non-genetic def of evol; heredity; non-biol evol
arlin at ac.dal.ca
arlin at ac.dal.ca
Sun Nov 10 17:53:06 EST 1991
1. The necessity of a non-genetic definition of evolution:
We could probably argue forever about whether biological evolution has
been reduced to population genetics, making a genetic definition of
evolution possible. Such an argument would perhaps be outside of the
scope and expertise of this forum. However, even those who argue in
favor of a genetic definition are logically obliged to admit that
there must at some time have been a non-genetic definition of
evolution that was reduced to the terms of the genetic definition.
Otherwise, we have no reason to believe that Charles Darwin, Larry
Moran and Stewart Schultz are all talking about the same thing.
2. Creationism and evolutionism
So what was Charles Darwin talking about? The
theory-that-evolution-has-occurred is the theory that species of
organisms alive today arose i) by a process of descent with
modification ii) from a smaller number of common ancestral species.
The alternative theory, creationism, was that species of organisms
alive today are the true-breeding descendents of an equal number of
ancestral species that arose by separate acts of creation.
It is not necessary to invoke a creator for the generic version of
creationism-- we could be talking about spontaneous generation or
extra-terrestrial innoculation as the source of true-breeding species.
However, the appeal of the creationist argument has always been that
it provides an explanation for the adaptedness of organisms: organisms
were adapted at the time of creation, *by design*. Thus,
*adaptedness* is a third big issue that evolutionists had to address
(because opposing theories have to address the same phenomena). The
phenomena of evolutionary change can thus be enumerated within the
framework of the necessary components of the
i) process(es) of descent with modification. all agree that there is
a process of descent, and thus biological lineages, but evolutionists
assert that a lineage may include forms that differ substantially from
each other (for instance, evolutionists would not hesitate to propose
a single lineage that included a fish, a reptile, and a bird).
ii) process(es) of speciation and extinction. In addition to
organisms in a lineage being modified over time, a lineage may go
extinct, or be separated into two lineages (a reptile lineage may
split into two lineages, one of which goes extinct, the other of with
survives to the present and is represented by a bird).
iii) process(es) of adaptation. Organisms alive today were not
created pre-adapted for fixed conditions, but have changed to become
adapted to new conditions (for example, a reptile lineage invades a
desert region and becomes adapted to the novel desert conditions), or
increased their adaptedness to old conditions.
3. The non-genetic definition of evolution.
Thus, the evolutionist theory pertains to the processes of change
involving the origins and transformations of biological organisms, and
the theory also makes mention of adaptation. Evolutionary biologists
tend to prefer the word "transformation" over the word "change", since
the former implies a more extensive difference in properties; they
tend to restrict evolutionary transformations to those that are
"irreversible": both of these terms help to distinguish evolution from
mere variation. Thus, evolution _in toto_ can be defined as the
accumulating effects of origins and extinctions of biological lineages
as they undergo serial irreversible transformations, some of which are
adaptations. In addition to speaking of evolution _in toto_, we can
also speak of more manageable chunks of evolution: different kinds of
evolutionary "events" or "episodes," including speciation, extinction,
irreversible transformations, adaptation.
It would be silly of me to assert that this definition is agreed upon
by all, since apparently most biologists don't know that a non-genetic
definition even exists, and those that do know don't agree entirely.
However, any non-genetic definition must address speciation,
adaptation, and transformation. The definition above looks really
tidy, but (as with most definitions) it actually gets quite
complicated when you have to define "lineage."
4. Genetics, heredity and non-genetic evolution.
Heredity loosely refers to the phenomenon that like begets like, and
more specifically refers the appearance of a trait in the child that
is due to the properties of the parent itself, as opposed to the
environment. The distinction is not particularly clear-cut, since in
learning organisms a parent can pass on a piece of its own stock of
knowledge to its child, but also to another child. Thus we can
distinguish biological inheritance from cultural and other types of
inheritance. Biological inheritance is inheritance due to the
necessary physiological relation between parent and child: the child's
cells arise from the parents' cells, and in many cases are nurtured by
the female parent as an embryo. The vast majority of instances of
biological inheritance are due to the templated replication of nucleic
acids, though a small but essential fraction can be ascribed to
templated modification of nucleic acids, maternal effects and to the
self-templated growth or replication of such things as membranes,
basal bodies, and cytoskeletal or cortical arrays.
