Re: The pooh-poohing of... Re: Haldane's Dilemma

Tim Tyler <seemy...@xxxxxxxxxxxxxx> wrote:
Kent Paul Dolan wrote:
Tim Tyler <seemy...@xxxxxxxxxxxxxx> wrote:
Here's a relevant link, for example:

http://www.blackwellpublishing.com/ridley/classictexts/haldane2.pdf

One need go no farther than Haldane's own writing
to debunk "Haldane's dilemma", and it doesn't
take some fancy new mathematical analysis to do
the trick, either.

Speaking of the peppered moth, Haldane says:

Now if the change of environment had been
so radical that ten other independently
inherited characters had been subject to
selection of the same intensity as that
for colour, only (1/2)^10, or one in
1024, of the original genotype would have
survived. The species would presumably
have become extinct.

Yet from Wikipedia

http://en.wikipedia.org/wiki/Peppered_moth

we learn:

The female lays about 2,000 pale-green
ovoid eggs about 1 mm in length into
crevices in bark with her ovipositor.

So with the usual two surviving offspring to
replace her and her mate, the peppered moth is
_already_ undergoing 1000::1 selection pressure,
and the species has _not_ become extinct.

Maybe. However, you can't necessarily conclude
that high selection pressures follow from large
numbers of offspring deaths.

That doesn't particularly matter; Haldane's claim
was that 1024::1 selection pressure would extinguish
the species, yet that is in fact the species' normal
mortality, so all that would happen is that what you
claim next to be "random" mortality would instead be
mortality as directed by natural selection, but it
wouldn't be _changed_ mortality.

Why?

Because as fast as the absolute count of peppered
moths dropped due to selection pressure, it would
rise again due to excess abundance of resources from
that diminished population level, as better fed,
healthier moths produced
excess-to-normal-expectations offspring.

No "excess deaths" would occur, demolishing the
basis for Haldane's entire argument.

An alternative hypothesis would be that the 1998
of the 2000 offspring which died were selected at
random - resulting in no selection pressure at all.

But that's nonsense.

It might apply in the case of the eggs of a single
moth, but it would not apply in the case of the
breeding cohort of the moth species.

Haldane wasn't describing some generic species, he
was describing a specific species with a specific
known selection event.

These weren't roughly cloned individuals, like
cheetahs are, there was in fact variation against
which natural selection could and did work.

To claim that the mortality of the entire species
was "random" is to deny evolution entirely.

Something a lot like that might happen if most of
the eggs were eaten before hatching - for example.

You might see being eaten as eggs as "random", but a
species some of whose members laid bright yellow
eggs self-flagged "poisonous as hell" would see it
as the punishment natural selection imposed on the
rest of the species for laying moss green eggs
clearly self-flagged "delicious and nutritious".

No doubt the reality often lies somewhere between
these extremes.

Again you've missed the point here, which was that
Haldane presumed a level of mortality supporting
simultaneous "50% mortality each" natural selection
for ten characteristics would be one that
exterminated the species, when it was in fact, that
species' usual mortality within a couple of percent,
for that particular exemplary species he had chosen
as his starting point for his argument.

Beginning with that false premise, the rest of his
argument fails in turn.

The calculations we're seeing from talkorigins here
ignore another characteristic of natural selection,
which is that it starts with what it's got, it
doesn't have a "pull needed mutation" functionality.

Thus, the usual starting point is a variation which
up until the new selection pressure is neutral _and
probably widely spread in the breeding population
already_.

Same for ten variations. Natural selection _isn't_
starting with ten instances of one extant variation
each, that's a complete misconception.

It is starting with a population where the neutral
variants have had _the entire lifetime of the
species up to the point of the new insults_ to have
been created by mutation and spread by genetic
drift, and in the most likely case, being truly
neutral, are some substantial fraction of all the
alleles of the particular gene locus, probably a
fraction quite close to 1/"number of long existent
neutral in relationship to each other alleles at
that locus".

Haldane also assumes incorrectly that the _normal_
situation is rapid environmental change. Asteroid
impacts and volcanos losing their tops excluded,
most environmental changes are fairly slow. It is
one of today's tragedies that we've pushed climate
rate of change far past its historic values, and
_now_ species are having trouble keeping up with
that change, which managed nicely to keep up with
normal change rates; but that just shows that the
rapidity of current change is _not_ the norm, the
opposite to what Haldane posited.

FWIW

xanthian.


.

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