Re: Fundamental Darwinism


"Larry Moran" <lamoran@xxxxxxxxxxxxxxxxxxxxxxx> wrote in message news:dsimlr$2seu$1@xxxxxxxxxxxxxxxxxxxxxx
On Thu, 9 Feb 2006 15:38:10 -0500 (EST),
Perplexed in Peoria <jimmenegay@xxxxxxxxxxxxx> wrote:
"Larry Moran" <lamoran@xxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:dsek61$16jt$1@xxxxxxxxxxxxxxxxxxxxxx
On Tue, 7 Feb 2006 23:57:00 -0500 (EST),
Perplexed in Peoria <jimmenegay@xxxxxxxxxxxxx> wrote:

[snip]

Steven Rose wrote,
However, whilst this is a mechanism of evolution, it is, as Darwin
himself recognised, not the only one. It is good at explaining how
species get better at doing their species thing, but [NS is] bad at
explaining how new species emerge. For this one needs other factors,
like founder effects, and above all sheer contingency - chance.

I think that the core of the Darwinian/NS explanation of speciation
is basically right. Speciation happens because a species occupies
two different environments, and it cannot adapt to both of them without
fissioning.

You are defending Fundamentalist Darwinism. I think you're wrong.
I believe that modern evolutionary theory does a much better job of
explaining speciation than the old-fashioned Darwinian theory that it
has replaced. Speciation mostly occurs by accident and adaptation is
not involved.

True enough if most speciation is allopatric.

Do you think that some other form of speciation is more common?

I really don't know. I doubt it. But lets stick to allopatric
speciation here, since that seems to be where we disagree.

But even here, adaptation can be involved.

I'm not arguing whether adaptation *can* be involved. I'm arguing with
your initial statement (see above) where you imply that adaptation
*must* be involved and natural selection (Darwinism) explains it.
I think you're wrong about that. Dont be so quick to rule out random
genetic drift and accident.

As soon as you admit to those other possibilities then you're no longer
talking about "Darwinism/NS." Instead, you're moving into the 21st century
where we've gone beyond Fundamentalist Darwinism.

Oh, I do admit to those other possibilities. And it was never my intention
to defend all of Fundamentalist Darwinism. What I said is basically that
there is a lot of truth to Darwin's ideas on speciation, including that a
successful speciation usually results in two species adapted to two
slightly different environments where before there was only one species
trying to achieve a compromise.

Just to make sure we are on the same page, and for the benefit of
eavesdroppers who think that words like 'allopatric' are condescending
jargon, let me first list points where I think we are in agreement.

1. In the biological species concept, the key event in a speciation
is the appearance of isolating mechanisms - features of one species
or both that prevent the formation of fertile hybrids.

2. Isolating mechanisms may be prezygotic or postzygotic. Postzygotic
mechanisms involve the inviability, infertility, or just general low
fitness of hybrids. Prezygotic mechanisms involve things like assortive
mating. The members of one species don't find the other sexually
attractive.

3. In an allopatric speciation, postzygotic mechanisms appear first
as a result of drift, founder effects, accident, or whatever. They
don't appear as adaptations - since the two species are geographically
isolated, they are selectively irrelevant. But if the ranges of the
two species are later rejoined, now prezygotic mechanisms may arise
as an adaptation. But that is more or less irrelevant - the speciation
has already happened. There may or may not be differential adaptation
to different environments by the two species. But that is also irrelevant -
at least in the conventional thinking.

4. A sympatric or peripatric speciation fits the 'Fundamentalist
Darwinism' idea more closely. Now, differential adaptation is the first
and crucial step. This can lead to prezygotic isolation as an adaptation.
This is at least possible in theory (see Joe's 'Santa Rosalia' paper, for
example) but it is not easy. In fact, sympatric speciation seems to be so
rare that RKS posts it to the newsgroup when someone finds an example
of it. ;-)

Are we in agreement so far? Do I escape your scorn as an ignorant
fundamentalist or adaptationist? If so, I would like to proceed by
taking mild issue with the 'conventional thinking' mentioned in point
#3 above.

The key moment in an allopatric speciation is when the ranges of the
two species remerge.

Yes, that's when the test happens. The evolution happened earlier.

Hmmm. I'm not sure how to respond. I wish I was a more regular reader
of talk.origins so that I would know how YOU respond when someone says
that NS is only the test; that the real evolution happened earlier when
the mutation took place.

The argument can be made on ecological grounds that if there is not a
difference between the two species in what kinds of habitats they are
adapted to, then it is likely that one of the two is going to go rapidly
extinct.

That's the adaptationist point of view. You begin from the point you're
trying to prove. The real question is "what caused the differences between
the two populations so that they are now different species?"

The conventional thinking is that this is the real question. And we are
in agreement on the answer to this question. In an allopatric speciation,
those differences arose by 'accident'. I am suggesting that there is an
interesting and relevant follow-up question: "What caused both species
to survive to the present day so that we can observe that a speciation
must have happened?"

You attempt to answer that question by *assuming* that they have diverged
by adapting to different environments then implicitly assuming that this
adatation will have led to genetic isolation by natural selection. Don't
you see the problem? The very way you phrase the question rules out
random genetic drift and accident. Your mind is already made up before
you even discuss the possible solutions.

You misinterpreted me. I hope that I have made this clear above. Sorry
for not making it clear earlier.

And if there is a difference in adaptation, then selection is involved -
species-level selection, which is still 'fundamentalist' though not
'neo-fundamentalist'.

Imagine the two separated populations as they are evolving. They don't
see each other genetically. They evolve independently along pathways that
alter the way they mate and/or reproduce. Enough changes take place
so that when they come back into contact they can't interbreed.

I understand that this is what happens in allopatric speciation.

How can there be *selection* against interbreeding?

See Joe's paper. It can happen, but it ain't easy. But lets stick
to allopatry.

Isn't the reproductive
isolation just an accidental consequence of independent evolution over a
long period of time? Can't it be due to *any* of the mechanisms of evolution
and not just natural selection?

Of course it can. And is. But sooner or later, those two species may
have to coexist and cohabit. And they are unlikely to be able to do so
long term if they are different biological species but identical
ecological species competing head on.


.

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