"Jim McGinn"  wrote in message
>
> If they don't claim one to one correspondenc then Genetic
> Drift is refuted as a cause separate from NS.  How is this
> not obvious to you.  (I suggest reading back through this
> thread.  Once we established a distinction between chaotic
> causation and chance (which is not causal) this discussion
> was over: genetic drift is a result of the gambler's
> fallacy, nothing more.
>
Entering the lions' den here, however.

A random process can be causal. For instance if I open a bottle of perfume
in a still room I will eventually smell scent. Everyone will say that this
is "caused" by diffusion through the room. I'm not a physicist so I won't
say whether the process is inherently random or just too complex to
calculate, but there is no way of knowing if a particular molecule will land
up in my nose or at the other end of the room.

Similarly genetic drift tends to cause alleles to be eliminated. Given a
sufficient number of generations, it is statisitically inevitable that one
allele will become fixed. With a large number of loci, it is also inevitable
that two populations, newly isolated, will eventually diverge so that by
looking at the genome you can tell which population an animal come from.

Natural selection can only operate where there is a difference in fitness
between two alleles. Then the more fit allele will tend to be fixed. However
if the fitness benefit is small and the allele is initially rare, then it
might be lost through genetic drift. That is how the two processes interact.

Any non-human agency that affects fitness qualifies as a natural selective
force. Eg an asteroid hitting the earth might eliminate big animals that
don't hibernate. Genetic drift doesn't affect the fitness of the population
it operates on so it doesn't qualify as NS.

However genetic drift could be a selective force in the same sense as the
asteroid. Consider you have a parasite, and several populations of hosts who
have diverged due to genetic drift. A parasite that is capable of adapting
to several slightly different immunoglobin genes might be selected for, and
in this sense genetic drift of the host has been a causal evolutionary
factor.
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