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Chapter
Thirteen
The
Cell as a Living System
The biological sciences are considered the most paradigmatically unified
fields of modern science. It is not just the theory of evolution which helped to
provide unification to otherwise disparate fields of biological study. In fact,
unity of the subject is implied by the Grand Unity of Living Systems on earth,
the fact that life probably arose once on earth, and has been continuous in its
divergent evolution of new life forms, and hence all living systems are part of
a common tree of ancestry reflected by shared genetic structures and common
molecular configurations.
Less well known than Darwin's theory of Natural Selection,Cell Theory
emerged about twenty years previously, as a product of a couple centuries of
close observation and recording of life forms at a microscopic level. This
theory, called the Cell Doctrine, was first published in 1838-9 by T. Schleiden
and M. Schwann, stressing that cells are the universal component of living
organisms, and subsequently developed to a modern synthesis by the Twentieth
Century, as more was learned about the cell's structure and behavior.. In short
form, it first threee tenets holds three fundamental principles of living
systems:
1. Every organism is composed of one or more cells.
2. The cell is the smallest unit of organization having the properties of
life (i.e., growth and reproduction)
3. The continuity of living forms arises as as consequence of the growth
and division of single cells.
John Baker provided a more thorough historical
synopsis of Cell Theory:
1.
Most organisms are composed of a large number of microscopic cells.
2. All cells share similar defining structural characteristics.
3. Cells always arise from preexisting cells through reproduction.
4. Cells constitute the living tissue of organisms in which new material
is synthesized. Non-cellular material is extruded by cells or built of
transformed cells.
5.
Cells have an individual character somewhat independent of the organism as a
whole
6.
Cells of multi-cellular organisms correspond in certain respects to the body of
a protist or single-celled organism.
7.
Muli-cellular organisms probably arose from the colonization of protists.
A modern synthesis of Cell theory is given by the
following tenets:
1. All cells store information in DNA
2. Genetic information is the same in all species of cells.
3. All cells decode genetic information using RNA transcription and
translation.
4. All cells synthesize proteins by means of ribosomal RNA translation
5. Folded protein structures (enzymes) govern the activities, functions
and morphological structure of all cells.
6. All cells utilize ATP as the main medium for energy utilization.
7. All cells are enclosed by a plasma lipid-protein membrane that serves
as a boundary layer through which there is an exchange of molecules.
Cells are in many ways the prototypical general
system, albeit on a microscopic scale. It was indeed the problem of the Cell,
then a relative Black Box, that drove Ludwig von Bertalanffy, a biologist, to
develop General System Theory. Cells have many of the prototypical
characteristics of a general system model: a boundary layer, feedback mechanisms
in the form of enzymes that facilitate or inhibit biochemical reactions, and
selective transport mechanisms that mediate between the inner environment of the
cell and its external environment. The size of cells are critically related to
their capacity to efficiently transport nutrients and other chemical agents
through the cell and from outside into the cell.
Cells perform to basic dynamic functions that are
also archetypically general system based--their main functions are 1) the
utilization and acquisition of energy for self-maintenance and growth, and the
2) replication, transcription, translation and reproduction of critical
information (DNA). These fulfill two of the basic paradigms of dynamic
systems--information and energy transaction.
The cell is the fundamental construct of living
systems. It is the common building block of all living tissue and the foundation
for all living systems, without exception. In many ways it is the best example
of a prototypical system that we can conjure up, and it is in many ways the
epitome of natural self-organization. Indeed, general systems science really had
its birth in the concern with holistic perspectives upon cellular function and
development, at a time when the internal organization and happenings of a cell
were still pretty much a mysterious "black box." We need only consider
how remarkable cellular evolutionary development has been, when we realize that
all living organisms have been basically the descendants of a continuous,
non-stop process of cellular growth, reproduction and division from the first
proto-biotic cellular formations, and it is possible that all life might have
originated from a single successful cellular system. I return to the examination
of the cell as a system, for beyond ecology, what little formal biological study
I've had has been focused upon the cell.
A systems based perspective upon the cell therefore
would be based upon not only the examination of the metabolism, behavior and
life-cycle of a cell as a prototypical biological system, but upon what can be
called "cell ecology" and properly "cellular meta-biotics"
or the nature of inter-cellular interactions that influence the outcomes of
microbial development and evolution. At some point, microbial populations would
begin exerting a significant influence upon their environment, and begin
altering their bio-geophysical contexts in the direction that encouraged further
evolutionary development taking place. In spite of the self-containing
environment within the cell membrane, all cells exhibit specialized
environmental adaptations. They exist in rather special and narrow contexts of
cell development, that define the limits of their growth and development.
Under normal conditions for a cell, a cell can be
expected to respond to its environment by growing in population to the natural
limits of its context, and then overstepping these limits in critical ways.
Death rates will eventually balance or exceed reproductive rates, and the
population will eventually crash or achieve some long term equilibrium.
A phenomenon called "endosymbiosis," the
encapsulization of the DNA machinery of one micro-organism by another, and the
appropriation of that machinery, seems to me a fitting demonstration of a
systems-based meta-biotic framework. Virus's and viroids are similar entities,
that, though associated with disease, demonstrate a kind of meta-biotic
complication of living systems that do not fit normal hierarchical frameworks.
Horizontal transmission of DNA, especially in some forms of soil bacteria, are
another case that clearly defies our received models of strict vertical and
intergenerational transmission of DNA from parent to offspring.
"Endosymbiosis" becomes the basis for the
emergence of Eukarya, more complex cells, and in turn for multi-cellular
organization, which features functional subordination and specialization of cell
types. A fertilized gamete will carry the blueprints that include the
instructions for the development of a large number of different specialized cell
types performing a host of integrated functions. The differentiation of so many
cell types from a single precursor resembles the controlled internalized
embodiment of the entire process of taxon evolution of complex forms from simple
parent cells.
It is evident therefore in the first place that all
cells are capable of evolutionary development and speciation through chance
genetic variation of structure. Microorganisms have been observed to be capable
of quite rapid speciation and evolutionary development, compared to more complex
living systems that are slower to replicate and reproduce. The earliest known
form of cells, presumably some primitive form of Prokarya, were of minimal
possible size and structure, probably less than five micrometers in diameter and
a micron in thickness. This was perhaps the optimal size for rapid
self-replication and immediate exploitation of whatever growth medium becomes
available. It seems that life seized on the basic principles involved in this,
and capitalized on it as much as possible.
It is the case therefore that in the war against
disease, there is a on-going struggle to develop effective vaccines against new
strains of old strains of bacteria that become immune to previous remedies
through evolutionary adaptation.
The principle function of the cell can be said to
provide a suitable environment for the storage and replication of DNA and the
machinery needed for this storage and replication, as well as for replication
needed for the components of the cell itself. A cell must therefore be capable
of faithfully reproducing its DNA informational database, and itself. It
requires transportable and usable energy, in chemical form, for carrying out its
many tasks, and it must be capable of somehow capturing and transporting energy
into itself across its membrane. Cellular reproduction is a normal part of cell
growth and its life-cycle.
Essential components of cells, besides DNA, are:
1. A cell wall and/or cytoplasmic membrane
2. Cytoplasm
3. A nucleus or nucleoid
4. Cellular Organelles, consisting of ribosomes
and/or mitochondrioon, endoplasmic reticula for the manufacture of proteins and
for the maintenance of cellular tissue structure, function and equilibrium.
The first distinction we draw is between simple
bacteria or prokaryotes, and complex cells referred to as eukarya or eukaryotes.
In general, prokaryotes are much smaller and simpler than eukaryotes, averaging
between 1 and 5 micrometers (versus about 25 micrometers for eukarya) and about
1 micrometer in depth. They have a cell wall, but otherwise lack many of the
structures common to eukarya.
Prokarya are simple one-celled organisms capable of
fairly rapid reproduction. They are presumably the first organisms, or the
direct descendants of the first forms of life, to have evolved on earth. Some
have even suggested the possibility that they may have been carried to earth in
a meteorite that crashed in the best of circumstances (cosmic seeding
hypothesis), and from there began reproducing and evolving. Prokarya are grouped
into bacteria and archaea, distinguished largely by the complex structures of
the cell walls and analytically by their growth characteristics in various
mediums and the ability to stain under a cover slip of a microscopic slide.
Eukarya evolved from Prokarya, with the suggested
mechanism of the symbiotic ingestion ("endosymbiosis") of one cell by
another to form a more complex structure of organelles like mitochondria and
chloroplasts. Eukarya include algae, fungi, protozoa and all multi-cellular life
forms we know of. Prokarya in general do not form multi-cellular structures of
any form. They lead an independent life contained within the narrow confines of
their cell wall. Under the right conditions, they are known to grow rapidly,
which growth is defined by the cellular division and propagation by mitosis at a
fairly fast doubling rate.
One possible scenario of the development of
proto-life was that the first forms to emerge were primitive extremophiles,
Archaea, that developed through chemosynthesis. These eventually differentiated
and evolved into forms that were less marginal and more tolerable of normal
conditions, and that possibly could find a broader range of energy resources.
From these developed what we know of as the prototypical generalized bacteria.
This bacteria became so successful as an environmental generalist, that the
first adaptive radiation of life was its spread by air, water or any other
medium to virtually the entire earth, to cover the whole earth in a thin,
invisible layer of life. When this prototypical bacteria encountered extreme
conditions, it possibly resumed characteristics of an extremophile form.
