Re: Fundamental Darwinism

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.

It's my impression that just as commonly, perhaps more commonly (except
when a species invades a formerly unoccupied island that has many
adjacent unfilled niches), what happens is that a species occupies two
identical environments that are physically separated, and over time
their genomes diverge sufficiently to achieve speciation, yet they
remain adapted to identical environments.

In your case, if they later meet, they might survive together, each
taking different resources, while in my case if they later meet, they
fight to the death, at least one of the two going extinct.

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.

*the* key event?? To my mind, there are two key events. First there's
the event that *causes* the splitting of the species to start. Second,
there's the signal event that by definition means there are now already
two species where formerly there were only one. The second event is
always an absolute or near-absolute (near 100%) reproductive isolation.
But the former event could be a partial reproductive isolation, or a
characteristic splitting of the niche, or a splitting of the geography
where the same niche resides, etc. For example, the splitting of
Gondwana, whereby a single species in a single niche was split across
the rift that was the beginning of the Atlantic Ocean, would be an
event of the first type. If an E.T. were to conduct breeding
experiments, he would find no speciation had yet occurred, yet barring
E.T. interference a speciation was inevitable at some later time.

(Talking to some other poster:)
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.

My way of thinking, taking the blatant definition of evolution as any
change in allelle frequencies, amended slightly to be any change in
allelle frequences beyond the normal range of statistical fluctuation:
A single new mutation creates one instance of a new allelle, which is
indeed beyond the normal range of fluctuation based on only old
allelles, but which is within the normal range of frequent non-neutral
mutations that are mostly immediately fatal or short-term fatal,
whereby they last only a part of a generation or a small number of
generations and never achieve any large numbers. If any new allelle
does in fact achieve significant population numbers, say three or more
copies, *then* it has finally risen beyond the noise and counts as
actual evolution. But that can't happen unless natural selection allows
it. It can't happen if there's strong selection against it. And since
it takes several generations to build up such significant population
count with the new allelle, natural selection has already happened, so
we might give credit to natural selection for choosing this particular
new allelle for fecund growth while eliminating the many more
strong-select-against mutations which are already gone, much as we give
the scluptor credit for the statue, even though all the sculpture did
was chip away all the unwanted parts, leaving just a part of the marble
which was all there from the start. Mutations are like the quarry which
produces blocks of marble with both good and bad part in them.
Selection is like the sculpter who removes the bad parts so that the
remaining parts have a pattern of fitness. Or you can think of the
metaphor of snowflake collectors. Natural processes make gazillions of
snowflakes. Somebody goes out and collects a few thousand of them, and
keeps only the really pretty ones. So who gets credit for the resultant
prize collection of pretty snowflakes, the cloud that made them, or the
snowflake-collector who selected the best of them? Or we can consider
the metaphor of copyright law. A simple listing of all people who have
telephones, with their associated phone numbers, is not copyrightable.
But a special list of those who are interested in purchasing a
particular kind of product *is* copywrightable, despite the fact it's
only a subset of the entire non-copyrightable listing.

So although it's mutation that makes the brand-new allelles, and
replication that makes many more copies of them, it's natural selection
which determines which of them will survive to make lots of copies to
exceed normal statistical fluctuations and which will fail to survive
and therefore be totally gone in a short time without ever having grown
to statistically significant numbers during their brief appearance.

On the other hand, without marble from the quarry, the sculptor could
never do his work, without clouds to make snowflakes there'd be nothing
to collect, without any telephones there'd be no master collection for
telemarketers to search for suckers, and without mutations there'd be
nothing for selection to act on. So mutations deserve *some* credit.

Maybe the problem is that our natural languages (English etc.) aren't
capable of expressing this kind of reality clearly.

What caused both species to survive to the present day so that we can
observe that a speciation must have happened?

Either the physical barrier hasn't yet gone away, and humans haven't
yet accidently transported one species to the other habitat to allow a
replacement, *or* the two species have evolved to different niches so
their re-meeting is no longer a death prediction for one or other.

Note: In the second case (different niches), if the niches are
sufficiently different this may be obvious from the morphology, such as
two bird species whose beaks are adapted to crack really hard nuts in
one case and to dip into honeysuckles and sip liquid in the other case,
where it would be obvious from the fossil record that they are
different species, even if one or both are extinct already so we can't
perform mating experiments. (Caveat: It's theoretically possible that
sexual dimorphism could be so gross that male and female beaks are
adapted to different food such as nectar and seeds. But that'd surely
qualify for Ripley's!)

How can there be *selection* against interbreeding?
... It can happen, but it ain't easy.

It seems easy enough to me. If first there's a partial reproductive
barrier between two races of a single species, such as a 50% reduction
in inter-racial success compared to same-race, then individuals who
choose strictly within their own race would have better success than
individuals who often choose mates of the other race, so there'd be
selection pressure in favor of racial intolerance (for mating).

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.

Given that the time to achieve speciation is usually about one million
years, and the average lifetime of a species is about ten million
years, yet marsupials in Australia have remained separate from
placental mammals in Africa for something like a hundred million years,
"sooner or later" clearly can be "very very later, virtually never"
when plate tectonics is responsible for the speciation. Except for
those very few human-releases of placental mammals in Austrailia, the
marsupials really haven't at all needed to worry about if and when they
have to eventually compete with African carnivores.
..

.

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