Tim Tyler  wrote 

> > As far as I can see, there is nothing wrong with an explanation that is 
> > "for the good of the species" (group, deme, etc.) so
long as it is not 
> > harmful to the individual. Individuals tend to compete with conspecifics, 
> > and in the case of a fixed carrying capacity any trait that benefits an 
> > individual will subtract from the fitness of the rest of the population. 
> > But what if the trait increases the carrying capacity? In this case it 
> > will still benefit the individual, but it will also benefit the species! 
> > In general such traits may face stiffer odds of spreading than traits 
> > that benefit just the individual, since the individual benefit is at 
> > first just a fraction of the overall benefit. But once established at 
> > even a relatively small frequency, they may survive better than traits 
> > that merely benefit the individual, since they reduce the odds of loss by 
> > sampling error by increasing the population. 
> 
> This is all well put.  However at the moment species selection faces
> the problem of not having any good examples of species-selected traits.

All traits are species selected traits.

> If trying to find evidence for species selection

How about the fact that species exist.  Is this not evidence?

 - to illustrate that
> is isn't totally impotent as a force in nature - examples where
> adaptations favour the species and the indiviual are not terribly
> useful - since the simple hypothesis of individual selection

Individual selection is not a hypothesis.  Nor is it a force.  It's a
perspective.

 only
> explains their existence rather well - and quantitative arguments
> in this area are harder to make convincingly.
> 
> It is cases where the trait is either neutral to the individual - or
> slightly deleterious - that would represent the best evidence for
> species selection.
> 
> This is why modern group selectionists have congregated around
> phenomena such as programmed death.  Death looks as though it
> offers little individual-level benefit - but arguments can
> be made that it improves group-level dynamics - e.g. by
> systematically removing organisms with high parasite loads
> from the population and preventing them from infecting other,
> unrelated members of the same population.
> 
> So far I'm not convinced that these folks have a case - but
> in terms of getting some evidence for high level selection
> goes, this is the right /sort/ of example.

I'd agree.  But I just think we need to be cognizant of the fact that
the tendency of scientists to object to this notion of selection
happening at levels of selection higher than the individual level of
selection invariably hinge on conventions of semantics rather than the
reality of the phenomena.  The classic mistake is that people think of
levels of selection (or units of selection) as tangible phenomena when
in actuality they are nothing but theoretical perspectives.  Natural
selection doesn't happen at levels, on levels, or to levels.  It
happens to biological phenomena.  And a change in biological phenomena
at one level of selection (or unit of selection) also represents a
simultaneous change in biological phenomena at all levels (or units of
selection).


Jim
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