One of the main functions of the cell-membrane is to
provide a medium for transport between the external environment of the cell and
the cell's self-maintaining internal environment. We know from the standard
general system model that such transport mechanisms and mediums are fundamental
to the definition of systems as order creating and order maintaining processes.
The cell membrane, therefore, with or without the added structural or buffer
support of a cell wall, is a vital component of all cell systems, for they are
the principal transport mechanisms of such systems that maintain internal
equilibrium and stability of the internal environment across a random and
external environment.
In the case of multi-cellular organisms, we must ask
what a cell gives up in terms of its independence as a system, and what it gains
in turn from the specialization of function and structures. Specialized cells
tend to take on definite shapes and configurations of structure, and they tend
to be capable of performing fairly specialized functions, either in a
chemo-mechanical manner or in terms of the production of special protein
structures or cellular metabolism. What is clear is that such cells, in become
specialized, become dependent upon the organismic contexts in which they
develop--they cannot survive apart from the super-cellular structures in which
they develop.
It is clear that from fairly early on cellular
evolution became a meta-biotic process, with cells respond to and adapting to
the presence and behavior of other cells as a part of their environment. The
most basic form of this kind of interaction was probably competition of
different strains of bacteria for the same resource substrates. Selection that
we can observe at this level is generally geared to those strains that can
effectively tolerate, adapt to and exploit a different medium. Symbiotic or
complementary relationships between different strains of bacteria may have
developed in time.
The earliest mechanisms of cellular metabolism
(catabolism and anabolism) was presumably some form of chemo-synthesis--the
derivation of usable chemical energy from some form of enzyme reaction with a
chemical substrate. Presumably, one of the first metabiotic forms of
relationship that may have developed between different species of bacteria may
have been that of predator-prey relations, or the capacity for one strain of
bacteria to attack and consume another form of bacteria for its energy and
material reserves. Photo-synthesis was known to have evolved from early Eukarya,
and presumably one of the first forms of endosymbiosis may have been in terms of
photosynthetic cloroplasts capable of synthesizing chemical energy from the
energy of the sun. Indirect symbiosis and interdependence also undoubtedly
occurred, by which the action and metabolism of one organism created the
environment suitable for the growth of a second organism.
Presumably, though there are many kinds of Prokarya
we know of today, their basic structure and function is not so very different
than that of their original precursors, and the diversity of life forms at this
level appears to be far lower overall than the diversity of more complex
multi-cellular organisms. Of all varieties of prokarya, the forms possibly most
similar to the ancestral "precursor" of life are possibly the archaea
though what we know of these prokarya today is that they have fairly specialized
cellular membranes and walls.
The
Cell as a Self-Replicating System
There has been an unusual unity of living systems.
From the organization of the first successful prototypical cell, there has been
a line of continuous self-replication and pattern variation that has led through
the entire natural history of evolution. In other words there has been an
unbroken chain of cells that have successfully reproduced themselves. Life seems
to have evolved only once, and once having achieved successful reproduction or
self-replication, its lines grew and diversified and never, as a whole, died out
over billions of years.
All living organisms are cellular, and we can study
all life as we know it on earth from the standpoint of the cell, its
reproduction and adaptation and its normal life-cycle.
The primary function of all cells is that of
self-replication, therefore the minimal amount of machinery-information
necessary to successfully achieve such self-replication is the primary
requirement of cell growth and metabolism.
The first cells had to have had at least a cell wall,
cytoplasm, ribosomes plus RNA transcription/translation structures, and some
kind of DNA bound to a nucleoid structure.
The functions of DNA are:
1. Its own copying.
2. Creation of structures that allow its copying.
3. Creation of the cellular structures that permit
the cell to survive as a distinct system.
4. Adaptation to varying environmental conditions.
In other words, the original and all subsequent DNA
had first 1) to replicate itself; 2) to replicate the replication machinery;
3)to replicate the cell as a house and factory for replication; 4. Perform
necessary cellular metabolism which involves energy-matter transactions with its
environment.
Cells perform secondary functions relating to their
adaptation in varying environmental circumstances.
DNA
as a Sequencing Clock regulating Cyclical Cell Growth
Cell growth and reproduction consists of a regular
cycle that occurs with fairly precise timing and periodicity. This suggests that
growth and self-replication is well regulated by a clock that is related to the
length and complexity of the central DNA and the related RNA
transcription/translation subcomponents that are necessary to complete the
cycle. It is also known that environmental factors, such as ambient heat, light,
relative presence or absence of nutrients or inhibitors, can slow or accelerate
this cycle substantially, and that there must be some maximum rate at which such
reproductive cycles can occur under the most optimum and ideal of circumstances,
which appear, for most organisms, to be rarely obtained in natural environments.
I suspect that the cyclical process of DNA
transcription/translation underlying cellular growth and reproduction involves a
cascading time-table of complex reactions and interactions of cellular
subcomponents, the complexity of which increases exponentially with time along a
logarithmic curve.
It is also known that cellular metabolism and
subcomponent reactions/interactions may occur at relatively high rates of speed,
especially when mediated by enzymes.
Cell replication and cell growth/metabolism follows a
clock, and this clock is the period required for a cell's complement of DNA to
perform its series of functions, on a scheduled time-table, until the cell
divides through cytokinesis and becomes essentially two new cells.
In a sense, bacterial or cancer cells do not die from
old age--an older cell becomes two
newer cells. Only in eukaryotic multi-cellular organisms, where cells have
specialized secondary functions to which cell growth is subordinate, can we
speak of a cell death that occurs as the product of the expiration of the
organism.
A multi-cellular organism is a highly organized
community of cells, so well organized that the community has organismic
properties and functions that transcend the functions of individual cells or
cell tissues.
DNA as a clock is the amount of time required for the
DNA to undergo complete transcription and for all subsequent translation
subprocesses to be continued. It is likely that these processes involve to some
unknown extent reiteration of transcription and translation, and this
reiteration or recursion itself must be controlled somewhat dynamically by the
DNA, or else this control comes built into the structure of the DNA sequencing
(and "con-sequencing") itself.
If we look at simple bacterial reproduction,
cytokinesis is followed by a latency period during which the cell itself must
increase in size to reach the normal limits of a prokaryote. This form of
morphological growth or expansion of the body of the cell must involve the cell
being busy with the process of manufacturing its own equipment and organic
resources from the natural substrates of its environment, up to its own
internalized limits or carrying capacities. At this stage, the process begins
repeating itself as a cycle.
The
Cell and DNA Transmission Mission as a Natural Computational Device
The amount of information contained in the DNA strand
of even a simple bacterium is indeed staggering, much less the full diploidal
complement of information, for instance, found in any given cell of the human
body, with its normal complement of 46 chromosomes reproducing the entire
library of the human genome. When we furthermore consider the millions of cells
that make up the various tissue structures of our body, with but few exceptions
of specialized cells like red corpuscles, etc., we end up with a staggering set
of statistics--a tremendous amount of information stored in spaces so small that
they cannot even be seen under the normal maximum magnification of a light
microscope. These kinds of considerations substantially diminish the
significance of our own recent
achievements in informational manipulation and storage, of which we are so
amazed.
DNA codon structure is founded upon the pairing of
four nucleic bases, in two complementary pairs each. This structure is
necessarily quaternary, versus the binary structures of our own
digital-electronic systems. A three codon series or unit yields a total of 64
possible combinations (4 x 4 x 4) which it would require a six codon series of a
binary system to yield as many combinations (2 x 2 x 2 x 2 x 2 x 2). This
strikes one as a inherently much more efficient, faster and versatile system
than achievable with binary encoding alone. In a vulgar sense, chromosomes with
binary encoding would have to be twice as long and large and would problem
require twice the amount of time for transmission to occur overall. That as we
know it now only 21 of the total number of 64 combinations are needed for making
all known protein structures, allowing for redundancy and substitution of
alternate codons for the same structures, allows not only an increased flexibity
but also an increased stability in the system.
In a sense the primary function of the cell, in being
self-replication, serves as a computational device the primary purpose of which
is the reading, transcription and translation of the DNA code it contains. This
DNA code is therefore somewhat analogous to the software that drives the
functioning of a computer to create a meaningful informational output. This kind
of computational device quickly reaches the scale of a microscopic, parallel
processing supercomputer--the simple act of reading the DNA code along a strand
quickly becomes the multiple events of RNA sequences
being translated into a very wide range of proteins serving multiple
functions.
If we wish to push this analogy with artificial
intelligence, then we must imagine a computing device that is capable of
recreating and reproducing its own hardware, of building from its available,
self-made store-house and factory of components two new computers.
Living systems have had four billion years to develop
its range and depth of forms and structures that we understand it today. It is
likely that for much of the first billion years replication was fairly confined
to a few limited and relatively simple life-forms. These early systems had to
solve basic problems through systematic variation of pattern--something like a
super-computer that must run at high speed day and night for a considerable
length of time, to achieve a new solution to complex problems.
The evolutionary exploration of new solutions to
problems of self-reproduction and adaptation by living systems is regarded in a
strict sense as "blind" being ultimately based upon a randomizing
agency of encoding error or genetic mutation, but the search achieved through
diversification and exponential increase in living systems was nonetheless
systematic and deterministic in that it resulted in the long run in stream-lined
optimal solutions to complex problem sets. This systematicity was largely
achieved by a kind of blind but compulsive "trial and error" in which
successful learning could only be measured by successful adaptation of emergent
forms and properties of living systems and by what can be called, in the
structure of the long run, taxon progress.