The hereditary factors *that are nucleic acids (DNA and RNA!)* are
called "genes" and their action is called "genetics." Thus,
"heredity" is not the same as "genetics" and cannot be reduced to it,
since there are hereditary factors that are non-biological and even a
few biological hereditary factors that are non-genetic. There is no
problem in conceiving of *non-genetic* evolution, and if life exists
elsewhere in the universe, it is likely to be non-genetic.
But the confusion about non-genetic evolution was possibly just
another semantic problem. The real question, I suspect, is whether
or not evolution can take place in non-hereditary organisms. I
would suggest that our notion of organisms is so closely tied to
reproduction, that we couldn't conceive of "non-hereditary organisms,"
the word "re-production" itself implying the appearance of parental
traits in the offspring. Non-reproductive living organisms (:-)
maybe this is what gaia is!) might undergo some large-scale changes,
but their "evolution" would be as dissimilar to biological evolution
as is the evolution of stars.
5. Biological and non-biological evolution.
My own questionable opinion is that there is reason to be cautious
about lumping together different things called "evolution."
Evolutionary theories of the cosmos, language, biology, etc., all
involve large-scale change, and assert that i) things were not always
as they are now; ii) things got to where they are by a natural (not
supernatural) process; and iii) this natural process was not
goal-directed. These three statements could be applied to a huge
variety of things. Each field should look closely at its own
evolutionary phenomena, to see what specific mechanisms of change may
be operating, before synthesizing with other fields. If it appears
that some mechanisms of evolutionary change may be shared, perhaps
principles and quantitative formulas may be shared as well.
Although we should be cautious, it is obvious already that biological
evolutionary principles can be applied profitably to other fields, and
that other fields can supply insight into biological evolution, as the
following examples show:
Example 1. Some principles of biological evolutionary analysis are
part-and-parcel of historical analysis. For instance, systematists
sometimes rely on arbitrary traits to understand the relationships of
organisms. It would be absurd to propose a taxonomic distinction
based on wings/no-wings, or legs/no-legs since wings and legs are such
great inventions that many different organisms have evolved them
independently: it is better to use more arbitrary features like the
number and arrangement of bones in the legs, on the assumption that
there ought to be many different ways to build a good leg, so that two
taxa sharing the arbitrary details of construction are likely to do so
because of common ancestry, rather than convergence. It is of
interest to martial arts historians whether or not Korean Hapkido and
Japanese Aikido were developed independently, or relied on shared
sources. Both martial arts are defensive styles that redirect an
attacker's momentum, and make extensive use of joint locks and throws.
That both styles use a wrist-lock is no evidence of shared sources,
since a wrist-lock is one of a few good ways to immobilize an
opponent. However, both styles apply the two-handed wrist-lock in a
peculiar way: the thumb and the three distal fingers are used to hold
the opponent's wrist, while the forefingers are extended upwards and
touch at their tips, to make an inverted "V." This shared arbitrary
feature of the wrist-lock (which the Japanese tradition would suggest
is a device for directing ki energy) is a sure sign of shared sources
between Aikido and Hapkido.
Example 2. A population geneticist named John Avise was instrumental
in developing the mathematical analysis of mitochondrial DNA
variation, which is playing a big role in current debates about human
origins. Avise developed some of his math from formulas pertaining to
the evolution of surnames in human societies. Surnames and
mitochondrial DNA share the property of predominantly uniparental
inheritance (paternal for surnames; maternal for mitochondria).
Although the some of the details of the systems are different, both
involve reproducing entities in finite populations.
Arlin at ac.dal.ca
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