> DM> Neo-Darwinian evolutionary theory claims that the most
>
> > significant cause of evolution is the adaptation of
> > populations of living organisms in response to
> environmental
> > changes. It further claims that adaptation is a result
> of
> > natural selection acting differentially on
> phenotypically
> > distinct members of a population, i.e. individual
> organisms
> > with inherited physical and genetic characteristics that
>
> > allow them to pass on the maximum number of their genes
> to
> > succeeding generations.
> >
> > Underlying this is the theory that genes exist only to
> > replicate. Those genes that are best at replicating
> > themselves into succeeding generations will obviously
> appear
> > most frequently in succeeding generations.
>
> This looks to me more like a particular family of emphases
>
> within neo-Darwinism, rather than the status of the theory
>
> itself.
I'd have to concede your point. It was not my intention, nor
was I asked, to fully describe the neo-Darwinian theories of
evolution. So I just touched briefly on what I considered to
be the high points.
> For example, the issue of the unit of selection is
> under debate (although it doesn't seem to be as public or
> ego-driven).
I'm not convinced that there is a single "unit of
selection". There is a *minimum* unit of selection, the
gene. But depending on the circumstances, multiple genes, an
organism or a population can a ct as a "unit of selection".
> [Mechanisms:]
> [mutations/crossover/etc]
>
> [selection]
>
> > Other high-level neo-Darwinian mechanisms are
> allopatric,
> > parapatric and sympatric speciation, coevolution and
> > extinction. Note that examples of sympatric speciation
> have,
> > as far as I am aware, not yet been found in nature.
>
> I'd call these more "descriptions" rather than
> "mechanisms."
> That is, allopatric speciation is something that happens
> for which
> neo-Darwinism tries to find a mechanism. It depends on
> how
> 'mechanism' is understood I guess--whether a way in which
> evolutionary history has transpired (by speciations of
> various
> sorts) or the processes which drive those events.
"Mechanism" wasn't my choice of word; I concede that
"process" would have been preferable. Allopatric speciation
could be described as a process composed of sub-processes
that occur in a particular sequence.
I see the use of the word "mechanism" as more of a semantic
issue than a substantive one.
> ["non neo-Darwinian mechanisms"]
>
> [stasis]
> [habitat tracking]
> [drift]
>
> Again, this seems like a particular slant on the theory to
>
> exclude these.
Yes, the neo-Darwinian slant - as opposed to the Punctuated
Equilibria (PE) slant.
> For one thing, selection may be just as
> much responsible for stasis and habitat tracking as it
> is for speciations.
If the scalar rate of genetic variation is relatively
constant over time (as observation and experiment appears to
strongly indicate), it can only be selection that keeps the
population as a whole in phenotypic stasis.
> It seems to me that including speciation
> as an evolutionary mechanism and excluding stasis leaves
> out a very important and interesting facet which
> neo-Darwinism
> has to address--indeed, this has been where Gould and
> Eldredge
> and more have pushed their angle.
The point I was making is that, while stasis certainly
affects the process of evolution, I see stasis as something
that occurs under the appropriate environmental
circumstances *instead* of evolution, rather than being a
mechanism of evolution. Again, this issue may be more
semantics than substance.
To clarify my understanding: neo-Darwinian processes only
cause evolution (change in the relative frequency of alleles
in a population) under the appropriate environmental
circumstances; under other circumstances the same processes
inhibit evolution.
> If you are using 'neo-Darwinian'
> to mean specifically a more selectionistic brand of
> evolutionary
> theory,
Only in the sense that neo-Darwinians tend to emphasise
selection more than the proponents of PE.
> you should know that people who are identified with
> that brand also think these things happen, and that drift
> is
> an important component of evolutionary history,
I agree.
> they just feel these things are more boring than not.
Probably for the same reasons that "aimless wandering" and
"running on the spot" are unlikely to ever make big bucks as
spectator sports. :-)
> "Selectionism vs. pluralism"
> is the way self-described 'pluralists' refer to this
> particular
> debate. I'm not sure what would rule them out as
> neo-Darwinists,
> though.
My reading of the debate, as it has been documented in the
popular science works of Dawkins, Gould and Eldredge, is
that it is frequently the proponents of PE that distance
*themselves* from the "gene-centric" and "selection-centric"
claims of neo-Darwinism. I have little difficulty
understanding the observations emphasised by proponents of
PE as a reasonable outcome of neo-Dawinian processes.
The other point is that much of the "neo-Darwinian vs.PE"
controversy is generated by creationists who hope thereby to
discredit evolutionary theory. This is curious, because they
generally cry "foul" when I use "Christianity vs. Judaism
vs. Islam" to discredit theism.
--RegardsDerek
-----------------------------------------------------| Derek McLarnen | dmclarne@pcug.org.au || Melba ACT | derek.mclarnen@telstra.com.au || Australia | | -----------------------------------------------------