Looking back, among a long trail of discarded
evolutionary experiments and legions of dead hulks and extinct sympatric
species, we find a series of mile-stones of evolutionary achievements that
opened the doors to the emergence of entire new lines and taxons of organism.
To the extent that we consider DNA as a natural
informational encoding device, and its transmission and translation into
alternate protein structures and functions, as a dynamic (i.e., non static) form
of informational processing, we must take the informational model of living
systems somewhat seriously and we must not dismiss the idea that from the
beginning the primary function of living systems, of all life in general as we
know it, has been one of computational self-replication.
Things like human intelligence, our big brain, and
mammalian intelligence in general, however instinct driven and determined, must
by comparison be seen primarily as the spin-off properties of emergent
complexity, secondary derivative functions of living systems that have been
serving first and foremost, without exception, its primordial, original function
of cellular self-replicaiton.
Microscopic
Life Forms
The DNA transcription process is the universal code
of life, and these result in the production of a very large array of complex
proteinstructures occurring within cellular matrices that can be said to be the
universal building blocks of all life. If we want to understand the basic
structure of all living things, then we must understand the structural patterns
of life upon these basic microscope levels. These basic molecular structures are
found in all living forms, and their dynamics constitute the foundation for
understand the patterning and behavior of all organic systems. It is likely that
living systems outside of our terrestrial system may assume completely new
shapes and forms based upon their essential amino acids that will be different
than our own, and result in entirely different protein structures. Of course,
many of the structual and basic mechanics of the two systems will be virtually
the same or convergently similar.
It is difficult to think of a large Sequoia tree as a huge multi-cellular
system that perpetuates itself through time and periodically regenerates and
replicates itself as other individual organisms. These cells are differentiated
in form and function based upon their specialization within the larger cell
matrix of the giant tree, and these form various functions in coordination with
one another to maintain the tree as a living organism. Similarly, when we think
of a whale that sounds the depths of the ocean, we do not normally think of it
as a vast complex of cells growing together in unison to compose a single
organism. The behaviors we attribute to the whale, its whistles and clicks, its
diving and breaching, its migration from north to south and back again, its
social behavior and nurturance of its offspring. They are difficult to explain
only in terms of the cellular components that make up the tissues of the whale.
These behavioral traits that we may attribute to whales as inherent instinct are
difficult to explain in terms of the analysis of the cellular systems that
compose the whale and underlie its behavior.
Cellular
Ecology and Evolution
Cellular, or microscopic ecology is a study of the
processes of biological systems and their organization at a microscopic level.
We cannot really understand macro-ecological systems until we can explain
micro-ecology. The first cellular organisms arose in certain environments that
was conducive to their survival and propagation. These conditions have been
maintained, or even influenced, by life forms, and to a great extent life forms
have evolved upon a cellular level in such a manner as to incorporate a
protected cellular environment into a larger multi-cellular system. The result
of this process is the ability for life forms to create their own internal
environments, and internal ecologies, that are necessary for the survival of
their cellular populations. At the same time, specialized functions must be
developed, in terms of motility, response, recognition, etc., that allows these
cellular organizations to effectively mediate with an external environment, and
to achieve thereby a dynamic equilibrium between the external and internal
world. The evolution of multi-cellular systems was largely the function of this
kind of dynamic equilibrium established early on and perpetuated and elaborated
into many different forms of life that we witness today.
If we confine ourselves strictly to the microbiological level of analysis
of ecological and evolutionary processes, introducing larger level
considerations only as control mechanisms in such systems, then it is possible
to develop basic models of such processes that can be said to be true of a broad
range of life in general. In general, we may say that all cellular life-forms
require certain stable external conditions for their survival, metabolism,
growth and reproduction. All cellular life forms will reproduce at basic rates,
and the variation of these rates of reproduction for cellular forms are more or
less equal. These rates, and metabolism and growth, will be influenced by the
ambient temperature and the fluctuations and overall stability of this
temperature through time. We may properly speak of micro-climates within which
cell-growth and reproductive functioning is optimized.
From the standpoint of energy dynamics and rate laws affecting
biochemical reactions and properties within cells and between cells, we can see
all cells as representing heterogenous second-order systems that mediate
boundary phase-transitions of basic molecules--internalized surface areas that
are the product of reticulation and convolution of cellular membranes and
structures is critical to the control of the rates of these reactions. The phase
transitions possible within the context of a cell are gas to solid, liquid to
gas, and liquid to solid type reactions. The common components of these
reactions are the basic elements and compounds found in cell structures and
molecules, and water. Most phase transitions therefore can be said to be
mediated within the framework of water as both a solvent for solutions and as a
substrate for the transport of more insoluble molecules. These reactions tend to
be complex, relatively fast and recurrent, and continuous through the life of
the cell. The cell does not normally appear to shut down for a long period of
dormancy or inactivity.
Most cells as they have evolved, depend upon the critical presence of
other kinds of cells for their survival. Most cells can be said to be
metabiotically interdependent. Only some of the most basic forms of life,
prokaryotic bacteria, can be said to exist in a form that is relatively
independent of the presence of other forms of life.
1. These forms have evolved basic means of
independent locomotion to enable them to carry themselves to environments that
are suitable for their functioning and survival, or else they rely upon physical
forces for their transport.
2. In the absence or loss of suitable growing
conditions, these kinds of organisms may otherwise become dormant and form
spores that allow them to survive for very long periods of time until conditions
arise that trigger their release and allow their growth to continue. This period
of reactivation can be fairly rapid.
3. These organisms have a well defined cell-wall that
serves to protect them their external environment and to mediate relationships
with their environment.
4. Though many of these organisms may be parasitic or
symbiotic with other forms of life, many of them are capable of extended growth
under fairly abiotic conditions as long as these conditions provide the
necessary physical factors for this growth to occur.
All other derivative forms of life have evolved in
such a manner as to be dependent in one way or another upon other forms of life
for their growth and survival, either in a directly mutualistic manner, or else
indirectly through participation in a metabiotic system that fosters a shared
bio-geophysical context suitable to life. Under such metabiotic conditions, we
would expect that all forms of life would exhibit the following bio-physical
characteristics:
1. The ability to be transported to favorable
locations or away from unfavorable locations, either actively or passively by
means of physical transport mechanisms.
2. The ability to either maintain internalized
conditions in metabiotic contexts that achieve a degree of dynamic equilibrium
with the environment in terms of heat and nutrients, inspite of external
fluctuations of these conditions, or else a derivative capacity to limit
functioning during periods that are beyond the optimal range of functioning.
If these biotically dependent organisms cannot
achieve either of these functions independently, then they must be achieved in
mutual relation with other organisms. They must achieve a degree of cooperative
organization and functional interdependency that allows the cells to provide a
common context for the survival of all the cells together.
All unicellular organisms will reproduce at a set rate, and will
automatically follow a principle of reproductive maximization under favorable
conditions. Cellular forms of life will follow, under optimal conditions,
standard rates of reproductive activity. Cell longevity will tend to be an
average function of regular cellular regeneration and replacement.
It appears that cellular systems, in metabiotic contexts in which their
reproductive potential is constrained by requirements of metabiotic survival,
will not be expected to undergo a process of reproductive maximization as would
be expected of independent unicellular forms. Their relative specialization of
function would result in the creation of external equilibrium conditions that
would entail an sub-optimum reproductive rate. This is perhaps in part accounted
for in terms of the basic differences between prokaryotic and eukaryotic
organisms, and especially in terms of the nuclear DNA sequestration that occurs
with the eukaryotic as opposed to that of the prokaryote.
In general, eukaryotic cells are larger and more
internally differentiated that the prokaryotes. Within such an arrangement,
cellular replication and division can be regulated by other mechanisms that
occur within the cellular environment. Just as such cells are capable of
regulating their rates of reproductive development within the metabiotic context
of other cells, they are capable of yielding this reproductive capacity over
completely and to only carry out simple cell division through mitosis without
conjugation. Such cells, within a more complex biological program, are also
capable of developmental differentiation through an extended life cycle of the
larger organism, during which cells will divide and grow into different shapes,
forms and functions. Such cells accomplish this process that represents a kind
of encapsulated evolution--the capacity of the cell to divide into functionally
different kinds of cells in the metabiotic context of the host organism.
We may speculate on some of the following principles:
1. Cells requiring greater metabiotic functions of
specialization generally tend to have more DNA to record and translate these
structures.
2. Cells having longer and more DNA sequences will
tend to divide or reproduce at slower rates, because transcription processes for
long DNA sequences take longer to transcribe.
We may add one more kind of observation:
On a microscopic scale of measurement, relatively small and discrete
differences in intial states can lead to major differences in outcomes.
Some DNA structures may be repeat, or "back-up code."
Some DNA structures may be archaic survivors that are neutral.
Some DNA structures may be "critical," others intermediate, and
the remainder epigenetic in terms of their outcomes and effects.
Thus, genetic modifications that affect repeated or archaic structures
may have no consequences for the organism beyond possibly the increase in
genetic load or the gradual erosion of any built-in evolutionary inertia in such
systems.
Furthermore, it is possible as well that some DNA may be active, or
dominant, and other may be passive or recessive. Alterations that occur to
active or dominant DNA structures may grossly affect the final outcomes, or else
cause otherwise passive or recessive DNA to become more manifest and pronounced.
It is possible that DNA may be variously switched on or off depending on the
type of alteration to the coding sequence.
