"Malcolm"  wrote in message
news:...
> "Jim McGinn"  wrote in message
> > > I asked you the question about beans being selected a) by a
> > > scoop and b) by a sieve. You replied that neither of these cases
> > > approximated to Natural Selection.
> >
> > Right.  They are analogies.  (IMO, NS is something that
> > does'nt become clear through analogy, it becomes more
> > vague and more confusing.)
> >
> These are not analogies. If we plant the beans we have selected, and use the
> rest for chili con carne, and if we repeat the process for many generations,
> we have two evolutionary systems going.
> >
> > I've been expecting you to develop your "bean falling
> > out of a sieve" argument.  And, supposedly, you were
> > going to clarify your position on caustion.  Now it
> > seems like you're backtracking and I don't know why.
> >
> OK. Now the argument goes that if we pick the beans out of the bucket using
> a sieve, so that smaller beans tend to fall out, a small bean will have less
> chance of being planted than a large bean. If bean size is a heritable
> trait, over time the beans will respond by becoming bigger.

Okay, I agree.

> 
> What will happen with the beans selected by the scoop? In this case, smaller
> beans won't tend to fall out. There will be no tendency for beans to get
> bigger. However you will get genetic drift effects

I thought you were setting up a scenario to test genetic drift.  Now
you are just telling us it exists.

 - I might get 51% above
> median size beans and 49% below median beans in the scoop on the first
> selection. On the second selection, assuming heritability, median bean size
> will have drifted up slightly. Bean size takes a random walk,

Now explain how NS cannot involve, "taking a random walk."

 until alleles
> determining genetic variation are fixed.
> >
> > I'm sorry, but I'm lost again.  Are you equating
> > phenotypic variation to genetic drift?
> >
> No. Genetic drift occurs independently of phenotypic variation. In fact,
> since no two phenotypes will ever have prcisely the same fitness, you could
> say that pure genetic drift only occurs when the phenotypes are identical.
> 
> An example would be a silent mutation that leaves the DNA codon still coding
> for the same amino acid. Two separated populations could fix different
> versions of this allele, and this could form the basis of a genetic test to
> determine the origin of an animal.
> 
> Phenotypic variation is necessary for NS (as I use the term) to operate.
> This is because the gene has got to contribute to its own chance of
> survival, which it does by influencing the phenotype - making the organism
> faster, or cleverer, or whatever is advantageous.

I don't see anything here that does anything more than reassert the
gambler's fallacy.
---
þ RIMEGate(tm)/RGXPost V1.14 at BBSWORLD * Info{at}bbsworld.com

---
 * RIMEGate(tm)V10.2áÿ* RelayNet(tm) NNTP Gateway * MoonDog BBS
 * RgateImp.MoonDog.BBS at 8/3/03 8:55:41 PM