[Damifino]

A wing is simply a modified foreleg. There is no "wing gene."

Yeah, I was being a bit tongue and cheek with it. The point I was trying to make is; in the million years or so for the foreleg to make its journey to flight, the appendage would be particularly unhelpful to flying or running. I'd think with a million year competitive disadvantage any species would be hard pressed to survive long enough to take wing (or most any other major transition).

[Junior]

Herein you're wrong. The wing developed on bipedal dinosaurs (therapods). Recent research of certain ground-dwelling birds in their juvenile state shows that even wings that do not permit flight still aid the animal in climbing out of danger. Flapping the undeveloped wings allows the animal to more effectively cling to the surface of the feature (tree, log, rock face) it is climbing to escape predators.

Any advantage in the game of life is likely to propagate throughout the gene pool.