It is evident from the observation of evolving traits of organisms that
such evoltion tends to be trait specific, relatively continuous, and to exhibit
a differential in terms of the relative plasticity to those that appear to be
evolving rapidly, hypothetically as the result of differential selective
pressures, and those other trait complexes that appear to be stable and
non-evolutionary. Whatever conditions, for instance, that favored the
development of larger and larger brains in the hominid line, these conditions
must have been long-term and relatively stable over time, and it is apparent
that it resulted in relatively greater plasticity of the hominid brain or
related traits, for instance nerve structures and cranial and other related
structures, such as the face, compared to other anatomical features such as the
big toe or the ball of the foot.
Therefore, though rates of genetic mutation or transcription error may be
relatively low, comparatively minor alterations can result in major variations
of pattern at higher levels. These outcomes would tend to be chaotic in their
patterning.
Upon the microscopic level, trait variation will be expressed in terms
that tend to be trait specific to the form, type, size, shape, and function of
the tissue structure that is involved.
Upon a metascopic level of the organism, trait variation will tend to
include both specific trait variations (eye color, hair follicle shape, etc.) as
well as general variation of forms and features.
The cell contains the entire DNA code for the entire mature organism. It
is clear that any particular cell, at any stage of the growth and development of
this organism, will use only a portion of this DNA code for its transcription,
and this may be regulated in a number of ways--the presence of regulator DNA
that switches some on and off in different schedules; the presence of a
regulator DNA that encodes all the different developmental pathways that cells
may take in the functional development of an organism; the relative presence or
absence of similar or different cells in a sub-metabiotic context that provides
the conditions for the signaling and further differentiation of cells. There
would be some terminal path-end, at which point the cell would stop dividing and
differentiating, and assume a function of simple growth and replacement.
One must entertain the challenge of being able to write a single kind of
equation that would, in its chaotic reiteration, result in the development of a
differentiated organism in a predictable manner. There may be no single
equation, but a set of interrelated equations, that accomplish such a function.
In this manner, how is it possible that DNA might function in a manner that is
programmable, and in a manner that may exhibit some form of fundamental organic
intelligence in terms of the processing of complex information as a kind of
biological algorithm or complex function.
To some unknown extent, external prevailing conditions in the metabiotic
environment may serve to regulate such patterns of growth and development as
well. Intercellular commication or other forms of interaction may provide
necessary components in the overall direction and control of such developmental
differentiation.
To the extent that there is inherent structural variability and
flexibility in the encoding and transmission process, and to the extent that a
cellular system can be said to be underdetermined, then the final outcomes of
expression will be a function of phenotypic influence by the environment upon
the system as a whole. Phenotypic flexibility can combine with genetic
plasiticity of trait-complexes, to produce rapid rates or variable of
evolutionary transformation of structure. Phenotypic flexibility and genetic
plasticity can result in a kind of feedback system that favors differential
trait selection. Phenotypic flexibility of the expression of a trait complex
would result in differential selective pressures and adaptive functioning of
different organisms.
We see phenotypic flexibility in the ontogenetic development of many
organisms--many derivative structures and patterns of organisms are unique to
that organism.
We see genotypic plasticity in conditions where adaptive-selective
pressures favor certain features, characteristics or trait complexes in
differential rates that are fairly discrete or continuous. If it is Darwin's
finches--it may be in terms of fairly discrete differences of beak shape and
size, or in terms of overall size of the individual bird, or in terms of a
preference to sit in trees or stay on the ground, etc.
Genotypical plasticity may itself be variable in an evolutionary or
ecological context--shifting or shutting down under circumstances that favor
other kinds of complex adjustments and adaptations. Many traits demonstrate a
kind of evolutionary equilibrium and do not appear to quickly modify themselves.
Human brains may have changed dramatically over the last two million years, but
human dentition and human legs may have remained relatively unaltered by
comparison.
Any cell therefore may undergo evolutionary development. The whole of
evolution was basically cellular evolution that was continuous from the first
proto-karyotic cells until now. All life is cellular, and upon a basic cellular
level, all life forms are interrelated. The cellular differences between
organisms and organic structures are the most basic and greatest differences
that exist in life. Evolutionary development of any cell involves a simple
process of selection and reproduction of the cell, and its differentiation of
DNA-RNA determined trait function and expression from one generation to the
next.
We may distinguish between intergenerational DNA differentiation that is
controlled, presumably either self-controlled within the DNA (possibly cell life
cycle) or controlled by other DNA (possible ontogenetic development) and DNA
differentiation that is random and uncontrolled, or at least stochastically
influenced by external environmental factors. Both kinds of DNA differentiation
may be occurring at the same time.
No two cells are exactly alike unless they are
cancerous clone cells, either in form or function, or in terms of their exact
DNA structures. The intergenerational difference between any two successive
cells may be only slight, but it may lead to substantial differences of
structure and function in subsequent generations, over just just a few
generations.
If cells replicate every hour, on average, and life is estimated to be
3.5 billion years old, then we can estimate that since life began, there would
have occurred more than 30, 660,000,000,000 cellular generations, during which
time all the life as we know it and as it has occurred in the natural history
record evolved. If we assigned a simple doubling time to the first organism,
over generations, then we can speculate that there would have occurred a
potential for a vast number of cells to have been formed (230,
660,000,000,000).
If we see evolution occurring on an hourly schedule, rather than by the
year or the century, the we can imagine that speciation may arise, under the
right circumstances, as a function of days and months, rather than in terms of
years and decades. Depending on the form of life we are dealing with, trait
variation or its expression at least, may be delayed a very long time. We are
talking about the exponential evolution of trait variation pattern at the
cellular level.
Exponential
Evolution
The natural history record proceeded in the beginning
upon a long and low curved runway. For the first billion years, life was mostly
constituted by rather simple forms of bacteria in interaction. How far these
spread over the world is unknown--it is possible that they effectively spread
via the oceans and even air transport to most surfaces of the range known now as
the biosphere.
It appears that a major achievement was the rise of
eukaryotic organisms with highly differentiated and compartmentalized internal
structures, and many of these internal structures appear to have been based upon
the incorporation of a cell by another cell, and either the transgenic or
epigenetic transmission of new DNA information to the larger cell. The second
step in this process was the deep invagination of the cell, possibly occurring
at the same time as the penetration by a mitochondria or a cholorplast-type
prokaryote, which led to the development of reticulated structures and the
formation of a nulcear membrane within the cell. Early selection must have
favored these secondary processes, as any deep invagination that is the result
only of epigenetic information would be unlikely to be replicated by cell
reproduction.
This poses an inherent dilemma, as it is difficult to
simply explain many of the fundamental cell structures and functions merely by
the invocation of DNA mutation, which process appears to be rather conservative
and infrequent. It may also be the case that early protokaryotic cells lacked
some of the backup mechanisms found in cells today that enabled DNA
transcription to proceed without error--thus error rates for early cells may
have been quite large. It is evident while most such errors would have resulted
in cell death, a small percentage of the total mutations would have exerted a
tremendous adaptive influence upon the first evolutionary stages of life. In
such a context, every next cell was the potential progenitor of an entire
Kingdom or phylum of life, and while cells eventually differentiated into
distinct colony and family lines, a few such cells actually accomplished such
success, perhaps against all odds. In this regard especially we must recognize
that DNA as a molecule, and the entire transcription process of DNA to RNA to
proteins, evolved also as a function of time. The protopathways that formed the
basis for these later developments did not arrive on the scene full-blown.
Thus, the first successful propagation of fully or partially eukaryotic
lines, and their subsequent evolutionary development into more variegated and
integrated structures, permitted the rise of multi-cellular organisms and many
other associated features and properties, one consequence of which was the
explosion of the diversity of life in all the major phylum still recognized
today, less a few lost lines. This pattern exhibits the exponential character of
evolutionary development, and of all living systems in general that have a
fundamental doubling time at some relatively constant rate.
We can only imagine the earlies proto-karyotic biosphere and its
environmental ecology that enabled certain colonies and communities of these
unicellular organisms to achieve long term equilibrium and the leap to proto-eukaryotic
structures. Even after mass extinctions, what is recognizable is a long lag
time, a period of delay, after which new life forms suddenly reemerge in yet
another biological explosion of growth and development.
We may state a basic principle of evolutionary development. For each
evolutionary epoch that is marked at the culmination by a major extinction
event, each epoch was ecologically dominated by the most advanced and
differentiated life-forms that were then extant. The most evolutionarily
advanced would be marked by the most differentiated biological structures, and
would be the basis for an epochal exponential bloom of life.
Overall, upon a cellular level, the conventional evolutionary model is
stabilized by the conservative character of DNA reduplication. Subsequent
processes of RNA transmission and transcription into complex protein structures
are more inherently error-prone and hence variable than initial DNA replication,
but these in general are not held to have any kind of evolutionary consequence
except in directly by influencing the outcomes of natural selection for or
against the cell. In other words, such post-DNA transcription errors would be a
major source of genotypic variability and phenotypic plasticity of all living
forms, but by itself it would not alter the basic DNA coding sequence to
influence subsequent generations of the same cell line.
The inherent accuracy and conservativeness of DNA transcription is in the
conventional model regarded as the backbone for all evolutionary events.
Variation is tolerated in RNA transcription, because it is evolutionarily
inconsequential except in a negative sense of selection. But the question must
be asked, in the evolution of living organisms, if living systems did not have
some alternative means of achieving adaptive genetic variation more rapidly and
more dramatically than what we have witnessed.
Presumably, most post-DNA transcription errors would be either negative
or neutral in effect, leading to loss of the cell.
