Re: Reproductive Selection

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,

Absent reproductive selection, RC is not being selected for, on the
other hand with reproductive selection, backward compatibility is
maintained. If you want to simultaneously retain RC and decrease
backward compatibility, then some other "force" is necessary.

and why we would respect a slow degradation of RC in each
successive generation without some active factor preventing it. If you
remember the 2-locus model, there is in fact no degradation of RC at all
between successive generations, yet we end up with total incompatibility
after a number of generations, and all without any mention of
reproductive selection.

You were right about that, however, without reproductive selection, RC
within successive generations will decrease to zero over
macroevolution. This is because the physical prerequisites (whatever
they may be, positive or negative) uniquely necessary to the RC of
each generation are not being selected for.

Consider, again, the other model, where "incompatability" at each
generation is small (within the average variation of the population)
but, by progressive increments over many generations, large
incompatbilities can be introduced. This is the "great dane can't
breed with chihuahua" model. Such divergence, with small incremental
steps, doesn't have any clear bounding on it, thus, given enough time
for enough small increments, incompatabilities can be arbitrarily
large. What you really need to demonstrate is some reason why there is
a finite upper bound on how many small increments can accrue. You
haven't done that.

Sure I have, and just did so again in this very post.

No, you have merely claimed that there is such a bound. Notice that with
the great dane/chihuahua example there is absolutely no incompatibility
between successive generations, yet we end up with major incompatibility
after many generations.

Setting aside "absolutely no incompatibility" for now, how do you know
a great dane and chihuahua are reproductively incompatible?

.

Relevant Pages

  • Re: Reproductive Selection
    ... Absent reproductive selection, RC is not being selected for, on the ... none of those mechanisms are sufficient to account for the ... And I will further note that reproductive incompatibility does not ... between successive generations, yet we end up with total incompatibility ...
    (talk.origins)
  • Re: Reproductive Selection
    ... other hand with reproductive selection, ... (which is a problem philosophers have with the biological species ... between successive generations, yet we end up with total incompatibility ...
    (talk.origins)
  • Re: Reproductive Selection
    ... other hand with reproductive selection, ... (which is a problem philosophers have with the biological species ... between successive generations, yet we end up with total incompatibility ...
    (talk.origins)
  • Re: Reproductive Selection
    ... Absent reproductive selection, RC is not being selected for, on the ... between successive generations, yet we end up with total incompatibility ... for enough small increments, incompatabilities can be arbitrarily ...
    (talk.origins)
  • Re: Reproductive Selection
    ... Absent reproductive selection, RC is not being selected for, on the ... between successive generations, yet we end up with total incompatibility ... for enough small increments, incompatabilities can be arbitrarily ...
    (talk.origins)