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.

However we have a fine example of such geographical variation in a
sexual species staring us in the face: human races.

Among the effects which seem to have been rather overlooked are:

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

In a little more detail:

* Habitat-specific selection arises when a single population is exposed to 
  a range of different environments - and is subjected to different 
  selection pressures in the different locations.

* Xenophobia facilitates the existence of cooperative groups.
  It biases favourable interactions towards previous givers of 
  altruism - and results in a healthy distrust of outsiders.
  Also, outsiders are normally less likely to be your cousin than 
  someone in your existing social group.

* Divergent selection arises when hybrid offspring between members of the 
  two groups have reduced viability. That could happen if the offspring 
  contained a mixture of traits - and is a "half-breed" - who winds up
  not being well adapted to the habitat of either of its parents.

I argue that these phenomena operate synergetically to erect group
boundaries - habitat-specific selection generates variation on the
basis of geography, and xenophobia and divergent selection both
act to amplify any existing between group differences by curtialing
interaction between the groups and by preventing inter-group breeding
respectively.

I hope the essay helps throw some light on the subjects of
group selection and environmental inheritance.

Enjoy,
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