A case for indirect feedback can be made that positively selected
alterations of post DNA coding errors might lead to a selective or stochastic
advantage for these errors being repeated in subsequent generations, if
alternatives are selectively eliminated and the DNA structures originally giving
rise to these variations were positively influenced to reproduce at more rapid
rates. Furthermore, selective advantage favoring a particular trait or
phenotypical profile would possibly create an evolutionary framework encouraging
greater selection for the trait complex thus expressed.
Only one mechanism that is suggested in this, but has
not yet been documented and that goes against the fundamental tenant of the
blindness of evolutionary process, is if there occurs any degree of feedback
between protein and RNA encoded sequences and the original DNA that gives rise
to these RNA. This may only be possible if RNA fragments might become spliced
into, or somehow back-translate, to DNA sequences. So far, DNA to RNA to Protein
transcription appears non-reciprocal.
Several alternative processes might be invoked to explain radical
reassembly or change of genotype in cell lines:
1. Transgenic insertion of alien DNA from a virus or
bacterial infection: tranduction and transfection; plasmic conjugation
2. Reduplication of extra chromosomal complements,
and the reorganization of these complements into new and active strands of DNA.
3. Accumulation of excess DNA material within the
chromasomes.
5. Rearrangement of the same DNA sequencies into
sub-sequences differently organized: i.e. transposition and recombination
6. Epigenetic transmission of information and or
material structures, and the incorporation of such information or substance:
transformation
Furthermore, proofreading mechanisms on a cell may
not be correctly proof-read, at least in precursor structures, and may permit
some inherent variability in the correction process itself. Such a mechanism
would open up the process of DNA replication to much greater rates and degrees
of variability than are otherwise permitted under the conventional model.
Each or all or any combination of these processes may have been involved
in one way or another, at one stage or another, in the evolutionary development
of living forms. There are evolutionary phenomena at the molecular level that
require sufficient explanation. These are the incorporation of mitochondria/cholorplasts
into larger cell structures; formation of the nuclei and related reticulated
structures; the rise of excessive and discrete chromasomal complements in cell
progeny.
We may distinguish possibly between old DNA and new DNA, from an
evolutionary standpoint, and active DNA and inactive DNA, that may remain for
the most part unexpressed in the organism that contains it. We might also
distinguish what can be called as "basic DNA" that encodes those
common structures shared by many organisms, or even universally, from
"derivative DNA" that is a function of many episodes of evolutionary
events, and that gets added to or inbetween the basic DNA complexes. We may
speculate that derivative DNA is added on top of or inbetween basic, older DNA,
possibly overpowering or swamping the expression of the older DNA, a form of
cellular character displacement. We may also say, from observations of the
natural history record, that older DNA may be less active or pronounced than the
newer DNA that comes to take its place. It is evident that much primitive DNA is
shared by many very different forms of life, which often gains expression in
vestigial or ephemeral traits during early developmental periods, leading into
the development of greater trait differentiation during later fetal or neonatal
development. We may say that newer DNA may be more degenerate than older DNA,
which may be more regenerate and more highly conserved.
In a logical sense, if all of life is descended from a universal common
ancestor, then a part of this ancestor's genetic code and the substances it
encodes may well remain within ourselves upon a fundamental level. This would be
found in every cell as perhaps the substrate of codon pairs in one or more basic
chromosomes that would be more representative of most creatures on earth today.
If all basic forms of eukaryotic phylogeny developed from a single period
following the organization and formation of eukaryotes, then the precursor
structures typical of these different phylogeny, particular between trophic
levels such as producers, consumers and decomposers, must have been expressed in
the variation of the proto-eukaryotic populations and in their subsequent
ecological community organization, even upon a unicellular level long before the
emergence of large and differentiated mult-cellulared organisms upon the planet.
We can imagine in this proto-eukaryotic phase an ecological differentiation of
function by different varieties of cells.
The basis of exponential evolution is the observation
of the stability of a unimodal exponential growth curve of all living organisms.
This pattern can be found in prokaryotic bacteria and free living eukaryotic
forms, and it recurs at all levels of biological organization in multi-cellular
lines, with the cloning functions of tissue cells traded-off for the survival of
the organism as a whole. In a true analytical sense, multi-cellular organisms
are nothing but a complex bundle of differentiated and specialized clone cells
that have traded off their reproductive function for survival and growth of the
organism as a whole, and entire populations of these multi-cellular organisms
create larger evolutionary populations and breeding lines. Mechanical functions
of cells becomes specialized and organized to the purposes of the systemic
function of the organism of which they are a part, including such complex
patterns as locomotion, environmental sensation and response, complicated neural
networks leading to complex information processing, food getting and
food-selecting behavior, etc.
At any level of biological organization, it can be said that the pattern
for population growth under favorable conditions will proceed exponentially at
rates of generation time roughly proportional to the size of the organism, until
that population achieves the maximum limits of its environmental carrying
capacity. During this phase of exponential increase, it can be said as well that
the degree of heterogenic, mutagenic and transgenic diversity will increase and
be augmented to a maximum level. This can be referred to as the pre-selectional
phase during which positive selectional factors relating to niche expansion and
adaptation are more favorable than negative selection factors. The growth curve
will taper off in a stationary phase which may be continued indefinitely if
equilibrium of environmental adaptation can be achieved. This phase can be
referred to as the medial-selectional phase during which both positiveand
negative selection factors may be operating in some kind of complex dynamic
equilibrium. Eventually, changing environmental conditions will result in the
increase in the rates of death of the population such that rates of death will
outpace rates of reproduction. This can be referred to as the post-selectional
phase during which negative selection increases far above positive selection
factors. Genetic diversity of a population will be bottleneccked during this
phase, and, depending upon the predominating direction and types of selection
occurring, certain specific phenotypic variants will be positively selected. At
the point of lowest ebb of the population, at a point of greatest genetic
bottleneck, which phase can also be prolonged indefinitely under some
circumstances, the possibility of both extinction and of speciation becomes
greatest. It can be said that in periods of bottleneck, rates of speciation from
an evolutionary frame of reference are accelerated through the drastic reduction
of variants. As a consequence, there occurs a niche vacuum, which may be either
broad spectrumed or narrowly focused, within which there occurs ecological
opportunity for new variants to adapt and achieve renewed population growth.
In exponential evolution, the structure of this cyclical pattern of
growth, development, stasis, decline and bottleneck are repeated over and over
again. Each time the genetic constitution of the surviving populations being
affected by such development becomes reshuffled and reorganized in new
phenotypic patterns and genotypic templates. This patterning occurs at all
levels of biological organization, and always occurs as well within a larger
metabiotic context in which there can be said to be some kind of complex,
dynamic equilibrium. What we get is a pattern of dynamic mosaic organization and
succession of species in complex variegated biotic communities.
The general picture of evolutinary development is that it proceeds in a
step wise fashion, in a complex form of punctuated equilibrium during which
phases of one kind of genetic diversification through population increase and
exchange, is followed by other kinds of phases during which different selection
regimes are operating upon a particular population. It is at the time when
populations are declining that the likelihood of speciation becomes the greatest
through bottleneck and subsequent founder effects. The likelihood of extinction
can also be greatest at this phase. This brings to mind a picture of all
populations of living organisms occupying some position along their own
evolutionary curves, during which certain predictable kinds of outcomes may be
determined for the group as a whole. These outcomes would dominate the lives of
the individual members of the population as basic operating constraints. We may
make the following kinds of observations:
1. Very small single celled organisms have very rapid
and short-lived cycles and therefore depend upon mechanisms of rapid
evolutionary development through short term ecological adaptation and global or
regional distribution.
2. Very large multi-cellular organisms tend on
average to have very slow and long-lived cycles, and therefore depend upon
mechanisms of gradual evolutionary development through long term ecological
adaptation and local distribution.
All living systems upon a cellular can be shown to
proceed in biological growth and development in an exponential manner, until
some upper limit eventually is reached by the cell growth, after which an
extended stationary period follows, during which cell growth is in equilibrium
with cell death, and at the final phase, cell death due to endo-proteolytic
functions takes over. Multicellular organisms follow a very similar pattern of
development.
It is evident that cells for instance have a number
of genetic mechanisms of exchange and change available and that not all of these
mechanism are bound by genomic reproduction and transmission. Cytoplasmic DNA
may be replicated and transmitted outside of the cells nucleus. Various plasmids,
mitochondria and ribosomes may contain DNA or RNA that functionally coexist
outside of the nucleus and that may have a part to play in genetic development
and evolution. Transgenic elements, particularly viruses, which are known to
occur in all forms of living cells, and operate completely outside of the
reproductive framework, also may have had an important influence in genetic
development and evolution upon a cellular level. They appear to be able to
confer upon cells certain adaptive properties during the cells lifetime,
suggesting that organisms as a whole, and populations, may be genetically and
phenotypically modified by these forms of extra-reproductive mechanisms.
Phenotypic changes of multicellular organisms would not affect the reproductive
genotype of these species unless the reproductive cells themselves became
transinfected by extraneous DNA, but it does provide an environmental window for
genotypic-phenotypic modification of post-reproductive organisms in a manner
that can critically influence their survival. Furthermore, it is apparent that
single celled organisms are not bound in this same way, and may acquire
environmentally traits that can be readily passed on to subsequent generations
as a normal functional part of their genetic machinery. The question naturally
arises as to intermediate levels of organization occuring between single celled
and multi-cellular organisms at which levels some kinds of process of
environmental transgenesis may be occurring leading to evolutionary development.
