Re: Reproductive Selection

On 19 Dec, 01:18, John Harshman <jharshman.diespam...@xxxxxxxxxxx>
wrote:
Nic wrote:
On 18 Dec, 06:04, Treus <treusd...@xxxxxxxxx> wrote:

Nic wrote:

On 17 Dec, 23:55, Treus <treusd...@xxxxxxxxx> wrote:

John Harshman wrote:

Treus wrote:

leland.mcin...@xxxxxxxxx wrote:

On Dec 16, 7:33 pm, Treus <treusd...@xxxxxxxxx> wrote:

<snip>

The two allele model does not sufficiently account for the complete
set of traits uniquely necessary to the RC of a population arbitrarily
different from whatever ancestor is taken as the starting point.

Presuming I understand your jargon right, yes, it does. You can
simply apply the two allele model repeatedly at different loci to
generate as large a difference as you like. Equally, once the
reproductive incompatability has been introduced (via, for example,
the two allele model) there's nothing keeping the populations from
diverging drastically by drift, and/or environmental and sexual
selection -- which is to say diverging arbitrarily.

Okay so far, but how are you retaining RC within the respective
populations over time without reproductive selection? Without the
(selection driven) co-evolution of R(Sn,x), where R(Sn,Sn) is at least
equal to R(Sn-1,Sn-1), for every Sn, you have a slow degradation of RC
in each successive generation.

Wrong question. The right question is why we would expect RC not to be
retained,

A fair question.

Absent reproductive selection, RC is not being selected for, on the
other hand with reproductive selection, backward compatibility is
maintained.

And a fair answer - it is perhaps that your reproductive selection
escapes notice because it is a fairly trivial observation along the
lines of selection-for-heart-valves-continuing-to-face-the-right-way.

If you want to simultaneously retain RC and decrease
backward compatibility, then some other "force" is necessary.

I think I see where you are coming from, so I think I can counter it
with the point that there may be no 'want' to decrease backwards
compatibility - any such decrease is an accident. A species' range
becomes divided say, by a mountain range. There is then a very long
time in which the two population's specieshood is not put to the test
(which is a problem philosophers have with the biological species
concept, in that the earliest time at which there might have been two
species is separated from the latest by >1MY, so what was their status
in the interim?). After this very long time has elapsed, it is either
business as usual for the single ancestral species, or there are *two*
new biological species and the ancestral one can be written off the
books as extinct.

Thanks for the explanation. Would you happen to know of a specific
instance of that sort of speciation (including an identified common
ancestor)? I've been looking for just that.

I have to ask back, do you know of a specific instance of remerging?

I do, more or less. Blue-winged and golden-winged warblers, mallard and
American black duck. That is, they were once separate species, but now
it appears that they are merging, or that one species is being submerged
within the other. The reason in each case is apparently that they were
once isolated by habitat preference, but disturbance created by European
settlement caused enough habitat change that the isolation no longer
operates. What does this have to do with anything?


Treus's question seemed odd to me, so I wanted to find out more.



For example, I've heard lions and tigers can interbreed, I don't know
about gorillas and orangs. Would you expect an emu and an ostrich to
do so? The facts aren't all in. There must be many related species
from different continents that wouldn't be able to coexist (because no
dimension of their niches is completely orthogonal), but which have
viable and interfertile first generation hybrids. You see it doesn't
matter if hybrids are viable and fertile, they have to be fertile back
to one of the parent populations, not just amongst themselves. If
they are fertile with either or both of the parent populations then
they can act as a 'leak' between gene pools, sometimes refered to as
introgression. Then and only then will the apparent allopatric
speciation spontaneously reverse.

Maybe I have more thinking to do on this because it occurs to me that
a speciation that would spontaneously reverse given the opportunity,
shouldn't have happened in the first place (unless of course it is all
just something geography 'does' to populations, in which case there is
no need to wonder which state -one or two species- is the more
stable).

What does "shouldn't have happened" mean here? What, in fact, does this
whole paragraph mean?

Oh it has to do with conjectures on sympatric speciation scenarios,
and genetic mechanisms thereof. But from the point of view of Treus's
question, I hope I came across as saying that it would be more
surprising if allopatric speciation didn't work than that it did. And
more surprising if lay general knowledge didn't bear this out than if
it did.

.

Relevant Pages

  • Re: Bipedalism in different substrates
    ... >>their mothers are on such ground. ... > our own species and would have been shared to a considerable extent ... major one about the speciation. ... >>that it has any bearing on how populations ...
    (sci.anthropology.paleo)
  • Re: The Paradox of Speciation
    ... means every species on Earth. ... EVERY pair of species shares a common ancestor, ... Despite those variations most of us can reproduce successfully. ... populations that have been reproductively isolated for vast streches ...
    (talk.origins)
  • Re: Reproductive Selection
    ... different from whatever ancestor is taken as the starting point. ... the two allele model) there's nothing keeping the populations from ... other hand with reproductive selection, ... (which is a problem philosophers have with the biological species ...
    (talk.origins)
  • Re: population sizes for colonising a planet
    ... which is called allopatric speciation) ... Divergence: the populations genetically diverge. ... the parents are from different species. ... >mentions a predecessor, Homo Ergaster, appearing at 1 Myr, followed by ...
    (rec.arts.sf.composition)
  • Re: Reproductive Selection
    ... different from whatever ancestor is taken as the starting point. ... the two allele model) there's nothing keeping the populations from ... other hand with reproductive selection, ... (which is a problem philosophers have with the biological species ...
    (talk.origins)
Loading