Re: Reproductive Selection

On Tue, 18 Dec 2007 09:28:44 -0800 (PST), Treus <treusdrie@xxxxxxxxx>
wrote:



Greg Guarino wrote:
On Mon, 17 Dec 2007 23:25:15 -0800 (PST), Treus <treusdrie@xxxxxxxxx>
wrote:

That argument is a retread with lots and lots of toy balloons and a
clown suit. I'm not impressed. Of course there are instances where
there is no need to "generate compatibility". That's been agreed
already. Are you claiming that every, or even most, of the species
alive today that require RC in order to reproduce can be traced as far
back in time as you like without finding an ancestor with respect to
whom the living specimen did not need to "generate compatibility"? If
so, please name a species.

That's a pretty convoluted sentence, but I believe the obvious answer
is "all of them".

And the obvious follow-up is: "What is your empirical evidence?"

I think it is fair to observe that a sudden request for empirical
evidence from a person carrying on an entirely theoretical argument
demonstrates that the "theory" hasn't been a winner. I am frankly
mystified by the idea that members of a a breeding group would need to
(re)generate reproductive compatibility when it already exists and is
inherited.

A case in point addressing one species will do. Then we can proceed.

I'm curious now about what you are asking for, specifically. You have
admonished others to narrow the topic when it seems like good
strategy, but when YOU ask for evidence it is on the broadest terms: a
challenge to demonstrate the mechanism for the diversity of all known
life.

But you're still hiding your light under a bushel. Are you asking for
evidence of universal common descent? Or do you accept that notion and
instead require evidence that the various "branchings" in the tree of
life were accomplished without "tinkering"? If the latter, what do you
suppose such evidence would look like?

Compatibility exists already and is inherited. Any change in the
genome that produces incompatibility in one generation ends with that
individual. You'd probably call that reproductive selection. With a
nod to our friend backspace, let's not forget that selection is not a
"force"; in this case the negative version is simply "failure to
reproduce".

The metaphorical "force" is used in this context in the literature. It
works .

Unlike a couple of our colleagues here, I'm not fond of semantic
arguments for their own sake. I think that "selection" is a fine
metaphor, but it is easy to forget what it means: differential
reproductive success. I bring that up because I cannot fathom how you
can make the argument you do when it has such obvious logical flaws in
it.

The main one, that I have yet to see you address, is how "selection"
can favor "reproductive compatibility" even if those individuals with
better "RC" leave fewer descendants. If a heritable trait confers
slightly less fertility but greatly more survivability, that is the
unavoidable consequence. And when it happens, we say that trait has
been "selected" for.

The above seems so obvious, that I have to wonder if maybe you have
some basic misunderstanding of the standard biology on the topic. Your
position would only make sense in the case of a heritable trait that
had NO other effect other than to lower fertility. Even at that, it
would have to be a situation in which lower fertility itself did not
increase aggregate survivability. If both those factors were true, I
would agree that such a trait would be selected against, meaning,
individuals that have it would place less desendants in the next
generation.

Is that possibly the impasse here? Are you arguing that
incompatibility is a stand-alone trait that has to evolve, but can't,
since it would be selected against? If so, be assured that no one
thinks that's the mechanism.

Species change and those changes pile up in their genomes. In the
first approximation that is all that is needed for reproductive
compatibility: two critters with similar enough genomes. This is
generally provided by heredity. Small changes between adjacent
generations can be accomodated. Any change large enough to prevent
reproduction with one's contemporaries is indeed selected against and
becomes a dead end.

But among different populations that don't interbreed, the changes can
go in different directions. Over a few generations a "foreigner" that
migrates back to a cousin group will still be able to breed, but over
many generations, the two groups can develop a degree of difference
that is sufficient to prevent reproduction between the groups.

Since all organisms fail to reproduce with their distant ancestors*
(by virtue of not living at the same time), the theoretical ability or
inability to do so cannot be acted on by selection. If you disagree, I
think you'll need to explain how selection can act where there is no
advantage or disadvantage, as is always the case among groups that
have no chance to interbreed.

Evolution produces changes in the genome. Changes in the genome in a
single generation that do not inhibit reproduction at all will not be
selected against on that basis. Changes that slightly reduce fertility
between the "new" and "old" genotypes but increase the rate of
survivability to a greater degree will be selected for despite the
"cost" in fertility. Moreover, that decrease in fertility will
disappear if the trait becomes fixed in the population,

Okay, so the incompatibility disappears. You still don't have then new
compatibility of S2

I'll forgo the string of exclamation points that are clamoring to
burst forth, but why in the world would we need NEW compatibility when
we have perfectly good existing compatibility?

where S2 is a remote descendent with a
significantly novel set of characteristics uniquely necessary to the
RC of S2.

You keep repeating that string of words "significantly novel set of
characteristics uniquely necessary", but I still don't know what it
could mean. The characteristics I need to mate successfully are more
or less the same as the ones chipmunks use, but we don't have similar
enough genomes. That's the necessary factor and it is conveniently
supplied to members of each generation of a breeding group.

<snip>

and thus does
not compund itself over time.

If you disagree with that last bit you'll have to explain how
selection, which is a shorthand term for "how many criiters with
certain traits live to reproduce, and how much", can always favor
fertility over other factors, even if the net result (of lower
fertility + greater survivability) yield more young in the next
generation.

It does not. This point has been made several times.

Then, again, what does that leave of your argument? I think that the
rest of us are basically saying two things:

A trait that allows an organism to have more surviving descendants
will be selected for, even of that trait also lowers reproductive
compatibility, a situation that could also be temporary if the trait
comes to dominate the population.

Reproductive incompatibility between separate populations can develop
even if NO individual trait or group of traits produces lower
fertility within the individual groups.

Greg Guarino

.

Relevant Pages

  • Re: Reproductive Selection
    ... there is no need to "generate compatibility". ... alive today that require RC in order to reproduce can be traced as far ... You'd probably call that reproductive selection. ... Changes that slightly reduce fertility ...
    (talk.origins)
  • Re: Reproductive Selection
    ... there is no need to "generate compatibility". ... alive today that require RC in order to reproduce can be traced as far ... You'd probably call that reproductive selection. ... Changes that slightly reduce fertility ...
    (talk.origins)
  • Re: The Paradox of Speciation
    ... compatibility over time is paradoxical in the context of natural ... at least as far as natural selection is concerned. ... *unrelated factor in the environment be less suited to reproduce than ... Reproductive incompatibility is not only a matter of "equipment". ...
    (talk.origins)
  • Re: The Paradox of Speciation
    ... compatibility over time is paradoxical in the context of natural ... at least as far as natural selection is concerned. ... *unrelated factor in the environment be less suited to reproduce than ... Reproductive incompatibility is not only a matter of "equipment". ...
    (talk.origins)
  • Re: Reproductive Selection
    ... there is no need to "generate compatibility". ... alive today that require RC in order to reproduce can be traced as far ... You'd probably call that reproductive selection. ... Changes that slightly reduce fertility ...
    (talk.origins)