Evolution upon a microscopic level proceeds
exponentially. This exponential function is not just the result of r-selected
forms of life that multiple quickly under suitable conditions. It is the result
of relatively rapid doubling rates for uni-cellular organisms, and the capacity
for such organisms therefore to quickly extend desirable genetic mutations
through a population within a few generational periods. Rapid and sweeping
trait-modifications can potentially occur within a short period of time within
the exceptional circumstances, while gradual trait modification would be the
normal rule under usual circumstances.
The consideration of exponential evolutionary trends is based upon
certain speculations about cellular structure and DNA structure in organisms
over evolutionary time. If we observe trends of phyletic size increase and
phyletic increase in differentiation and specialization of trait functions, then
we must speculate about how this is reflected in terms of the DNA structure,
composition and arrangement. We may speculate on the following kinds of
hypotheticals:
1. In general, in evolutionary time, there is
expected to be an increase in length of Chromosomal DNA segments that is
reflective of phyletic size increase.
2. In general, in evolutionary time, there is
expected to be an increase in the number of Chromosomal DNA segments that is
reflective of phyletic increase in differentiation of trait function.
If this general model holds true, it can be expected
for instance that mammals have on average more chromosomes than plants or
reptiles, and that fish will have more chromosomes than algae. In all these
instances, we are refering to eukaryotic cells where the chromosomal content is
isolated in the nucleus in a form, exists in a haploidal DNA form, and where its
transcription processes may be regulated and punctuated by one or more controls
within the cell itself. What I wish to describe by this means in terms of
evolution, is not the mere genetic mutation of chains, but the actual addition
new genetic material to old chains. This appears to be a process that has been
consistent with phyletic differentiation of species. The addition of new genetic
material to a chromosome, or even of entire chromosomes to a nuclear structure,
has not yet been described as a major contributory factor of evolutionary
development, and how this may happen exactly remains a mystery. There are
possible several alternative mechanisms for such increase in size and number of
chromosomes:
1. Errors in normal transcription processes may
result in added sequences to a chain, or else in the addition of multiple
segments or chains as a whole.
2. Introduction of extraneous DNA material by some
mechanism, as for instance by viral infection, or by symbiotic incorporation,
such as may occur with primitive organisms, or that may occur in instances of
sexual reproduction.
3. Addition or modification of RNA transcription
chains that intermediate between successive DNA chains that may result in
alternation of the final DNA coding sequence.
4. Point mutations in DNA or RNA sequences may result
in repeat or repair structures being added to the DNA or RNA chain, with the
result that point mutations may "drift" in their effect upon the
genetic outcomes overall.
It may be that the structure of genetic encoding
encourages repeat structures or sequences as a means of providing backup
reliability in information transmission processes. It is possible that what
emerged as a design to protect against errors or random point mutations, may
have resulted in an accelerative trend in evolutionary development of organisms
in the first place.
It is apparent at the same time that many organisms may be carrying
around more than a full complement of chromosomes, and that these chromosomes
carry far more information than is actually necessary for the completion of the
life-cycle of a single organism. Therefore, increase in size and amount of DNA
over time, a process that cannot be accounted for by mutation alone, implies as
well the likely accumulation of excess genetic material and hence a heavier
genetic load than otherwise thought possible. It may be that relatively
K-selected species in fact tend to carry a heavier than average chromosomal
load, reducing the rates of transcription and transmission respectively.
It is apparent that life may have evolved on basic levels the tendency to
accumulate and gradually add to the DNA sequences that are the common thread of
all life, but they did not evolve a complementary method for excising or
removing excessive chains or segments from the system. It may be a kind of
system that is so complex in terms of its interconnections, that an addition to
a chain may or may not be deleterious or beneficial, but the removal of a
segment would almost always assure a destructive or deleterious consequence to
the cell or organism as a whole.
It is also possible that some species may develop to a relatively high
level of population saturation and increased K, and then back down the
evolutionary period to a smaller size and more basic sense of production. Under
such circumstances it would be expected that some genetic material that was once
active and vital may suddenly become inactive and excessive. This excess code
may not be excised away, but may only become deactivated and made dormant. We
can expect therefore an gradual accumulation of archaic DNA structures, which
structures may relate us as human beings back to the age of the Dinosaurs and
before. We might see the role then of basic DNA structures that are shared
between phylogenetically different organisms, on top of which are built
different derivative sequences. Vestigial traits emerging and disappearing
during ontogenetic development may be a reflection of such archaic DNA
structures with a temporary influence upon the organism.
Such an accumulation of genetic material may result
as well in the accumulation of "bad" DNA or dysfunctional sequences.
In time, such accumulation may have negative effects upon trait development of
organisms, and may even underlie the occurrence of sudden extinction of species
in the fossil record.
Another aspect of DNA structures is the built in presumption of a
one-gene/one-trait correspondence, and a potential ignorance of the complexity
of DNA informational processing in which different DNA sequences may be
interlinked though not proximate at the same place or position within a larger
strand. This may be especially true in multi-chromosomal structures, in which
there is possible some kind of inter-DNA communication occurring, presumably in
the form of a specialized RNA.
Clearly, account has not been fully taken of the addition of DNA strings
and sequences to the normal complement of cells, and it is apparent that this
increase in number, size and complexity of such sequences may have been the
basis for evolutionary differentiation in life. Such addition must have been
gradual and rather slow in occurrence. Addition of DNA to the normal complement
of a species would result in fundamental and radically pronounce acquisition of
new trait patterns over time.
The line drawn in the normal definition of species, that of reproductive
success, may in some hybrid cases be blurred a little bit, if differences
between mating pairs occur at a sub-species or even in a broader level. It is
possible that, in closely related species or highly differentiated sub-species,
that occassional interbreeding may result in the formation of entirely new
species, on in a process that can be referred to as evolutionary amalgamation
leading to the emergence of a new type. Distance in this case may be a matter of
heterogeneous trait expression, as is commonly experienced.
On the other hand, there are also numerous examples
of cases of prolonged in-breeding and the bottlenecking of populations to rather
narrow margins of genetic variability. In such cases, the tendency for the
expression of deleterious traits becomes marked, and the tendency for genetic
maladaptability to changing environmental circumstances is also pronounced.
Cases also appear of prolonged functional inbreeding as the result of small
sizes of isolated populations or of functional sexual segregation in highly
competitive environments, with similar kinds of results that can be expected.
This kind of development may be expected for instance of highly K-selected
creatures who have come to define for themselves very narrow and highly
specialized niches and territories. In such circumstances the capacity for
mating and mate choice may be narrowed so much that genetic variability over
successive generations may be reduced. In such circumstances, high equilibrium
would entail a sense of long-term stability that would be conducive to
intergenerational patterns of breeding.
The picture that is being painted in terms that I refer to as exponential
evolution is that though the total genetic informational complement for an
organism may have a fairly broad base, the margin for expression and continuity
of a genetic type may be in the long run quite narrow, such that it can tend
toward rapid phyletic differentiation in adaptation, or possibly towards sudden
and deleterious expression of mutations and defects that are normally kept
silent. Creatures may exhibit in this regard fairly robust and broad-based
adaptations, but there is a limit either in terms of adaptability or dysfunction
beyond which the entire genetic system of a population may loose its equilibrium
and fall into a condition of general disequilibrium.
To expound a basic set of postulates for exponential evolution, we may
make the following statements:
1. Phyletic increase in size and differentiation of
function is reflective of the increase in size and number of DNA sequences
involved in the transmission processes of a kind of organism.
2. Increase in number of DNA must therefore be a
major factor in evolutionary differentiation and development of species, as both
a compensatory factor for the random rise of deleterious sequences and DNA, and
as just a normal process of increasing genetic load.
3. Addition of genetic material may be both
deleterious and beneficial, and is usually deleterious in the long run.
4. Genetic encoding becomes more complex in terms of
its intensive differentiation and interconnection of function, as well as more
extensively developed.
5. The gradual increase in DNA size, amount and the
ensuing genetic load tends to alter species from an r-type toward a K-type mode
of development and adaptation, and can be expected to arise as a result of
K-type selection factors.
6. A supercritical point will be reached in loading
of DNA such that the system becomes informationally noisy and possibly breaks
down in its capacity to confer trait adaptability to a species or type of
organism, as a result of which extinction can be expected, especially in a
context when such a heavy genetic load may intefere with an organisms ability to
become more r-adapted to changing circumstances. This would be evident in lower
rates of fertilization, conception and successful births, as well as more
frequent cases of immature organisms failing to develop properly to mature
reproductive form.
7. In the long run, additive process to DNA seem to
occur far more frequently, at a much greater rate, than deletive processes. This
entails that deletive processes in the fossil record are probably unusual and
exceptional. Deletion of DNA from gene pools probably takes the form of negative
selection that favors lower loads of variability between individuals.
From the standpoint of this theory, the rise of
haploidy in chromosomes represented a major development. Sexual reproduction
guaranteed a kind of metabiotic dependency for transmission on other organisms,
and that each cell would normally carry a double complement of genetic
information. We know from gene studies that for every trait or trait complex
there will be two alleles that are possibly represented. We do not yet
understand the mechanisms involved that assures the dominance of expression of
one allele over the recessive counterpart. It is possible that more than one
kind of recessive or dominant allele can occur in multi-trait systems. Haploidy
may have assured a backup system in case of error in genetic coding sequences,
and it may also have provided a basis by which genes had to be regularly
exchanged between organisms to prevent or at least forestall perhaps the rise of
monogenetic trait systems. It may have provided as well a context within which
DNA had a basis for additive accumulation in a manner that may have minimized
the deleterious effect of such processes. Haploidal systems comprise in general
a greater range of trait variability that would enable such systems to better
adapt through population growth, given that such systems are in a fundamental
sense, when compared to more primitive bacteria, in general slower to reproduce
and more complex in their organizational structure. Haploidy therefore may have
provided the platform of builtin intergenerational genetic variation to enable
more complex trait-systems to be developed. It certain provided the frame work
for an inherent increase in the number of genes available to do the work.
