals in the Wild
The vast majority of wild adult mammals are fully biomechanically efficient- their spinal muscle action translates fully to limb action. Fascia serve to complement the action of primary muscles by forming patterns between muscle groups, acting as a sort of dynamic linkage system (with the ability to add its own action to supplement primary muscle action). Fascia form these patterns across areas without impeding or interrupting spinal force, instead complementing spinal action, supplementing it, and redirecting it when necessary. This is because in a fully efficient mammalian biomechanical system, fascia remain slack unless directly in use. So when a wild horse changes between its four different gaits, the fascia direct the fundamental spinal action into different sets of muscle patterns without impeding the force transmitted via tendons from the spine.
This video of a wild leopard hunt shows the incredible fluidity of movement available to a fully efficient wild mammal
Try to imagine a crocodile or a lizard (or a goose or an ostrich) creeping along with the subtlety and smoothness of a stalking cat- it is impossible. The mammalian variety and versatility of movement is enabled by a system that dynamically allows individual muscle groups across areas to activate together, or to work independently. The muscular system, instead of being a relatively rigid series of levers and pulleys like in other tetrapods, is instead a system with endless permutations and complexity.
The difference between wild mammalian biomechanical systems and those of other tetrapods is highlighted by current predatory niches. Mammals are supreme is every area where movement fluidity is an advantage- both on land and in the sea. In an even pitched battle, a mammal will easily out-compete a similarly-built non-mammal. Where other tetrapods hold the advantage is in their energy efficiency- even a fully efficient mammalian system will be less energy efficient than a tetrapod system without additional fascial tissue. So crocodilians, snakes, and raptors inhabit niches that maximize their efficiency, using very little energy to either lie in wait (snakes, crocodilians), or soar through the skies (hawks). These tetrapods also utilize means of locomotion that suit their relatively rigid biomechanical systems- in water or moving quickly through air, relatively minor movements are multiplied greatly in their effects via the resistance of the medium. A hawk need not expend much movement energy to descend rapidly and attack prey. Neither does a crocodile swimming through the water. Snakes meanwhile are essentially nothing but spinal muscles, maximizing efficiency by forgoing limbs entirely.
Yet for all the advantages of the fascial system in movement possibilities, there is also an upkeep cost. The fascial system may be visualized as a dense series of parallel wires connecting deep into all the striated muscle tissue in the body. And like any dense/ complex series of wires, it is possible for entanglements to occur (muscle knots being the clearest example). Free unrestrained movement enables wild mammals to keep these wires unencumbered by regularly applying tension to each of the wires. Regular grooming is also a necessity, since these wires connect at the surface level. Wild mammals spend a fair portion of each day simply keeping their fascial system at full health- stretching, grooming, sleeping, and moving.
So what happens when the fascial system does become encumbered- when the wires become crossed on a regular basis?
(click here to continue to part 3)