What Use Is Half A Wing?

Darwin asserted that a new anatomical feature like a wing would have to evolve gradually, directed at each stage by natural selection. That poses the question, what use is half a wing? Why would there be any pressure to evolve a partial wing? The answer comes from watching young birds of many species. They can run up logs and trees of various angles to escape predators by beating their tiny useless wings. They use their wings to push their bodies against the trunks, gaining extra traction.

~ Roedy (1948-02-04 age:70)