Haploidy leads into polyploidal systems, and polyploidy has also been observed
to occur in a limited number of cases that are to be considered aberrant.
The kind of system we see is a long term evolutionary advantage to
increased trait systems of DNA, and to the inherent variability these systems
afford in terms of trait-differentiation and adaptation, even at the expense of
short term stability or deleteriousness of carrying a heavy genetic load. This
works as a kind of cybernetic feedback system such that increasing DNA structure
increases adaptability, which in turn may foster conditions leading to further
addition of DNA.
The gradual accretion and organization of DNA is simply accountable in
terms of the basic biochemical processes that occur in the construction of DNA
in the first place--it is possible that the signals that shut down the
construction of DNA may result in the addition of more DNA material than is
normally required or encoded for. DNA construction may on occasion fail to stop
or go into a kind of overdrive that results in a kind of experimentation of the
system through systematic variation. Cancer cells would represent one kind of
DNA transcription system that has gone awry, leading to the continuous
replication of new cells, but without genetic variation.
This theory is based upon a very fundamental premise about basic
biological variability. It can be summarized thus:
Every living cell that is produced as the product of
cellular division, is biochemically unique in its overall trait-properties.
No two cells, however related, are exactly identical
to one another. All cells have a degree of variation within which they can
achieve expression, and this variation occurs within the framework of the cell's
membranes and internal structure, as well as in its DNA encoding. What I will
call as inherent fundamental variability is really the basis for all variation
of pattern and evolutionary change in living forms. It provides the basis for
the successive cellular differentiation of cells within some developing tissue
matrix that results in the eventual differentiation and specialization of cell
function in multi-cellular organisms. This variation is continuous and occurs at
a continuous rate, and can be accounted for by the shear bio-chemical and
macro-molecular complexity observed within all cellular life-forms. Cells, as
heterogenous, enzyme based rate systems, depend upon speed of reactions within a
very small area in order to accomplish their metabolic and growth/reproductive
functions.
Inherent fundamental variability of cellular systems
is the basis for the biological relativity of living systems and for
evolutionary irreversibility of such systems through time. It assures that
changes will occur in an historically forward direction, as once new systems
emerge, they will continue to vary, and will not return to the state of previous
systems.
We can therefore understand those few very conservative systems in nature
that appear to change very slowly. They must exhibit a system in which inherent
fundamental variability, and its integrative, chaotic effects in mature
organisms, is kept in check and minimized. The mechanism of control in this case
may be an narrow adaptive equilibrium that assures a minimization of genetic
load and the selective elimination of any strong variants. This may be
reinforced sexual by built in systems of preference that serve to minimize the
crossing of heterozygous forms and that may lead to a long crane-like
bottlenecking of genetic variability represented by such species.
Genetic addition can be seen therefore as a buil-in function of systems
of DNA production and replication in which the processes of DNA transcription
and replication are decoupled from the processes of other cellular metabolism,
growth and reproduction, and in which case control mechanisms exist that may
permit the accumulation of excess DNA without deleterious effects upon the
functioning of the cell, or even in its reproductive phase. Such systems are
clearly represented by the eukaryotic domain, and they are represented
essentially by the incorporation of prokaryotic forms, chloroplasts and
mitochondria, as internalized forms. It is possible that the DNA from these
prokaryotic subunits was contributed to the DNA of the enlarged proto-eukaryotic
cell to enable a platform for greater differentiation of form and function than
was otherwise possible.
This may also have set the stage for multi-cellular organization of
increasingly more complex systems. Such systems are represented by shared
inheritance of a single complex of DNA trait material that controls the
differential growth and function of all the cells with each successive
generation. The cells of such a system yield reproductive function, and usually
motility, in order to enhance the productive function of the system as a
whole--they gain from this an environment that is minimal optimal and suitable
to their survival. That reproductive function must be yielded to increase the
potential for social organization is a principle that was not lost upon social
insects, and it appears to be an important emerging concern for oversaturated
human populations as well. Human systems have accomplished this by the
superimposition of monogamy, or alternative the alpha predominance of indivduals
who are exclusively polygamous. Further increase in human population is creating
a demand for further control of human reproduction to monoparous families.
The rise of multi-cellular systems again can be seen
as having been made possible by the functional segregation of sexual
reproductive function from normal cellular metabolism, growth and division
replacement, which was the product of separating processes of DNA encoding and
replication from the encoding and replication of the cell body itself. In such a
context, generations of cells stemming from the same parent generation can be
increasingly organized in such a way that some cells carry reproductive
functions selectively on behalf of the entire cellular community, while other
cells provide other functional roles in the organization of the community
structure.
It can be seen that DNA transcription may therefore result in a
systematically changing genetic structure through time for successive
generations of these organized cells, such that specialized functions of select
cells become increasingly expressed by the subsequent copies of the DNA. This is
possible if we conceive that in a DNA detached system, the RNA transcription
process may introduce regular and systematic variations of structural encoding
at regular intervals. Again, as mentioned previously, this may be the result of
a master or controlling DNA, or of built-in pathways within the genetic coding
itself, or by some genetic signaling system we do not yet understand, or else by
the common environment or emerging tissue matrix in which the cell itself is
embedded. In this regard, a base stem cell may become differentiated in its
growth in any number of alternative directions depending upon the biochemical
nutrient base and other properties made available to it. Hormones, steroids and
certain kinds of enzymes in combination appear to me to be particularly
implicatable in such differentiation processes. Such biochemical signals may
stimulate and activate the transcription of some genetic sequences, and repress
or deactivate the transcription of other alternative sequences simultaneously.
These reactions would all occur within the context of the cell itself, and in
the exo-cellular tissue environment in relation to other cells. Cells may in
this regard be exchanging chemical signals in a regular and influential manner.
We may speak of possible regulator sites in chromosomal complexes, in
organelles, as well as in cell tissue complexes that serve to control the
formation and development of cell tissue patterns and functions. Such a prospect
suggests something fundamental about genetic systems, that genetic systems of
one cell may have a metabiotic and adaptational influence upon the systems of
other cells, even possibly affecting the differential expression of genetic
traits.
This suggests in turn that genetic chromosomal systems may in fact be
communication systems that exhibit a duality of patterning, or even a
multiplicity of patterning, that allows the same genetic sequences to be used in
fundamentally different ways within different complex arrangements. Folding
structures may be the basis for these kinds of systematic differences. Duality
of patterning suggests that all traits complexes are both pleiotrophic and
polygenic in nature. How the same chromosomal structure may be used to different
purposes remains an unanswered mystery. We see a translational structure in
successive translation of genetic sequences leading to different forms and
functions of the same basic genetic material.
It must be understood in this that genes control exclusively the cellular
structure and function of the cell body they inhabit, and they control the
transcription process to the next generation of cells. Therefore, however we
describe genetic function within a cell, it must be in strict terms of the
metabolism and organization of the cell itself. DNA does not work remotely
between cells in any direct manner. They function only in terms of the cell that
it is situated in, and indirectly upon cells that are near it or that are
functionally related, and those cells that it gives rise to through growth and
reproduction. That some of these functions may take on extrasomatic properties
in relation to other cells is a moot but not unimportant point. A gene that
confers, for instance, color to hair, must find expression in the cells that
produce the hair follicle, and not in the cells that produce toenail in the big
toe. The gene that produces the hair follicle may be the same gene found in the
big toe, only differently expressed in combination to other genes. DNA
structures must differentiate in the process of ontogenetic growth, just as they
do in evolutionary processes of speciation.
Genetic complexes can be seen therefore to control trait-complexes in
sophisticated ways. That folding structures of genetic material, with the
secondary bond formations that occur, may be important in the organization of
these complexes and in influencing epigenetic trait expression.
It is doubtful in this regard that we could take the genetic material
from a skin cell in the tip of the big toe, and inject it into the egg cell, and
from it derive a replica of the same person who was attached to the big toe. The
organizational structure of the DNA in the big toe may not be exactly the same
or of the same organizational structure as that in the
DNA is not passed wholly from one generation to the
next--it is transcribed and translated afresh with each new generation. The
reproductive growth of cells represents a fundamental exponential increase in
the total amount of DNA material that is being encoded and used in all of the
cells. We may refer therefore to ontogenetic life-cycles of DNA development,
differentiation and increasing elaboration from basic and source code to
derivative and end-code. In this regard, the rate of DNA replication must be
synchronized with the growth of tissue, such that once tissue has reached its
stage of full development, growth is switched over to a slower rate of repair
and replacement. External limiting factors may fundamentally control these
processes, with mature cells obtaining a kind of equilibrium of internalized
community structure that represents a saturated cellular system.
With these processes of continuous and successive transcription of DNA,
multiple occassions arise in which the average amount of DNA available to a cell
may increase through transcription itself. In other words, DNA is continously
replicating itself, thus providing the basis for production of excessive code.
