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