Re: Biochemistry of Genetic Mechanisms


"yahooterry@xxxxxxxxx" <terryhilleman@xxxxxxxxxxx> wrote in message news:ded8qb$ni$1@xxxxxxxxxxxxxxxxxxxxxx
> If I am correct (could be wrong), Darwin used "fatal Competition" in a
> stable environment as an explanation for natural selection (the
> preservation of favorable variations and the rejection of injurious
> variations); the role of the environment was minimized.

I would put it like this. In order for NS to work, it is essential
for there to be variation in genotypes. Whether there is variation
(in time or space) in the environment is irrelevant.

That is the standard viewpoint on "microevolution" (the source of
adaptation) as I understand it. The standard viewpoint on "macroevolution"
(speciation and increased complexity over time) does see an essential
role for variation in the environment. But variation in genotypes
is also necessary for macroevolution to work under NS.

> Natural
> selection today is seen as "a change in gene frequencies in a
> population, owing to fitness of phenotypes' reproduction or survival
> among the variants" (Levinton).

I know of one "evolutionary" process that works on environmental variation
alone - it does not require variation in genotypes. I put scare-quotes
around "evolutionary" because this kind of evolution does not result
in gene frequency changes. I like to call this process geo-Darwinism,
with the 'geo' standing for geography. Here is how this process works:

Imagine an environment which varies in space. Scatter organisms around
the globe. Organisms belong to fixed, immutable species. Those organisms
which happen to be situated in environments to which they are adapted
will thrive, those which are not adapted will not. Over time species
become more adapted to their environments - not because the species change,
but because their ranges change.

Now insert some environmental variation in time. Assuming that organisms
can move randomly by a kind of diffusion, the ranges of the various species
will move as well, maintaining their state of adaptation to the environment.

This is a real evolutionary process, and an important one - even if doesn't
involve a change in gene frequencies. However, since this process in
isolation cannot alter the average character of the organisms in a species,
it is relatively unimportant in explaining the kinds of elaborate
adaptations that Darwin was so interested in explaining.

> My point is that the environment is
> not passive; it is anything but stable, and it plays a role in
> evolution that is comporable to that of natural selection. Extinction
> occurs when acquired adaptations are no longer relevant to survival of
> a species that is confined to a changing environment. Environmental
> selection is the primary agent of extinction in both catastropic and
> constant extinction; this implies an greater role than that of "fatal
> competition," alone, [remainder snipped]

My 'geo-Darwinism' can be described as a cause of extinction. But
geo-Darwinism without the neo-Darwinistic change in the gene frequencies
of populations is a fairly impotent force for change.

So I have to ask: what does your "environmental selection" do that my
"geo-Darwinism" doesn't do?


.

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