COMPARATIVE ANTHROPOLOGY OF FAST AND SLOW NEURAL TISSUES
Basic evolutionary differentiation and elaboration of functure: Throughout
evolution, from the first self-replicating proto-individuals onwards, every
----every bud come potential branch and lineage of the "Tree of
Evolution"---- have been challenged and selected (or pruned) in or out by
their ability (or inability) to
respond in such a way that they cope with and survive a smorgasbord
(served-up to them by the environment) of informational clues to and impacts
Adversity and Opportunity.
Such natuarally selective 'Situations' constitute the various "selective
pressures" towards suitable survival solutions.
Environmental "situational challenges" in early phylogenetic times were
overall more inert or more gradually changing than those of more recent
epochs. The inevitable
result of natural selection during this early era of biologic
Evolution----when situational "opportunity" and "adversity" were generally
of a more "tonic"
character-----was a prevalence of 'neural creatures' with predominantly
tonic responses. This also implies that any sensory and motivational cells
environmentally required to be mainly capable of a relatively slow mode of
response and signal-transmission.
In other words, 'successful Nervous Systems' typical of this era, would have
needed to have neurophysiologic characteristics adequate for a comparatively
'sedentary' fashion of living and coping. That is, "RAT" ["reticular
activating type"] neurons became the norm.
This view is supported/reflected by the anatomical differences between, and
matching developmental timing (in ontogeny) of, 'slow' (RAT type or
"nonspecific" neurons) and 'fast' neural tissues (specific type neurons) .
As the biosphere 'heated up' ---- i.e. became more complex, with faster and
more frequent and variable inter-species interactions (perhaps most
significantly as a result of the advent of predation-related
challenges)-----such an environment tended to more frequently "naturally
select *for*" nervous systems with an additional and complementary rapid and
phasic type of
sensory and motivational neurons.
Is it not still so that there is a predominance of slow and tonic type
neurons in animals with a simple, presumably 'early-model' nervous systems,
such as molluscs and
The evolution of more rapid and phasic, elaborate and finely discriminatory
behaviour, was achieved in part by way of an increasingly refined inhibitory
existing tonically motivated behavioural programs. But also, generally put,
this refinement was achieved by the opportune addition and integration of
new and further
specialised 'generations' of more rapidly and selectively sensing and
motivating neural circuits (or circuit-forming nerve cells).
These slow and the fast 'themes' of neural functure would have been
naturally "composed" early in evolutionary history and subsequently
embroided upon (as if they were enduring themes in a fugue with variations).
Summary: There seems to exist a tendency within Evolution towards ever
greater complexity, diversity and integration. Correspondingly, in
and responses to A and O type factors have tended to be selected-in by a
gradually more complex and rapidly and phasically challenging environment.
This implies a
corresponding naturally selected increased functional refinement of
'structions/functures' which carries out a descending inhibitory control of
tonic drives and responses typical
of lower/earlier nervous 'functures'. Conversely, this trend towards a more
complex and lively biosphere is linked to a correspondingly naturally
selected increase of the
anatomical proportion of neurons with a rapid/phasic and precise regulatory
output. The sequence of these changes is mirrored by the ontogeny and the
sequentially layered anatomy of animal (including human) brains.