Tim Tyler wrote:

JMenegay:
> > Two criteria for identifying a species-level 
> > trait that may be subject to species-level 
> > selection:
> > 1. The trait must be emergent at the species 
> > level.  A fleet herd of deer should be 
> > interpreted as a herd of fleet deer.  Fleetness 
> > is not emergent, and should therefore be 
> > explained by individual-level selection.

TT:
> The speed of a herd of deer is a group phenomenon 
> - which is not simply the additive sum of the 
> running speeds of individual deer.  If it were, 
> the fastest deer would migrate to the front, and 
> the herd would stretch out into a long line.  The 
> deer would also have no reason to head in the same 
> direction.  Factors such as the size of the herd 
> will influence their collective running speed - 
> and are simply not a factor for an individual deer.

> In practice, the idea of group or species traits 
> being simple sums of individual traits rarely 
> stands up to close inspection.  Often, there are 
> some emergent properties of some kind involved.

JMc:
Very well stated.  I don't know if you realize it, 
Tim, but what you are saying here refutes the notion 
the individual selection is a principle.  IOW, what 
you are saying here is that not only are individual 
selection and group selection not mutually exclusive, 
(or not always mutually exclusive) but often, as in 
this example here, they are complimentary.  

I suspect that Jim Menegay will reply to this with 
something along the lines that since this can be 
described from the perspective of individual 
selection/behavior that therefore it is individual 
selection but this is a nonsense argument similar 
to saying that since distance can be measured in 
inches that therefore it can't be measured in 
meters.  Jim's a smart guy, however, and I'm sure 
he'll eventually get it.  (Along these line, Jim, 
it will help if you work to maintain the 
epistemological distinction between units of 
selection, which are units of measure or points of 
view, and levels of biological phenomena, which 
are real, measurable, empirical.)

Jim
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