Re: The Paradox of Speciation

In message <389d7c15-fbb7-496d-a912-470b88d454b3@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, ErikW <bryophyta@xxxxxxxxxxx> writes
On Dec 6, 3:32 pm, michael <yost...@xxxxxxxxxxx> wrote:
On Thu, 6 Dec 2007 06:19:49 -0800 (PST), ErikW <bryoph...@xxxxxxxxxxx>
wrote:



>On Dec 5, 5:45 am, treusd...@xxxxxxxxx wrote:
>> ErikW wrote:
>> > On Dec 2, 12:40 am, treusd...@xxxxxxxxx wrote:

>> > snip (didn't understand and seem unecessary)

>> > > Therefore, describing the origin of a diversity of species in terms of
>> > > natural selection results in a paradox. Insofar as a mutation
>> > > contributes to speciation, it also, by definition, reduces
>> > > reproductive compatibility with available mates and is thus
>> > > detrimental to fitness. For a group to be infertile with any of its
>> > > progenitors implies the success of a transitional physiology of
>> > > reproduction with a significantly impaired ability to reproduce. A
>> > > mechanism other than mutation and natural selection is necessary to
>> > > explain the evolutionary transition between two reproductively
>> > > incompatible populations.

>> > In e.g. sympatric speciation something rather close to what you write
>> > is indeed a real issue and is probably one of the most common
>> > arguments as to why sympatric speciation seem to be rare (scrap your
>> > talk about transitional physiology). For speciation in isolation it is
>> > not an issue of course.

>> > Think about it like this: we look at two genes (a and b) with the same
>> > fixed variants in two populations.

>> > pop1 - aabb
>> > pop2 - aabb

>> > Now in pop1, a gets substituted for another variant A. A is compatible
>> > with b and a (= no fitness loss for Aabb or AAbb). In pop 2, b gets
>> > substituted for the variant B which is compatible with a and b (aabB
>> > and aaBB are fit). However B is incompatible with A (AxBx are unfit),
>> > thus the two populations, fixed for A and B respectively, are now
>> > reproductively isolated. In this case there was no fitness loss at any
>> > stage but still isolation was achieved.

>> > In sympatry there would have been a fitness disadvantage with mating A
>> > with B individuals. For reproductive isolation to happen anyway there
>> > has to be selection _for_ isolation to overcome the selection
>> > _against_ isolation. Several models exist for how this can happen.

>> Seems reasonable enough. If this actually happens, i.e. if its not
>> merely a representation of an hypothesis, this would indeed accomplish
>> what you claim.

>Yes. At first it was a hypothetical model made popular by the work of
>Dobzhansky and Muller at the end of the 30s and beginning of the 40s.
>With the increased knowledge of genetics it turned out to be a very
>reasonable one. Investiagtions on the genetics responsible for
>reproductive isolation in Drosophila in more recent years has shown
>that almost all hybrid inviability/sterility/etc are caused by between
>locus incompatabilities, and mostly as Dobzhansky Muller
>incompatabilities (i.e. as described in the previous post) allthough
>in recent years some researchers are pushing for a role of meotic
>drive as an additional important cause.

>/ErikW

I can go into any country anywhere in the world, any
nationality, any race, find a woman of child bearing age,
and mate and produce offspring, even though isolated
for thousands of years.

How long does this reproductive isolation take?

There are papers on that too :)

On the other hand there are blood types in humans that are
incompatible with each other (at least I learned that in school). All
you need know is to split humans into two populations and have them
fixed for two incompatible types. Voila.

If you're think about Rhesus blood types, it's not absolute, and it's only one-direction. a Rhesus-negative woman generates an immune reaction to a *second* Rhesus-positive foetus. A Rhesus-positive woman has no problem (related to Rhesus factors) in carrying Rhesus-negative foetuses to term.
--
alias Ernest Major

.

Relevant Pages

  • Sympatric Speciation or Speciation without Changes in Genes
    ... Sympatric Speciation or Speciation without Changes in Genes ... natural populations of invertebrate and vertebrate animals. ... and mitochondrial DNA of both populations and reproductive isolation ...
    (sci.bio.evolution)
  • Re: Species diversity through time
    ... Speciation is the evolution of reproductive isolation between ... Generally this happens when two populations become ... getting nectar from one type of flower, ...
    (talk.origins)
  • Re: Re: Evolution is not a fact
    ... You don't have reproductive isolation with sympatric speciation. ... In some cases this might be congruent with sexual selection, ... the result of a macroevolutionary change- I would place the evolution ...
    (talk.origins)
  • Re: The Paradox of Speciation
    ... reproductive isolation and reproductive incompatibility. ... So your species concept is not the usual one in biology. ... laboratory populations, and there are many experiments that show this. ... never lose reproductive compatibility, ...
    (talk.origins)
  • Paper: Does reproductive isolation evolve faster in larger populations via sexually antagonistic coe
    ... Does reproductive isolation evolve faster in larger populations via sexually ... antagonistic coevolution and reproductive isolation. ...
    (sci.bio.evolution)