Human existence

Summary of theory why Homo, the human genus, arose due to  brain expansion dependent novel bipedal, dexterity and vocalization abilties. Bookmark and Share

For full referenced theory:  "Respiratory, postural and spatio-kinetic motor stabilization, internal models, top-down timed motor coordination and expanded cerebello-cerebral circuitry: a review".)

Human motor abilities are biological novel. Each of the three major motor faculties that characterize humans (dexterity, bipedality and vocalization) on close examination show radical differences in their functional and neurological motor biology to their nonhuman motor equivalents.

This uniqueness has a similar nature in all three cases and links to enhanced feedforward stabilization. Human dexterity, bipedality and vocalization all in their proficiency show a common shift to a motor control ability based upon anticipatorily/feedforward control used to execute and stabilize highly practiced top-down timed coordinated movements across multiple motor elements. Such accurate and precise timing of leant action adjustments can be seen in the task dependent timing of different muscles, for example, during the anticipatory stabilization of human specific motor expertise capacities involved in stone-tool knapping.

Stabilization by top-down adjustment derived from internal models across independent body/artifact movement units. The human ability to do top-down timed adjustment derives from the use of highly developed time-based predictive internal modeling of the body’s kinematics, kinetics and action interactions. Many actions—such as knapping, anticipatory postural adjustment while standing, and vocal tract synchronization during human song and speech vocalization—can as a result be executed and stabilized by the use of several different and separated bodily movements that are actively orchestrated together in a centrally determined and precisely timed manner. This allows that correction movements can occur in the most effective ways at the millisecond exact times needed to counteract any disruptive perturbations or unwanted movement side-effects.

Top-down adjustment derived from internal models requires a protracted period to acquire expert mastery. Human motor function to acquire fully competent modeling requires extensive daily practice over many years. Humans, indeed, have a highly prolonged period of immaturity before adolescence and adulthood in which motor skills such as speech and walking are skillful without having full adult motor expertise, a motor mastery most notably shown in the extreme robustness of adults compared to children against unexpected disruption. This lack of full adult proficiency exists in spite of the fact that by adolescence such skills would normally have been in continual daily use for over ten years, and so in many respects already highly proficient. Likewise, the full mastery rather than mere skillfulness of the expertise needed for many specialized adult motor skills is only achieved in many cases, for example, in sport and musical instrument playing, after at least ten years of daily deliberate practice.

Top-down adjustment derived from internal models interacts with higher-cognition. Internal models also enhance the higher level executive/ organizational control that provide actions with cognitive flexibility by enabling them to be (i) temporally planned and subtask set shifted in terms of hierarchized and sequentialized goal priorities, and (ii) monitored and modified during performance in regard to errors and error correction. Indeed, a key part of motor skill mastery lies in integrating motor faculties with cognitive ones that arise from such expanded higher internal model based abilities.

Nonhuman motor function is stabilized by evolved musculoskeletal system local preflexes and reflexes. In contrast, to humans, nonhuman motor control only enables a limited repertoire of highly evolved stereotypical movements. These are largely stabilized within the musculoskeletal system through preflexes and spinal adjustment reflexes. They lack as a result human levels of cognitive-motor complexity and task adaptability.

Human motor action involves multiple independent motor elements. Human task-determined actions usually consist of multiple motor elements that arise either

(i)        from the incorporation of artifacts (tools, projectiles, musical instruments, vehicles) into motor control, or

(ii)       from treating existing parts of the musculoskeletal system as independent control units that are otherwise in nonhumans animals “locked” together as nonindependent elements by the low-level stabilizing effects of musculoskeletal preflexes and reflexes.

Human enhanced motor stabilization arises from the expansion of cerebello-cerebral circuits. The internal model enhancement of human motor control arises directly from Homo brain expansion and its enlargement of cerebello-cerebral cortex circuitry (particularly involving the posterior parietal, ventral premotor and prefrontal areas). This expansion massively increased the capacity of Homo relative to nonHomo brains to create musculoskeletal internal models with (i) fine-level temporal resolution, and (ii) the action-organization levels needed to provide enhanced higher cognitive control over them (sections 7 and 8.3.).

Human motor faculties share neural resources. In the case of each of the three major unique human motor faculties (dexterity, bipedality and vocalization), this internal model enhancement arises, at least in part, from internal model related attentional, executive and other capacities that are drawn upon as common, shared, and, to some degree, effector nonspecific neural resources. This is evidenced, for example, in dual-task interference during which different areas of motor control (and even nonmotor faculties) are compromised in their performance when they attempt to concurrently employ such resources, and the developmental neuroimaging correlates that exist between them, particularly in the cerebellum.

Motor innovations closely link to human evolution. Since the motor control of bipedality, dexterity and vocalization need not happen as concurrent activities during hunter-gathering (nothing required early Homo to walk and knap, at the same time, for instance), this raises the possibility that their enhancement evolved as a nonspecific cross-faculty pleiotropic adaptation.

 (i)       brain expansion would have largely increased cerebello-cortical circuitry nonspecifically, and so

(ii)       the nonspecific availability of internal modeling that enhances motor skills. Further,

(iii)      the enhancement in each of the three motor faculties in the form of long-distance travel, high-energy food extraction tools, and more effective communication would have worked together in a highly synergetic manner.

The combined effect of them could have been responsible for the evolutionarily critical shift by early Homo to high-energy food—the hunter-gathering specialization of Homo until the recent advent of agriculture. This is because the enhancement and synergies involved would have created novel kinds of feedbacks leading to further motor function selection. Notably, high-energy foods would support larger brains and the prolonged nonadult maturation period required for refining the internal models needed for acquiring highly developed motor skill mastery.