Perplexed in Peoria  wrote or quoted:
> 
> "Tim Tyler"  wrote in message
news:cf693l$hb5$1{at}darwin.ediacara.org...
> > I wrote an essay about group selection recently.
> > It can be found at:
> >   http://alife.co.uk/essays/reviving_group_selection/
> > A brief summary here:
> > Many of the theoretical arguments against group selection deny that sexual
> > groups vary much from place to place - because the stirring effect of
> > sexual recombination is too great for this to happen - and partial group
> > isolation and population viscosity are normally not enough to prevent it.
> 
> In the first place, sexual recombination has nothing to do with any 
> "stirring".  Perhaps you meant to refer to the stirring effects of 
> intergroup migration and crossbreeding.

This is a mysterious comment.  Genes _do_ get stirred together in sexual
populations by sexual recombination.  Without such recombination,
organsims would be asexual - and no cross-breeding would occur.

> But more importantly, "stirring" can only reduce variation
between groups
> if there was already significant variation to be "stirred". 
Your essay
> says absolutely nothing about how such variation arises.

Variation arises by mutation.  My essay is not about mutation - I take
the existence of mutations for granted.

> Furthermore, variation between groups for any trait subject to 
> individual selection must decrease even without "stirring".

It is not clear what you mean.  You are suggesting variation between 
groups for any trait subject to individual selection must decrease?!?  
That is not correct - the groups can diverge if they are subjected to 
mutations and insufficient gene flow between them.

> Your essay seems to be more about how speciation can start peripatrically
> than about how a single species can evolve new traits and maintain old ones
> through group selection.

My essay is not about speciation at all.  It is about group selection.
I deliberately avoided discussing speciation - my essay is about
groups which are not in complete isolation - and are still connected by 
gene flow.

Species selection is already on firm theoretical ground - it is group 
selection in sexual groups where the main controversy in the area lies.

> > However we have a fine example of such geographical variation in a
> > sexual species staring us in the face: human races.
> 
> Your mention of human races in the context of group selection is very
> mysterious to me.  Are you suggesting that primitive man recognized who
> was in the group and who was outside by cues that we today would call racial?

I believe my discussion of that area was in terms of xenophobia.
I think that primitive man recognised in-group and out-group members
and distinguished between them - using a range of cues.

Since - until modern times - different human races were widely
geographically separated, the issue of primitive man enountering 
individuals of radically different races to his own seems likely
to have arisen less frequently than it does today.

However there's evidence that (for instance) that Cro-Magnon man
coexisted with Neatderthal man in some places:

``Hybrid skeletons sharing Neanderthal and Cro-magnon features have been 
  found in Portugal, proving that the two species did interbreed.''

 - http://www.campusprogram.com/reference/en/wikipedia/n/ne/neanderthal.html

....so - when individuals of different races /were/ encountered, the 
differences may sometimes have been much larger than the differences 
between the most distantly-separated humans are today.

> Or, perhaps you are saying that the existence of races today is evidence
> that viscosity was fairly high and that species-wide stirring was minimal
> until recently.

That was indeed (pretty much) my point.  There may still have been a fair 
bit of "genetic stirring" going on - but if so then there was some 
countering selection on specific traits as well.

> Perhaps that is true, but I don't see how that says anything
> useful about group selection.

It is relevant since the usual arguments against group selection
in sexual populations assert that groups in sexual populations
don't form - because gene flow between the groups homogenises
the population and prevents much variation between groups arising.

As I put it in my essay:

``However, theoretical considerations have indicated that the rate of 
  between-group migration would have to be very low - or - equivalently - 
  population viscocity would have to be very high in order to make the 
  effect [group selection in sexual groups] work - and observations of 
  actual groups of individuals suggest such partial-isolation conditions 
  are rarely met in practice.''

However there's a clear counter-example - where significant geographical
variation exists in a sexual population - in our own species.

A trip to Africa followed by a trip to Iceland illustrates clearly that 
the notion that gene flow homogenises interbreeding sexual populations
is incorrect in practice.

In my essay I suggest three factors that have been rather neglected
by group selection's critics that may assist group selection's operation:

* Habitat-specific selection;
* Xenophobia;
* Divergent selection;

http://alife.co.uk/essays/reviving_group_selection/
-- 
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