> Simple: The efficiency of the C4 carbon fixation would be of little benefit to the plant itself. Evolution optimizes for the benefit of the gene-bearer.

I don't know if this is a good example, but suppose for argument's sake that flocking behavior in migratory birds contributed to the likelihood of gene propagation. Off-the-reservation individuals wouldn't benefit from this cooperation and would therefore be unlikely to enjoy having their genes propagated.

Could we posit / test for a similar selection effect in trees or other plants, in which the benefit to the individual is accrued through behaviors of the group? My first attempt at thinking about this was to consider whether trees that promote more stable weather patterns might have an easier time reproducing, but I think it's harder than this because the benefits obviously benefit other species that don't have the same kind of behaviors. All things being equal, this tends to status quo, not out-competing your neighbors.