It is in this production of excessive code that the possibilities for variation
and evolution arise. It is possible that even within cell tissues of an
organism, genetic material may slowly accumulate in successive generations,
which accumulation may have a critical effect in the regulation and timing of
metabolic and reproductive growth functions. In this, the growth of any tissue
would therefore be seen to follow a normal unimodal growth curve that is very
flat. Each successive generation of cell would represent an instantaneous point
upon this growth curve. The slope of this curve at any point is quite variable
between different kinds of species, and the time required for an organism to
reach full maturity may vary from days to months to years or even decades. Cell
tissue in old-age would eventually break down in function and structural
integrity by the exhaustion of a DNA complex systems that has reached a stage of
supercritical chaos in its organization.
The received model of DNA structure is that it is a fairly stable
backbone of life. The transcription process is inherently stable, with back up
mechanisms to safeguard against error. DNA transcription in eukaryotic life
forms passes to messenger RNA as a single large strand. The sequences are
linearly encoded with segments of introns. The messenger RNA is then broken down
into its sequential units, and transported outside of the cell to ribosomes
where it is translated into transport RNA, which RNA then manufacture the
protein chain encoded in the sequence. It is the proteins that show the greatest
variability of form and structure, and the shape of protein molecules will be
critical to determining its enzymatic function and the resulting geometric
structure that cell tissue will take. The variability that is demonstrated in
life upon a fundamental level is best expressed at the stage of the folding
structures of the protein molecules, and the larger structures these molecules
form. These sequences are discretely determined by the precise DNA coding
sequences. It is known that point mutations occur in DNA sequences with regular
frequencies, and there are recording errors in the transcription process as well
that may result in mishapen end products down the line. DNA sequences can be
spliced and juxtaposed. There appears possibly to occur room for variation in
the second stage of the slicing up of the mRNA and its transport and
transcription back to tRNA. The disassembly of the starter mRNA might result in
alteration of sequences.
The entire problem of evolution can be described upon a microscopic level
in terms of the process of DNA transcription through RNA sequences in the
production of a vast array of different kinds of proteins that constitute the
true building blocks of life. Selection will be determined by cell death or by
its ability to survive alterations, and by its ability to confer adaptive
advantage to the organism of which it is a part.
In the diagram above, we can see the multiple steps
involved in the sequence of cellular actions that result ultimately in the
outcome of cellular demise or reproductive success. With each step, the degree
of variability of pattern becomes magnified exponentially. At the same time,
with each successive step, the potential for error pattern to arise randomly and
for its effects to become pronounced magnifies exponentially as well.
1. Random changes that occur in more basic and
earlier steps are likely to have more pronounced and generalized consequences.
2. Random changes that occur in the final steps of
the process are less likely to have major or pronounced effects, and will only
affect specific protein molecules.
Previous to the final step, it is possible that what
I call endo-somatic factors may play a part in determine the structural and
functional outcomes of the process. In the final step, it is apparent that
extrasomatic factors will play a decisive part in determining the outcomes for
the continuation of the cell line. These factors may be independent of
endosomatic factors or resulting structures, for instance, chance death of an
organism due to some natural disaster. It is expected that the majority of
mutation events are likely to be either negative or neutral in their
evolutionary effects, and this can be accounted for by the fossil record that
suggests that the vast majority of life forms eventually became extinct. Neutral
build up of genetic mutations are likely to have in the long run a negative
effect upon the subsequent population as a whole, but may confer a wider range
of adaptability to a select number of offspring.
It is evident that there are entire families of proteins that share amino
acid sequences in a non-random manner and that indicate some measure of genetic
relationship and common inheritance of structure. The repertoire of protein
structures and functions has evolved in time, as have the necessary genetic
precursors--the DNA sequences, that determine these protein structures. The
pattern observed in protein sequence coding of related proteins, indirectly
reveals patterns of change that occur in the underlying DNA sequences.
Regardless of this, it is apparent that DNA change is the basis of
evolutionary development. Though the greatest genetic variability is found in
terms of the folding structures of proteins, and their derivative structures, it
is clear that the basis for variability of these structures begins with the DNA
material itself. DNA material must exhibit a minimal degree of variability in
coding sequences. It is evident for instance that point mutation may result in
the attempt of the DNA strand to repair itself not by the excision of the
mutated component, but by the addition of more components that correct for the
coding error and possibly mask this error. Haploid sets of genes may have been a
device for the protection against random genetic mutuation, which effects might
result in the suppression of the traits encoded, and the activation of the
complementary set of genes that are tied to the same trait complex.
It is apparent that genetic mutations must build up over time upon a
single chromosome, and that eventually this will result in this chromosome
having a fundamentally different set of sequences than the complementary one. It
is known that all chromosomes come in sets of two, and that all chomosomes are
whole. There are never half or quarter chromosomes in organisms. This suggests
that at some point, differentiated pairs of chromosomes may in fact separate
from one another and become replicated as two independent sets. Separate
chromosomes will differentiate more and more as a function of time. The
alternative is that a chromosome may grow in size and sequence length until it
becomes divided into two separate and independent strands, or becomes divisible
by some mechanism.
To what extent must chromosomal variation of gene sequence occur before
the resulting organisms are biologically separate from their progenitors is
unknown. Presumably it does not require too much difference for this to occur.
The fact that this variation occurs only in the sperm and egg cell constrains
the model somewhat, except that we must realize that new sperm and egg cells are
being produced or exist via mature sexual organs within the body. This provides
a pathway within the context of the larger organism for the occurrence of
further genetic mutation that may have a direct evolutionary consequence.
Mutations occurring in toe-cells are not likely to have the same evolutionary
effect.
Most mutations are probably deleterious in the long
run, but continuous mutation and transcription error will create changes in
protein structures that will open the door to the possibility of non-deleterious
or even beneficial changes to happen. The amazing trait plasticity of living
forms, evidenced by so many different kinds of organisms that seem so well
streamlined and adapted to their main host environments, is accountable for
purely in terms of this protein variability that is the result of a number of
different mechanisms possibly occurring at the same time.
The question to be answered is to what extent must DNA material become
altered before there can be said to occur speciation and reproductive isolation
between two or more organisms. In this context, with multicellular organisms,
the alterations must affect only the DNA material located within the sexual
gametes of the parents. The mutation of genetic materials in other cell
components of the parent organism may indirectly affect the survival of the
organism, but these factors will not be replicated or become expressed in the
genotypes of the offspring. One of the trade-offs in terms of controlled
reproduction for muli-cellular organisms is that the generation time between
reproduction at which time evolutionary changes can be expressed becomes
extended over considerable periods of time, and in general loses its exponential
growth function. As length of generation time increases, the rate of
evolutionary development must slow down accordingly. There must be a
corresponding increase in the potential for genetic variation in larger, more
differentiated organisms, that is due to the larger complement of genes
necessary for encoding and for their slower rates of replication, but this is
perhaps balanced by the confinement of reproductive cells to specialized
classes.
It is evident that there occurs phyletic increase in the size and number
of chromosomes available for sexual reproduction. In this case, we see no
"half" units. We find in the sexually reproductive world only paired
sets that occur in discrete numbers.
Exponential
Evolution, DNA-Insertion, RNA Back-Translation, Viral Addition and Polyploidal
Differentiation of Eukaria
The basis for the argument of exponential evolution
is the idea that mutation mechanisms alone, that tend to be conservative, cannot
explain by itself a fundamental feature of evolutionary divergence, and that is
the enlargement of the chromosomal complement of the genome with increasing
speciation. Other unknown mechanisms must be invoked to explain this increase in
gene numbers besides mutation rates or even simple transpositions. Both these
mechanisms describe how genes differentiate on a fundamental level, but not how
they accumulate or increase in number. I propose a list of viable candidates,
all but one of which are based upon empirically described mechanisms that
normally occur in cells, or that are known to have occurred in cells during
their evolutionary development from prokaryots to eukaria. These mechanisms are
listed below:
1. DNA Insertion: Extraneous DNA from other microbes,
or from organelles in the cell known to contain DNA, become incorporated at some
stage into the genome of the nucleus of the cell and become a permanent part of
the DNA structure, either as a whole structure, or as segmentable substructures
that could be variably incorporated into already preexisting DNA molecules.
2. RNA Back Translation: This is only a hypothetical
pathway that suggests that foreign RNA might somehow become involved in a
process of back-translation of DNA, as is known to occur, for instances, in the
life-cycles of retroviruses.
3. Viral Addition: Viruses are known to carry a DNA
or RNA complement that can be inserted systematically into a cell nucleus or
into its relevant ribosomal RNA structures, and there be incorporated into the
normal complement. It is possible that in certain instances, such inserted
strands may become a permanent part of the DNA strand of the host cell, thereby
fundamentally augmenting the number of DNA. A chance mutation of such a strand
in the process of insertion or during its period of insertion may affect the
subsequent function and recognition of the insertion.
4. Polyploidal Differentiation: This theory suggests
that polyploidal is a natural consequence of chromosomal replication that leads
to the formation of multiple pairs of chromosomes, which may or may not be
active within the genome, but which would subsequently diverge and differentiate
in terms of mutation and transposition of available elements. Polyploidy can be
explained in terms of the ability of cells to withstand high rates of genetic
mutation, providing "back up" copies of genes that can be "turned
on" in the case of genetic failure of the master gene.
Two other sets of pathways must be suggested in this process. The first is some combination of any or all of the pathways above, and the second is some combination of any of these pathways with or of unknown and as yet undescribed pathways employing other kinds of mechanisms of genetic alteration.
Blanket Copyright, Hugh M. Lewis, © 2005. Use of this text governed by fair use policy--permission to make copies of this text is granted for purposes of research and non-profit instruction only.
Last Updated: 08/25/09